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Brush Electrical Machines Ltd. PO Box 18, Loughborough, Leicestershire, LE11 1HJ, England Telephone: +44 (1509) 611511 Telefax: +44 (1509) 610440 E-Mail: [email protected] Web Site: http://www.fki-et.com/bem T T r r a a i i n n i i n n g g M M a a n n u u a a l l SONAHESS PRISMIC PMS SYSTEM 237 (English Version) Manual No: TP00001242 Issue: A Date: January 2008

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Page 1: Training brush generator

Brush Electrical Machines Ltd. PO Box 18, Loughborough, Leicestershire, LE11 1HJ, England

Telephone: +44 (1509) 611511 Telefax: +44 (1509) 610440 E-Mail: [email protected] Web Site: http://www.fki-et.com/bem

TTTrrraaaiiinnniiinnnggg MMMaaannnuuuaaalll

SONAHESS PRISMIC PMS SYSTEM 237 (English Version)

Manual No: TP00001242 Issue: A

Date: January 2008

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SONAHESS PRISMIC PMS TRAINING MANUAL (English Version)

Manual No: TP00001242 Issue: A Date: January 2008 Page: 2 of 5

© Brush Electrical Machines Ltd. 2008

TRAINING MANUAL

CONTENTS

1 INTRODUCTION ........................................................................................................................................ 3 2 GUIDE TO TRAINING MANUAL ............................................................................................................... 3 3 PROJECT DOCUMENTATION ................................................................................................................. 3 4 TRAINING MODULES ............................................................................................................................... 4

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SONAHESS PRISMIC PMS TRAINING MANUAL (English Version)

Manual No: TP00001242 Issue: A Date: January 2008 Page: 3 of 5

© Brush Electrical Machines Ltd. 2008

1 INTRODUCTION

This Training Manual is intended to provide Operators with a understanding of the concepts and procedures used in the design and manufacture of generators and ancillary equipment. In addition to general background information, the Training Manual incorporates details of basic design concepts and project specific information as appropriate. A schedule of the training modules provided, and a summary of their content is given in Section 4.

2 GUIDE TO TRAINING MANUAL

Electronic copies of the Training Manual are provided in Adobe Acrobat format (PDF files), which includes bookmarks or links to enable the user to navigate between the various Sections within the manual. To move to the required Section, 'click' on the bookmark in the left hand portion of the screen.

3 PROJECT DOCUMENTATION

The Training Manual is designed to supplement the information given in other project documentation i.e. Operating & Maintenance Manual comprising Installation & Commissioning procedures, Operation

& Maintenance procedures, Drawings, Control & Monitoring Equipment and Suppliers Data. Instruction Manuals/Handbooks for Brush ancillary equipment Quality Dossier incorporating as shipped equipment settings and, where Brush has an involvement,

as commissioned settings.

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SONAHESS PRISMIC PMS TRAINING MANUAL (English Version)

Manual No: TP00001242 Issue: A Date: January 2008 Page: 4 of 5

© Brush Electrical Machines Ltd. 2008

4 TRAINING MODULES

01 GENERAL 01.01.01 Introduction To Brush Electrical Machines Ltd.

FKI plc; Brush Electrical Machines History; Brush Electrical Machines 01.02.01 Safety

Warning Symbols; Health & Safety At Work Act (1974); Control Of Substances Hazardous To Health (COSHH Regulations 1999); Operation & Maintenance; Protection & Monitoring Devices

01.03.01 Maintenance Philosophies Maintenance; Machine Deterioration; Maintenance Philosophies; Sensory Perception

01.04.01 Principles Of AC Generation Faraday's Law Of Electromagnetic Induction; Three Phase Generation; Generator Excitation Control Systems

04 GENERATOR SYSTEMS 04.01.01 Power Generation Systems

Prime Mover/Generator; Generator Operation; Automatic Voltage Control; Parallel Operation; Governor Droop; Generator Output

04.02.01 Generator Synchronising Introduction; DC Generators; AC Generators; Synchronising AC Generators; Lamp Synchronising; Synchroscope; Synchronising At The Switchboard/Control Panel; Automatic Synchronising; Check Synchronising; Closing Onto Dead Busbar

04.03.01 Capability Diagrams Introduction; Stator Current; Power Output; Rotor Current; Stability Of The Rotor; Temporary Limitation; Use Of Capability Diagram; Capability Diagram For Synchronous Motor; Capability Diagram For Synchronous Condenser

04.07.01 Electrical Device Numbers & Functions Introduction; Device Numbers

04.08.01 Equipment & Switchgear Labelling (BS3939) Introduction; General; Prefix Letter; Wire Numbers; Suffix Letters; Numbering Table

04.09.01 High Voltage Phasing Checks Introduction; Phasing Out Of HV Systems; Phasing Sticks

04.10.01 Electrical Power Resistance, Inductance & Capacitance; Current & Voltage; Active Power; Reactive Power; Power Factor & Apparent Power; Three Phase Power, Tariffs & Power Factor Correction.

07.01.03 PRISMIC Power Management System (PMS) Introduction; Applications; Features

07.05.01 Stability Settings Using Keyboard Entry (PRISMIC 'A') Introduction; Active Power Sharing (MW) Commissioning; Reactive Power Sharing (MVAr) Commissioning; Connecting To The Grid Network; After Commissioning

07.06.02 Calibration Procedures (PRISMIC 'B') Introduction; Analogue Cards; Voltage Sensing Unit; Power Measurement System; PRISMIC Calibration On Site; Typical Calibration Problems

07.06.03 Calibration Procedures (PRISMIC PMS) 07.07.01 Set Management

Introduction; Starting; Stopping Of Sets; Duty Selection And Hours Run; Fail To Synchronise Alarm; Incorrect Duty Alarm; Minimum Sets To Run; Critical Sets; Large Motor Starting; Split Bus Operation; Grid Tariffs

07.08.02 Load Shedding (HMI Systems) Introduction; Modes Of Operation

07.09.01 Spinning Reserve Introduction; Solid Bus System; Detached System

07.10.01 Data Communications Introduction; Communications - What Is It?; What Is Data Communications; Historical Background; Information Transfer Systems; Telecommunications Systems; Data, Audio & video Communications; Communications Interface; Interface Standards Overview; Smart Instrumentation; Modern Systems

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07.11.03 Fault Finding - PRISMIC PMS

Introduction; Rack And External Input Faults; External Faults; PRISMIC Generated Alarms; Fault Scenarios

07.12.03 System Maintenance - PRISMIC PMS Introduction; General Maintenance; Routine Checks; Calibration Of Generators/Grid Feeders; Calibration Of Load Feeders; Load Inhibits; Spinning Reserve Alarms; Set Management Maintenance, Load Shedding Maintenance; Printers And HMI Systems; Records

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INTRODUCTIONTO BRUSH ELECTRICAL MACHINES LTD.

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01.01.01 (A) Introduction To BEM.doc © Brush Electrical Machines Ltd. 2002

INTRODUCTION TO BRUSH ELECTRICAL MACHINES LTD.

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CONTENTS1 FKI PLC...................................................................................................................................................... 3

1.1 Introduction.......................................................................................................................................... 31.2 FKI Energy Technology....................................................................................................................... 31.3 Companies In The FKI Energy Technology Group ............................................................................. 4

2 BRUSH ELECTRICAL MACHINES LTD. - HISTORY .............................................................................. 62.1 Charles Francis Brush......................................................................................................................... 62.2 Development ....................................................................................................................................... 62.3 Other Brush Products.......................................................................................................................... 72.4 Generators .......................................................................................................................................... 72.5 Diversification ...................................................................................................................................... 82.6 Development ....................................................................................................................................... 82.7 Brush Loughborough Site ................................................................................................................... 9

3 BRUSH ELECTRICAL MACHINES LTD................................................................................................. 103.1 Introduction........................................................................................................................................ 103.2 Products ............................................................................................................................................ 103.3 Industries Served .............................................................................................................................. 113.4 Quality ............................................................................................................................................... 113.5 After-Sales Service & Training .......................................................................................................... 11

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1 FKI PLC

1.1 Introduction

FKI plc is a major international engineering group. FKI has world leading positions in itsspecialised business areas of automated logistic solutions, lifting products and services,hardware and energy technology products.

FKI was incorporated on 6 March 1920 in England under the companies Acts 1908 to 1917and was re-registered on 3 June 1982 as a public limited company under the Companies Acts1948 to 1980. The Group has operations in more than 30 countries and in the year ended 31March 2002, its turnover amounted to £1.6 billion, and employs just under 16,000 people.

1.2 FKI Energy Technology

FKI Electrical Engineering Group was established in 1996 following the acquisition of theHawker Siddeley Electric Power Group and Marelli Motori. These acquisitions, added to theexisting presence of Whipp & Bourne, Laurence Scott & Electromotors and Froude Consinewithin FKI, made up a Group of world class stature with synergies of technology,manufacturing, purchasing and sales. FKI Electrical Engineering, along with the Measurementand Controls Division, formed FKI plc’s Engineering Group. In July 2001, this became FKIEnergy Technology.

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FKI Energy Technology is a leading independent supplier of rotating machines, particularlyturbogenerators, switchgear and transformers; measurement and control products and is asignificant supplier of other electrical products. Products and systems are sold tomanufacturers of turbines, pumps, compressors, fans and other machines and to a widevariety of Customers in industry, power generation, oil and gas supply, air separation,petrochemical and contracting.

Main businesses in the FKI Energy Technology group are:

Rotating Machines: High, medium and low voltage electric motors; turbo, medium and lowvoltage generators; industrial drives, control equipment, frequency changers, engine andvehicle test systems.Switchgear: Indoor switchgear, outdoor circuit breakers, ring main units, pole mountedreclosers and DC switchgear.Transformers: Power, system and distribution transformers, pole mounted transformers andon load tap changers.Traction: Rail locomotive manufacture and refurbishment.Measurement and Control : Measurement and control devices and systems.

1.3 Companies In The FKI Energy Technology Group

Many of the individual companies have histories going back over 100 years. Thesecompanies include:

Brush Electrical Machines Ltd.: Located at Loughborough in the UK and is designated asFKI's Centre of Excellence for the design and manufacture of power management systemsand air cooled 2-pole turbogenerators up to 150MVA.

Brush HMA bv: The company, formerly known as 'HMA Power Systems' and before that'Holec Machines and Apparaten', has been established for over 115 years and became part ofFKI Energy Technology at the beginning of 2000. Brush HMA is FKI’s Centre of Excellence forthe design and manufacture of 4-pole generators with ratings between 10MVA and 65MVA.

Brush SEM sro: Located at Plzen in the Czech Republic and designated as FKI's Centre ofExcellence for the design and manufacture of air cooled 2-pole turbogenerators above150MVA, hydrogen cooled generators and hydrogen/water cooled generators up to 1100MVAand the refurbishment of hydro generators up to 355MVA.

Brush Transformers: Based in Loughborough, UK, Brush Transformers is a majorinternational manufacturer of transformers. With over a century of experience, BrushTransformers manufacture a wide range of distribution, power, dry type, cast resin andtraction transformers, along with flameproof transformers and switchgear.

FKI Industrial Drives: Formed by the merger of Heenan Drives and Brush Industrial Controls,and now provide state of the art variable speed drive products from a new centrally locatedfacility in Loughborough. Products also include AC sensorless flux vector inverters,synchronous motor drives and DC thyristor drives covering a power range from 0.37kW to20MW. Fully engineered drive systems designed to customer specifications are available..

Hawker Siddeley Power Transformers: Based in Walthamstow, London, Hawker SiddeleyPower Transformers is a major international manufacturer of power transformers includinggenerator transformers for steam, hydro, nuclear and gas turbine power stations.

Hawker Siddeley Switchgear: Based in Blackwood in South Wales, Hawker SiddeleySwitchgear are an international producer of Switchgear. The Blackwood site is a centre ofexcellence for switchgear manufacture, producing a range of indoor and outdoor distributionswitchgear.

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Laurence Scott And Electromotors: Are the UK's premier manufacturer of electric motors(high and low voltage, ac and dc) and electro-mechanical power transmission products(gearboxes, geared motors, eddy current variable speed drives, electro-pneumaticclutch/brakes). Brand names include LSE, NECO, EPG, TASC, NORAC, HEENAN, PSS,GLENPHASE, EDC, SLENDAUR, CENTAUR.

Marelli Motori: Produce a range of low and medium voltage asynchronous motors, DCmotors and synchronous generators in a large variety of designs and power ranges up to3,000 kW. The factory is situated in Vicenza in the north of Italy, and has more than onehundred years of experience in the production of rotating electrical machines.

South Wales Transformers: Based in Blackwood, South Wales, South Wales Transformersis a major international manufacturer of distribution transformers and substations. TheBlackwood site is a centre of excellence for distribution transformer manufacture, producing awide range of liquid-filled distribution transformers, both pole- and ground-mounted, andpackaged substations.

Whipp & Bourne: Established in 1903, and based in Rochdale, Lancashire, Whipp andBourne has long been a leader in heavy duty electrical switchgear. Products include a rangeof DC Circuit Breakers, Switchgear and Auto Reclosers.

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2 BRUSH ELECTRICAL MACHINES LTD. - HISTORY

2.1 Charles Francis Brush

Figure 1: Charles Francis BrushThe original company was the Anglo-American Brush Electric Light Corporation which wasestablished in 1879 in Lambeth, London, to exploit the inventions of Charles Francis Brush(1849-1929). Brush, born in Cleveland, Ohio, had developed his first dynamo in 1876 andfounded the American Brush Company in 1881. This American company lasted until about1891.

2.2 Development

Lighting equipment (both arc lamps and incandescent lights) was the main product at first,expanding with the formation of lighting supply companies throughout the country. After anearly boom in the promotion of lighting companies, the Electric Lighting Act of 1882 laid downnew and onerous conditions of operating so that a general period of stagnation followed in thenewly-born electrical industry.

However, there were some developments prior to the repeal of the Act in 1888, mainly in thefield of industrial electrification. Thus the company was able to thrive on the manufacture ofdynamos, motors, switchgear and small transformers. Trade again increased after 1888 andthe works in Lambeth were no longer adequate for the vast increase in orders. New premiseswere required and, in the following year, the Falcon Engine and Car Works in Loughboroughwas purchased.

Figure 2: Brush Works (Early)

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The title of the company was changed soon after the movement to Loughborough. At first,only the heavier manufacturing was transferred from Lambeth, but by 1895 most of theproduction was concentrated in the Falcon Works which by now incorporated largeextensions.

2.3 Other Brush Products

Figure 3: Brush 'Products'Prior to the First World War, tramcars and electrical engineering were the mainstays ofproduction. The works employed about 2,000 men around 1910. Wartime production wasmainly concerned with munitions although vehicle bodies and even aircraft were constructed.

2.4 Generators

Figure 4: 5000kW Brush-Ljungstrom Turbogenerator

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Electrical equipment sales remained steady during the period after World War 1. Turbineproduction experienced a great boom after 1918 when some 20 complete turbines with theattendant equipment were delivered each year. The size of these machines was in the 1,500kW, 3,000 kW and 5,000 kW ranges, and they were well suited to the small municipal andcompany electricity works then in vogue.

2.5 Diversification

Employment in the works fell from a peak in 1925 when about 2,500 were employed to 1,500some ten years later. The area of the works altered little, from 33 acres in 1924 to 35 acres in1935 when the workshops covered about five acres.

The first heavy oil engine made its appearance in 1935 and three years later in an attempt todiversify the range of products and to cater for an increasingly important line of business, thefirm of Petters Ltd was taken over. Petters had been established in Yeovil, Somerset since themid-19th century and had developed their first internal combustion engine in 1895. All theproduction was transferred to Falcon Works and remained there until 1948 when the formerLagonda Works at Staines, Middlesex were bought.

After World War II the demand for heavy electrical equipment, dormant for many years,returned to the company making good the damage of wartime losses, and also encouragingrenewal of large-scale capital investment in power generation. The new companies in theBrush Group were now more competitive in modern conditions and the two branches, ABOE(Associated British Oil Engines) and Brush, were complimentary in engine building andelectrical equipment. Four-wheeled battery electric vehicles first appeared in 1947 and in thesame year the Company returned to railway work after a lapse of many years, when dieseland diesel-electric locomotives were built in conjunction with W.G Bagnall Ltd of Stafford.

Further companies joined the Group in 1950 when the National Gas & Oil Engine CompanyLtd, Hopkinson Electric Company Ltd and the Vivian Diesels & Munitions Company Ltd ofCanada were taken over. The title was changed to the "Brush - ABOE Group of Companies".

This was a period of great expansion with a large export drive and increasing capitalinvestment in the industry. The £40 million of orders in 1951 were more than twice those of1950.

2.6 Development

In April 1957 an offer of £22 million from the Hawker Siddeley Group was adopted andamalgamation took place. The Brush Group of companies was incorporated into the HawkerSiddeley Group under the name of Brush Electrical Engineering Co., Ltd. and had offices inDukes Court, Duke Street, St James's, London S.W.1.

In November 1991, the Hawker Siddeley Group was taken over by BTR plc in a £1.5 billionbid. In the subsequent re-organisation Brush Electrical Machines Ltd became a majorcompany within the BTR Electric Power Group, and the company's Traction Division becamea separate company, Brush Traction Ltd.

In November 1996, the FKI Group of Companies acquired the Hawker Siddeley ElectricPower Group from BTR, Brush Electrical Machines and the other Brush companies joining theGroup's Engineering Division. Following this, Brush Traction Ltd reverted to being a division ofBrush Electrical Machines Ltd, and the Company's Industrial Controls Division became part ofFKI's LSE Division.

Brush Electrical Machines Ltd. is now one of FKI Energy Technology's Rotating Machinescompanies and is designated as the Centre of Excellence for the design and manufacturemanufacture of power management systems and air cooled 2-pole turbogenerators up to150MVA. Brush BEM joined with sister companies Brush HMA and Brush SEM to found theBrush Turbogenerators organisation.

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2.7 Brush Loughborough Site

Figure 5: Brush Works, LoughboroughIn October 1960 the Falcon Works employed about 4,300 workers in the 40 acres ofworkshops in a total site area of 59 acres. A majority of workers, 3,700, were employed onheavy electrical work whilst 500 were in the Traction Division and 100 on electric vehicleconstruction. The main production of the works still centred on electrical engineering withheavy transformers, generators, motors, switchgear etc.

In 1970 Hawker Siddeley Power Engineering, a project engineering group, was formed as aseparate company with an office at a nearby site in Burton-on-the-Wolds and another atChelmsford in Essex. Twelve months or so later, in 1971, the product divisions of the BrushElectrical Engineering Company Ltd were formed into separate manufacturing companies.Initially these comprised Brush Electrical Machines Limited, Brush Switchgear Ltd and BrushTransformers Limited, with Brush Switchgear taking on the responsibility of the FusegearDivision until January 1973 when Brush Fusegear Ltd was formally constituted.

By this time there were approximately 5,000 workers on the Loughborough site.

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3 BRUSH ELECTRICAL MACHINES LTD.

3.1 Introduction

Figure 6: Brush Electrical Machines Ltd. LogoBrush Electrical Machines Ltd. is now one of FKI Energy Technology's Rotating Machinescompanies and is designated as the Centre of Excellence for the design and manufacturemanufacture of power management systems and air cooled 2-pole turbogenerators up to150MVA. Brush BEM joined with sister companies Brush HMA and Brush SEM to found theBrush Turbogenerators organisation.

Company turnover for the financial year 2001/2002 was approximately £90 million. Over 90%of production was exported.

The company employs approximately 770 people, of whom 500 are in production.

3.2 Products

Our product portfolio, including relevant FKI Energy Technology products, includes:

CONTROLSPRISMIC PMS power management systems for marine power and propulsion, offshoreand onshore oil and gas applications, industrial and dockland installations.A range of automatic voltage regulators and excitation control equipment for generatorsand synchronous motors.

GENERATORSAir cooled 2-pole turbogenerators for gas and steam turbine drive up to 200MVA, 15kV.Hydrogen and combined cooled 2-pole turbogenerators up to 1100MVA, 25kV.Air cooled 4-pole turbogenerators up to 65MVA, 15kV.Multi-pole synchronous types for diesel engine drive up to 30MVA, 15kV.

MOTORSMulti-pole synchronous single, multiple and variable speed types up to 20MW, 15kV.20-pole induction types up to 20MW, 15kV.LV cage induction types up to 1.5MW.DC types up to 120kW.Traction types up to 1000kW.Flameproof types.

SWITCHGEARWithdrawable/fixed vacuum circuit breakers, rated up to 15kV, 3150A, 40kA.Withdrawable fused vacuum contactors, rated up to 7.2kV, 400A, 40kA.

TRANSFORMERSDistribution transformers 315kVA to 2500kVA.Power Transformers 2.5MA to 60MVA up to 145kV.System transformers up to 180MVA, 150kV.

VARIABLE SPEED DRIVESAC inverters up to 7MW, 1800V.AC synchroconverters up to 20MW.DC drive systems up to 3.5MW

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3.3 Industries Served

Brush provides a complete electrical service to all sectors of the power industry. From aproduct portfolio encompassing generators, including control systems, for base load orintermittent duty, synchronous motors, power management systems and fully co-ordinatedpackages of electrical equipment. Brush can provide equipment and services to meet themost demanding specifications.

Brush is renowned for the kind of robust yet versatile designs of generators and motors wellsuited to the harsh operating environments encountered at oil and gas installations bothonshore and offshore. This has led to Brush gaining an excellent reputation as a world classsupplier to this demanding market.

Brush also provides a complete electrical service to the marine industry. From generators andcontrol systems, to complete electrical propulsion and auxiliary power system packages fornaval, merchant and special purpose vessels.

In addition, Brush can select and configure systems built from components sourced fromthroughout FKI Energy Technology group and elsewhere, including generators, motors,control systems, variable speed drives, switchgear and transformers, etc.

3.4 Quality

Figure 7: QA RegistrationSince 1991, the Company has been registered to ISO 9001 standard, which governs thequality of design, manufacture and service. Maintaining this registration has become acornerstone of management policy. All equipment complies with relevant European, Americanand International standard specifications.

3.5 After-Sales Service & Training

A comprehensive service is offered by the Service Department, located at Loughborough,dealing with the commissioning, service, repair and maintenance requirements on a world-wide basis. In addition, service centres in the USA, Malaysia, The Netherlands and Canada,along with local service partners in many other countries, can offer on-the-spot assistance.Comprehensive operator training courses for all products and systems are available either atthe factory or at site.

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SAFETY

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CONTENTS1 WARNING SYMBOLS ............................................................................................................................... 32 HEALTH & SAFETY AT WORK ACT (1974) ............................................................................................ 33 CONTROL OF SUBSTANCES HAZARDOUS TO HEALTH (COSHH REGULATIONS 1999) ............... 4

3.1 Introduction.......................................................................................................................................... 43.2 COSHH Data For Standard Components ........................................................................................... 5

4 OPERATION & MAINTENANCE............................................................................................................... 65 PROTECTION AND MONITORING DEVICES.......................................................................................... 6

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1 WARNING SYMBOLS

Warning symbols used in manuals are as follows:

Mandatory Notice - Instruction to be followed.

Danger, General - Caution to be exercised. Appropriate safety measures to be taken.

Danger, Electricity - Caution to be exercised. Appropriate safety measures to be taken.

Danger, Harmful or Irritating Substance - Caution to be exercised. Appropriate safetymeasures to be taken.

2 HEALTH & SAFETY AT WORK ACT (1974)

The information hereunder is supplied in accordance with Section 6 of the Health and Safety at WorkAct 1974 with respect to the duties of manufacturers, designers and installers in providing health andsafety information to Customers. The information advises of reasonably foreseeable risks involved withthe safe installation, commissioning, operation, maintenance, dismantling, cleaning or repair of productssupplied by Brush Electrical Machines Ltd.

Every precaution should be taken to minimise risk. When acted upon, the following precautions shouldconsiderably minimise the possibility of hazardous incidents.

Delivery Checks: Check for damage sustained during transport. Damage to packing cases must beinvestigated in the presence of an Insurance Surveyor.

Handling: Sling packing cases where indicated. Equipment not in a packing case, or removed from apacking case must only be lifted by the lifting points provided. Do not lift complete machines by lugs onheat exchangers or air silencers etc.

Storage: Unless the equipment has been designed for outside use or specifically packed for outsidestorage, store inside in a dry building, in line with the manufacturer's recommendations.

Installation: Where installation is made by engineers other than Brush Electrical Machines Ltd.personnel, the equipment should be erected by suitably qualified personnel in accordance with relevantlegislation, regulations and accepted rules of the industry. In particular, the recommendations containedin the regulations with regard to the earthing must be rigorously followed.

Electrical Installation:IMPROPER USE OF ELECTRICAL EQUIPMENT IS HAZARDOUS.

It is important to be aware that control unit terminals and components may be live toline and supply voltages.

Before working on a unit, switch off and isolate it and all other equipment within the confinesof the same control cubicle. Check that all earth connections are sound.

WARNING: Suitable signs should be prominently displayed, particularly on switches andisolators, and the necessary precautions taken to ensure that power is not inadvertentlyswitched on to the equipment whist work is in progress, or is not yet completed.

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Adjustment and fault finding on live equipment must be by qualified and authorised personnel only, andshould be in accordance with the following rules: Read the Instruction Manual. Use insulated meter probes. Use an insulated screwdriver for potentiometer adjustment where a knob is not provided. Wear non-conducting footwear. Do not attempt to modify wiring. Replace all protective covers, guards, etc. on completion.

Operation & Maintenance: Engineers responsible for operation and maintenance of equipment shouldfamiliarise themselves with the information contained in the Operation & Maintenance Manual and withthe recommendations given by manufacturers of associated equipment. They should be familiar alsowith the relevant regulations in force. It is essential that all covers are in place and that all guards and/or safety fences to protect any

exposed surfaces and/or pits are fitted before the machine is started. All adjustments to the machine must be carried out whilst the machine is stationary and isolated

from all electrical supplies. Replace all covers and/or safety fences before restarting the machine. When maintenance is being carried out, suitable WARNING signs should be prominently displayed

and the necessary precautions taken to ensure power is not inadvertently switched on to theequipment whilst work is in progress, or is not yet complete.

When power is restored to the equipment, personnel should not be allowed to work on auxiliarycircuits, eg. Heaters, temperature detectors, current transformers etc.

Lifting Procedures: Ensure that the recommendations given in the manual are adhered to at all times.

3 CONTROL OF SUBSTANCES HAZARDOUS TO HEALTH (COSHH REGULATIONS 1999)

3.1 Introduction

The data provided hereafter satisfies the responsibilities detailed in the COSHH Regulations1999, and includes details of substances commonly used on standard components suppliedby Brush Electrical Machines Ltd. This data is not contract specific, and therefore may includesubstances not used Contract specific information can be obtained from our ServiceDepartment.

ALWAYS USE SUBSTANCES IN ACCORDANCE WITH MANUFACTURERS'INSTRUCTIONS.

IF AFTER APPLYING THE SUGGESTED FIRST AID PROCEDURES,SYMPTOMS PERSIST, SEEK IMMEDIATE ADVICE FROM QUALIFIEDMEDICAL STAFF. NEVER INDUCE VOMITTING, OR GIVE ANYTHING BYMOUTH TO AN UNCONSCIOUS PERSON.

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SAFETY

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01.02.01 (A) Safety.doc © Brush Electrical Machines Ltd. 2002

3.2 COSHH Data For Standard Components

COSHH data for substances used in standard components supplied by Brush ElectricalMachines Ltd. are summarised:

PERSONAL PROTECTION/FIRST AIDSUBSTANCE TYPE SUBSTANCE USAGE HEALTH HAZARDDATA EYE CONTACT SKIN CONTACT INHILATION INGESTION

DEGREASANT/CLEANER(Oil Based)

Low toxane (highlyrefined paraffin) orOrange Oil

Degreasant/ Cleanerremoval ofpreservative

Flash Point > 55oC.Use good ventilation

General care.RINSE WITH FRESHWATER

Wear PVC gloves/barrier creams.RINSE WITH FRESHWATER

General care.REMOVE TO FRESHAIR

Avoid.DRINK MILK/ WATER.DO NOT VOMIT.CALL DOCTOR

DEGREASANT/CLEANER(Spirit Based)

Industrial MethsAEROSOL FORMONLY

Brake disc cleaningonly.USE SMALLQUANTITIES

EXTREMELYFLAMMABLEUse good ventilation

General care.RINSE WITH FRESHWATER

Wear PVC gloves/barrier creams.RINSE WITH FRESHWATER

General care.REMOVE TO FRESHAIR

Avoid.DRINK MILK/ WATER.DO NOT VOMIT.CALL DOCTOR

DO NOT USE: PETROL/GASOLINE, 111 TRICHLORETHANE (GENKLENE) OR CARBON TETRACHLORIDEADHESIVE/SEALANT

Loctite 542

Loctite 572

Fine thread sealantPipe sealant(Maintenance

Do not inhale vapours.Use adequateventilation

General care.FLUSH WITH WATERFOR 15 MINUTES -CALL DOCTOR

General care.WASH WITH SOAPAND WATER

General care.REMOVE TO FRESHAIR

Avoid.DRINK MILK/ WATER.DO NOT VOMIT

DO NOT USE LOCTITE PRODUCTS WITH EXPOSED BROKEN SKINJOINTINGCOMPOUND

Hylomar PL32(Medium)

Sealant for bearingsand other joints

Avoid bad ventilation Wear goggles.FLUSH WITH WATERFOR 15 MINUTES

Wear PVC gloves.WASH WITH SOAPAND WATER

General care.REMOVE TO FRESHAIR - DO NOTEXERCISE

Avoid.DRINK MILK/ WATER.DO NOT VOMIT

JOINTINGCOMPOUND

Biccon X13 PT Diode mounting paste None Wear goggles.FLUSH WITH WATER

Wear PVC gloves.WASH WITH SOAPAND WATER

None None

JOINTINGCOMPOUND

Unial Electrical joints Avoid open cuts orsores. Wipe with whitespirit soaked rag.Rinse with soap andwater

Wear goggles ifcontact likely.FLUSH WITH WATER

Wear PVC gloves/barrier creams.RINSE WITH SOAPAND WATER

General care.REMOVE TO FRESHAIR

Avoid.DRINK WATER.DO NOT VOMIT

GREASES Lithium basedMobilplex 48Castrol Helv.OSilicone basedMolybdenumdisulphide

Diode fixing Use adequateventilation

Wear goggles ifcontact likely.FLUSH WITH WATER

Good hygiene.WASH WITH SOAPAND WATER

General care.REMOVE TO FRESHAIR

Avoid.DRINK WATER.DO NOT VOMIT

MINERAL OILS Mobil DTE oils (Allgrades - ISO VGClass)

Bearing lubrication oil Exposure limit 5.0mg/m3 for oil mist

None.FLUSH WITH WATER

Good hygiene.WASH WITH SOAPAND WATER

None with goodventilation.NONE

Avoid.IF IN DISCOMFORTCALL DOCTOR

INSULATIONMATERIALS

Epoxy NovolacCorona Paint GlassCordSynthetic ResinShellac/NomexMicanite

Insulation materialsmay be exposedduring maintenance/repair

All materials are inert.Physical sanding/abrasionMAY CREATEHARMFUL DUST

Wear goggles.FLUSH WITH WATER

Good hygiene.WASH WITH SOAPAND WATER

Wear disposable dustrespirators 3M type8709.REMOVE TO FRESHAIR

General care.DRINK WATER.DO NOT VOMIT

FILLER Epoxy resin putty Armature coil gap fillrepair only

Dry sanding of epoxypaints and fillerscontaining chromates.WILL CREATEHARMFUL DUST

Wear goggles.FLUSH WITH WATER

Wear vinyl gloves/barrier creams - goodhygiene.WASH WITH SOAPAND WATER

No risks with goodventilation.Is sanding wear RacalBreathe Easy unit withtoxic dist cartridgeREMOVE TO FRESHAIR

Avoid.DRINK WATERDO NOT VOMIT

PAINT MATERIALS Dry paint finishes Surface finish/protection may beexposed during repair

Dry sanding of epoxypaints and fillerscontaining chromates.WILL CREATEHARMFUL DUST

Wear goggles.FLUSH WITH WATER

Good hygiene.WASH WITH SOAPAND WATER

Wear Racal BreatheEasy unit with toxicdist cartridgeREMOVE TO FRESHAIR

General care.DRINK WATER.DO NOT VOMIT

AIR CONTAMINANT Airborne dust particles Cooling air circuitfilters (Maintenance)

During maintenance adust hazard may exist

Wear goggles.FLUSH WITH WATER

Good hygiene.WASH WITH SOAPAND WATER

Wear disposable dustrespirators 3M type8709.REMOVE TO FRESHAIR

General care.DRINK WATER.DO NOT VOMIT

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SAFETY

Training Module: 01.02.01 Issue: A Date: September 2002 Page: 6 of 6

01.02.01 (A) Safety.doc © Brush Electrical Machines Ltd. 2002

4 OPERATION & MAINTENANCE

When working on this equipment it is important that a safe environment is achieved i.e. Isolate all electrical supplies including heaters. Ensure adequate ventilation and lighting. Use proper support for heavy items. Maintain access ways. Wear suitable protective clothing.

Safety guards and covers must be fitted, unless the equipment has been made safe behindthe guard or cover.

On-site safety procedures are to be followed as appropriate, in particular 'Permit To Work'type systems are be followed rigorously.

Attention should be given to the advice given in Clause 2 (Health & Safety At Work Act(1974)) and Clause 3 (Control Of Substances Hazardous to Health (COSHH Regulations1999))

Details of substances used on equipment that are potentially hazardous to health are detailedin Clause 3.2 and the Suppliers Data that forms part of the Operation & Maintenance Manual.

IMPROPER USE OF ELECTRICAL EQUIPMENT IS HAZARDOUS.

5 PROTECTION AND MONITORING DEVICES

WARNING: It is essential that any protection or monitoring device for usewith generators or ancillary equipment should be connected and operationalat all times unless specifically stated otherwise. It should not be assumedthat all necessary protection and monitoring devices are supplied as part ofBrush Electrical Machines Ltd. scope of supply.

Unless otherwise agreed, it is the responsibility of others to verify thecorrect operation of all protection and monitoring equipment, whethersupplied by Brush Electrical Machines Ltd. or not. It is necessary to providea secure environment that ensures operator safety and limits potentialdamage to the generator and ancillary equipment. If requested, BrushElectrical Machines Ltd. would be pleased to provide advice on any specificprotection application issues or concerns.

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SAFETY

Training Module: 01.02.01 Issue: A Date: September 2002 Page: 1 of 6

01.02.01 (A) Safety.doc © Brush Electrical Machines Ltd. 2002

SAFETY

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SAFETY

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01.02.01 (A) Safety.doc © Brush Electrical Machines Ltd. 2002

CONTENTS1 WARNING SYMBOLS ............................................................................................................................... 32 HEALTH & SAFETY AT WORK ACT (1974) ............................................................................................ 33 CONTROL OF SUBSTANCES HAZARDOUS TO HEALTH (COSHH REGULATIONS 1999) ............... 4

3.1 Introduction.......................................................................................................................................... 43.2 COSHH Data For Standard Components ........................................................................................... 5

4 OPERATION & MAINTENANCE............................................................................................................... 65 PROTECTION AND MONITORING DEVICES.......................................................................................... 6

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SAFETY

Training Module: 01.02.01 Issue: A Date: September 2002 Page: 3 of 6

01.02.01 (A) Safety.doc © Brush Electrical Machines Ltd. 2002

1 WARNING SYMBOLS

Warning symbols used in manuals are as follows:

Mandatory Notice - Instruction to be followed.

Danger, General - Caution to be exercised. Appropriate safety measures to be taken.

Danger, Electricity - Caution to be exercised. Appropriate safety measures to be taken.

Danger, Harmful or Irritating Substance - Caution to be exercised. Appropriate safetymeasures to be taken.

2 HEALTH & SAFETY AT WORK ACT (1974)

The information hereunder is supplied in accordance with Section 6 of the Health and Safety at WorkAct 1974 with respect to the duties of manufacturers, designers and installers in providing health andsafety information to Customers. The information advises of reasonably foreseeable risks involved withthe safe installation, commissioning, operation, maintenance, dismantling, cleaning or repair of productssupplied by Brush Electrical Machines Ltd.

Every precaution should be taken to minimise risk. When acted upon, the following precautions shouldconsiderably minimise the possibility of hazardous incidents.

Delivery Checks: Check for damage sustained during transport. Damage to packing cases must beinvestigated in the presence of an Insurance Surveyor.

Handling: Sling packing cases where indicated. Equipment not in a packing case, or removed from apacking case must only be lifted by the lifting points provided. Do not lift complete machines by lugs onheat exchangers or air silencers etc.

Storage: Unless the equipment has been designed for outside use or specifically packed for outsidestorage, store inside in a dry building, in line with the manufacturer's recommendations.

Installation: Where installation is made by engineers other than Brush Electrical Machines Ltd.personnel, the equipment should be erected by suitably qualified personnel in accordance with relevantlegislation, regulations and accepted rules of the industry. In particular, the recommendations containedin the regulations with regard to the earthing must be rigorously followed.

Electrical Installation:IMPROPER USE OF ELECTRICAL EQUIPMENT IS HAZARDOUS.

It is important to be aware that control unit terminals and components may be live toline and supply voltages.

Before working on a unit, switch off and isolate it and all other equipment within the confinesof the same control cubicle. Check that all earth connections are sound.

WARNING: Suitable signs should be prominently displayed, particularly on switches andisolators, and the necessary precautions taken to ensure that power is not inadvertentlyswitched on to the equipment whist work is in progress, or is not yet completed.

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SAFETY

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01.02.01 (A) Safety.doc © Brush Electrical Machines Ltd. 2002

Adjustment and fault finding on live equipment must be by qualified and authorised personnel only, andshould be in accordance with the following rules: Read the Instruction Manual. Use insulated meter probes. Use an insulated screwdriver for potentiometer adjustment where a knob is not provided. Wear non-conducting footwear. Do not attempt to modify wiring. Replace all protective covers, guards, etc. on completion.

Operation & Maintenance: Engineers responsible for operation and maintenance of equipment shouldfamiliarise themselves with the information contained in the Operation & Maintenance Manual and withthe recommendations given by manufacturers of associated equipment. They should be familiar alsowith the relevant regulations in force. It is essential that all covers are in place and that all guards and/or safety fences to protect any

exposed surfaces and/or pits are fitted before the machine is started. All adjustments to the machine must be carried out whilst the machine is stationary and isolated

from all electrical supplies. Replace all covers and/or safety fences before restarting the machine. When maintenance is being carried out, suitable WARNING signs should be prominently displayed

and the necessary precautions taken to ensure power is not inadvertently switched on to theequipment whilst work is in progress, or is not yet complete.

When power is restored to the equipment, personnel should not be allowed to work on auxiliarycircuits, eg. Heaters, temperature detectors, current transformers etc.

Lifting Procedures: Ensure that the recommendations given in the manual are adhered to at all times.

3 CONTROL OF SUBSTANCES HAZARDOUS TO HEALTH (COSHH REGULATIONS 1999)

3.1 Introduction

The data provided hereafter satisfies the responsibilities detailed in the COSHH Regulations1999, and includes details of substances commonly used on standard components suppliedby Brush Electrical Machines Ltd. This data is not contract specific, and therefore may includesubstances not used Contract specific information can be obtained from our ServiceDepartment.

ALWAYS USE SUBSTANCES IN ACCORDANCE WITH MANUFACTURERS'INSTRUCTIONS.

IF AFTER APPLYING THE SUGGESTED FIRST AID PROCEDURES,SYMPTOMS PERSIST, SEEK IMMEDIATE ADVICE FROM QUALIFIEDMEDICAL STAFF. NEVER INDUCE VOMITTING, OR GIVE ANYTHING BYMOUTH TO AN UNCONSCIOUS PERSON.

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SAFETY

Training Module: 01.02.01 Issue: A Date: September 2002 Page: 5 of 6

01.02.01 (A) Safety.doc © Brush Electrical Machines Ltd. 2002

3.2 COSHH Data For Standard Components

COSHH data for substances used in standard components supplied by Brush ElectricalMachines Ltd. are summarised:

PERSONAL PROTECTION/FIRST AIDSUBSTANCE TYPE SUBSTANCE USAGE HEALTH HAZARDDATA EYE CONTACT SKIN CONTACT INHILATION INGESTION

DEGREASANT/CLEANER(Oil Based)

Low toxane (highlyrefined paraffin) orOrange Oil

Degreasant/ Cleanerremoval ofpreservative

Flash Point > 55oC.Use good ventilation

General care.RINSE WITH FRESHWATER

Wear PVC gloves/barrier creams.RINSE WITH FRESHWATER

General care.REMOVE TO FRESHAIR

Avoid.DRINK MILK/ WATER.DO NOT VOMIT.CALL DOCTOR

DEGREASANT/CLEANER(Spirit Based)

Industrial MethsAEROSOL FORMONLY

Brake disc cleaningonly.USE SMALLQUANTITIES

EXTREMELYFLAMMABLEUse good ventilation

General care.RINSE WITH FRESHWATER

Wear PVC gloves/barrier creams.RINSE WITH FRESHWATER

General care.REMOVE TO FRESHAIR

Avoid.DRINK MILK/ WATER.DO NOT VOMIT.CALL DOCTOR

DO NOT USE: PETROL/GASOLINE, 111 TRICHLORETHANE (GENKLENE) OR CARBON TETRACHLORIDEADHESIVE/SEALANT

Loctite 542

Loctite 572

Fine thread sealantPipe sealant(Maintenance

Do not inhale vapours.Use adequateventilation

General care.FLUSH WITH WATERFOR 15 MINUTES -CALL DOCTOR

General care.WASH WITH SOAPAND WATER

General care.REMOVE TO FRESHAIR

Avoid.DRINK MILK/ WATER.DO NOT VOMIT

DO NOT USE LOCTITE PRODUCTS WITH EXPOSED BROKEN SKINJOINTINGCOMPOUND

Hylomar PL32(Medium)

Sealant for bearingsand other joints

Avoid bad ventilation Wear goggles.FLUSH WITH WATERFOR 15 MINUTES

Wear PVC gloves.WASH WITH SOAPAND WATER

General care.REMOVE TO FRESHAIR - DO NOTEXERCISE

Avoid.DRINK MILK/ WATER.DO NOT VOMIT

JOINTINGCOMPOUND

Biccon X13 PT Diode mounting paste None Wear goggles.FLUSH WITH WATER

Wear PVC gloves.WASH WITH SOAPAND WATER

None None

JOINTINGCOMPOUND

Unial Electrical joints Avoid open cuts orsores. Wipe with whitespirit soaked rag.Rinse with soap andwater

Wear goggles ifcontact likely.FLUSH WITH WATER

Wear PVC gloves/barrier creams.RINSE WITH SOAPAND WATER

General care.REMOVE TO FRESHAIR

Avoid.DRINK WATER.DO NOT VOMIT

GREASES Lithium basedMobilplex 48Castrol Helv.OSilicone basedMolybdenumdisulphide

Diode fixing Use adequateventilation

Wear goggles ifcontact likely.FLUSH WITH WATER

Good hygiene.WASH WITH SOAPAND WATER

General care.REMOVE TO FRESHAIR

Avoid.DRINK WATER.DO NOT VOMIT

MINERAL OILS Mobil DTE oils (Allgrades - ISO VGClass)

Bearing lubrication oil Exposure limit 5.0mg/m3 for oil mist

None.FLUSH WITH WATER

Good hygiene.WASH WITH SOAPAND WATER

None with goodventilation.NONE

Avoid.IF IN DISCOMFORTCALL DOCTOR

INSULATIONMATERIALS

Epoxy NovolacCorona Paint GlassCordSynthetic ResinShellac/NomexMicanite

Insulation materialsmay be exposedduring maintenance/repair

All materials are inert.Physical sanding/abrasionMAY CREATEHARMFUL DUST

Wear goggles.FLUSH WITH WATER

Good hygiene.WASH WITH SOAPAND WATER

Wear disposable dustrespirators 3M type8709.REMOVE TO FRESHAIR

General care.DRINK WATER.DO NOT VOMIT

FILLER Epoxy resin putty Armature coil gap fillrepair only

Dry sanding of epoxypaints and fillerscontaining chromates.WILL CREATEHARMFUL DUST

Wear goggles.FLUSH WITH WATER

Wear vinyl gloves/barrier creams - goodhygiene.WASH WITH SOAPAND WATER

No risks with goodventilation.Is sanding wear RacalBreathe Easy unit withtoxic dist cartridgeREMOVE TO FRESHAIR

Avoid.DRINK WATERDO NOT VOMIT

PAINT MATERIALS Dry paint finishes Surface finish/protection may beexposed during repair

Dry sanding of epoxypaints and fillerscontaining chromates.WILL CREATEHARMFUL DUST

Wear goggles.FLUSH WITH WATER

Good hygiene.WASH WITH SOAPAND WATER

Wear Racal BreatheEasy unit with toxicdist cartridgeREMOVE TO FRESHAIR

General care.DRINK WATER.DO NOT VOMIT

AIR CONTAMINANT Airborne dust particles Cooling air circuitfilters (Maintenance)

During maintenance adust hazard may exist

Wear goggles.FLUSH WITH WATER

Good hygiene.WASH WITH SOAPAND WATER

Wear disposable dustrespirators 3M type8709.REMOVE TO FRESHAIR

General care.DRINK WATER.DO NOT VOMIT

Page 29: Training brush generator

SAFETY

Training Module: 01.02.01 Issue: A Date: September 2002 Page: 6 of 6

01.02.01 (A) Safety.doc © Brush Electrical Machines Ltd. 2002

4 OPERATION & MAINTENANCE

When working on this equipment it is important that a safe environment is achieved i.e. Isolate all electrical supplies including heaters. Ensure adequate ventilation and lighting. Use proper support for heavy items. Maintain access ways. Wear suitable protective clothing.

Safety guards and covers must be fitted, unless the equipment has been made safe behindthe guard or cover.

On-site safety procedures are to be followed as appropriate, in particular 'Permit To Work'type systems are be followed rigorously.

Attention should be given to the advice given in Clause 2 (Health & Safety At Work Act(1974)) and Clause 3 (Control Of Substances Hazardous to Health (COSHH Regulations1999))

Details of substances used on equipment that are potentially hazardous to health are detailedin Clause 3.2 and the Suppliers Data that forms part of the Operation & Maintenance Manual.

IMPROPER USE OF ELECTRICAL EQUIPMENT IS HAZARDOUS.

5 PROTECTION AND MONITORING DEVICES

WARNING: It is essential that any protection or monitoring device for usewith generators or ancillary equipment should be connected and operationalat all times unless specifically stated otherwise. It should not be assumedthat all necessary protection and monitoring devices are supplied as part ofBrush Electrical Machines Ltd. scope of supply.

Unless otherwise agreed, it is the responsibility of others to verify thecorrect operation of all protection and monitoring equipment, whethersupplied by Brush Electrical Machines Ltd. or not. It is necessary to providea secure environment that ensures operator safety and limits potentialdamage to the generator and ancillary equipment. If requested, BrushElectrical Machines Ltd. would be pleased to provide advice on any specificprotection application issues or concerns.

Page 30: Training brush generator

GENERATOR MAINTENANCE PHILOSOPHIES

Training Module: 01.03.01 Issue: A Date: September 2002 Page: 1 of 4

01.03.01 (A) Generator Maintenance Philosophies.doc © Brush Electrical Machines Ltd. 2002

GENERATOR MAINTENANCE PHILOSOPHIES

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GENERATOR MAINTENANCE PHILOSOPHIES

Training Module: 01.03.01 Issue: A Date: September 2002 Page: 2 of 4

01.03.01 (A) Generator Maintenance Philosophies.doc © Brush Electrical Machines Ltd. 2002

CONTENTS1 MAINTENANCE......................................................................................................................................... 32 MACHINE DETERIORATION.................................................................................................................... 33 MAINTENANCE PHILOSOPHIES............................................................................................................. 3

3.1 Curative Maintenance ......................................................................................................................... 33.2 Preventive Maintenance...................................................................................................................... 4

3.2.1 Time-Based Maintenance ............................................................................................................ 43.2.2 Condition-Based Maintenance..................................................................................................... 4

4 SENSORY PERCEPTION ......................................................................................................................... 4

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GENERATOR MAINTENANCE PHILOSOPHIES

Training Module: 01.03.01 Issue: A Date: September 2002 Page: 3 of 4

01.03.01 (A) Generator Maintenance Philosophies.doc © Brush Electrical Machines Ltd. 2002

1 MAINTENANCE

The term maintenance can be applied to a broad range of activities. In general, maintenance includesall activities necessary to enable the safe and efficient functioning of a machine or system, throughoutits working life.

Maintenance can be said to encompass the following activities:

1) Maintain Proper ConditionPrevent the malfunction of the machine or system.

2) Judge The Current ConditionObtain information of the actual condition of the machine or system.

3) Recondition To The Original ConditionMaintenance must be performed to repair a fault.

Recommendations for the implementation of these activities are detailed in the Operating &Maintenance Manual, but the actual maintenance programme should be determined by the end user (orhis representative) in order to reflect local site conditions e.g. operating regime, site location, operation& maintenance staff skills and availability, etc.

2 MACHINE DETERIORATION

The factors that cause machine deterioration include: When Running

Outgoing Load Thermal Load Internal Magnetic Load Internal Mechanical Load, including imbalance or misalignment. External Mechanical Factors, including forces exerted by the prime mover, and external

vibrations. Ambient Conditions, including dust, water, corrosive atmospheres

At Standstill External Mechanical Factors, including external vibrations. Ambient Conditions, including dust, water, corrosive atmospheres

From the above it can be concluded that the machine is 'subject to wear and tear' during its entire life,irrespective of the number of hours run. Any machine will therefore need to undergo a maintenanceinspection or check from time to time. The purpose of this inspection is to detect possible abnormalitiesthat, sooner or later, may disrupt its operation, or in the case of a breakdown, determine the extent ofthe damage.

3 MAINTENANCE PHILOSOPHIES

The availability of a machine has a direct influence on the wellbeing of a company. An unexpectedbreakdown can cause considerable inconvenience and financial loss. To keep a machine functioningefficiently throughout its working life can often cost more than the original cost of the machine itself,consequently the way in which maintenance is carried out is important. The objective is high reliabilitywith minimum interruption of machine operation, with minimum outlay.

There are two basic maintenance philosophies that can be adopted:

3.1 Curative Maintenance

With curative maintenance (or run-to-breakdown maintenance) a major overhaul is onlyperformed after a breakdown. Overhauls cannot be planned and interruptions in operationoccur unexpectedly.

This policy is thus only appropriate when the machine’s condition is likely to deteriorateabruptly, which is not usually the case with electrical machines. Certain components can, ofcourse, always breakdown suddenly.

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GENERATOR MAINTENANCE PHILOSOPHIES

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01.03.01 (A) Generator Maintenance Philosophies.doc © Brush Electrical Machines Ltd. 2002

3.2 Preventive Maintenance

With preventive maintenance, overhauls are planned ahead and take place in time to preventa breakdown. This means that the machine’s condition should only be expected to deterioratein a steady and predictable manner. For instance, the longer the machine is in operation themore likely the chance of a breakdown.

In practice, particularly for electrical machines, preventive maintenance is preferred because itis more likely to ensure dependable plant operation.

Preventive maintenance can be divided into two sub-categories, but in practice a combinationof the two philosophies is used:

3.2.1 Time-Based Maintenance

With time-based maintenance the machine is overhauled on the basis of calendartime and/or hours of operation e.g. once a month, year, etc. or every so manyhours.

In most cases this is acceptable, however there is the disadvantage that somecomponents will be replaced before the are completely worn out. For example, thebearing would still be functioning correctly.

3.2.2 Condition-Based Maintenance

With condition-based maintenance, the time when preventive action must beundertaken is determined by the machine’s condition. The assessment of themachine’s condition must be carried out by means of monitoring equipment andskilled engineers who know how to interpret the measurements.

4 SENSORY PERCEPTION

Sensory perception means: Looking Touching Smelling Listening

Sensory perception plays an important part in maintenance, since it is often possible to detect abnormalbehaviour or an abnormal situation at an early stage, without the use of any measuring equipment.

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PRINCIPLES OF AC GENERATION

Training Module: 01.04.01 Issue: A Date: September 2002 Page: 1 of 10

01.04.01 (A) Principles Of AC Generation.doc © Brush Electrical Machines Ltd. 2002

PRINCIPLES OF AC GENERATION

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PRINCIPLES OF AC GENERATION

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01.04.01 (A) Principles Of AC Generation.doc © Brush Electrical Machines Ltd. 2002

CONTENTS1 FARADAY'S LAW OF ELECTROMAGNETIC INDUCTION..................................................................... 32 THREE PHASE GENERATION................................................................................................................. 73 GENERATOR EXCITATION CONTROL SYSTEMS ................................................................................ 8

3.1 Conventional Excitation System (DC Generator Commutator Exciter)............................................... 83.2 Static Excitation System...................................................................................................................... 83.3 Brushless Excitation System............................................................................................................... 9

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01.04.01 (A) Principles Of AC Generation.doc © Brush Electrical Machines Ltd. 2002

1 FARADAY'S LAW OF ELECTROMAGNETIC INDUCTION

Figure 1: Electromagnetic InductionFaraday's Law Of Electromagnetic Induction, illustrated in Figure 1, states that, if a conductor is movedin a magnetic field, then an electromotive force (emf) - or simply, a voltage - is induced in thatconductor.

It follows that, if the ends of the conductor are connected to an external load, then an electric current,driven by that voltage, will flow from the conductor, through the load and back again.

Faraday showed that if a wire moves in a magnetic field, an artificial charge, or voltage, will be createdin that wire. Faraday also showed that the magnitude of the voltage induced in the moving conductordepends on the strength of the magnetic field and the speed of movement, and on nothing else. Thesetwo laws form the whole basis of electrical power generation, both AC and DC.

Fleming's Right Hand Rule for generators determines how this is achieved. Figure 2 illustrates therelationship between the magnetic field (North to South), direction of motion and direction of emf(voltage) induced in the conductor.

Figure 2: Fleming's Right Hand Rule

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PRINCIPLES OF AC GENERATION

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01.04.01 (A) Principles Of AC Generation.doc © Brush Electrical Machines Ltd. 2002

Figure 3 shows a loop of stiff wire on a shaft which can be turned. Suppose each end of the wire isconnected to a slipring, insulated from the shaft, upon which there are brushes that are connected to aload.

Figure 3: AC Generation - Fixed FieldAs the shaft is turned, one bar passes the N-pole as the other passes the S-pole. Voltage is inducedone way in one bar and the opposite way in the other. Figure 4 illustrates how an alternating currentwaveform (sine wave) is induced in the rotating coil as it passes the fixed magnetic field.

Figure 4: Alternating Current

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PRINCIPLES OF AC GENERATION

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01.04.01 (A) Principles Of AC Generation.doc © Brush Electrical Machines Ltd. 2002

Faraday's theory required only that the conductor should be moving through a magnetic field i.e. thatthere should be relative motion between conductor and field. It would work just as well if the magneticfield moved past the conductor. In the arrangement shown in Figure 5 this is just what's happening.

Figure 5: Rotating Field (Permanent Magnet)In the above diagram, the stiff wire loop is fixed, and the permanent magnet is rotated past it and insideit. As a pole passes a fixed conductor a maximum voltage is induced in it, opposite voltages on oppositesides, and they add up to give double voltage at the terminals or at the voltmeter.. In this arrangementno sliprings or brushes are needed which would be advantageous for a number of reasons, not leastthe reduced maintenance requirement.

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PRINCIPLES OF AC GENERATION

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01.04.01 (A) Principles Of AC Generation.doc © Brush Electrical Machines Ltd. 2002

So far only permanent magnets have been considered for producing the magnetic field. Far betterresults can be achieved by using an electromagnet, which can produce much stronger fields andtherefore much higher induced voltages (See Figure 6).

Figure 6: Rotating Field (Electromagnet)In this case however DC power must be provided to the coil which magnetises it. This can come from abattery or other DC source, but a pair of sliprings and brushes must be used to bring the battery currentto the moving magnetising coil - called the 'field coil'. This coil is said to 'excite' the field and the wholeprocess is called 'excitation'.

Because the field magnet is not permanent but is an electromagnet, it is possible to vary the coil currentby a resistance and so vary the strength of the magnetic field itself. This in turn will vary the amount ofthe induced voltage.

Using this principle, it is possible for an Operator to control the machine's voltage (remotely) by varyingthe excitation. This is illustrated in the following diagram.

Figure 7: Voltage Control

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PRINCIPLES OF AC GENERATION

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01.04.01 (A) Principles Of AC Generation.doc © Brush Electrical Machines Ltd. 2002

2 THREE PHASE GENERATION

Figure 8: Three Phase Generation - Windings The above diagram illustrates how the basic AC generator principles are applied to produce the threephase generation waveforms shown in Figure 9.

Figure 9: Three Phase Generation - Waveforms

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01.04.01 (A) Principles Of AC Generation.doc © Brush Electrical Machines Ltd. 2002

3 GENERATOR EXCITATION CONTROL SYSTEMS

Figure 7 showed how it would be possible (for an Operator) to control the main machine's voltage byadjustment of the resistance which in turn varies the excitation i.e. If the Operator knows the voltage hewants to see on a voltmeter connected to the generator output, he can adjust the resistance until therequired value is achieved. This is called 'excitation control'.

To make the process automatic, an electronic device called an Automatic Voltage Regulator (AVR) orExcitation Controller is used to sense the output voltage and compare it with a datum which haspreviously been set by hand. The AVR decides whether the output voltage is correct, too high or toolow.

There commonly used types of excitation control systems for ac generators output control are:

3.1 Conventional Excitation System (DC Generator Commutator Exciter)

GENERATOR

DC Exciter

AVR

SensingOnly

Figure 10: Excitation System - ConventionalIn this system, a dc control signal is fed from the excitation control to the stationary field of thedc exciter. The rotating element of the exciter then supplies a direct current to the fieldwinding of the main ac generator. The rotating armature of the dc exciter is either driven fromthe same shaft as the rotating main field of the generator, or can be on a separate motordriven shaft. In both cases, a dc commutator is required on the exciter, and brushes andsliprings (collector rings) are required on the rotating generator field to carry the maingenerator field current. This system is sometimes used on smaller or older machines.

3.2 Static Excitation System

GENERATOR

AVR

SensingAnd Power

StaticExciter

Figure 11: Static Excitation System

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Static excitation systems obtain power from the electrical output of the generator or from theconnected system to feed rectifiers in the regulating system, which in turn supply directcurrent to the main field winding of the generator through brushes and sliprings.

3.3 Brushless Excitation System

Brush generators are now almost exclusively fitted with 'brushless' excitation systems in whichthe exciter shares a common shaft thus doing away with the need for sliprings and brushes.Since a DC generator used as an exciter would require the brushgear to rotate, the mainexciter is another, but smaller, AC generator with stationary field and rotating armature. TheAC output from this armature is taken converted to DC through 'rectifiers' rotating with theshaft, and then fed to the rotating field winding of the main generator.

AVR

Main ACExciter

RotatingRectifier

Generator SensingAnd

Power

Figure 12: Brushless Excitation SystemIn this system the ac armature of the exciter, the rotating three phase diode bridge rectifier,and the main field of the ac generator are all mounted on the same rotating shaft system. Allelectrical connections are made along or through the centre of the shaft.

It is common to add a small second, or 'pilot' exciter (or permanent magnet generator - PMG)to excite the main exciter.

AVR

Main ACExciter

RotatingRectifier

Generator VoltageSensing

OnlyPilotExciter

Power

Figure 13: Brushless Excitation System With Pilot Exciter

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AVR

Main ACExciter

RotatingRectifier

Generator Power AndVoltageSensing

Short-CircuitCurrent

Transformers

Figure 14: Brushless Excitation System (Without Pilot Exciter)Some Customers prefer a brushless excitation system that does not use a pilot exciter. Thisarrangement is illustrated in the above diagram.

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POWER GENERATION SYSTEMS

DCAC

AVR

SENSINGVT

CT

ROTOR

STATOR

PMG EXCITER

ROTATINGRECTIFIER

LOAD

PRIMEMOVER

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CONTENTS1 PRIME MOVER/GENERATOR.................................................................................................................. 3

1.1 Arrangement........................................................................................................................................ 31.2 Prime Mover & Governor .................................................................................................................... 31.3 Generator & AVR ................................................................................................................................ 4

2 GENERATOR OPERATION ...................................................................................................................... 52.1 General................................................................................................................................................ 52.2 Island Operation .................................................................................................................................. 52.3 Parallel Operation................................................................................................................................ 6

3 AUTOMATIC VOLTAGE CONTROL......................................................................................................... 74 PARALLEL OPERATION.......................................................................................................................... 8

4.1 Quadrature Current Compensation..................................................................................................... 84.2 Machines In Parallel .......................................................................................................................... 10

5 GOVERNOR DROOP .............................................................................................................................. 115.1 Introduction........................................................................................................................................ 115.2 Case 1 - Zero Droop (Isochronous) .................................................................................................. 125.3 Case 2 - With Droop.......................................................................................................................... 12

6 GENERATOR OUTPUT........................................................................................................................... 13

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1 PRIME MOVER/GENERATOR

1.1 Arrangement

Figure 1: Main Components Of A Generating Package

1.2 Prime Mover & Governor

The prime mover is mechanically linked, or coupled, to the generator either directly or by agearbox. It would typically be a turbine (gas, steam, water or wind) or a diesel engine. Itsfunction is to rotate the generator. As the generator is usually a synchronous machine, therotational speed is required to be kept fairly constant and this is the function of the governor.

Modern governors are normally electronic, providing a fast, closed loop control but the outputmay take many forms to suit the prime mover being controlled. The governor output can be afuel, water or gas valve; being opened to increase speed or closed to reduce it. Some form ofspeed signal is fed to the governor and compared with an adjustable reference. Thedifference, the error, is used to control the output.

The speed to which the governor controls, the speed datum, is adjustable over a small range;the adjustment usually being made by means of a ‘speeder motor’ in the case of mechanicalgovernors or by an up/down counter in electronic units. The raise/lower signals might comefrom a control switch, an automatic synchroniser or an automatic control system.

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1.3 Generator & AVR

The Generator converts rotational mechanical energy produced by the prime mover intoelectrical energy.

Figure 2 illustrates how the various elements are connected to a brushless generator AVRsystem.

DCAC

AVR

SENSINGVT

CT

ROTOR

STATOR

PMG EXCITER

ROTATINGRECTIFIER

LOAD

PRIMEMOVER

Figure 2: Generator/AVR Block DiagramThe purpose of the pilot exciter is to provide a source of excitation power whenever themachine is running. The pilot exciter is a single phase permanent magnet generator (PMG),with the magnets mounted on the shaft, and the AC output being generated in the stator.

The main exciter is of the brushless type and comprises a fixed part called the main exciterstator, and a rotating part called the main exciter armature. The main exciter stator iscomprises laminated steel field poles around which are the field coils.

The three phase AC output from the main exciter armature is connected to the rotatingrectifier assembly, which converts the AC output to the DC input required in the generatorrotor winding (See Figure 3) . The rotating rectifier assembly is a three phase full wave bridgeconfiguration, with fuses in series with each rectifier diode. On larger machines more thanone fuse/rectifier diode may be fitted to each arm of the bridge. Electrical connectionsbetween the rectified output and the generator rotor winding are carried in the central borethrough the machine shaft.

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ExciterField

Winding

ExciterArmatureWinding

GeneratorStator

Winding

Negative Heat Sink

Positive Heat Sink

Silicon Diode

Fuse

Gen

erat

or F

ield

Win

ding

Rectifier Assembly

Rotor

Figure 3: Brushless Generator SchematicThe voltage regulator allows the Operator to control the generator's voltage by variation ofexcitation. This is called 'excitation control'. To make the process automatic, an electronicdevice called an Automatic Voltage Regulator (AVR) or Excitation Controller is used tosense the output voltage and compare it with a preset datum. The AVR decides whether theoutput voltage is correct, too high or too low.

The power output of the machine is produced in the generator stator windings.

2 GENERATOR OPERATION

2.1 General

The power (MW, kW, W or Watts) supplied at the generator terminals is provided by the fuelsupplied to the prime mover (turbine or engine), which is determined by the prime movergovernor.

When a generator is used to supply power, it can be operated isolated, sometimes referred toas island mode, or in parallel with a system or other machines.

2.2 Island Operation

In island operation, the machine speed is determined by the load and fuel supply, and thegenerator voltage is determined by the excitation. Because the unit operates in isolation, thegenerator power factor is equal to the load power factor.

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FUELREGULATOR

PRIMEMOVER

MECHANICALPOWER

FUELGENERATOR

ELECTRICALPOWER

GOVERNORSPEEDSIGNAL

FIELD

VOLTAGESIGNAL

LOAD

VOLTAGEREGULATOR

Figure 4: Island Mode OperationWhen operating in isolation, an increase in load will have two effects:

1) Speed will initially fall because the energy being supplied by the fuel is less than thatrequired by the load.

The speed reduction is detected by the governor, which opens the prime mover fuel valveby the required amount to maintain the required speed.

2) Voltage will initially fall because the generator excitation is too low to maintain nominalvoltage at the increased load.

The voltage reduction is detected by the automatic voltage regulator (AVR) whichincreases the excitation by an amount required to maintain output voltage.

2.3 Parallel Operation

FUELREGULATOR

PRIMEMOVER

MECHANICALPOWER

FUELGENERATOR

ELECTRICALPOWER

GOVERNORSPEEDSIGNAL

FIELD

LARGEPOWERSYSTEM

VOLTAGEREGULATOR

V

ISENSINGSIGNALS

Figure 5: Parallel OperationWhen a machine operates in parallel with a power system, the voltage and frequency will befixed mainly by the system.

The fuel supply to the prime mover determines the power which is supplied by the generatorand this is controlled by the governor.

The generator excitation determines the internal emf of the machine and therefore affects thepower factor when the terminal voltage is fixed by the power system.

The governor and AVR are arranged to have characteristics which allow them to be stablewhen the generator is operating in parallel with a power system. (See Section 4 - ParallelOperation).

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In single and parallel operation it is important to realise that power is determined by the fuelsupply to the prime mover, and that excitation determines voltage when single running, andpower factor when parallel running.

3 AUTOMATIC VOLTAGE CONTROL

PILOTEXCITER

BRUSHLESSGENERATOR

VOLTAGE& CURRENT

SENSINGTRANSFORMERS

EXCITERFIELD

CONTROLLEDRECTIFIER

CONTROLSIGNAL

AMPLIFIERERRORSIGNAL

ADJUSTABLEREFERENCE

VOLTAGE

SENSINGSIGNAL

STABILISINGNETWORK

Figure 6: Principal Components Of A Generator And AVRThe above diagram shows the principal components of the generator and its AVR.

The voltage transformer (VT) provides a signal proportional to line voltage to the AVR where it iscompared to a stable reference voltage.

The difference (error) signal is amplified and then used to control the output of a thyristor rectifier whichsupplies a portion of the PMG output to the exciter field.

If the load on the generator suddenly increases the reduction in output voltage produces an error signalwhich, when amplified, causes an increase in exciter field current resulting in a corresponding increasein rotor current and generator output voltage.

Conversely, load reduction will cause the generator voltage to suddenly increase, and in this case theamplified error signal will cause a reduction in exciter field current resulting in a corresponding reductionin rotor current and generator output voltage.

Because of the high inductance of the generator field windings, it is difficult to make rapid changes infield current. This introduces a considerable 'lag' in the control system which makes it necessary toinclude a stabilising circuit in the AVR to prevent instability and optimise the generator voltage responseto load changes. Without a stabilising circuit, the regulator would keep increasing and reducingexcitation and the line voltage would continuously fluctuate above and below the required value.

Modern voltage regulators are designed to maintain the generator line voltage within better than ±1% ofnominal for wide variations of machine load.

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4 PARALLEL OPERATION

4.1 Quadrature Current Compensation

As mentioned earlier when a generator is connected in parallel with another power system itmay be incapable of significantly influencing the system line voltage, with the level ofexcitation now determining the reactive power developed by the generator. If line voltage wereless than that called for by the voltage regulator, it would supply maximum available excitationin an attempt to increase line voltage and excessive lagging reactive line current would flow.

Similarly, if line voltage were high, excitation would be reduced to zero in an attempt to reduceline voltage, and excessive leading line current would flow. Under such circumstances thegenerator could pole slip (run asynchronously) if any significant power were flowing.

A standard method of overcoming the above problem is to modify the voltage control systemso that as lagging reactive load on the generator increases, the line voltage that the regulatordemands is reduced as shown in Figure 7 in which it will be seen that as the system voltagefalls from level A to level B the lagging reactive current increases. For a fixed line voltage,,generator reactive current may be varied by adjustment of the voltage setting potentiometerwhich adjusts the position of the AVR characteristic.

AVRCHARACTERISTIC

GENERATORLINE VOLTAGE

A & B REPRESENTTWO SYSTEM VOLTAGES

A

B

LEADING LAGGINGREACTIVE CURRENT

0

Figure 7: Voltage Control Characteristic For Parallel OperationA method of achieving the above AVR characteristic is known as Quadrature CurrentCompensation (QCC). A voltage proportional to one line current is added to the voltageacross the other two lines and the amplitude of the vector sum is regulated by the AVR asillustrated in the following diagram.

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AVR

V

ISCHEMATIC DIAGRAM

V

ABC

1

C

VECTOR DIAGRAMSφ

φI

I

I

A

C

B

A

C B

V

VVAB

C

1

Figure 8: Quadrature Current Compensation

It will be seen that the sensing voltage, V1, is the vector sum of line voltage and a voltageproportional to the line current signal, VC. If line voltage is much greater than VC, the followingapproximation way be made.

V1 = VBA + VC sin φ

where φ is the phase angle.

Thus as lagging reactive load increases, so does the last term of the above expression whichis proportional to reactive current, and therefore line voltage is reduced as the AVR acts tomaintain V1 constant. For leading reactive currents, line voltage is increased. The reduction inline voltage for rated current at zero power factor lagging is typically 5%.

Provided line voltage does not vary, reactive current will be controlled to a level determined bythe voltage setting potentiometer of the AVR. If, however, line voltage varied appreciably, anOperator would have to continually adjust the potentiometer to prevent excessive lagging orleading currents. Under such circumstances it may be desirable to use an automatic reactivecurrent or power factor control system.

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4.2 Machines In Parallel

Where a number of machines are operated in parallel, it is usual to adjust the regulators togive a similar amount of droop. This will ensure that the total VAR loading on the systemremains reasonably balanced between generators.

If droop settings are not equal, the machine with the least droop will tend to take more than itsshare of the load VARs. This means that the set with least droop will run at a lower laggingpower factor than the others.

LOAD

A B C

TOTAL VARS(SET BY LOAD)

A & B HAVEEQUAL DROOP

C HASLESS DROOPTHAN A & B

VOLTAGE

LEAD 0 LAG VARsVARs OnA & B

VARs OnC

A & B

C

SYSTEM VOLTAGE

Figure 9: Three Machines In Parallel On Independent LoadIn the above diagram, machines A and B have identical droop and at a particular line voltagewill supply equal VARs.

Machine C has less droop and will therefore supply more VARs than A or B, at the same linevoltage.

When a machine operates in parallel with an infinite busbar as shown in the followingdiagram, the busbar behaves like a machine with zero droop, therefore if the busbar voltageremains constant, the generator will produce constant VARs.

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A

INFINITE BUSBAR

GENERATORVOLTAGE

LEAD 0 LAG VARs

Y

SYSTEM VOLTAGEXX'

Y'CHARACTERISTICOF MACHINE A

INCREASINGAVR SET POINT

Figure 10: Machine In Parallel With Infinite BusbarTo adjust the VARs on the machine it is necessary to raise or lower the position of line X-Y byadjusting the AVR datum. This is the usual method of manually adjusting VARs or PowerFactor.

5 GOVERNOR DROOP

5.1 Introduction

When operating in parallel the prime mover fuel control system is also changed from aconstant frequency control system to one which can operate when the frequency isdetermined by the grid system. A simple arrangement often used is known as governor droopwhere the governor speed datum is reduced as the load increases.

SPEED(FREQUENCY)

POWER

Y

SYSTEMFREQUENCY

YY'

Y'

INCREASINGGOVERNOR SET POINT

0 100%

Figure 11: Governor Droop CharacteristicIn this simple arrangement the system frequency determines the point on the characteristic,and adjustment of the governor datum will raise or lower the line Y-Y and allow the load to beadjusted.

As in generator controls, wide variations of system frequency would give rise to large powervariation and in such cases it would be normal to include an automatic load control system inthe governor.

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5.2 Case 1 - Zero Droop (Isochronous)

To explain the need for speed droop consider firstly the case of two generating packageswithout droop. These are required to run in parallel on an ‘Island’ system such as an isolatedoil rig.

Consider Package A, set to 50Hz, already on the bars and loaded to about half full load - noproblem here. If the load should vary, the governor will adjust the fuel to bring the speed backto 50Hz.

Now if Package B was needed, it would be synchronised to the bars usually by setting it alittle faster, say 50.1Hz. Once the breaker is closed, the two sets are locked together and thetroubles begin. The common speed of the two packages is likely to be somewhere between50 and 50.1Hz. The governor on Package B will see this speed as too slow and increase thefuel supply. At the same time Package A’s governor will see the speed as too fast and reducefuel. Neither of these actions change the situation and the governors continue to fight,Package B will take all the available load and Package A will trip on reverse power.

5.3 Case 2 - With Droop

Now consider what happens when this is repeated but with the governor of Package B havingdroop. As before, Package B’s governor sees the speed as too low and increases fuel andagain Package A’s fuel is reduced, but, as the power provided by B increases so its speedsetting is reduced automatically by the droop mechanism and soon falls to 50Hz at whichpoint both governors are happy.

The governor of Package A with zero droop is said to be ‘isochronous’. Figure 12 shows thecharacteristics of two such packages, one with droop and one isochronous.

Figure 12: Isochronous/Droop Characteristics

If further sets are needed on the bars then they too must have speed droop. Just one set maybe left in the isochronous mode and this set then effectively controls the frequency of thewhole power system.

Such an arrangement may seem ideal but, apart from the difficulty of ensuring that one, andonly one of the sets is isochronous, there is another problem: any load change is thrownsolely onto the isochronous set.

It is more common to give all sets equal droop and in this way any load changes are sharedequally between the running sets. The slight reduction in frequency as load is applied is asmall penalty to pay for an inherently stable arrangement. In any case, a power managementsystem such as PRISMIC will off-set this and keep the system frequency constant in the longterm.

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6 GENERATOR OUTPUT

The generator is usually the only load driven by the prime mover and this produces a three phaseoutput at a voltage to suit the distribution arrangement of the power system. Typical nominal voltagesare 600V, 3300V, 6600V, 11,000V or 13,800V.

The design of the generator determines the voltage it can produce, but merely spinning the machine willonly generate about 5% nominal volts (produced by the residual magnetism of the rotor). To producefull voltage the generator has to be excited. In the case of a brushless generator this is done byapplying a DC voltage to the exciter field. The control of the generator output voltage by this means isthe job of the automatic voltage regulator (AVR).

The task of any AVR is to maintain the generator voltage at a set level. A dip in voltage caused by anincreased load on the machine will be compensated by increasing the voltage applied to the field.Modern AVRs employ semi-conductor devices to provide excitation and offer a fast response tomaintain line voltage in the face of varying loads.

Like the governor, the AVR has a droop characteristic but, in this case, it is the voltage that falls andwith increasing reactive rather than real power (See Training Module 04.10.01). The voltage droop iscan be set between 0 and 10%, a value of 4% being common. The droop allows the generator to sharereactive power stably with other paralleled machines.

The generator is selected to match the speed and power of the prime mover; the output frequency isgiven by the following formula:

f= N x p

where: f is the generator frequencyN is generator speed in revs per secondp is the number of pairs of poles on the generator

Thus a four-pole generator running at 1500 rpm (25 revs/second) will give a frequency of 50Hz.

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BLANK PAGE

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SYNCHRONISING

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CONTENTS1 INTRODUCTION........................................................................................................................................ 32 DC GENERATORS.................................................................................................................................... 33 AC GENERATORS.................................................................................................................................... 44 SYNCHRONISING AC GENERATORS .................................................................................................... 55 LAMP SYNCHRONISING.......................................................................................................................... 6

5.1 The 2-Lamp Method............................................................................................................................ 65.2 The 3-Lamp Method............................................................................................................................ 7

6 SYNCHROSCOPE..................................................................................................................................... 87 SYNCHRONISING AT THE SWITCHBOARD/CONTROL PANEL .......................................................... 88 AUTOMATIC SYNCHRONISING .............................................................................................................. 99 CHECK SYNCHRONISING ....................................................................................................................... 910 CLOSING ONTO DEAD BUSBAR ...................................................................................................... 10

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1 INTRODUCTION

The idea of synchronising is not new. Every time you change gear in a car you synchronise the engineto the road speed so that, when the clutch is let in, both shafts are running at the same speed and thereis no jerk. Conversely, if you synchronise badly there is a jerk, stress on the engine and possibly a lot ofnoise.

In electrical engineering, synchronising is to either electrically 'join' the output of an AC generator to alive busbar, or join live bus sections together. Generator synchronising is applicable to installations thathave more than one generator and/or are connected to another (external) network or grid.

When synchronising two electrical systems, the moment the circuit breaker closes the systems aremechanically locked through the busbars. Any synchronising displacement will cause the smaller of thesystems to lock very quickly resulting in mechanical stresses in the both the prime mover and generatorrotors and foundations. In turbines blades can be damaged. In generators windings and rotating diodescan be damaged due to the high transient currents that can occur during this 'fault' condition.

2 DC GENERATORS

The simplest case of synchronising occurs with dc generators.

Figure 1: DC Generators Figure 1 represents two dc generators, both on open circuit but about to be paralleled by a switch.Each is separately excited such that machine 'A' has an open-circuit voltage VA and machine 'B' VB.Machine 'A' is assumed to be the 'running' generator, and machine 'B' , is the 'incoming' generatorwhich is to be paralleled to 'A'.

Before closing the switch which puts the two generators in parallel it is necessary only to ensure thattheir voltages are the same -that is, that VB = VA ; then the switch may be closed, and no suddencurrent will flow - there will be no electrical 'jerks'.

If the voltages were different, suppose that VA is greater than VB. On closing the switch there will be aclosed loop with the emf's VA and VB opposing one another. Since VA is greater than VB there is a netclockwise emf in the loop, which will cause a clockwise current IC to flow round it (shown in red), limitedonly by the resistances of the two armatures. This current appears suddenly as the switch is closed,putting a sudden load onto generator 'A' so causing it to slow with a jerk, and causing generator 'B' tomotor, making it accelerate with a jerk.

This circulating current, which occurs on closing the switch whenever VA and VB are not equal, is alsocalled the 'synchronising current'. To avoid it and its consequent jerking effect on the system, theincoming machine voltage must first be matched to the voltage of the running machine - normally doneby trimming the field of the incoming generator.

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3 AC GENERATORS

With ac generators the problem is more complicated. It can be seen in the dc case how a circulatingcurrent is caused by differing opposing voltages. In dc this is straightforward, but in ac a voltagedifference can be caused either by differing voltage amplitudes or, for the same voltage amplitudes, bydiffering phase.

Figure 2: Voltage And Phase DifferenceIn Figure 2(a) the two voltages VA and VB are in phase with one another, but their amplitudes aredifferent. At any instant such as time T, the instantaneous voltage of machine 'A' is TA and that ofmachine 'B' is TB. Therefore there is, at that instant, a voltage difference AB which will cause acirculating current to flow between the generators when the paralleling switch is closed. This is true atany instant other than a common voltage zero.

In Figure 2(b) the two voltages have equal amplitudes but are displaced in phase, VB lagging on VA .Atany instant such as time T the instantaneous voltage of machine 'A' is TA and that of machine 'B' is TB.Although the two voltages are equal in amplitude, there is still an instantaneous difference of voltage ABwhich will cause a circulating current to flow between the generators when the paralleling switch isclosed. Therefore, even though the voltage levels (as read by voltmeters) are the same, a difference ofphase will still cause a circulating, or 'synchronising', current to flow between the machines, causingone to accelerate and the other to decelerate and to jerk them into phase with each other as the switchis closed.

Therefore, to prevent sudden circulating currents occurring and to achieve smooth paralleling, thevoltages of both machines must first be equalised and the machines then brought into phase. This isdescribed in the following section.

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There is one further requirement. As when changing gear in a car, the two generator speeds must alsobe equalised before paralleling. If this is not done, the faster machine will be jerked back and the slowerjerked forward, which could cause serious mechanical problems in large machines, as well as to thecouplings, gear trains and prime movers.

If the two machines are running at different speeds before paralleling, this will show as differentfrequencies on the frequency meters. Therefore a preliminary to synchronising is to equalise as nearlyas possible not only the machine voltages but also their frequencies, using the switchboard voltmetersand frequency meters.

The following conditions must be equal before closing the circuit breaker: Voltage Frequency Phase Phase Rotation

In some situations it may be preferable to have the generator being synchronised running sllghtly fast(super-synchronous) at the moment of circuit breaker closure so that power flows from the primemover into the busbars.

Conversely, it may be preferable to have the generator being synchronised running sllghtly slow (sub-synchronous) at the moment of circuit breaker closure so that power flows from the busbars into theprime mover. This may however cause the generator 'reverse power' protection system to operate.

4 SYNCHRONISING AC GENERATORS

It is assumed that one machine' A ' (the 'running' generator) is already in service on the busbars and ison load, and that a second machine 'B' (the 'incoming' generator) has been started and run up and isready to be put in parallel with 'A' in order to share its load. Before this can be done the incominggenerator 'B' must be synchronised with the running machine 'A'.

As already described, the first step is to match the incoming to the running voltage by reference to thevoltmeters on the two generator control boards, and by using the incoming voltage regulator to trim it.Similarly the incoming frequency is matched to the running frequency by reference to the two frequencymeters and by trimming the incoming speed regulator. Note that the running machine controls shouldnot be touched - the incoming machine is always matched to the running, not vice versa.

It now remains to bring the generators into phase. Even after matching the frequencies by meter, thespeeds will still not be exactly equal, and one machine will be slowly overtaking the other. As thisoccurs, their phase relationship will be steadily, but slowly, changing. The idea is to make this takeplace as slowly as possible and, as they momentarily pass through the 'in-phase' state, to catch them atthat point, to close the paralleling switch and to lock them there.

There are two ways in which the correct phase may be detected - the first is by lamps, and the other isby an instrument called a synchroscope.

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5 LAMP SYNCHRONISING

5.1 The 2-Lamp Method

Figure 3: Lamp Synchronising (2-Lamp Method)Synchronising by lamps makes use of the circuit shown in Figure 3; two lamps in series areconnected across the same phase of each generator. Only when the two systems are inphase is the voltage across the lamps continuously zero, and both lamps are out. At all othertimes there is a voltage difference, and the lamps glow. This is known as the 'lamps dark'method of synchronising.

The voltage phase vectors of both generators are shown. Machine No 1 is the 'running' and itsvectors are in full line. Machine No 2 is the 'incoming' and its vectors are dotted. It isapproaching synchronism with No 1.

When the machine frequencies are nearly equal, the lamps are switched on and alternatelyglow and go out, giving a slow flashing appearance. The nearer the frequencies are to beingequal, the slower the lamp flashing period. Therefore to achieve phase matching, theincoming machine's speed is slowly trimmed until the lamps are flashing very slowly; then, asthey are changing from bright to dark, the operator places his hand over the breaker controlbutton or handle and, at the moment when the lamps go completely out, operates it to closethe breaker. The lamps then stay out, but they should be switched off after completing thesynchronising.

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Note: The lamps could be connected to burn at their brightest, instead of being dark, whenthe systems are in phase, but this 'lamps bright' method is seldom used today. It is easier todetect the exact point of 'no light' in a lamp than to estimate when it is at its brightest. The'lamps dark' method is almost universally found.

It is necessary to use two lamps in series because, when the systems are fully out of phase(lamps at brightest), the voltage difference is then double the system phase voltage.

5.2 The 3-Lamp Method

Figure 4: Lamp Synchronising (3-Lamp Method)An alternative method, known as '3-lamp synchronising' can also be used. It is shown inFigure 4.

The three lamps are connected as shown: No.1 (yellow-to-yellow)I No.2 (blue-to-red) andNo.3 (red-to-blue). In the centre diagram the full lines refer to generator 'A' (R1, Y1 and B1),and the dotted lines to generator 'B' (R2, Y2 and B2). Machine 'B' is shown approachingsynchronism with machine' A '.

With the lamps so connected, the voltage across No.1 lamp (Y1 - Y2) is small, and the lampglows dimly. The voltages across No.2 and No.3 lamps (B1 - R2 and R1 - B2) are large, andboth lamps are bright. As synchronism is reached (left-hand of the three lowest diagrams)No.1 lamp goes out and the other two have equal brightness.

When the two generators are 120o out of synchronism (centre of the three diagrams) it can beseen that it is No.2 lamp (B1 - R2) which has no voltage and goes out. 120o later (right handdiagram) No.3 lamp (R1 - B2) goes out.

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Thus, as generator 'B' catches up with generator 'A', each lamp goes out in turn, and at adecreasing rate, as synchronism is approached. Finally, at synchronism, No.1 lamp remainsextinguished long enough for the generator breaker to be closed.

The lamps are arranged either in a triangle with No.1 at the top, or in a line with No.1 in thecentre. They may be lettered 'A', 'B' and 'C' instead of being numbered. Depending onwhether the order of going out is clockwise or anti-clockwise with the triangular arrangement,or left-to-right or right-to-left with the inline arrangement, the operator can deter-mine whetherthe incoming generator ,is fast or slow - which cannot be done with the 2-lamp method.

6 SYNCHROSCOPE

Figure 5: Synchroscope A typical synchroscope is shown in Figure 5. It is an instrument with a movement similar to that of apower factor meter, but with the two windings fed from the running and incoming voltages. Whereas in apower factor meter the current/voltage phase relationship is fixed and the pointer is stationary, in asynchroscope the phase relationship between the two voltages is constantly changing and the pointerrotates continuously, the direction of movement depending on whether the incoming machine is rotatingfaster or slower than the running. The face is marked with arrows denoting FAST or SLOW; these termsalways refer to the incoming generator. When the pointer passes through the 12 o'clock position, themachines are momentarily in phase. Some synchroscopes are marked '+' and '-'. The plus signcorresponds to FAST and the minus to SLOW).

Standard specifications often require lamp back-up to the synchroscope.

Many early synchroscopes are short time rated, and it is necessary to switch off these units when thesynchronising operation has been completed.

7 SYNCHRONISING AT THE SWITCHBOARD/CONTROL PANEL

Most switchboards/control panels control two or more generators, and some systems have sectionbreakers or interconnectors to other generator systems, anyone of which may have to be synchronisedwith running machines. It would not be economic to have a separate synchroscope for each one, as it isused only infrequently.

Common practice is therefore to have one synchroscope (sometimes with back-up lamps) in a centralor conspicuous position on or near the switchboard/control panel together with selector switcheswhereby any chosen machine may be made the 'Incomer'. Selection may be by manual switch, key orplug. The running side is usually taken from the busbar. Where the switchboard handles high voltagethe incoming and running voltage signals are taken through voltage transformers. The synchroscope isnormally provided with fuses and an isolating switch, as it is not good practice to leave it in circuit whenit is not in use.

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To use the synchroscope, having selected which is to be the incoming generator, the voltages andfrequencies are first matched as already described in Section 4. The synchroscope is then switched on;its pointer will be rotating. The incoming speed regulator is trimmed until the pointer is moving veryslowly in the FAST direction. As it next approaches the 12 o'clock position, the hand is placed over thebreaker control button or handle and, just before the pointer reaches 12 o'clock, it is operated to closethe breaker. The synchroscope will then stop and remain locked in the 12 o'clock position as thegenerators remain in synchronism. Finally, the synchroscope should be switched off.

The reason why the incoming generator should be running the faster is that, when the breaker isclosed, it will immediately take up a small part of the load. If it were running slower, that load would benegative - that is, the machine would 'motor' - and a reverse power situation would exist. Thegenerator's reverse power protection might then cause the breaker to trip.

8 AUTOMATIC SYNCHRONISING

It is common for switchboards/control panels to be provided with an automatic synchronising feature.The automatic synchroniser compare the incoming and running voltages and frequencies as well astheir phase relation. Should any of these be outside limits, the incoming voltage regulator or speedregulator is automatically trimmed. Only when all three are within predetermined limits is a signal givenautomatically to the circuit breaker to close.

Here again there is usually only one auto-synchronising unit to each switchboard; it is connectedautomatically to whichever machine is being started so long as the synchronising selector switch is setto AUTO.

Auto-synchronising is usually reserved for generators only. All other synchronising - for example acrosssection breakers or interconnectors or on L V switchboards - is normally by hand.

9 CHECK SYNCHRONISING

In many instances, particularly with smaller generators and in the cases just mentioned, automaticsynchronising is not used, and the exercise must be carried out manually by lamp or synchroscope. Insuch cases there is a danger that, if the manual synchronising is carried out unskilfully, the switch couldbe closed at the wrong instant and severe damage could result to expensive machinery.

This can be prevented by 'check synchronising'. The equipment is similar to that used for auto-synchronising, but it does not automatically trim the incoming voltage, frequency and phase - it onlymonitors them. Nor does it carry out the final act of closing the circuit breaker automatically; these allhave to be done manually by the operator. However it does inhibit the breaker's manual closing circuitso that, unless all three synchronising conditions are satisfied together, the operator cannot close thebreaker even though he presses the CLOSE button. If the breaker then fails to close, the wholesynchronising process must be repeated.

Some check synchronising units sense only phase angle difference and do not monitor voltage orfrequency differences. They rely on manual adjustment of voltage and frequency and only inhibit theclosing of the breaker when the phase angle difference is excessive. It should be noted that voltagedifference will cause circulating reactive current only. Although this is not desirable, it does not causeany mechanical shock and consequent damage to the transmission or the turbine since no active poweris involved.

When, and only when, the check synchroniser is satisfied that the voltages, frequencies and phasedifference are within acceptable limits (or, in the case of the 'phase only' type, that the phase differenceis within limits), it closes a contact which 'arms' the circuit-breaker closing circuit, so permitting closurewhen the operator presses the CLOSE switch. The same contact on the check synchroniser can alsomomentarily light an IN SYNCHRONISM or READY TO SYNCHRONISE lamp, indicating to theoperator that the breaker is ready for closing. Once this lamp has gone out again, he cannot close thebreaker until it illuminates a second time.

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Where check synchronising is fitted, it is brought automatically into circuit whenever a second orsubsequent generator has been started and selected for switching on-line; it so serves as a protectionagainst incorrect operation.

Check synchronisers may also be fitted across section breakers, interconnectors and L V incomersfrom transformers - in fact at any point in the network where it might be possible to close across twounsynchronised systems accidentally. They are also fitted across main generator incomer breakerseven when auto-synchronising is provided. They are usually arranged to come into action automaticallyif manual synchronising is selected.

Sometimes operators form the bad habit of holding the breaker control switch closed beforesynchronism is reached, and relying on the arming contact of the check synchroniser to complete theclosing circuit. This is bad practice and must be avoided.

10 CLOSING ONTO DEAD BUSBAR

If it is required to connect an incoming generator, or L V transformer incomer, onto a dead busbar, thecheck synchroniser will not allow it to happen because, one side being dead, the two sides can neverbe in synchronism. In that case the check synchroniser must be temporarily 'cheated' while theconnection is made. On most switchboards/control panels a special switch is provided for this purpose.It is spring-Ioaded to return to the OFF position so that the check synchroniser cannot be leftpermanently out of operation. This cheating switch may be tagged CLOSE ONTO DEAD BUSBAR orCHECK SYNC. OVERRIDE or other similar wording.

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CONTENTS1 INTRODUCTION........................................................................................................................................ 32 STATOR CURRENT .................................................................................................................................. 33 POWER OUTPUT ...................................................................................................................................... 34 ROTOR CURRENT.................................................................................................................................... 45 STABILITY OF THE ROTOR..................................................................................................................... 46 TEMPORARY LIMITATION....................................................................................................................... 57 USE OF THE CAPABILITY DIAGRAM ..................................................................................................... 68 CAPABILITY DIAGRAM FOR SYNCHRONOUS MOTOR....................................................................... 89 CAPABILITY DIAGRAM FOR SYNCHRONOUS CONDENSER ............................................................. 9

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1 INTRODUCTION

The principal limitations on the output of a generator are as follows: Current heating of the stator (armature). Power Output of the prime mover. Current heating of the rotor (field). Stability of the rotor angle.

There are other limitations such as the heating due to iron losses, harmonic currents, negative and zerosequence currents, etc., but the four listed above have the most decisive limiting effect.

2 STATOR CURRENT

Consider first the stator. The I2R, or 'copper', losses due to the load current are, together with the ironlosses, the main sources of stator heating. With a given cooling system there is clearly an upper limit tosuch continuous stator currents no matter what their power factor may be. Stated another way, there is alimit of MVA beyond which the generator must not be allowed to go continuously, and this limit applies atall power factors.

Figure 1In Figure 1, if the reactive (MVAr lagging) loading is taken as the x-axis and the active (MW) loading asthe y-axis, then for any given loading P (PN being the active component and PM the reactive), the line OPrepresents the MVA of that load (= √PN2 + PM2), and the angle POM is the phase angle of the load. If asemi-circle is drawn about the origin O and with radius equal to the maximum permitted MVA, then onlythose loads (such as P) within that semi-circle are within the capacity of the generator.This is the first limitation.

3 POWER OUTPUT

The electrical MW rating of an engine driven generating set is limited by the mechanical output of theprime mover. Therefore, if a horizontal line is drawn across the MW axis at a level equal to the maximumoutput of the prime mover (OA), the top part of the semi-circle is cut off, since it represents MW powerwhich is not attainable from the engine. Therefore the loading of the generator must be confined to pointswithin the remainder of the semi-circle. This is the second limitation and is shown in Figure 1 as a dottedline.

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4 ROTOR CURRENT

To achieve the rated MVA loading or, a certain level of excitation is required. This calls for a certain rotorcurrent, with its consequent I2R losses which cause rotor heating. The cooling system takes this, togetherwith the stator heater heating, into account. Any increase in excitation beyond this level - and hence inrotor current - will cause rotor overheating; so at first sight the load point P should remain to the left of theline RB.

Figure 2However, there is a point E* on the other side of the origin such that the line ER represents the emf of thegenerator when operating at its rated load and power factor. ER then represents not only the emf but alsothe excitation - and so the rotor current - needed to produce it. Constant excitation at various maximumloads and power factors is therefore represented by an arc of a circle through R, centre E, shown by thearc RQ in Figure 2. This arc this represents the maximum allowable rotor current at different maximumloads and power factors. To avoid overheating the rotor, therefore, the load point must lie to the left of thearc RQ (not to the left of line RB as first suggested above) This is the third limitation.

Note: *Though not strictly necessary to know for the purpose of this explanation, the position of point E isdetermined from the generators synchronous reactance. If this is n per unit (= percent/100), then thelength OE is 1/n times the radius of the semicircle. Thus if n = 200% (fairly typical), E is halfway betweenO and the circumference.

5 STABILITY OF THE ROTOR

When the machine is generating, the rotor is driven ahead of the stators rotating magnetic field at anangle depending on the actual active load - it is called the 'Power Angle', symbol λ. The opposing torquedeveloped by the generator on the engine is due to the magnetic back-pull on the rotors poles by thestators magnetic field. The greater the power angle, the greater the back torque. The driving torquedelivered by the engine is just balanced by this back torque from the rotor, and the rotor is stable.

When the loading is lagging reactive, armature reaction in the stator causes the field poles to becomepartly demagnetised. The consequent loss of air-gap flux reduces the net emf and so the terminal voltage;this is detected by the AVR, which causes increased excitation to restore the air gap flux and so the emf.

With leading reactive loading the opposite effect occurs. The leading stator current causes the field polesto become more magnetised at first. The gain of air-gap flux increases the net emf and so the terminalvoltage; this is detected by the AVR, which then decrease excitation to restore the air-gap flux.

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If this process were allowed to continue and the leading load to increase further, the point would bereached where the excitation of the rotor poles would be reduced to nothing, and all the air-gap flux wouldbe provided by the stator alone. There would then be no rotor poles upon which the stator could pull back.The prime mover would drive the rotor ahead out of synchronism, and the generator would go unstable,pulling out of step.

This situation would occur if the reactive loading reached a value equal to OE (leading), since at E theexcitation is reduced to zero. Therefore the load point P must never be allowed to go to the left of thevertical line through E - that is, the leading MVAr must never be allowed to exceed the value OE. This isthe fourth limitation and is shown in Figure 3.

Figure 3Clearly such a limitation must never be allowed to occur or even to be approached, as the generatorwould become difficult to control. There is therefore a limit to the amount of leading current (or MVA)which a generator may be allowed to produce. The theoretical limit set in the previous paragraph istherefore in practise too high. The practical limit will be appreciably less and is represented by the dottedcurve ST in Figure 3; the calculation of this curve is complicated, and it is merely indicated here. Its shapewill depend on whether the rotor is cylindrical or has salient poles. In practise, however, leading loads onplatforms should never arise.

So in Figure 3 the theoretical semicircle inside which the loading of the generator must lie is limited at thetop and now at both sides, and the only 'usable' part is the coloured area if the generator is to run within itsrating and remain stable.

The coloured part of Figure 3 is called the 'Capability Diagram' of that generator set. It provides a constantguide not only on the loaded state of the generator but also on its maximum allowable further loading. Itshows whether any intended additional loading will still remain within, or go outside of, the rating of thegenerator set, and it therefore indicates whether or not s further machine should be started up. All that isrequired to determine the existing load point on the capability diagram are the generator MW and MVArinstrument readings.

6 TEMPORARY LIMITATION

A special case arises when large motors are to be started. They impose a large, but temporary, reactiveloading while starting, which fails to a much smaller value when run up to speed. The extra excitationneeded for this can if necessary be found from the AVR's field forcing circuits, which provide extra fieldcurrent above the normal maximum. This, although above the steady current limit of the rotor windings(arc RQ), may be tolerated for a short time without damaging the rotor.

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For this reason capability diagrams are sometimes furnished with one or more additional rotor currentlimitation arcs with a specified time limit of, for example, 30 seconds, as shown in Figure 4. This meansthat, within this time, the reactive loading may be increased to the indicated higher limit to allow the motorto start, provided that it falls back to within normal limits within the specified time when the motor has runup to its steady speed. On some systems, if the rotor current goes beyond the higher limit, or if it fails toreturn to within normal limits within the specified time, the generator is tripped.

Figure 4If the total reactive load on starting falls outside even this higher temporary limit and automatic tripping isnot fitted, it goes beyond the field forcing limit of the AVR, and a prolonged dip of the system voltage willresult, besides risking damage to the rotor.

7 USE OF THE CAPABILITY DIAGRAM

To use the capability diagram, the Operator looks at the wattmeter and varmeter of the generator which isto be further loaded and he plots the point P on the diagram corresponding to the MVAr and MW standingload readings see Figure 5. He notes, or calculates, the additional load in the MVAr and MW which heintends to put on top the generator ; these he adds to the MVAr and MW values of the point P. If theresulting point P1 lies within the coloured area, the generator can accept the additional lad. If not, he mustbe prepared to start an additional load. If not, he must be prepared to start an additional generator toshare the total load. If the excess is marginal, he must use his discretion.

Figure 5

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Particular care is needed if a large motor is to be started. Although the additional MVAr and MW at fullload may be acceptable to the generator, the MVAr due to the large starting current may not. Forexample, a certain gas export compressor motor has an input of 5MW at 0.85 PF, giving a full loaddemand of 2.6 MVAr and 5.0MW, which might be acceptable on top of the standing load. But the startingcurrent is approximately 1500A at 0.25 PF, giving a starting demand of about 25MVAr and 7MW.

While even the 7MW might be acceptable to the generator, the capability diagram would show that theadditional 25 MVAr on the starting almost certainly would not be, even taking into account any temporarymargin allowed. The operator would need to put on line extra generators to accommodate this start, evenif he took them off again once the motor had run up. The following illustrates this point with a differentmotor.

When a second generator is put on line, it is assumed that both share the load equally; therefore the MWand MVAr loadings on each are half what they were with one generator only. This means that the 'workingpoint' P has half the previous values and is therefore much nearer the centre. This leaves more room foradditional loading, remembering also that the additional load itself on each generator is also halved.

Example

A 6.6kV generator is rated 15MW at 0.85PF. At a certain moment it is carrying a standing load of 8MWand 6 MVAr (represented by point P in Figure 5) as given by its switchboard instruments. It is desired tostart and run a 3600kWm, 0.8PF water injection motor (efficiency 96%) on this generator. The motorsstarting current is four times full load current at 0.25PF. The capability diagram, including the temporarylimitation curve is given in Figure 5.

Can this generator carry the extra load, and can the motor be started on it? If not, what action should betaken?

(In the following calculations all results have generally been rounded off to the nearest 10 units.Operations at a generated voltage of 6.8kV has been assumed).

GeneratorGenerator rating 15MW at 0.85pF and 6.6kV (6.8kV operation) (15MW)

Full-load current (l) = 15000 = 1500 √3 x 6.8 x 0.85

cos Φ = 0.85, ∴sin Φ= 0.53

Full-load reactive power = √3 x kV x l x sin Φ = √3 x 6.8 x 1500 x 0.53 = 9360 (say 9.4 MVAr)

Motor (Running)Motors output is 3600kWm at 0.9 efficiency;

Motor input is 3600 = 4000kWe at 0.8pF (4.0MWe) 0.9

cos Φ = 0.8, ∴sin Φ = 0.6

Full-load current (lFL) = 4000 = 425A√3 x 6.8 x 0.8

Full-load reactive power = √3 x kV x lFL x sin Φ = √3 x 6.8 x 425 x 0.6 = 3000KVAr (3.0MVAr)

Motor (Starting)Starting current (lST) = 4 x full-load running current (lFL) = 4 x 425 = 1700A at 0.25pF

cos Φ = 0.25, ∴sin Φ= 0.968

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Starting active power = √3 x kV x lST x cos Φ = √3 x 6.8 x 1700 x 0.25 = 5010KWe (say 5.0MWe)

and starting reactive power = √3 x kV x lST x sin Φ = √3 x 6.8 x 1700 x 0.968 = 19380KVAr (say19.4MVAr)

CombinationWhen running:

standing load is 8.0MW & 6.0MVArmotor load is 4.0MW & 3.0MVAr

Total: 12.0MW & 9.0MVAr

Plotted on the capability diagram, this gives point P1 which is well within the coloured diagram limits and istherefore acceptable.

When starting:standing load is 8.0MW & 6.0MVArmotor load is 5.0MW & 19.4MVAr

Total: 13.0MW & 25.4MVAr

Plotted on the capability diagram, this gives point P2, which lies outside the diagram and even beyond thetemporary limit. The starting of this motor is therefore not acceptable, even though the current could becarried continuously once running. Before starting, therefore, either the standing load must be sufficientlyreduced or another generator set must be started and put on-line.

8 CAPABILITY DIAGRAM FOR SYNCHRONOUS MOTOR

Although the capability diagram so far described takes the form of a semi-circle, it can be continued belowthe horizontal axis to become a complete circle. In that case the y-axis, representing active power (orMW), is negative and so indicates negative active power supplied by the machine. This is equivalent toactive power being received by the machine; that is to say, the machine is absorbing true power and istherefore motoring. The x-axis, representing lagging or leading machine power supplied, is not affected.

Figure 6

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The two lower quadrants shown in Figure 6 thus represent the machine operating as a motor - that is, asa synchronous motor. The left-hand lower quadrant indicates such a motor running under excited andtherefore supplying some leading VAr's to the system, equivalent to drawing lagging VAr's from it.

The right hand lower quadrant indicates a motor well excited and supplying lagging VAr's to the system -equivalent to drawing leading VAr's from it.

It should be noted that the excitation can be adjusted so that the machine is drawing neither leading norlagging VAr's (point Q) - that is, it is taking no reactive power at all, only active power. Such a motor isthen running at unity power factor - a useful feature of the synchronous motor.

It is possible to go even further. The machine can be deliberately run as a motor overexcited i.e, in thefourth quadrant - where it will draw active power from the system as it motors, but it will at the same timesupply lagging VAr's, and it will therefore run at a leading power factor. If a mixed load of induction motorsand a large synchronous motor is installed, the synchronous motor run in this manner can helpcompensate for the poorer power factors of the induction motors.

Below the horizontal the prime mover output limitation clearly no longer applies, but the rotor and stabilitylimitations apply as before. The 'working point' P must therefore fall within the coloured area of Figure 6 ifthe motor is to work within its design limits.

When determing the working point P, all losses (including friction and windage losses) must be added tothe known mechanical power of the motor drive, since all go into the total power absorbed. The losses canbe calculated from the efficiency of the motor at that particular loading.

There are no synchronous motor drives in offshore or onshore installations, but they are used elsewhereonshore in larger plants where exact constant speed operation is required.

9 CAPABILITY DIAGRAM FOR SYNCHRONOUS CONDENSER

A synchronous motor, whenever excited, can be used as if it were a bank of static capacitors.

Figure 7Figure 7 represents the capability diagram of such a synchronous machine. The full semi-circle above theline depicts its generation mode, as discussed previously. The y-axis represents generated active power(MW). If extended downwards it represents negative active power - that is, motoring instead of generatedpower. The x-axis to the right represents lagging reactive power (MVAr) given out by the machine whethergenerating or motoring and is associated with the degree of excitation.

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Imagine such a machine used as a generator and driven up to speed by its prime mover andsynchronised onto the system, where it takes up its share of the active and reactive loads. The workingpoint of the capability diagram of Figure 7 would be, say, P. Suppose then that the prime mover isunclutched, or that its fuel is cut off, but that the machine is well excited and its excitation remainsunchanged. Mechanical drive to the machine then ceases, but it continues to rotate in synchronism withthe system. It draws from the system only enough active power to keep itself going without driving anyexternal load - it behaves as an unloaded motor, drawing just enough active power to make good itslosses - a 'reverse power' situation. Plotted on the capability diagram of Figure 7, the working point wouldnow be Q, with slightly negative MW but delivering rather more lagging MVAr as before due to itsunaltered excitation.

Such a machine would then be supplying reactive lagging power (megaVAr's) but no active power(megawatts). Supplying lagging VAr's is the same thing as receiving leading VAr's, since one is thenegative of the other. Therefore a machine operating as described above can be regarded as drawingleading reactive power - that is to say, it behaves as a static capacitor. The machine is then called a'synchronous capacitor', although the old name 'synchronous condenser' remains in common use.

Moreover, the amount of leading reactive power drawn will be determined by the degree of over-excitation. Therefore the 'capacitance' is infinitely variable as required by the changing system loadconditions, unlike that of a bank of static capacitors which can only be switched.

If a synchronous condenser is not available to correct the power factor of a system, a corresponding effectcan be obtained by running any synchronous motors in the system in an over excited state. In thiscondition they will draw leading reactive current in addition to their active current. This will compensate forthe large lagging currents drawn by many induction motors by providing a useful contribution to thelagging VAr's needed by those motors instead of calling on the generators to do so.

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ELECTRICAL DEVICE NUMBERS & FUNCTIONS

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04.07.01 (A) Device Numbers.doc © Brush Electrical Machines Ltd. 2003

CONTENTS1 INTRODUCTION........................................................................................................................................ 32 DEVICE NUMBERS................................................................................................................................... 3

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04.07.01 (A) Device Numbers.doc © Brush Electrical Machines Ltd. 2003

1 INTRODUCTION

Devices in switching equipment are referred to by numbers, with appropriate suffix letters whennecessary, according to the function they perform.

These numbers are based on a system adopted as standard for automatic switchgear by IEEE, andincorporated in American Standard C37.2-1970. This system is used in connection diagrams, ininstruction books, and in specifications.

2 DEVICE NUMBERS

Device No. Device Definition and Function1 Master Element This is the initiating device, such as a control switch, voltage relay,

float switch etc., which serves either directly, or through suchpermissive devices as protective and time-delay relays to place anequipment in or out of operation.

2 Time-Delay Starting orClosing Relay

This is a device which functions to give a desired amount of timedelay before or after any point of operation in a switching sequence orprotective relay system, except as specifically provided by devicefunctions 48, 62, and 79 described later.

3 Checking or InterlockingRelay

This operates in response to the position of a number of otherdevices, (or to a number of predetermined conditions), in anequipment, to allow an operating sequence to proceed, to stop, or toprovide a check of the position of these devices or of these conditionsfor any purpose.

4 Master Contactor This device, generally controlled by Device No.1 or equivalent, andthe required permissive and protective devices, that serves to makeand break the necessary control circuits to place an equipment intooperation under the desired conditions and to take it out of operationunder other or abnormal conditions.

5 Stopping Device This control device is used primarily to shut down an equipment andhold it out of operation. [This device may be manually or electricallyactuated, but excludes the function of electrical lockout (see devicefunction 86) on abnormal conditions]

6 Starting Circuit Breaker The principle function of this device is to connect a machine to itssource of starting voltage.

7 Anode Circuit Breaker Is used in the anode circuits of a power rectifier for the primarypurpose of interrupting the rectifier circuit if an arc back should occur.

8 Control PowerDisconnecting Device

This is a disconnecting device - such as a knife switch, circuit breakeror pullout fuse block, used for the purpose of connecting anddisconnecting the source of control power to and from the control busor equipment.Note: Control power is considered to include auxiliary power whichsupplies such apparatus as small motors and heaters

9 Reversing Device This is used for the purpose of reversing a machine field or forperforming any other reversing functions.

10 Unit Sequence Switch Used to change the sequence in which units may be placed in andout of service in multiple-unit equipments.

11 Reserved for futureapplication

12 Over-Speed Device This is usually a direct connected speed switch which functions onmachine over-speed.

13 Synchronous-SpeedDevice

For example centrifugal-speed switch, a slip-frequency relay, avoltage relay, an undercurrent relay or any type of device, operates atapproximately synchronous speed of a machine.

14 Under-Speed Device Functions when the speed of a machine falls below a predeterminedvalue.

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Device No. Device Definition and Function15 Speed or Frequency,

Matching DeviceFunctions to match and hold the speed or the frequency of a machineor of a system equal to, or approximately equal to, that of anothermachine, source or system.

16 Reserved for futureapplication

17 Shutting or DischargeSwitch

This switch serves to open or to close a shutting circuit around anypiece of apparatus (except a resistor), such as a machine field, amachine armature, a capacitor or a reactor.Note: This excludes devices which perform such shutting operationsas may be necessary in the process of starting a machine by devices6 or 42, or their equivalent, and also excludes device 73 functionwhich serves for the switching of resistors.

18 Accelerating orDecelerating Device

This is used to close or to cause the closing of circuits which are usedto increase or to decrease the speed of the machine.

19 Starting-to-RunningTransition Contactor

This device initiates or causes the automatic transfer of a machinefrom the starting to the running power connection.

20 Electrically OperatedValve

This is an electrically operated, controlled or monitored valve in a fluidline.Note: The function of the valve may be indicated by the use of thesuffixes

21 Distance Relay This device functions when the circuit admittance, impedance orreactance increases or decreases beyond predetermined limits.

22 Equalizer CircuitBreaker

This breaker serves to control or to make and break the equalizer orthe current-balancing connections for a machine field, or forregulating equipment, in a multiple-unit installation.

23 Temperature ControlDevice

Its function is to raise or lower the temperature of a machine or otherapparatus, or of any medium, when its temperature falls below, orrises above, a predetermined value.Note: An example is a thermostat which switches on a space heaterin a switchgear assembly when the temperature falls to a desiredvalue as distinguished from a device which is used to provideautomatic temperature regulation between close limits and would bedesignated as 90T.

24 Reserved for futureapplication

25 Synchronising orSynchronism-CheckDevice

This device operates when two ac circuits are within the desired limitsof frequency, phase angle or voltage, to permit or to cause theparalleling of these two circuits.

26 Apparatus ThermalDevice

This device functions when the temperature of the shunt field or thearmortisseur winding of a machine. or that of a load limiting or loadshifting resistor or of a liquid or other medium exceeds apredetermined value; or if the temperature of the protected apparatus,such as a power rectifier, or of any medium decreases below apredetermined value.

27 Undervoltage Relay This device functions on a given value of undervoltage28 Flame Detector Monitors the presence of the pilot or main flame in such apparatus as

a gas turbine or a steam boiler.29 Isolating Contactor Expressly used for disconnecting one circuit from another for the

purposes of emergency operation, maintenance, or test.30 Annunciator Relay This non-automatic reset device gives a number of separate visual

indications upon the functioning of protective devices, and which mayalso be arranged to perform a lockout function.

31 Separate ExcitationDevice

Connects a circuit such as the shunt field of a synchronous converter,to a source of separate excitation during the starting sequence; orone which energizes the excitation and ignition circuits of a powerrectifier.

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Device No. Device Definition and Function32 Directional Power Relay This functions on a desired value of power flow in a given direction or

upon reverse power resulting from arc back in the anode or cathodecircuits of a power rectifier.

33 Position Switch Makes or breaks contact when the main device or piece of apparatus,which has no device function number, reaches a given position.

34 Master SequenceDevice

This device such as a motor operated multi-contact switch, or theequivalent, or a programming device, such as a computer, thatestablishes or determines the operating sequences of the majordevices in an equipment during stopping or during other sequentialswitching operations.

35 Brush-Operating, orSlipring Short CircuitingDevice

This is used for raising, lowering, or shifting the brushes of a machine,or for short circuiting its sliprings, or for engaging or disengaging thecontracts of a mechanical rectifier.

36 Polarity or PolarisingVoltage Device

Operates or permits the operation of another device on apredetermined polarity only or verifies the presence of a polarisingvoltage in an equipment.

37 Undercurrent orUnderpower Relay

Functions when the current or power flow decreases below apredetermined value.

38 Bearing ProtectiveDevice

Functions on excessive bearing temperature, or on other abnormalmechanical conditions, such as undue wear, which may eventuallyresult in excessive bearing temperature.

39 Mechanical ConditionMonitor

This device functions upon the occurrence of an abnormalmechanical condition (except that associated with bearings ascovered under device function 38), such as excessive vibration,eccentricity, expansion, shock, tilting, or seal failure.

40 Field Relay Functions on a given or abnormally low value or failure of machinefield current, or on an excessive value of the reactive component ofarmature current in an ac machine indicating abnormally low fieldexcitation.

41 Field Circuit Breaker Is a device which functions to apply, or to remove, the field excitationof a machine.

42 Running Circuit Breaker The principle function of this device is to connect a machine to itssource of running or operating voltage. This function may also beused for a device, such as a contactor, that is used in series with acircuit breaker or other fault protecting means, primarily for frequentopening and closing of the circuit.

43 Manual Transfer orSelector Device

This transfers the control circuits so as to modify the plan of operationof the switching equipment or of some of the devices.

44 Unit Sequence StartingRelay

Is a device which functions to start the next available unit in amultiple-unit equipment on the failure or on the non-availability of thenormally preceding unit.

45 Atmospheric ConditionMonitor

This functions upon the occurrence of an abnormal atmospherecondition, such as damaging fumes, explosive mixtures, smoke, orfire.

46 Reverse-Phase, orPhase Balance, CurrentRelay

This relay functions when the polyphase currents are of reverse-phase sequence, or when the polyphase currents are unbalanced orcontain negative phase sequence components above a givenamount.

47 Phase SequenceVoltage Relay

Functions on a predetermined value of polyphase voltage in thedesired phase sequence.

48 Incomplete SequenceRelay

This relay generally returns the equipment to the normal, or off,position and locks it out if the normal starting , operating or stoppingsequence is not properly completed within a predetermined time. Ifthe device is used for alarm purposes only, it should preferably bedesignated as 48A (alarm).

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Device No. Device Definition and Function49 Machine or Transformer,

Thermal RelayThis relay functions when the temperature of a machine armature, orother load carrying winding or element of a machine, or thetemperature of a power rectifier or power transformer (including apower rectifier transformer) exceeds a predetermined value.

50 InstantaneousOvercurrent, or Rate-of-Rise Relay

This functions instantaneously on an excessive value of current, or ona excessive rate of current rise, thus indicating a fault in theapparatus or circuit being protected.

51 AC time overcurrentRelay

Is a relay with either a definite or inverse time characteristic thatfunctions when the current in an ac circuit exceeds a predeterminedvalue.

52 AC Circuit Breaker This is used to close and interrupt an ac power circuit under normalconditions or to interrupt this circuit under fault or emergencyconditions.

53 Exciter or dc generatorrelay

This forces the dc machine field excitation to build up during startingor which functions when the machine voltage has built up to a givenvalue.

54 Reserved for futureapplication

55 Power Factor Relay This operates when the power factor in an ac circuit rises above orbelow a predetermined value.

56 Field Application Relay Is a relay that automatically controls the application of the fieldexcitation to an ac motor some predetermined point in the slip cycle

57 Short Circuiting orGrounding Device

This primary circuit switching device functions to short circuit or toground a circuit in response to automatic or manual means.

58 Rectification FailureRelay

Functions if one or more anodes of a power rectifier fail to fire, or todetect an arc-back or on failure of a diode to conduct or blockproperly.

59 Overvoltage Relay Functions on a given value of overvoltage.60 Voltage or Current

Balance RelayOperates on a given difference in voltage, or current input or output oftwo circuits.

61 Reserved for futureapplication

62 Time Delay Stopping orOpening Relay

Serves in conjunction with the device that initiates the shutdown,stopping, or opening operation in an automatic sequence.

63 Pressure Switch Operates on given values or on a given rate of change of pressure.64 Ground Protective Relay Functions on failure of the insulation of a machine, transformer or of

other apparatus to ground, or on flashover of a dc machine to ground.Note: This function is assigned only to a relay which detects the flowof current from the frame of a machine or enclosing case or structureof a piece of apparatus to ground, or detects a ground on a normallyungrounded winding or circuit. It is not applied to a device connectedin the secondary circuit or secondary neutral of current transformer,connected in the power circuit of a normally grounded system.

65 Governor Is the assembly of fluid, electrical or mechanical control equipmentused for regulating the flow of water, steam, or other medium to theprime mover for such purposes as starting, holding speed or load, orstopping.

66 Notching or JoggingDevice

Functions to allow only a specified number of operations of a givendevice, or equipment, or a specified number of successive operationswithin a given time of each other. It also functions to energize a circuitperiodically or for fractions of specified time intervals, or that is usedto permit intermittent acceleration or jogging of a machine at lowspeeds for mechanical positioning.

67 AC DirectionalOvercurrent Relay

Functions on a desired value of ac overcurrent flowing in apredetermined direction.

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Device No. Device Definition and Function68 Blocking Relay Initiates a pilot signal for blocking of tripping on external faults in a

transmission line or in other apparatus under predeterminedconditions, or cooperates with other devices to block tripping or toblock reclosing on an out-of-step condition or on power swings.

69 Permissive ControlDevice

Generally a two position, manually operated switch that in oneposition permits the closing of a circuit breaker, or the placing of anequipment into operation, and in the other position prevents the circuitbreaker or the equipment from being operated.

70 Rheostat This variable resistance device used in an electric circuit, which iselectrically operated or has other electrical accessories, such asauxiliary, position, or limit switches.

71 Level Switch Operates on given values, or a given rate of change, of level.72 DC Circuit Breaker Used to close and interrupt a dc power circuit under normal conditions

or to interrupt this circuit under fault or emergency conditions.73 Load Resistor Contactor Used to shunt or insert a step of load limiting, shifting, or indicating

resistance in a power circuit, or to switch a space heater in circuit, orto switch a light, or regenerative load resistor of a power rectifier orother machine in and out circuit.

74 Alarm Relay Is a device other than an annunciator as covered under DeviceNo.30, which is used to operate in connection with, a visual or audiblealarm.

75 Position ChangingMechanism

Used for moving a main device from one position to another in anequipment; as for example, shifting a removable circuit breaker unit toand from the connected, disconnected, and test positions.

76 DC Overcurrent Relay Functions when the current in a dc circuit exceeds a given value.77 Pulse Transmitter Used to generate and transmit pulses over a telemetering or pilot-wire

circuit to the remote indicating or receiving device.78 Phase Angle Measuring,

or Out-of-StepProtective Relay

Functions at a predetermined phase angle between two voltages orbetween two currents or between voltage and current.

79 AC Reclosing Relay Controls the automatic reclosing and locking out of an ac circuitinterrupter.

80 Flow Switch Operates on given values, or on a given rate of change, of flow.81 Frequency Relay Functions on a predetermined value of frequency - either under or

over or on normal system frequency - or rate of change of frequency.82 DC Reclosing Relay Controls the automatic closing and reclosing of a dc circuit interrupter,

generally in response to load circuit conditions.83 Automatic Selective

Control or TransferRelay

Operates to select automatically between certain sources orconditions in an equipment, or performs a transfer operationautomatically.

84 Operating Mechanism This is the complete electrical mechanism or servo-mechanism,including the operating motor, solenoids, position switches, etc., for atap changer, induction regulator or any similar piece of apparatuswhich has no device function number.

85 Carrier or Pilot WireReceiver Relay

Operated or restrained by a signal used in conjunction with carriercurrent or dc pilot-wire fault directional relaying.

86 Locking Out Relay Operated hand or electrically reset, relay that functions to shut downand hold an equipment out of service on the occurrence of abnormalconditions.

87 Differential ProtectiveRelay

Functions on a percentage or phase angle or other quantitativedifference of two currents or of some other electrical quantities.

88 Auxiliary Motor or MotorGenerator

Used for operating auxiliary equipment such as pumps, blowers,exciters, rotating magnetic amplifiers etc.

89 Line Switch Used as a disconnecting load interrupter, or isolating switch in an acor dc power circuit, when this device is electrically operated or haselectrical accessories, such as an auxiliary switch, magnetic lock etc.

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Device No. Device Definition and Function90 Regulating device Regulates a quantity, or quantities, such as voltage, current, power,

speed, frequency, temperature, and load, at a certain value orbetween certain (generally close) limits for machine, tie lines or otherapparatus.

91 Voltage DirectionalRelay

Operates when the voltage across an open circuit breaker orcontactor exceeds a given value in a given direction.

92 Voltage and PowerDirectional Relay

Permits or causes the connection of two circuits when the voltagedifference between them exceeds a given value in a predetermineddirection and causes these two circuits to be disconnected from eachother when the power flowing between them exceeds a given value inthe opposite direction.

93 Field ChangingContactor

Functions to increase or decrease in one step value of field excitationon a machine.

94 Tripping or Trip-freerelay

Functions to trip a circuit breaker, contactor, or equipment, or topermit immediate tripping by other devices; or to prevent immediatereclosure of a circuit interrupter, in case it should open automaticallyeven though its closing circuit is maintained closed.

95 Used only for specific applications on individual installations wherenone of the assigned numbered functions from 1 to 94 is suitable.

96 Used for `trip circuit supervision' monitoring tripping supplies and(sometimes) circuit continuity

97 Used only for specific applications on individual installations wherenone of the assigned numbered functions from 1 to 94 is suitable.

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EQUIPMENT & SWITCHGEAR LABELLING

Training Module: 04.08.01 Issue: A Date: April 2003 Page: 1 of 6

04.08.01 (A) Switchgear Labelling.doc © Brush Electrical Machines Ltd. 2003

EQUIPMENT & SWITCHGEAR LABELLING

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EQUIPMENT & SWITCHGEAR LABELLING

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04.08.01 (A) Switchgear Labelling.doc © Brush Electrical Machines Ltd. 2003

CONTENTS1 INTRODUCTION........................................................................................................................................ 32 GENERAL .................................................................................................................................................. 33 PREFIX LETTER........................................................................................................................................ 34 WIRE NUMBERS....................................................................................................................................... 45 SUFFIX LETTERS ..................................................................................................................................... 46 NUMBERING TABLE ................................................................................................................................ 4

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1 INTRODUCTION

BS3939 is the Specification for Standard Numbering of Small Wiring for Switchgear and Transformerstogether with their Associated Relay and Control Panels.

2 GENERAL

a) Each wire shall have a letter to denote its function, eg control of circuit breaker, current transformerfor primary protection, voltage for instruments, metering and protection. The function letter shall befollowed by a number identifying the individual wire. Every branch of any connection shall bear thesame identification mark. Where it is necessary to identify branches which are commoned (e.g.current transformer leads), different identification marks for the branches may be employed only ifthey are commoned through links, or are connected to separate terminals which are thencommended by removable connections. Suffix letters shall be used as indicated in Section 5.

b) Numbering shall read from the terminals outwards on all wires.

3 PREFIX LETTER

a) Where part of a circuit is common to more than one function, the first in alphabetical order of theappropriate function letters in the table shall be used for the common part. Where the circuits split asa separate contact (eg fuse, link, switch or relay contact) the function letter shall change if necessaryfrom the splitting point onwards.

b) Circuits having functions not included in the function letter table shall not have prefix letters. Forexample, circuits of devices which provide a continuous indication, such as remote windingtemperature indicators or resistance thermometers, shall not have a prefix letter unless the circuit ofthe particular indication already has a function letter. Where, however, an indication or alarm isinitiated by the opening or closing of an auxiliary contact prefix 'L' or 'X' should be used asappropriate.

c) Where the manufacturer has been unable to ascertain from the purchaser the function letters andnumbering to be assigned to equipment wiring by the time that wiring is required, the manufacturershall himself provide wire numbers preceded by the letter 'O'. Where the appropriate function letteronly can be determined, it shall be preceded by an 'O' and followed by the manufacturers ownnumber. The same procedure my be applied to equipment or parts of equipment not assigned tospecific contracts at the time of manufacture, subject to the purchasers approval and to the use offerruling in accordance with approved standard diagrams as far as these are applicable.

d) Where relays are employed, the coil and the contact circuits do not necessarily bear the samefunction letter; this should be determined by the function of the individual circuit eg the coil circuit of aseries flag relay may be 'K' but the contact circuits may bear letters such as 'X', 'L' or 'N' asappropriate.

e) The following rules shall apply to current and voltage transformer function letters:

i) Current Transformers for ProtectionPrefix 'C' shall be used for all types of over-current protection (whether used as primary orback-up protection), standby earth fault, generator negative phase sequence, transformerwinding temperature protection, and instruments fed from separate current transformer.Where duplicate primary protection is applied prefix 'A' shall be used for both, the secondline being distinguished by adding 300 to the number.

ii) Interposing and Auxiliary TransformersThe function letters shall follow through any interposing and auxiliary current and voltagetransformers, including such transformers when used for light current circuits, provided thatthese are not used as isolating transformers to couple circuits which have differing functions.

When an ac supply, reflecting the primary quantities and derived from a current or voltagetransformer, is rectified for the operation of instruments or relays, the dc circuit shall carrythe same function letter as the ac circuit.

iii) Current Transformer Connections for Line Drop Compensation or CompoundingPrefix 'D' shall be used for these circuits, including the current side of the isolatingtransformer. The connections to the voltage circuit from this transformer shall have prefix 'F'.

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iv) Voltage Transformer Connections for Automatic Voltage ControlPrefix 'F' shall be used for these circuits.

f) Light current equipment may require numbering schemes differing from the above for completeidentification. In such cases, where connections from such equipment are associated with powerequipment wired in accordance with this Recommendation, the numbering of such connections shallinclude the appropriate prefix letter (J, W, X or Y) to distinguish them. The letter 'W' is generally usedfor the light current side of interposing relays for control purposes.

4 WIRE NUMBERS

The wire number may consist of one or more digits as required. For functions A-G, H, J and M, thenumbers shall be given in the column under 'Wire Numbers'. DC supplies from a positive source shallbear odd numbers and dc supplies from a negative source shall bear even numbers. Where coils orresistors are connected in series the change from odd to even shall be made at the coil or resistor leadnearest to the negative supply.

5 SUFFIX LETTERS

Where similarly numbered leads from separate primary equipments are taken to a common panel (eg buszone protection, summation metering, banked transformers, etc), suffixes A, B and C, etc, should be usedto distinguish them. Where similarly numbered leads from different parts of a unit of primary equipmentare taken to a common panel (eg generator and unit transformers, HV and LV sides of a transformer, etc),the leads of the subsidiary or lower voltage equipment shall be distinguished by adding 500 to the wirenumbers. When more than two sets of leads require to be distinguished, specific wire numbering schemesappropriate to the case shall be issued by means of a standard diagram showing the scheme to beadopted. The method of distinguishing between sets of leads shall be shown on the individual schematic(circuit) and wiring diagrams.

The distinguishing suffixes or numbers apply only in the common panel or junction box, and at each endof the interconnecting cores. When specified, however, suffixes may be omitted from the ends of theinterconnecting cores.

6 NUMBERING TABLE

Letter Circuit Function Wire numbersA Current transformers for primary

protection excluding overcurrent10-29 Red Phase30-49 Yellow Phase50-69 Blue Phase70-89 Residual circuits & neutral current transformers90 Earth wires directly connected to earth bar91-99 Test windings, normally inoperative

B Current transformers for busbarprotection

C Current transformers for overcurrentprotection (including combined earthfault protection) and instruments

D Current transformers for metering andvoltage control

E Reference voltage for instruments,metering and protection

F Reference voltage for voltage controlG Reference voltage for synchronisingH AC and AC/DC supplies 1-69 Switchgear & Generators

70-99 TransformersJ DC Supplies 1-69 Switchgear & Generators

70-99 TransformersK Closing & tripping control circuits Any number from 1 upwards

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Letter Circuit Function Wire numbersL Alarms and indications initiated by

auxiliary switches and relay contacts,excluding those for remote selectivecontrol and for General Indicationequipment

Any number from 1 upwards

M Auxiliary and control motor devices eggovernor motor, rheostat motor,generator AVR control, spring chargingmotors, transformer cooler motorcontrol, motors for isolator

1-19 Switchgear20-69 Switchgear70-99 Transformer

N Tap change control, including AVC, tapposition and progress indications

O An indication that the ferruling is not onaccordance with the general schemeand that if it is not altered doubleferruling will be required for co-ordination with the remaining equipmentin the station (see 1b (3))

Any number from 1 upwards

P DC Tripping circuits used solely forbusbar protection

Any number from 1 upwards

R Interlock circuits not covered above Any number from 1 upwardsS DC instruments and relays, exciter and

field circuits for generatorsAny number from 1 upwards

T Pilot conductors (including directlyassociated connections) betweenpanels, independent of the distancebetween them, for pilot-wire protection,for interrupting or for both

Any number from 1 upwards

U Spare cores and connections top sparecontacts

Spare cores shall be numbered from 1 upwards in eachcable, and shall be so arranged that they can be readilyidentified on site with the cable containing them. This shallbe achieved by suitable grouping, and unless the locationof each group is clear from the diagram, the groups shallbe labelled. Alternatively the core number shall bepreceded by the cable number

V Automatic switching circuits not integralwith circuit breaker control schemes, ieseparately supplied, or isolatable from,the circuit breaker control scheme

Any number from 1 upwards

W Light current control connections (seerule 1b (6))

Any number from 1 upwards

X Alarms and indications to and fromGeneral Indication and remote selectivecontrol equipments

Any number from 1 upwards

Y Telephones Any number from 1 upwardsNotes:If, for functions A-G and for functions H. J and M, more numbers are required, add multiples of onehundred (e.g. 10-29 may be extended to 110-129, 210-229, etc.)

The term 'remote selective control' denotes 'control at a point distant from the switchgear by thetransmission of electrical signals through common communication channels using selective means tooperate one of a number of switching devices'.

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BLANK PAGE

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HIGH VOLTAGE PHASING CHECKS

Training Module: 04.09.01 Issue: A Date: April 2003 Page: 1 of 6

04.09.01 (A) HV Phasing.doc © Brush Electrical Machines Ltd. 2003

HIGH VOLTAGE PHASING CHECKS

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HIGH VOLTAGE PHASING CHECKS

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04.09.01 (A) HV Phasing.doc © Brush Electrical Machines Ltd. 2003

CONTENTS1 INTRODUCTION........................................................................................................................................ 32 PHASING OUT OF HV SYSTEMS ............................................................................................................ 33 PHASING STICKS..................................................................................................................................... 5

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HIGH VOLTAGE PHASING CHECKS

Training Module: 04.09.01 Issue: A Date: April 2003 Page: 3 of 6

04.09.01 (A) HV Phasing.doc © Brush Electrical Machines Ltd. 2003

1 INTRODUCTION

The fundamentals of phasing out of high voltage (HV) power systems are detailed hereafter.

WARNING: Specialised HV training is required before entering any HV switchgearpanels.

When synchronising a generator to a busbar system it is imperative to check that the VoltageTransformers (VT's) to the synchronising gear reflect correctly the phase rotation and phase differencebetween the two systems. Some switchgear breakers have no VT's fitted, these are normally ring mainunits or auxiliary switchgear. In these situations the only way of checking these is Phasing Sticks (SeeSection 3).

Phase displacements between the output lines of a three phase ac generator are 120 electrical degreesapart. This is to assure power is taken equally during the rotation of the prime mover. These lines can bereferred as Red, Yellow, Blue phases, or L1, L2, L3, or R, S, T or U, V, W dependant on whichinternational standard is used. It is important to ensure the order in which the line voltages rise. Thisdefines the phase rotation of the system. With an ac generator the phase rotation is set by the direction ofrotation of the prime mover. Nowadays phase rotation is U, V, W irrespective of mechanical rotation for anac generator.

During phasing checks we cannot rely on HV cable core identifications, as any joints in the cable would becarried out to suit the lay of the connectors and not the continuity of the core numbers by the cable jointer.Likewise with the secondary of the VT's the cabling may pass through several interconnecting terminalblocks before arriving to the synchronising instrumentation.

2 PHASING OUT OF HV SYSTEMS

Before joining two systems the following criteria must be met:1) Voltages on both systems must be equal.2) The frequency of both systems should be identical.3) The phase difference between supplies should be zero.4) The phase rotation of both supplies should be the same.5) Vector windings should be identical (Transformer in circuit only).

In practice 1) to 3) are unobtainable due to fluctuating site load so there are acceptable limits that willallow the two systems to be joined. Any voltage mismatch will cause reactive currents to flow between theinterconnected systems and with any phase difference this creates a mechanical shock to the generatorrotor system and therefore the stator assembly. This should be minimised. Any phase displacementbetween the two systems caused by slip between a generator and a busbar frequency will cause thegenerator to electrically lock into synchronism the instant the generator breaker is closed. It is normalpractice to synchronise with the Prime Mover slightly above synchronous speed, this assures that poweris taken up by the set the instant the breaker is closed. This prevents the set tripping out on reversepower.

Figure 1: Typical Generator To Be Synchronised

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Figure 1 shows a typical situation where a generator is to be synchronised to a network. Where possiblethe following procedure should be performed to ensure that the following criteria are met: Phase rotation of the set is correct. The VTs are correctly reflecting the status of the HV system. External wiring to control/synchronising panel is correct. The correct phasing of the incoming machine is correct, ie Red phase to Red phase etc.

WARNING: The use of Low Voltage Phase rotation meters on an unexcited HV set is adangerous practice and should not be performed.

The following is a typical exercise to synchronise a machine as shown in Figure 1:1) Isolate bus coupler and Generator breaker as per current safety rules. Isolate any synchronising

breaker signals ensuring that none of the breaker close signal cabling can 'short down' to earthedmetalwork.

2) Confirm that three phase VTs are used. Check the earthing of the VT Winding (eg yellow earthed orneutral earthed). Providing VT earthing is identical the following procedure may be followed.

3) Earth bus section as per current safety rules.4) Isolate and insulate the three machine output cables. If not insulated, remove the generator neutral

'star' connections.

Note: Isolate at the machine terminals should it be suspected that due to the age of the machine theends of the windings been swapped due to stator leakage currents. However not all machines weregraded for line voltage to the star point.

5) Remove bus section earthing and return to normal operation with generator leads still isolated andinsulated as per current safety rules.

6) Close bus coupler and energise up the RHS busbar.7) Close Generator breaker. (This is referred to as back-energising the generator).8) Check and record phase rotation of VT1 (generator).9) Check and record phase rotation of VT2 (busbar). 10) Produce phasing chart as shown in Table 1. Verify the phasing by measuring the VT secondary ac

voltages. Verify (if connected) that the synchroscope is reading twelve o'clock and that the checksynchroniser unit contacts are closed (if fitted).

Table 1: Phasing Chart

RHS Voltage Transformer (VT2)VT1 Red Yellow BlueRed Zero 110V 110V

Yellow 110V Zero 110VBlue 110V 110V Zero

At this stage the phasing of the VT's across the breaker have been prove using the busbar supply. Thephase rotation of the running supply has been verified.

11) Isolate bus coupler and generator breaker as per current safety rules.12) Earth bus section as per current safety rules.13) Reinstall generator HV cabling.14) Remove bus section earthing and return to normal operation.15) Ensure bus coupler is open and locked off16) Start generator and deadbar. Close generator breaker onto RHS busbar.17) Check and record phase rotation of VT1 and 2. Ensure that this is the same as in steps 8) and 9)

(this proves that the phase rotation of both machine and busbars are the same).18) Produce phasing chart as shown in Table 1. Verify the phasing by measuring the VT secondary ac

voltages. Verify (if connected) that the synchroscope is reading twelve o'clock.

At this stage the phasing of the VT's across the breaker have been proven, using the busbar supply.The phase rotation of both the running (busbars) and incoming (generator) supplies are correct.

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3 PHASING STICKS

The final check is to verify the HV cabling, this is done using a combination of live line tester withphasing sticks. Refer to the manufacturer's instructions before using this equipment.

Figure 2: Phasing Stick ConnectionsFigure 2 outlines the connection for the equipment. Firstly, using the live line tester only, verify thevoltages A1, B1, C1, A2, B2, C2, individually to earth and record in a chart similar to Table 2.

Table 2: Voltage Verification Chart

Line Voltage 11kV System 13.8kV System 33kV SystemA1 6.35 * 8 * 19 *B1 6.35 * 8 * 19 *C1 6.35 * 8 * 19 *A2 6.35 * 8 * 19 *B2 6.35 * 8 * 19 *C2 6.35 * 8 * 19 *

A1 & A2 12.7 in phase ** 16 in phase ** 38 in phase **A1 & B2 6.35 ** 8 ** 19 **A1 & C2 6.35 ** 8 ** 19 **B1 & A2 6.35 ** 8 ** 19 **B1 & B2 12.7 in phase ** 16 in phase ** 38 in phase **B1 & C2 6.35 ** 8 ** 19 **C1 & A2 6.35 ** 8 ** 19 **C1 & B2 6.35 ** 8 ** 19 **C1 & C2 12.7 in phase ** 16 in phase ** 38 in phase **

* Phase to neutral volts = Line Volts√3

** Volts on phasing sticks when in synchronism = 2 x Line Volts√3

Connect up the phasing sticks and now verify the remaining readings between incoming and runningphases. Ensure that the reference synchroscope is reading 12 o'clock by trimming the incomingmachines governor. When all readings are acceptable synchronising is permissible.

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BLANK PAGE

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ELECTRICAL POWER

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CONTENTS1 RESISTANCE, INDUCTANCE & CAPACITANCE ................................................................................... 3

1.1 Resistance........................................................................................................................................... 31.2 Inductance........................................................................................................................................... 31.3 Capacitance ........................................................................................................................................ 4

2 CURRENT & VOLTAGE............................................................................................................................ 53 ACTIVE POWER........................................................................................................................................ 84 REACTIVE POWER................................................................................................................................. 105 POWER FACTOR & APPARENT POWER............................................................................................. 106 THREE PHASE POWER ......................................................................................................................... 157 TARIFFS AND POWER FACTOR CORRECTION ................................................................................. 15

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1 RESISTANCE, INDUCTANCE & CAPACITANCE

1.1 Resistance

Ohm's Law establishes that the relationship between voltage and current in a simple dc circuitis constant i.e. V/I = Constant. During Ohm's experiments he found that this constant variedfrom sample to sample. The ratio V/R is called 'resistance' or R, which in electrical terms canbe considered as opposition to flow of electrons. In a mechanical analogy, electricalresistance is like friction.

Resistance is present in all ac electrical circuits. The amount of resistance is usually relativelysmall, but can be high in devices such as heaters etc. and are referred to as 'resistive' loads.

1.2 Inductance

Wherever a magnetic field is produced by an electric current passing through a circuit, thatcircuit displays the phenomenon of 'inductance'.

A mechanical analogy would be a large grindstone with a turning handle. Because it is old itsbearings are stiff and rusty, giving a lot of friction. When we try to turn the handle, we mustovercome this friction, causing heat and loss of energy at the bearings and making ourselveshot with the effort expended.

Figure 1: Grindstone AnalogySince the grindstone is heavy, in addition to friction we also need to overcome its inertia inorder to provide the wheel with an accelerating force for it to gather speed. The greater theweight or inertia, the greater the force needed to accelerate.

An electric circuit exhibits the same effects. It has resistance (friction in the mechanicalanalogy), and, in order for a current to flow, a pressure in the form of a voltage is needed toovercome it (our efforts in the mechanical analogy).

An electrical circuit has inertia too. It opposes any attempt to speed up the current or to causeit to grow. This inertia in an electrical circuit is called 'inductance' and is due to the fact thatany electric current causes magnetisation. This effect is greatly increased by the presence ofiron for example (which magnetises easily).

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Figure 2: Electromagnetic InductionFaraday's Law of Electromagnetic Induction states that, if a conductor moves in a magneticfield, an emf (or electro-magnetic force or voltage) is induced in it. The opposite is also truei.e. an electric current in a wire gives rise to a magnetic field along its axis (Oersted'sPrinciple).

To explain how inductance arises in a circuit due to its magnetisation, which causes it todisplay electrical inertia or 'sluggishness', can be explained by the following example.Consider a coil of wire through which a current is flowing, there is a magnetic fieldconcentrated along its axis. If the current increases, then the magnetic field also increaseswhich, by Faraday's Law induces creates an emf (voltage) in each turn. The direction of theemf would be such as to oppose the change i.e. in this case to try to prevent the currentincreasing, and is therefore often referred to as the 'back-emf'.

Circuits incorporating equipment that have coils, especially those with iron such asgenerators, motors and transformers, have both resistance and inductance. They aregenerally referred to as 'inductive' loads.

1.3 Capacitance

Capacitance in electrical terms is the ability to store energy. This should not be confused withthe word 'capacity'. Care is needed to distinguish between 'capacitance' and, 'capacitor' whichis a device for storing energy.

A mechanical analogy of an electric capacitor would be a large, closed tank filled with water,fitted with a flexible membrane down the middle, and fitted a pressurised water supply on oneside and a suction outlet on the other side.

Figure 3: Water Tank Analogy

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Initially, with the valve closed both sides of membrane are at equal pressure and themembrane is undistorted.

When the valve is opened water under pressure flows into the right hand side of the tank andout through the left side. Water movement through the tank itself compared to the flowthrough the pipes is small compared to the large cross-section of the tank, hence themembrane will distort right to left as illustrated in Figure 3. Eventually when the distortion issuch as to produce a pressure equal to the incoming water, water flow will cease, and themembrane will be in a state of elastic strain.

Closing the valve at this point, the right hand side of the tank is under pressure with staticenergy stored in the stretched elastic membrane. Although water can move through theexternal piping, there is no transfer of water within the tank across the membrane.

In an electric capacitor, the current entering one side and leaving the other side is the'charging current', which is like the water flow in the pipes in the water tank analogy.

In the water tank, reversing the process would cause the stretched membrane to relax orrelease the static energy. Similarly passing a current into a capacitor 'discharges' it andrecovers the stored energy or capacitance.

Examples of 'capacitive' loads are obviously capacitors, overheads lines and some long,straight cable runs.

2 CURRENT & VOLTAGE

For a simple dc circuit that is purely resistive, Ohm's Law states that V/I = R (Voltage/Current =Resistance), i.e. the relationship between voltage and current is constant. In an ac circuit this constantrelationship is illustrated in Figure 4.

Figure 4: Resistive Load WaveformsWhen the circuit is switched on, the voltage and current waveforms coincide and are said to be 'inphase'.

In an inductive dc circuit however the current rises slowly at first since the applied voltage is overcomingthe 'back-emf', or inertia of the system to make the current grow. This characteristic has a significanteffect on the voltage-current waveform relationship in a purely inductive ac circuit.

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Figure 5: Inductive Load WaveformsIn Figure 5 the switch in a purely inductive ac circuit is closed when the voltage wave is at the positivepeak. Because the load is inductive, the first application of voltage will cause the current to rise slowly,and it will continue to rise in this manner until 'A', by which time the voltage wave has fallen to zero. Atthis point there is no more voltage drive and the current ceases to rise i.e. maximum positive 'P'.

After this point the voltage becomes increasingly negative, opposing the current flow and causing thecurrent to reduce. During the times 'B' and 'C' the voltage is negative, so the current becomesincreasingly negative. After 'C' the voltage passes through zero, and with no voltage drive the currentceases to decrease i.e. maximum negative 'Q'.

During time 'D' the voltage becomes positive again, opposing the current's negative flow. The currentbecomes less negative and returns to zero at 'D' when the voltage is at its positive maximum. Thecondition at 'D' is the same as the start time 'O' and the whole cycle begins again.

It can be seen from Figure 5 that the current wave is 'late' compared to the voltage wave by one quarterof a cycle. It is said to 'lag'. If one cycle is 360o, the current waveform lags the voltage waveform by 90o.

In a capacitive dc circuit a charging current is set up as the voltage is applied, and the growing chargeon the capacitor increasingly opposes the applied voltage until the charging current has decayed andceased. The effect of this characteristic in a capacitive ac circuit on the voltage-current waveformrelationship is illustrated as follows.

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Figure 6: Capacitive Load WaveformsIn Figure 6(a) the ac charging current is considered to be square shaped instead of the classical sine-wave shape. Between 'A' to 'B' the charging current is constant and positive and the capacitor ischarging at a constant rate. At the same time its charge voltage Ec , which is opposing the appliedvoltage V, is decreasing negatively to its negative maximum at 'P'. At this point the applied voltage V isat its maximum positive.

Between 'B' and 'D' the charging current has reversed and is constant and negative and the capacitor isdischarging at a constant rate. At the same time its charge voltage Ec , which is opposing the appliedvoltage V, is increasing positively to its positive maximum at 'Q'. At this point the applied voltage V is atits maximum negative. At 'C' the capacitor has no charge.

From 'D' to 'E' the charging current is once again constant and positive, and its charge voltage Ec isdecreasing negatively towards its negative maximum, passing through zero at 'E'. Beyond this point theconditions are the same as the start and the whole cycle begins again.

For the purpose of explanation a square shaped charging current was assumed. This would not thecase in practice where the charging current wave would normally be a sine-wave. In Figure 6(a) thesquare topped and angled lines are 'rounded off' implying a gradual rather than a sudden change,which approaches the sine-wave shapes shown in Figure 6(b).

From Figure 6(b) it will be noted that the current I is ahead in time of the applied voltage V, and thecurrent is said to 'lead' the applied voltage. If one cycle is 360o, the current waveform leads the voltagewaveform by 90o.

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Figure 7: Inductive & Capacitive CurrentsFigure 7 illustrates on the same diagram how inductive circuit currents lag the applied voltageby 90o and how capacitive circuit currents lead by 90o. It will be noted that since each currentis displaced 90o either side of the voltage wave, there is 180o between them, or in other wordsinductive and capacitive current waves are exactly opposite to each other in phase.

Convention considers that capacitive loads 'supply' current , whilst inductive 'take' current,which is important to remember since most practical circuits are a combination of capacitive,inductive and resistive loads.

3 ACTIVE POWER

The purpose of most electrical systems is to generate electrical power and to convey it to thoseconsumer installations which will use it. When an electric generator is delivering this energy, or the rateof delivering 'real' power, it is at the same time usually delivering another type of 'false' energy whichmay also be required by certain consumer equipment. To distinguish between them, 'real' power, whichrepresents real energy, is called 'active power' (sometimes also called 'wattful', 'actual', 'true', 'real' or'working' power). The other kind, which is the rate of delivering 'false' energy, is termed 'reactivepower' (sometimes also called 'wattless' or 'blind' power). 'Reactive' power is dealt with separately inSection 4.

'Active' power may be used to energise a mechanical drive, or to provide heating and lighting, or toenergise control and communication systems such as instrumentation or radio and telephoneinstallations. All of these things consume energy, and that energy is absorbed at a stated rate i.e. powerconsumption. 'Real' power consumption is measured in 'watt' (W), kilowatt (kW) - one thousand watts,or megawatt (MW) - one million watts.

Electric power is usually obtained from a generator, which receives its power from a prime mover(engine - petrol, diesel or gas; turbine - gas, steam, water or wind). With the exception of water andwind driven sets, the energy delivered by the prime mover to the generator is derived from the fuelwhich they burn i.e. the energy source is ultimately a chemical one.

Voltage is a pressure, and current is a flow. In mechanical engineering, power -the rate of doing work -is the product of pressure and volume flow. In electrical circuits, power is the product of voltage andcurrent i.e. Power = V x I. If V is measured in volts and I in amps, their product is the power in watts(W).

In dc this presents no problem. Both V and I are steady quantities and their product is a direct measureof the power in watts. With ac however the same rule applies, but these quantities are constantlychanging as the voltage and current alternate. It is therefore necessary to look at this product instant byinstant to see if it has an average value.

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Figure 8: AC Power - Resistive LoadConsider an ac voltage feeding a purely resistive load. If the top wave of Figure 8 represents thevoltage, the second wave represents the current is in phase with the voltage.

The power at any instant is the product of the voltage and current at that instant. At t0, t4 and t8 bothwaves are at zero, so their product is also zero. At any time in the first half-cycle voltage and current areboth positive, so their product is also positive, and is greatest at time t2, where both are at theirmaximum. At any time in the second half-cycle voltage and current are both negative, so their product isagain positive and is greatest at t6, where both are at their negative peaks.

The power wave is therefore the bottom waveform in Figure 8. It is of double frequency i.e. two peaksfor every one voltage peak) and is wholly above the line (positive). It represents pulses of power,always positive, and the average value of that power is midway between the power peaks and troughs.

In this case, for a purely resistive load the average, or mean (peak to peak) power P = V x I (watts) andis the 'active' or 'true' power, and is the same as in a similar dc circuit.

'Active' power is measured by a wattmeter, which automatically calculates the value of 'real' power inthe ac (or dc) circuit.

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4 REACTIVE POWER

Figure 9: AC Power - Pure Inductive LoadFigure 9 shows waveforms for a purely inductive load, in which the current 'lags' the voltage by 90o.Using the same principles as before to determine the instantaneous values of the product of current andvoltage, results in the 'active power' waveform shown at the bottom of Figure 9. Because of the 'phase-shift' between current and voltage, the average, or mean (peak to peak) value of 'active power' is zero.

Similarly, for a purely capacitive load, in which the current 'leads' the voltage by 90o, the average, ormean (peak to peak) value of 'active power' will also be zero.

If there is nett power in a purely resistive ac load only, there is a need to reconsider the rules fordetermining power for the more usual ac loads that include inductive, capacitive and resistive elements,since simple multiplication of current and voltage values do not represent the 'true' power in watts.

In circuits incorporating inductive and/or capacitive elements i.e. non-pure systems, the product ofvoltage and current is known as 'Reactive' or 'Wattless' or 'False' or 'Blind' power is measured in VAr(volt-amp reactive), and is a measure of the energy stored (but not consumed) in a magnetised system.

In installations that incorporate transformers and motors, which all need to be magnetised, the demandfor VAr's can be considerable

'Reactive' power is measured by a varmeter, which automatically calculates the value of 'reactive'power in an ac circuit.

5 POWER FACTOR & APPARENT POWER

Only power in purely resistive and purely reactive (inductive and capacitive) circuits has beenconsidered so far. Figure 10 shows the general case for a more typical circuit incorporating bothresistive and inductive elements.

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Figure 10: AC Power - General CaseThe resistive part of the load draws in-phase current, and the reactive part a current lagging 90o.Between them they draw a single current somewhere between in-phase (0o lag) and 90o lag, as shownon the second curve. The actual phase angle between current and voltage is usually written φ (Greek'phi' for 'phase').

If the same process is used, as before, of multiplying the voltage by the current at each instant of time,the power wave produced (bottom of the figure) would again be double-frequency but will now be partlyasymmetrical, and its average value will be positive and will lie somewhere above the zero line. Thismeans that, in the general case, the average active power (watts) will always be less than the maximumvalue which occurs in the purely resistive case, where the nett power is V x I watts.

Because in the early days of electricity power was always the simple product of V and I, which is correctfor dc circuits, a correcting factor was introduced for power in ac circuits. This correcting factor wasgiven the name 'power factor' ('PF') and is the cosine (cos) of 'phase difference' angle between thecurrent and voltage. Thus for an ac circuit nett power is V x I x cosφ.

For ac circuits incorporating capacitive elements, where the current 'leads' the voltage i.e. opposite or'negative' compared to inductive loads, the nett power formula above is still valid since for a particularangle, the cosine for a positive or negative angle is the same.

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Watts and VAr can be drawn as vectors. VAr is drawn at right angles to W and is the measure of'Reactive' power. The vectorial summation of W and VAr is known as 'Apparent' or 'Total' power whichis measured in volt-amperes (VA or kVA or MVA). The angle between Watts and VA, φ or Φ, is thepower factor angle, which has the same value as the phase difference angle between the current andvoltage (See Figure 11).

Figure 11: Power Vectors (Lagging PF)

The power factor (cosΦ) can be calculated by dividing the real power (W) by the apparent power (VA)i.e. cosΦ = Real Power/Apparent Power = W/VA.

Figure 11 shows a lagging power factor and the VAr's are called lagging VAr's. It is also possible tohave a load with a leading power factor as shown in Figure 12.

Figure 12: Power Vectors (Leading PF) By convention, lagging VAR's are considered to be positive, whilst leading VAR's are considered to benegative.

It is common to say that a generator is operating at a certain power factor, say 0.8 lagging, yet in allcases, it is the load determines the power factor. If for example you are operating an isolated system(like an isolated oil rig) with just one generator then the generator’s power factor must be the same asthat of the load. If there were two generators, it would be possible to run each at a different power factorbut the combined power factor would, as before, be the same as that of the load. Figure 13 shows howthe diagrams for the two generators can be combined.

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Figure 13: Power Vectors (Two Generators)If one generator is being operated in parallel with the National Grid then the whole National Grid loadstill sets the power factor, but any individual generator can be operated at any power factor because itso relatively small. It is only the total system Watts and VAr's that is fixed.

It can be seen from Figure 13 that it is permissible to add and subtract Watts, and to add and subtractVAr's. Adding and subtracting VA's however produce a non-meaningful result.

Figure 14: Power Factor MeterPower factor meters as shown in Figure 14, are calibrated to read cos φ and always show a positivenumber but are arranged to indicate lagging or leading power factors.

It is often convenient for operators to consider 'active' and 'reactive' power separately, though inpractice both are present together, travel down the same cables and wires, and are produced by thesame generator.

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Figure 15: Active & Reactive Motor PowerFigure 15 shows how active and reactive power to a motor is generated, distributed and consumed.Active or 'true' power originates from the generator's prime mover as mechanical output from theturbine. On the other hand reactive power emanates from the generator's excitation system through itsmain field.

Both powers come from the generator itself through a common cable. At the switchboard they give acommon current indication on the generator ammeter, and both combine to give a common powerfactor indication. They separate to give independent wattmeter and varmeter indications. Theyrecombine to feed the motor through a common cable. At the motor the reactive power is used tomagnetise the machine, and the active power supplies the (variable) mechanical load and also thelosses.

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6 THREE PHASE POWER

Consider a three phase system incorporating a star-connected three phase generator connected to athree phase star connected load as shown in Figure 16. The load is 'balanced' consequently the neutralcurrent is zero.

Figure 16: Three Phase SystemEach of the three phases are considered separately, with each generator winding having a phasevoltage e.g. VR, developed in it. Because the load is balanced, the line current in each phase is thesame e.g. IL = IR an so on.

The active power transmitted in each phase is:VR x IL x cos φ

thus the total for all three phases is:3 x VR x IL x cos φ

The line-to-line voltage VL , is √3 x Phase voltage, e.g. √3 x VR, thus the total power three phase activepower is:

P = √3 x VR x IL x cos φ watts

The above formula is correct for whether the source or load is star or delta connected.

7 TARIFFS AND POWER FACTOR CORRECTION

Installations where some or all of the electrical power is imported will be subject to a charge or tariff forthe provision of this power by the supply Authority or Utility. This tariff will in general be in two parts -one based solely on the energy consumed to meet the suppliers fuel and other running costs, thesecond part of the tariff is required to meet each consumer's contribution to the suppliers capital costswhich relate to the provision and ongoing repair/replacement of generating and distribution plant.

To meet suppliers fuel and running costs, the consumer is provided with a meter which records the totalenergy consumed in kWh (kilowatt-hours) or MWh (megawatt-hours) and is charged at the appropriaterate per 'unit' (kWh or MWh). This is usually the only charge for domestic installations, which areessentially resistive loads.

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To meet the suppliers capital costs, which is a reflection of the generation capacity that needs to beinstalled, the tariff is based on a comparison of the consumers expected maximum load (stated by theconsumer prior to commencement of the supply contract) and the actual maximum load in kVA i.e.'Maximum Demand kVA'. In practice maximum demand is not measured at any given instant, but isaveraged over successive periods of (usually) 30 minutes.

To limit this part of the payment it is in the consumers interest to limit the magnitude of kVA demand tothe stated expected maximum load, or below. To achieve this it is good practice to operate plant asefficiently as possible, which in electrical terms means operating equipment at the best power factor toproduce the lowest kVA demand as explained below.

Figure 17: Power Factor CorrectionFigure 17 shows a typical power vector diagram for an inductive load e.g. an induction motor. It will benoted that for a given power rating W, the VAr reduces from VAr1 to VAr2 as the power factor improvesfrom φ1 to φ2, and there is a resultant reduction in the VA value (VA2 compared to VA1). When W andVA are equal the VAr value is zero and the power factor angle φ is 1.0 or Unity.

Power factor improvement is often achieved by the introduction of special power correction equipmentinto the system, which incorporates capacitors which have a leading VAr characteristic. Usuallysystems are operated slightly under-corrected i.e. the power factor is less than unity, since the extramaximum demand amount remaining is small compared to the cost of extra capacitance required toachieve full correction. It will be noted that it is also possible to over-correct the power factor such that aleading reactive power (VAr) element is present, but this is not usual since the reactive power elementwill increase the value of the apparent power or maximum demand VA.

Generally, where practical and safe, electrical equipment should be operated at full load since mostequipment is designed to operate at it's most efficient at full load. Operating at part load can beinefficient and may result in a poor power factor that may have an impact on the overall plant maximumdemand kVA.

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PRISMIC POWER MANAGEMENT SYSTEM(PMS)

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PRISMIC POWER MANAGEMENT SYSTEM (PMS)

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CONTENTS1 INTRODUCTION........................................................................................................................................ 32 APPLICATIONS......................................................................................................................................... 4

2.1 Industrial .............................................................................................................................................. 42.2 Offshore............................................................................................................................................... 42.3 Marine ................................................................................................................................................. 42.4 Dockyards ........................................................................................................................................... 4

3 FEATURES ................................................................................................................................................ 43.1 Governor And AVR Adjustment .......................................................................................................... 43.2 Generator Set Management................................................................................................................ 53.3 Load Shedding .................................................................................................................................... 53.4 Other Features .................................................................................................................................... 5

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1 INTRODUCTIONPRISMIC PMS is a rack mounted microprocessor system with interface modules specificallydesigned for power system control and load shedding applications.

Figure 1: PRISMIC PMS SystemThe racks and associated equipment are fitted into a panel incorporating a touch screen humanmachine interface (HMI).

Figure 2: PRISMIC Touch Screen HMIPRISMIC PMS offers a number of benefits for the operator of any power generation systemincluding: Improved supply security Reduced manning levels Optimum usage of plant Power system data gathering

Since installation of the first system in 1980, PRISMIC PMS power management systems havebeen commissioned in diverse installations around the world. During this time continuousimprovement and introduction of new technologies have been combined with generatorapplications experience to produce a mature and highly capable product.

The user need have no specialist knowledge of PLC programming as PRISMIC PMS is suppliedcomplete with software to suit the site power system configuration. The functionality of eachsystem is verified using a power system simulation thus eliminating extensive on-siteprogramming.

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2 APPLICATIONS2.1 Industrial

Large industrial sites such as paper mills and petrochemical refineries, small to medium sizedutility power stations, water utilities, banks, airports, universities, sports stadia and other largepublic buildings all require secure power generation systems.

Different modes of operation are available, such as grid target power and power factor orgenerator base output

2.2 Offshore

Figure 3: Offshore InstallationOil and gas installations, often in remote locations, demand a substantial and secure electricalpower system. PRISMIC PMS provides fast acting load shedding to prevent cascade failure in theevent of unscheduled loss of generating plant.

Plant personnel levels can be reduced by enabling automatic start/stop facilities to operate,initiated by changes in load demand.

2.3 MarineMany vessels operate on the electric ship principle with propulsion and all other electric loadssupplied from a common electrical power source. This gives flexibility of operation, distribution ofplant weight and improved manoeuvrability.

For marine systems the PRISMIC PMS control requirements are similar to offshore applicationsexcept that the load profiles can be erratic. Specialist applications include: electrical propulsion,thruster control, synchronous compensator control and interface to dynamic positioning systems.

2.4 DockyardsWhere grid/utility supplies are 50Hz then frequency changer sets are used to provide 60Hzsupplies for moored ships or submarines. PRISMIC PMS has been used to control these systemsby making adjustments to AVR setpoints and stator racking gear to facilitate power sharing.

3 FEATURESThe following features can be incorporated into the PRISMIC PMS system:

3.1 Governor And AVR AdjustmentGovernor and AVR setpoints of each on line generator are adjusted to provide the followingcontrol features: Frequency and Voltage Control: of islanded power systems. (For systems not connected to

another virtually infinite power system). Generator MW and MVAr Load Control: PRISMIC PMS may be configured for power

sharing where load is evenly distributed according to the capability of each generator. Othermodes of control such as MW target, power factor target and temperature derating are alsoavailable.

Grid/Utility MW and MVAr Load Control: By generator load adjustment, the PRISMIC PMScontrols the import or export of power from a grid or utility.

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3.2 Generator Set ManagementStarting and or stopping of generator sets as follows: Automatic initiation of generator starting and stopping as site load increases and

decreases. Algorithms based upon load demand, tariff agreements or detection of failure of agrid/utility supply may be implemented as required.

Operator request via PRISMIC PMS HMI or DCSISCADA: may be used to initiate startingand stopping after appropriate checks have been made by PRISMIC PMS.

Engine start and stop signals may be issued by the PRISMIC PMS. Generator synchronisingequipment may be included with the PRISMIC PMS if needed. Governor and AVR adjustmentsare normally used to provide load take-up for starting generators and offloading before breakeropen signals are issued and engines stopped.

3.3 Load SheddingSelected load feeder breakers are opened by the PRISMIC PMS during fault conditions to avert acascade failure of the power system. This is typically initiated by the following conditions: System Under Frequency: Causes shedding of site adjustable blocks of load feeders. Sudden Loss of Generating Capability: If the remaining on-line generators are overloaded,

fast acting shedding occurs. Gradual Overload of Generators: If the on-line generators are overloaded for a period of

time related to the magnitude of the overload, then gradual overload shedding occurs. Other Fault Monitoring: may be used by PRISMIC PMS to initiate shedding as necessary.

Priorities are site adjustable to suit operating conditions. Load shedding uses intelligent algorithmso that only sufficient load feeders are removed to avoid generator overload resulting in maximumcontinuous use of plant.

3.4 Other Features Load Feeder Inhibition: Starting of certain load feeders may be inhibited when the on-line

generators have insufficient capability. Load Reconnection: When the on-line generators have sufficient capability, load feeders

may be automatically re-closed in a controlled manner after load shedding. Controlled Load Reduction: To avoid the need for load shedding, it is sometimes possible

to reduce load by reduction of thruster pitch or phasing back variable speed drives whilstfurther generators are started.

Operator Control via HMI: Control modes and target levels may be changed and variouscircuit breakers opened and/or closed via the HMI. For critical actions the PRISMIC PMSmakes appropriate checks before execution.

Data Transfer to DCS/SCADA Systems: PRISMIC PMS may be configured to communicatewith many different systems providing overall plant monitoring. PRISMIC PMS controlsequences and target value changes may be initiated from the DCS/SCADA system.

On Line Support: A modem may be fitted to the PRISMIC PMS HMI to facilitate remote faultdiagnosis by engineers at Brush in Loughborough.

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STABILITY CONTROLS USING KEYBOARD ENTRY (PRISMIC 'B')

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CONTENTS1 INTRODUCTION........................................................................................................................................ 3

1.1 General................................................................................................................................................ 31.2 Keyboard Adjustable Presets.............................................................................................................. 31.3 Site Adjustable Controls...................................................................................................................... 3

2 ACTIVE POWER SHARING (MW) COMMISSIONING............................................................................. 33 REACTIVE POWER SHARING (MVAR) COMMISSIONING.................................................................... 44 CONNECTING TO THE GRID NETWORK ............................................................................................... 55 AFTER COMMISSIONING ........................................................................................................................ 5

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1 INTRODUCTION1.1 General

Stability controls are provided in the PRISMIC system to allow prime movers and generators ofdifferent sizes and governor and AVR characteristics to operate when connected in parallel onthe same power system. For example consider two paralleled generators, the first being a largegas turbine and the other being a small standby diesel. In a situation arise where the two sets arerequired to share power, a long governor raise signal on the turbine could 'swamp' the power onthe small set possibly causing it to trip out on the generator reverse power protection system.

1.2 Keyboard Adjustable PresetsThe presets are adjusted using the Man Machine Interface (MMI) keyboard. These are storedwithin battery back-up RAM or 'flash' ROM on the PRISMIC central processor card. Should thismemory be corrupted, back-up 'safe' settings are substituted which are held in EPROM.

1.3 Site Adjustable ControlsThe PRISMIC 'B' system incorporates site adjustable controls which effectively set thegovernor/AVR pulse lengths 'ON' and 'OFF' times to maintain system stability whilstcompensating for frequency and voltage fluctuations on the power system, and correcting activeand reactive power sharing errors between interconnected generating packages. Voltage,frequency, power and reactive deadband controls are provided to prevent system instability and'nuisance pulses' emanating from the AVR and governor control relays.

The PRISMIC system uses proportional control to control both the AVR and governors on thegeneration packages. Figure 1 shows a typical train of control pulses.

Figure 1: Typical Train Of Control PulsesThe slug period is defined as the period between successive pulses. The slug duration (which isadjustable between zero and 25.5 seconds) is fixed during commissioning to obtain optimumstability within the control system. Since the AVR and governor response times are slow, the slugperiod allows a 'settling' time for the system to respond to the pulse before proceeding with thenext control signal.

2 ACTIVE POWER SHARING (MW) COMMISSIONINGOn an islanded system (i.e. the machines are not connected to a grid network) the governor pulsehas to compensate for any imbalance in the active power sharing (MW) between interconnectedsets and any frequency fluctuations on the system. The greater the error of these two parametersthe larger the control pulse.

A Frequency Error is defined as the difference between the PRISMIC frequency set pointed andthe actual bus frequency.

The Power Sharing Error is the difference between the actual MW on the generating packageand the target MW value based on the total load on the bus and the actual MW capacity of theprime mover and the number of sets on the bus.

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Where a set is connected to a grid system, then as the frequency remains constant, only thetarget MW error is accounted for.

A governors signal duration is calculated by:

Signal Duration = Frequency Error + MW Sharing ErrorFrequency Attenuation MW Attenuation

The greater the attenuation (adjustable between 0 and 15) the smaller the pulse length.

Stable frequency control is verified by either adjusting the PRISMIC frequency set point datum orplacing load on the system.

With stable frequency control, the power sharing commissioning may commence:1) Reduce the power sharing deadband and adjust the power sharing attenuation preset for

optimum stability.2) Place a set in manual control and increase the governor datum on that set, return the set

back to PRISMIC control. This should result in stable operation.

As the interconnected sets are in droop control, power sharing due to load fluctuations is takencare of by the governors and the power sharing control only comes into play when a set is beingintroduced onto the busbars. Various permutations of sets should be tried to prove stability.

3 REACTIVE POWER SHARING (MVAR) COMMISSIONINGAfter successful commissioning of the power/frequency control, the voltage and reactive (VAr)power sharing should commence. Re-install the voltage control relays but isolate the governor control relays. During AVR commissioning maintain system frequency and power sharing between on-line

sets manually.

On an islanded system (i.e. the machines are not connected to a grid network) the AVR pulse hasto compensate for any imbalance in the reactive power sharing (MVAr) between interconnectedsets and any voltage fluctuations on the system. The greater the error of these two parametersthe larger the control pulse.

A Voltage Error is defined as the difference between the PRISMIC voltage point and the actualbus voltage.

The Reactive Power Sharing Error is the difference between the actual MVAr on the generatingpackage and the target MVAr value based on the total load on the bus and the actual MVAcapacity of the prime mover.

Where a set is connected to a grid system then as the voltage remains constant, only the targetMVAr error is accounted for.

An AVR signal duration is calculated by:

Signal Duration = Voltage Error + MVAr Sharing ErrorVoltage Attenuation MVAr Attenuation

The greater the attenuation (adjustable between 0 and 15) the smaller the pulse length.

Stable voltage control may be verified by either adjusting the PRISMIC voltage set point datum orplacing load on the system.

With stable voltage control the reactive power sharing commissioning may commence:1) Reduce the reactive power sharing deadband and adjust the reactive power sharing

attenuation preset for optimum stability.2) Place a set in manual control and increase the AVR datum on that set, return the set back to

PRISMIC control, This should result in stable operation.

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As the AVRs on the interconnected sets are in droop control, reactive power sharing due to loadfluctuations are taken care of by the AVRs and the reactive power sharing control only comes intoplay when a set is being introduced onto the busbars. Various permutations of sets should betried to prove stability.

4 CONNECTING TO THE GRID NETWORKIf the system is used in conjunction with a grid network, it should now be commissioned.

As the frequency and voltage is maintained by the local supply authority the prime moversgovernor controls only the power swings between the machine and the grid.

Base load control is where PRISMIC maintains the MW's on the machine to optimise fuelefficiency, whilst peak lopping is where the import or export MW values on the grid feeder aremaintained to optimise local supply authority tariffs.

The AVR now controls reactive power between the machine and the grid. If power factor controlis selected the PRISMIC will either control the power factor based on the machine, or grid MW'son the grid or the machine, depending upon the design of the system. If VAR control is selectedthe PRISMIC will control the VAr's on either the grid or the machine.

Due to the grid network voltage and frequency remaining fairly constant, both governor and AVRcontrols become more active when the set is connected to a grid.

5 AFTER COMMISSIONINGHaving successfully commissioned both governor and AVR control, re-install all governor andAVR voltage control relays and record all preset settings.

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CALIBRATION PROCEDURES (PRISMIC 'B')

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CALIBRATION PROCEDURES (PRISMIC 'B')

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CONTENTS1 INTRODUCTION........................................................................................................................................ 32 ANALOGUE CARDS ................................................................................................................................. 33 VOLTAGE SENSING UNIT ....................................................................................................................... 44 POWER MEASUREMENT SYSTEM......................................................................................................... 55 PRISMIC CALIBRATION ON SITE ........................................................................................................... 56 TYPICAL CALIBRATION PROBLEMS..................................................................................................... 8

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1 INTRODUCTIONThe general principles in calibrating the PRISMIC Power Management System are detailedhereafter, but care must be exercised since each system is tailored to individual Customers'specifications. For a more detailed explanation please refer to the Operating & MaintenanceManual.

2 ANALOGUE CARDSThe PRISMIC system uses three types of analogue cards which require calibration:

1) Analogue Output Card (PB-AO)These cards provide analogue signals to external metering, or pass signals on to othersystems. Each card has four eight-bit output channels and can be configured to providestandard voltage and current output ranges. Calibration is normally performed by using aPRISMIC Data Module which simulates the output data from the microprocessor.

2) Analogue Input Card (PB-AI)These cards accept a wide range of analogue input signals from the outside world. Each cardhas eight eight-bit input channels which may be configured to accept standard voltage andcurrent output sources normally fed from transducers and external potentiometers.

Typical inputs are MW load feeder information for load shedding, turbine capability signalsand general data for displaying on an HMI system. The resolution is limited to eight-bitaccuracy.

As the inputs are fed from calibrated transducers, calibration is normally performed bydisconnecting the output of the transducer and substituting the card input with a knownvoltage or current source to simulate the transducer output.

By simulating the minimum output of the transducer, the appropriate analogue inputs 'offset'control can be set and then, by simulating full output of the transducer, the input channelsappropriate 'gain' potentiometer may be adjusted to suit. Refer to the contract card functionsheets for channel ranges etc. Repeat this procedure several times to achieve accuratecalibration checking at half scale for linearity.

3) Power Transducer Card (PB-PT)This card has eight input channels, four are dedicated for power and VAr measurement usingthe voltage sensing unit in conjunction with interposing CT's whilst the four remainingchannels are for analogue inputs.

This is the only card to measure in twelve-bit accuracy. Full scale in hexadecimal is 0FFFhex.

Before the advent of the PC based HMI systems these inputs were utilised for datum settingpotentiometers. A 0V and +10V reference signal would be connected across an externalpotentiometer and the wiper signal would be fed into the input channel. This feature still existson the cards although rarely used. Today these inputs are used to monitor busbar voltages inconjunction with the auxiliary card and also analogue inputs where input card numbers havebeen rationalised.

These analogue inputs have no gain and offset controls associated with them. The card givesus twelve-bit accuracy (0.024%) of the analogue input signal. The input range is 0V to +10Vand requires transducers tailored to suit. It is most important that during the calibrationprocedure all sets remain in manual control as adjusting the MW calibration levels adjusts thespinning reserve figure, possibly causing a load shed situation.

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3 VOLTAGE SENSING UNITThe unit is to comprise two independent transformers fitted together to form a composite unit.Each transformer to be as follows:

Primary: 110V 50/60HzSecondary 1: 50V 5VA Class 3Secondary 2: 29V 5VA Class 3

Earth screen between windings.

The transformers to be wired to stud terminals and clearly marked A1, A2, A3, B1, B2 and N asshown in Figure 1, voltages also to be marked.

Figure 1: Voltage Sensing UnitLine voltage is monitored via an analogue input channel on the Power Transducer Card. Theauxiliary card is provided with a supply from each individual busbar VT. This is then steppeddown via a transformer, rectified and attenuated before providing a nominal 5V dc signal into theinput channel. A nominal 5V corresponds to half of the input scale on the channel which is 7FFhex in the RAM store. On an 11kV system the input range will be zero to 22kV.

Although no offset and gain controls are provided for the analogue inputs on the PowerTransducer Cards potentiometers are supplied on the auxiliary boards to 'trim' busbar voltagevalues.

The PRISMIC voltage sensing unit (VSU) shown in Figure 1 is fed by a three phase nominal110V ac supply from the busbar VT that the generator is coupled to. A single phaseinstrumentation class CT is derived from the generator busbar. The VSU unit secondary windingsare wound in 'open delta' which produce a 50V signal in phase with the line current at unity powerfactor and another introducing a ninety degree phase shift.

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4 POWER MEASUREMENT SYSTEM

Figure 2: Power Measurement SystemFigure 2 shows the power measurement system used within the PRISMIC system. An interposingCT is fitted in the incoming line to provide isolation between the main Generator CT and thePRISMIC Power Transducer Card. It is often a case that the main CT secondary winding isearthed for safety reasons.

Two 2.2Ω resistors form a burden on the 1A secondary winding of the interposing CT, this is tosupply the current input to the card with a voltage whose amplitude and phase directly matchesthat of the generator or grid feeder being measured. The three phase supply is configured to suitthe phase in which the measurement CT is fed from.

Active Power (Watts) is equated in a three phase system as √3 VI cosΦ. Where V is line volts, Iis line current and cosΦ is the cosine of the phase angle displacement between line volts and linecurrent. The PRISMIC Power transducer card measures reactive power by multiplying the inphase voltage reference by the CT reference current.

Reactive Power (VAr) is equated in a three phase system as √3 VI sinΦ. Where V is line volts, Iis line current and sinΦ is the sine of the phase angle displacement between line volts and linecurrent. The PRISMIC Power transducer card measures active power by multiplying thequaduature phase voltage reference by the CT reference current.

On HV systems it is normally assumed that, as most of the loads are HV motors, load isdistributed evenly between each of the three phases and therefore it is prudent to monitor onlyone phase of the generator's output.

Power transducer cards within the PRISMIC system use the outputs from the VSU unit inconjunction with this CT signal to derive generator output MW and MVArs.

On multi-set systems the number of VSU units is rationalised by fitting them on the busbarsections rather than on each individual generator VT.

5 PRISMIC CALIBRATION ON SITEA PRISMIC system supplied in a control panel is normally pre-calibrated at our works makingcalibration simply a case of verifying on site. In our works we will have injected line volts andcurrent using a three phase supply using a series of Variacs and 'padder' resistors or a threephase protection relay injection set.

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The system is secondary tested using the known Customer's CT and VT ratios. Figure 3 andFigure 4 outline how this is achieved. To simulate a MW input signal we inject a phase to neutralcurrent signal. The phase selected is the one the CT is connected in. Reactive power may beprovided by injecting a current sourced from the opposite two phases to the line current.

Figure 3: Watts Injection

Figure 4: VAr InjectionOn site however, it is often impracticable to do this so we can alternatively use the generator as asource of power. To verify the secondary power being fed into the PRISMIC panel we mustmonitor the input three phase VT supply and single phase coming from the machine.

In most of the handbooks/manuals reference was made to the two Wattmeter method of powermeasurement. This meant in the early days carrying around two rather bulky, delicate analogueinstruments which each had multiplying factors within them. Later instruments contained thesetwo instruments in one case.

The two wattmeter method of power measurement in a three phase system is the most commonlyused. The advantages are that three phase power can be measured regardless of the state ofbalance, waveform phase sequence or load connection (star or delta). Figure 5 outlines theconfiguration of the system.

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Figure 5: Two Wattmeter Measurement MethodIn this method the Wattmeter current coils are connected in any two lines, the voltage coils beingconnected between each of these two lines and the third line.

The sum of the readings obtained is the total three phase load entering the PRISMIC panel fromthe generator. If we multiply this by the VT and CT ratios we can then calculate the actual MWvalue being generated by the set.

The reactive component (VAr) may be calculated by the difference between the two Wattmeterreadings multiplied by 1.732.

With the advent of modern solid state devices new digital Wattmeters are becoming available. Inthe Training area we use a Nanovip handheld instrument which uses a single phase clamp CT tomeasure the current signal whilst monitoring the VT signal with voltage probes. With thisinstrument we are able to read MWs, VArs, line voltage and current, frequency and VA.

As we are measuring on the secondary side of the CT's and VT's we need to include the CT andVT ratios into our calculations. On the training rig the VT ratio is 11,000: 415 and the CT ratio is150:5. Therefore the actual MW and MVAr on the set is given as:

Watts or VArs on set = (Actual W or VAr reading) x (11000/415) x (150/5)

This assumes the instrument is measuring three phase power. Whilst the set is on-line byshorting out the incoming CT signal with the SAK terminal link the power measurement channeloffset control potentiometer may be adjusted to indicate zero power on the channel. Opening theCT shorting link and placing load on the set will allow the gain of the channel to be adjusted viathe appropriate potentiometer. The greater the load on the set the more accurate the calibration islikely to be.

Re-check the offset for any drift as well as checking at different set loadings to verify calibrationlinearity. This will highlight any 'phasing problems'.

Refer to the contract card function sheets for input channel scaling and calibration potentiometerreferences.

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As reactive power on a generator can be both 'Lagging' and 'Leading' the offset control isnormally set mid range i.e. 7FFh at zero VArs whereas with the MW scaling this is normally set at100h at zero MW . This is used during an offloading sequence so that if the power on set (MW)goes into reverse power then PRISMIC will know that to offload the set it must issue a raisegovernor signal.

On earlier systems zero MW equalled 000h, it was therefore important to ensure that whilstsetting the offset controls on the MW channels that the display showing the hexadecimal value ofthat channel was indicating a slightly positive value.

It is important at this stage to verify the customers metering at this stage to ensure both systemstally as this could possibly lead to doubt at a later date if the two readings do not correspond.

6 TYPICAL CALIBRATION PROBLEMSTypical problems associated with the initial calibration of the power transducer channels duringcommissioning are outlined hereafter.

Should the calibration procedure be totally unobtainable verify all three phases are present on theVSU, verify phase rotation is correct and if this is correct verify CT is in the correct phase. Shouldthe latter be the case, transpose the VSU input cables to suit.

Should the MW channels not be reading set the offset controls slightly positive, increase MWloading on the set and if the reading decreases then the CT direction is incorrect.

Should neither the MW or MVAr channels operate check whether the CT shorting link is in circuit.If the channel gain is not attainable remove one of the channels CT burden resistors on theauxiliary board. Should the channel gain be high even with the gain pot reduced to minimum thenreduce the CT burden resistors on the auxiliary board.

Note: Changing the values of these resistors affects the calibration of both the Watts and VArchannels.

From past experience on site, Customers instrumentation is often limited and if a three phasepower measuring device is not available then use must be made of this instrumentation. Figure 6outlines various three phase formula's for calculating power within a system allowing for missinginstrumentation.

Figure 6: The Power TriangleUsing trigonometry we can represent Watts, VA and VArs as a right angle triangle. Where we seenotation cos-1 this is a simple way of reversing the cosine of the voltage and current phasedisplacement back to electrical degrees.

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To calculate the MW loading on a generator or grid feeder where no power instrumentation isavailable sometimes a polyphase kWh meter is fitted in circuit. This instrument is similar to themeter found in our houses to monitor how many Kilowatt hours of electricity we have consumed.This device provides very accurate readings. The speed at which the instruments mechanismrevolves is directly proportional to the power being delivered by the generator it is connected to.This method relies on fairly constant MW loading on the feeder or set to be successful. Figure 7shows such a device.

Figure 7: Polyphase kWh MeterThese instruments are often calibrated for the primary input on the busbars so they will give adirect reading of the generator or feeder MW values. The instrument in Figure 7 has a conversionfactor of 30 revs per kWh.

This means for 1kW flowing for 1 hour, then the aluminum disk will revolve 30 times.

Therefore 1 kW = (30/60) revs per minute = 0.5 rpm

If the disk was timed over a 1 minute period which resulted in 200 revolutions of the disk then thepower supplied by the power source would be:

Power = (200 [Reading]/5 [rpm]) x 1kW [Base Scale] = 400kW

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CALIBRATION PROCEDURES (PRISMIC 'B')

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LOAD SHEDDING(USING HMI)

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LOAD SHEDDING(USING HMI)

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CONTENTS1 INTRODUCTION........................................................................................................................................ 32 MODES OF OPERATION.......................................................................................................................... 3

2.1 Gradual Overload................................................................................................................................ 32.2 Fast Acting Load Shedding ................................................................................................................. 42.3 Under Frequency Load Shedding (Stage One) .................................................................................. 42.4 Under Frequency Load Shedding (Stage Two) .................................................................................. 5

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1 INTRODUCTION

The principles of the load shedding functions within the PRISMIC system are outlined hereafter. As thedocument outlines general principles care must be taken in the interpretation of this data sheet as eachcontract is tailored to individual customers specifications and various options may be omitted or modified.For a more detailed explanation please refer to the Operating & Maintenance Manual.

PRISMIC load shedding is designed to trip various loads on the busbar(s) in a pre-defined sequence toelevate cascade tripping of generating packages. The tripping levels are all adjustable through a PCkeypad. PRISMIC load shedding protection is normally graded so that loads will be tripped before anysystem protection relays operate. This keeps generating plant on-line thus preventing a complete siteshutdown.

The priority in which the loads tripped is referred to as the 'load shedding priority matrix' which can be setusing a PC keypad. Each load is allocated a priority the least priority load being tripped first during asystem overload.

Loads are classed as either monitored or non-monitored, the monitored loads being large drives or motorswhich can operate over a wide load cycle. These load are normally fitted with MW transducers whichmonitor the exact power taken by the load so PRISMIC can trip loads more accurately during an overloadsituation. Non-monitored loads are normally pump motors which have a constant MW loading. These areall adjustable through a PC keypad.

Should an overload occur on the system loads will be shed in the pre-defined shedding sequence with theexception of loads not being on or in split bus where PRISMIC only trip loads on an overloaded bus.Should a load fail to trip PRISMIC will ignore that load and proceed to trip loads further down the matrix.

Where a load selection is missing or one load has multiple selections, software prevents incorrectselection of the priority being made. All the three modes of load shedding operate in both solid and splitbus modes and all work in conjunction with each other.

2 MODES OF OPERATION

The three modes of load shedding are as follows:

2.1 Gradual Overload

As it's name suggests the gradual overload comes into operation when the system load'creeps' above the system capacity. To prevent nuisance tripping an IDMT timer is used ratherlike in protection relays whereby the load is shed quicker with a large overload than with asmall one. The overload timer is given in units of MW seconds per Generator and, as it is afunction of the prime mover. This figure is supplied by the prime mover manufacturer. Thiscounter may be viewed using the PRISMIC diagnostic unit.

A typical scenario might be one set on the bars with an overload setting of 12MW Secondsper set, should a 1MW overload be superimposed on the busbar then the load shedding willoperate in 12 Seconds. Should a 12MW overload be superimposed on the busbar then theload shedding will operate in 1 Second. Two sets on the bars the gradual overload counter willcount up twice as slow i.e. 24MW Seconds. Should at any time the overload disappear duringthe timer integrating up then it automatically will be reset to zero.

During an overload situation where the gradual overload counter has expired PRISMIC willcalculate the load that needs 'ditching' as the spinning reserve at this time will be negative.PRISMIC will then calculate the load that requires shedding and by working down the prioritymatrix trips sufficient load to produce a small positive spinning reserve value using themonitored and non monitored load values. The instant all these load(s) are shed a 'load shedretrip timer' is started which prevents further load shedding until the power generation systemre-stabilises. After this timer expires should there still be an overload imposed on the systemfurther load shedding will commence, if not the gradual overload timer will be reset so that thenext overload will again go through the inverse timer counter.

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2.2 Fast Acting Load Shedding

This mode of load shedding is used to prevent cascading failure of the generation system. It isinvoked by either a protection relay operating or the generator breaker opening. In thissituation the system spinning reserve is re-calculated instantly based on new number of setson the busbar and should there be an overload then load(s) will be tripped instantly down thepriority matrix to remove the overload on the remaining machines therefore by-passing thegradual overload timer.

Normally the digital signals for all the generator auxiliary breaker contacts and protectionrelays pass through an I/O card which produces an interrupt signal to the processor to tell itthat a set's breaker has changed state and to invoke the fast acting software routine. After theinitial trip the load shed retrip timer is invoked as in the gradual overload situation.

2.3 Under Frequency Load Shedding (Stage One)

This mode of load shedding is invoked due to either fuel blockages or very high prime moverloading where the prime mover is becoming stalled. Whilst the PRISMIC is attempting tocontrol busbar frequency to the nominal setting during this situation it may be assisted byremoving load.

During a under frequency situation the line Voltage is likely to be depressed due to AVR fluxlimiters operating In this case we cannot rely on the MW loading figures on the sets so, we tripon under frequency.

Figure 1 shows a typical arrangement of under frequency settings.

Figure 1: Typical Arrangement Of Under Frequency Settings

The set point is the level at which PRISMIC controls the nominal busbar frequency to bytrimming the governor signals. Should the frequency fall below the trip level for the duration ofthe under frequency stage one level a single load will be shed (refer to contract handbook).Atthis instant the under frequency re-trip timer will be started and should the frequency notrecover above the `under frequency recovery level' after this timer has expires then furthertripping of single loads will continue. The time between tripping is the duration of the underfrequency re-trip timer. After the busbar frequency rises above the `under frequency recoverylevel' for the duration of the `under frequency re-trip timer' then the `under frequency triptimer' is reprimed. It is important to ensure that PRISMIC frequency control is set to give agood frequency recovery response to minimise under frequency load shedding.

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Figure 2 shows a typical under frequency scenario. Initially the frequency is being controlledto the set point. Suddenly due to a fault condition the frequency falls below the underfrequency trip point. Whilst this is happening PRISMIC tries to return the system to nominalfrequency by issuing raise signals to all available on-line sets. Having failed to return thesystem frequency above the under frequency trip level for the period of the under frequencytrip timer (t1) a single load is shed. The retrip timer is started (t2) and, as the system has notrisen above the recovery level further tripping of single loads proceeds in intervals of t2.

Figure 2: Typical Under Frequency Scenario

2.4 Under Frequency Load Shedding (Stage Two)

Should the under frequency situation become more serious then the second stage of loadshedding will be invoked. Should the frequency fall below the under frequency stage trip levelthen instantly blocks of load are shed. The number of loads in the block are set up within thePRISMIC system.

Second stage load shedding is not utilised very often and is not recommended for `splitshafted' turbines where large loads can transiently cause the turbine speed to drop below theunder frequency trip level.

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SPINNING RESERVE

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07.09.01 (A) Spinning Reserve.doc © Brush Electrical Machines Ltd. 2003

SPINNING RESERVE

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SPINNING RESERVE

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CONTENTS1 INTRODUCTION........................................................................................................................................ 32 SOLID BUS SYSTEM ................................................................................................................................ 33 DETACHED SYSTEM................................................................................................................................ 4

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1 INTRODUCTION

The general principals for calculation of spinning reserve values on which the starting and stopping ofprime movers, load shedding, spinning reserve alarms, power sharing and load start inhibit signals arebased are detailed hereafter.

Note: Refer to Operating & Maintenance Manual for any deviations contract specific information.

2 SOLID BUS SYSTEM

Assume a solid bus system where all on-line sets are electrically interconnected through a continuousbusbar system.

The prime mover, diesel or turbine, supplies the mechanical power referred to as Watts into the load andtherefore all calculations are based on the 'real power' component of the supply. Figure 1 shows thesystem capacity and system load displayed in a similar fashion to an analogue meter scale. Under healthyconditions, the capacity line will have a higher reading than the load.

Figure 1: System Capacity1) Capacity

The capacity is normally calculated by summating the individual prime movers capacity of the on-linesets selected for PRISMIC automatic operation plus the actual load on any on-line set selected formanual control. This is because PRISMIC cannot assume that the full output of a manually selectedset can be attained.

The nominal MW capacity of a prime mover can be set as follows:(a) Manually set within the PRISMIC system(b) Via an analogue input from the turbine control panel (often referred to as TMAX)(c) A combination of (a) and (b), where the nominal zero degree Celsius MW capacity of the

turbine is manually set within the PRISMIC system either through preset switches or via a PCkeyboard. PRISMIC then takes in an RTD ambient air temperature signal for the software toderate the turbine capacity, based on the turbine manufacturer's data.

2) System LoadThis is derived by summating the MW values of all on-line sets, whether selected for PRISMIC controlor not.

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SPINNING RESERVE

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3) Spinning ReserveThis is the MW value of the system capacity minus the system load. Under normal conditions, this is apositive value and is the `spare capacity' remaining before the on-line prime movers becomeoverloaded. A negative spinning reserve will normally invoke load shedding due to a system overload.

3 DETACHED SYSTEM

Operational situations or system faults can cause the busbars to become detached through bus couplers.PRISMIC detects this situation in the following examples by examining the status of all bus-coupler andinterconnector breakers, calculating the bus capacity, bus load and spinning reserve for each bus section.

Note: Take care when switching sets from AUTO to MANUAL control, as the spinning reserve figure willbe reduced.

Figure 2 includes the `critical spinning reserve' and the 'excessive spinning reserve alarm'.

Figure 2: Critical Spinning Reserve

Should the spinning reserve level fall below the critical spinning reserve setting for the duration of thecritical spinning reserve timer, then an alarm is issued by the PRISMIC system informing the Operatorthat, should the load rise further, load shedding will occur.

Should the spinning reserve level increase above the excessive spinning reserve setting for the durationof the excessive spinning reserve timer, then an alarm is issued by the PRISMIC system informing theoperator that there are too many machines running on the bus. The Operator is given the opportunity toshut a set down.

Having too many sets on the bus increases the reliability of the system should a set fail, but tends to runthe sets inefficiently. Most engines optimum efficiency is approximately 90% of their full load rating.

Figure 3 shows the 'set stop' and 'set start' margins. These determine when sets are stopped or started.

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Figure 3: Set Stop/Set Start MarginsTimers are used to prevent transient stopping and starting of the engines. Normally, when setmanagement is included in the PRISMIC system, sets are automatically started before the critical alarm isactivated.

Should the spinning reserve level increase above the set stop margin for the duration of the set stop timer,then a shutdown signal is issued to the highest duty running engine available for PRISMIC control.

Should the spinning reserve level fall below the set start margin for the duration of the set stop timer, thena start signal is issued to the next available engine.

Figure 4 includes 'load inhibit levels'. Where there is a possibility of causing an overload on the system bystarting a large load, the PRISMIC system uses the following feature.

Figure 4: Load Inhibit Levels

If the spinning reserve falls below the `restart load MW' value and the load feeder is open, an inhibit signalis issued to that breaker preventing it from being closed manually.

The `load restart MW' values are set either using preset switches or via a PC keyboard on the PRISMICsystem. They are set higher than the nominal running MW value of the load to allow for starting currents.

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As most of a motor starting current is reactive and loads the generator rather than the prime mover, thesoftware logic can be configured to ensure that enough generators are on line to supply this reactivepower, as well as spinning reserve.

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DATA COMMUNICATIONS

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07.10.01 (A) Data Communications.doc © Brush Electrical Machines Ltd. 2003

DATA COMMUNICATIONS

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DATA COMMUNICATIONS

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CONTENTS1 INTRODUCTION........................................................................................................................................ 32 COMMUNICATIONS - WHAT IS IT?......................................................................................................... 33 WHAT IS DATA COMMUNICATIONS ...................................................................................................... 34 HISTORICAL BACKGROUND TO DATA COMMUNICATIONS SYSTEMS............................................ 45 INFORMATION TRANSFER SYSTEMS ................................................................................................... 66 TELECOMMUNICATIONS SYSTEMS AND NETWORKS ....................................................................... 67 DATA AUDIO AND VIDEO COMMUNICATIONS..................................................................................... 78 THE COMMUNICATIONS INTERFACE.................................................................................................... 79 OVERVIEW OF THE EIA RS-232, 423, 422 & 485 INTERFACE STANDARDS ..................................... 810 'SMART' INSTRUMENTATION.............................................................................................................. 911 MODERN INSTRUMENTATION AND CONTROL SYSTEMS............................................................ 10

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DATA COMMUNICATIONS

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07.10.01 (A) Data Communications.doc © Brush Electrical Machines Ltd. 2003

1 INTRODUCTION

The following examines what Data Communications is, why it is needed and outlines where the subjectfits in with other types of communication systems. It also provides an overview of the historicalbackground of Data Communications and traces its development up to modern times.

It introduces some of the basic concepts of data communication leading up to a brief review of thecommonly used serial interface standards such as RS-232, RS-423, RS- 422 and RS-485. The concept of'smart' instrumentation is introduced to emphasise the increased need for data communications in amodern control system. It then briefly outlines the application of data communications in a modernIndustrial Control System.

2 COMMUNICATIONS - WHAT IS IT?

The goal of a Communications System is to transfer a message from one place to another. The type ofinformation to be transferred will often determine which communication method can be used. In moderntimes, we are accustomed to transferring the following types of information: Data (Combination of Characters) Audio (Voice and Music) Video (Complex Picture Images)

This information can be transported over great distances quickly and reliably via one of several mediumssuch as Air (Radio, Microwave, Satellite Link), Metal Conductors (Landlines, Underground Cables,Undersea Cables), Road/Rail/Air (Postal Service) and Optic Fibre Cables, using a wide range of energyfrequencies and wavelengths.

The main purposes are for business, news, entertainment and military needs. This has become such anintegral part of our lives that it is sometimes difficult to imagine the difficulty that was experienced in earliertimes with communications.

To illustrate the concepts, a well known form of communication, still commonly used today, is the writingand mailing of letters. In centuries past, information was recorded in the form of Characters on stonetablets and later on sheets of paper. In modern times, information can be recorded electronically onFloppy Disks, Hard Disks, Magnetic Tapes and, more recently, on Compact Disks. Characters are stillused as the basic component of any recorded data.

In historical times, the recorded information was transported from one place to another by camels, horsesand sailing ships; later by steam trains and ships and now by electric trains, road transport and jetaeroplanes. In all these cases, the following common factors exist: Some Information needs to be Transferred from one location to another. There is a Transmitter of the information. There is a Receiver of the information. A Communication Link, or series of links, is available to transport the information from the sender to

the receiver.

The subject of Communications has almost limitless scope. The material in this course is aimed at onlyone small part of the overall subject, being: The subject of Data Communications. In the context of Industrial Automation and Process Control.

3 WHAT IS DATA COMMUNICATIONS

The subject of digital Data Communications is concerned with the electronic transfer of Data from oneplace to another, via any medium.

Data (plural of datum, meaning an item of information), is the general term used to describe thecomponents of a message or information. Messages are usually made up of characters or numbers,which may be recorded on a piece of paper or electronically. In data communications, the data aredisassembled into bits, transferred bit by bit as electronic pulses, then reassembled at the receiving end.

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A Character is the general term that is used to describe any alphabetic letter, punctuation mark, numberor symbol commonly used for the recording, processing and transferring of information. When thesecharacters are combined into words, equations, sentences, paragraphs and reports, the combination ofcharacters becomes known broadly as a Message or more generally as Data.

Data can be any combination of any characters, binary numbers, etc. We are very familiar with the 26characters of the English alphabet and the specific rules for combining these characters into the languageof English. There are also a number of other similar languages, however, using a slightly differentalphabet (e.g. German, Swedish, Spanish, Dutch, etc) and some different languages using completelydifferent alphabets (eg. Japanese, Chinese, Russian, etc).

From the point of view of Data Communications, any of these characters or combinations of them, aretreated the same. It makes no difference to the communications system what the characters are or howthey are combined. Any message that can be reduced down to individual characters is suitable for transferby data communications.

The data is transferred in the form of a binary digital code. Each character is assigned an individual codemade up of 'bits' (Binary digits). Provided every character has a unique code assigned to it, any messagecan be encoded, transferred, decoded and read at the other end. When gathered together for transferover the communication link, these series of bits are usually referred to as data. In this course, the worddata will be used when referring to these strings of bits, encoded for transfer.

Data Communications describes the activity of transferring data from one location to another, withoutbeing precise about the methods of communication that are available.

4 HISTORICAL BACKGROUND TO DATA COMMUNICATIONS SYSTEMS

As mentioned previously, the writing and mailing of a letter is a simple form of Data Communications. Thismethod of communication was made possible a few thousand years ago by the development of variouscharacters and alphabets by the Egyptians, Hebrews, Greeks, Romans, etc. This method of datacommunications, of inscribing characters on a letter and transporting it over a considerable distance, hasbeen used successfully for a number of centuries and is still an important and cost effective component ofmodern data communications. The main problems with the writing and mailing of letters is the long timetaken to prepare them and to transfer them from the sender to the receiver, even today with modernAirmail.

There has always been a need to transfer information, motivated mainly by the need for personalcommunication between friends and families, for the transfer of business information and for governmentadministration and military purposes. The successful development of world trade since the IndustrialRevolution has rested firmly on the ability to communicate data from a sender to a receiver. This need totransfer data has increased rapidly over the years as the technical developments have made the ability tocommunicate easier and quicker.

Modern electronic data communications can trace its background to the development of the Telegraph, aword derived from the Greek words graph and tele, meaning 'making marks from afar'. In the early 1800's,soon after the discovery of electricity, the first attempts at telegraph systems tried to transfer messages byusing several voltages simultaneously across several wires in parallel, using some sort of code for eachcharacter. This seemed to be the logical way to do things at that time. It soon became clear that a systemof parallel wires was bulky, difficult to handle and not a practical proposition for long distancecommunications. Consequently, attempts at parallel transfer were soon abandoned in favour of serialcommunication systems, where attempts were made to transfer the message sequentially along a 2-wireline.

The first practical serial data communications system, which included both the hardware and a code(software), is usually attributed to an American, S F B Morse, although there has been considerabledebate about this. Even if he was not the first, he certainly has become the best known for the code thathe developed for serial communication, called the Morse Code.

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In this code, the entire alphabet, numbers and some punctuation (approx. 40 characters) are representedby a series of 'dots' and 'dashes'. By today's standards, it is a complex code and not really suitable forelectronic encoding.

The length of the Morse code for each character varies from one pulse for a character such as E, to sixpulses for a colon. There was no logical way of remembering the code for each letter, so it had to belearnt by the early telegraph operators .

Morse's data communication system comprised a sounder, a key, a communication link, the Morse codesand an operator at each end. All of the activities associated with data transmission then still have theirequivalent components in a modern serial data communications system i.e. Message: An operator is given a message written in English. Encode: The operator uses his brain and coding tables to convert each character to the Morse Code. Transmit: The operator controls the key to send the coded signal across the communications link. Receive: A second operator receives the message at the other end by listening to a sounder, which

he may record. Decode: The operator uses his brain and coding tables to convert each code back to a series of

English characters. Print: The operator then writes the message down in normal language for others to read.

The difficult and time consuming task of manual transcription of the telegraph code was soon developedinto the separate technology of Teleprinting ('printing from afar'). Initially, the electronic impulses wererecorded at the receiving end by a stylus onto a rotating drum with a paper tape to provide a "hard copy"of the received code. The period when the stylus was in contact with the paper became known as Markingand the period when it was not became known as Spacing. These terms are still commonly used today inserial data communications, although they tend to be quite confusing, when used in the modern context.

From that time, efforts were directed towards developing a machine that could directly encode charactersfor transmission and, at the other end, decode them and reproduce the actual characters, rather than justhave marks and spaces. The success in this direction was governed by the rate of development in otherfields of electrical engineering.

Early versions of a teleprinting machine that actually printed characters consisted of an inked wheel withthe typeface uniformly distributed around the circumference. The series of electrical impulses coming inacross the pair of wires caused the wheel to ratchet up to the desired character at which point an armcame up behind a paper tape to make an imprint of the character on the paper tape. Unfortunately, everytime there was interference on the line and an electronic pulse was gained or lost, the result was aspelling error.

Later versions of the teleprinter used a complicated electromechanical system that included a rotatingwheel, driven by a small synchronous AC motor, at both the sending and receiving ends. These wheelswere held in synchronism by the fact that the AC power supply system at both ends stayed insynchronism through the interconnected power network. At the correct instant, a pulse was sent down theline which engaged a complicated mechanism which then printed the desired character. The majorproblem of the day was to keep the two ends in synchronism. Rotating head machines were used right upto the 1920s. The difficulty of maintaining synchronism between the sending and receiving end finally ledto the downfall of this system and it was superseded by one of greater tolerance to frequency variation atthe two ends.

In addition to the mechanical and electrical problems of a teleprinting machine, the code was a severelimitation on the early efforts of electronic serial communications. The Morse Code was essentially afree-form code with a variable number of elements for each character and it is difficult to imaginedesigning a machine that could respond to this diversity.

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A French Telegraphic Engineer, Maurice Emile Baudot, is usually credited with the invention of the firstuniform-length 5-bit binary code in the late 1800s. A standard code, based on his coding method, waslater adopted by the CCITT (Consultative Committee for International Telephone and Telegraph) forinternational data communications by teleprinter and is commonly called the Baudot Code. This code hasbeen the basis of 'Telex' communications even to the present time. A 5-bit code can identify up to 32Characters, which comfortably includes the 26 letters of the alphabet. When adopted by CCITT, a 'smart'feature of the code was the ability to 'shift', like a typewriter, into a supplementary set of 32 characters,mainly for numbers and figures.

In the machine, complex electromechanical devices (relays and levers) were used at both ends to encodeand decode the message. At the sending end, pressing a character on a keyboard would encode thecharacter into a unique 5-bit code for transmission over a pair of wires. When a message was sent, a'Start' pulse was first sent down the line to the receiving end to synchronise the two ends. From then on,synchronism depended on the power supply frequency and the synchronous motor driving each machine.A similar mechanism would decode the message and print it onto a paper tape. Understandably, thespeed of this complex electromechanical system was fairly slow.

The above historical review describes how serial data communication evolved over the last century andoutlines some of the technical problems associated with its development. In recent years, telex has largelybeen superseded by modern forms of teleprinting, based on microprocessor technology. The mostcommon examples are facsimile, computer data links and other PC based systems using modems.

5 INFORMATION TRANSFER SYSTEMS

It should not be forgotten that the main purpose of data communications is to transfer data from one placeto another rapidly and reliably for whatever purpose. As the volume of information has increased, thespeed of transfer has had to increase and with it came the need to control the flow of data to prevent thereceiver from becoming overwhelmed with unexpected data. The detection and correction of errors in thedata, mainly due to interference, has always been a problem that has affected the reliability of theinformation.

To cope with this increasing traffic and to automatically identify errors, protocols have been developed toregulate the transfer of data. Protocols are computer programs which embody all the rules governing thetransfer of the data, such as who sends first, how many bits at a time, how to identify when there is anerror, what to do with the error, etc. The various types of protocol will be discussed in greater detail later.

The fundamental requirements of an Information Transfer System are: Procedures to regulate the Flow of Data so that both ends can cope with the quantity of data. Procedures to regulate the Accuracy of Data and to define what to do when an error has been

detected. Protocols to ensure that the Sender and the Receiver work co- operatively at both ends.

6 TELECOMMUNICATIONS SYSTEMS AND NETWORKS

The subject of Telecommunications ('communication from afar') has primarily been concerned with voicecommunication over long distances. Modern telecom systems use a wide variety of electronic equipmentto meet the increasing needs of telephone users. Communication takes place by wire, radio, microwaveand fibre optic cables. Contact between two users may simultaneously include one or more of thesemedia.

Older telecommunications media are limited by the quantity and rate of information that can be transferredand an inherently higher level of interference from environmental factors such as the weather andlightning. These are rapidly being replaced by optical fibre connections which can cope with far greaterdata rates and are less susceptible to interference.

The telecom system is part of a large network which spans not only the entire country but is alsoconnected into the national networks of other countries. It provides users with a cost effective private2-way voice and data communications to almost any part of the world. The system enables the user todial and be connected by switching circuitry to the desired receiver.

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7 DATA AUDIO AND VIDEO COMMUNICATIONS

Data Communications is concerned with the transfer of information in the form of characters, each ofwhich is in the form of a code. This type of communication is referred to as being 'digital' because the datato be transferred is first broken down into bits 'O's or '1's before being transmitted electronically as 'off' or'on' voltages on the line. As outlined above, digital data communications is not a new invention but hasbeen in use for over a century.

Audio Communication is essentially concerned with the transmission of analogue sounds and speech thatare in the audible frequency range of about 10Hz to 20kHz. An analogue signal is one that is continuouslychanging within certain limits of voltage and frequency.

The telephone system is the most well known of the audio communication systems. Another example ofaudio communication is the radio. For radio transmission, modulation techniques such as AM (AmplitudeModulation) and FM (Frequency Modulation) are used to prepare the audible information for broadcast byradio signal. Radio receivers are used to decode the signal, amplify it and bring it back to the 10Hz-20kHzaudible range.

The signals used for digital data communications are not directly compatible with the telephone system,which is designed for analogue audio communication. These signals have to be converted to compatiblesignals by some interface equipment, called Modems. The Modem is a device that takes digital signalsand converts them into a form suitable for the communication link.

Video Communication is mainly oriented towards entertainment in the form of television. TV is anextremely complex system because it must convert a two-dimensional picture into electronic signalssuitable for transfer across a communications link and, simultaneously, also transfer the audio signal. Thetechnical problems of TV were overcome during the period between 1920 and 1950 and are still in acontinuous state of development.

TV has used analogue VHF and UHF carriers to transfer the video signals by air or coaxial cables. Thesehigh frequency signals contain a vast amount of information (video, audio and synchronising signal) andoccupy a frequency bandwidth of 6 MHz. Digital video signals for television are not yet a viable alternativeto analogue because of the very high rate of data transfer that would be required (approx 70 Mbps!).

Facsimile or Fax, which uses some of the principles of television to convert two-dimensional images to anelectronic signal, uses digital data signals suitable for transmission over a telephone network. This is a'still' picture, however, with no sound and with only a few shades of grey and a much longer time ispermitted for the data transfer. Data compression and error correction techniques have enabled facsimileto transfer a single page image in less than one minute.

8 THE COMMUNICATIONS INTERFACE

The communications Interface is the point of contact between two different communications environmentsor between two different types of equipment.

The meaning of the word Interface, in this context, may be illustrated by the example of an interfacebetween the power supply company and our homes. Electric power is usually transported at high voltages(132kV, 11kV, etc) while power in the home is usually used at lower voltages. The power company needsthe high voltages for economic transfer of power, while the home owner needs the low voltage to safelyoperate electrical appliances.

To connect power to the home, the power company must reduce the voltage through a transformer andconnect it to the home via a suitable meter box. The standards associated with this connection system aredictated by the power company and the wiring in the home must conform with these standards. This'hook-up' is called an Interface and the standards that define the technical details are the InterfaceStandards, which are published documents and open for all to see and comply with. The Interface fulfilsseveral criteria: Prevents damage to power company's electrical system. Prevents damage to the electrical system in the home. Provides a usable and workable system.

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The Interface between a computer and data communication system should fulfil similar objectives. Themain objective is to provide a medium for transfer of data from one system's environment to another.Once such an interface has been established, the transfer of data from a terminal to a communicationssystem and back is then possible.

Obviously, there are many different ways that this could be achieved and every manufacturer could havea different idea about the most effective way of doing this. This potential diversity raises one of the biggestproblems in data communications - compatibility with other equipment.

When computers arrived on the scene they became very useful tools for the processing of data. Thetransmission of data to remote locations became the natural development. Short distances could easily bespanned by separate cables, but it soon became clear that access to distant locations could also beachieved by using a well established telephone network. Telephone networks, already in place, wentalmost everywhere and, best of all, they could be rented relatively cheaply. Telephone networks areusually owned by the state or very large corporations, so it is not surprising that these organisationsinsisted that strict interface standards should be adhered to before any equipment could be connected tothe system.

Digital equipment, commonly used for data communications, is not suitable for direct connection to theanalogue type telephone network. In addition, the telephone system has a limited bandwidth, so anyinterface device would have to operate within those limitations. The result was the development of atranslating device designed specifically for telephone networks, called a Modem(MODulator/DEModulator).

Initially, many different types of modems were developed for this purpose. This stimulated thedevelopment of one of the best known standards in the field of Data Communications - the EIA-RS-232-CInterface Standard.

9 OVERVIEW OF THE EIA RS-232, 423, 422 & 485 INTERFACE STANDARDS

The EIA-RS-232 Interface Standard was developed and issued in USA in 1969 to define the electricaland mechanical details of the interface between Data Terminal Equipment (DTE) and DataCommunications Equipment (DCE) which employ serial binary data interchange.

For serial Data Communications, the communications system comprises: A data sending terminal (e.g. a Computer), called the Data Terminal Equipment (DTE), that is the

source of the data, usually a series of characters, coded into a suitable digital form. A suitable data transmitter (e.g. a Modem), called the Data Communications Equipment (DCE), that

converts the signal into a form suitable for the communications link. The communications link itself (e.g. Telephone system). A suitable receiver (e.g. a Modem), also a DCE, that converts the signal back to a form suitable for

the Receiving Terminal. A data receiving terminal (e.g. a Printer), also a DTE, that is the receiver of the digital pulses for

decoding back into a series of characters.

The RS-232-C Interface Standard describes the interface between a Terminal (DTE - Data TerminalEquipment) and a Modem (DCE - Data Communications Equipment) specifically for the transfer of serialbinary digits. RS-232-C leaves a lot of flexibility open to the designers of the hardware and softwareprotocol.

With the passage of time, this standard interface has been adapted for use with numerous other types ofequipment, such as personal computers (PC's), printers, programmable controllers, PLC's, instrumentsetc. To recognise these additional applications, the latest version of the standard, RS-232-D, has changedthe words associated with DCE to the more general "Data Circuit-Terminating Equipment". But RS-232also has a number of inherent weaknesses that make it unsuitable for data communications forinstrumentation and control in the industrial environment.

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Consequently, several other EIA interface standards have been developed which overcome some ofthese limitations. Those that have become most commonly used for instrumentation and control systemsare RS-423, RS-422 and RS-485.

1) RS-423 Interface StandardUnbalanced system similar to RS-232, with increased range and data transfer rates, with up to 10 linereceivers per line driver.

2) RS-422 Interface StandardBalanced differential system, with same range as RS-423 but increased data rates, with up to 10 linereceivers per line driver.

3) RS Interface StandardBalanced differential system, with same range as RS-423 but increased data rates, with up to 32 linetransmitters/receivers per line.

The RS-485 interface standard is very useful for instrumentation and control systems where severalinstruments or controllers may be connected together on the same multipoint network.

10 'SMART' INSTRUMENTATION

In the 1960's, the 4...20mA (or 0...20mA) analogue interface became established as the standard forinstrumentation technology. As a result, the manufacturers of instrumentation equipment had a standardcommunication interface on which to base their products and users had a choice of instruments andsensors from a wide range of suppliers which could be integrated into their control systems.

In the 1980's, with the advent of microprocessors and the development of digital technology, the situationhas changed. Most users appreciate the many advantages of the new digital instruments, such as moreinformation, local and remote display, reliability, economy, self tuning, diagnostic capability, etc. And it isalso fairly clear that there is a gradual changeover from the analogue to the digital technology.

The one major difficulty that is standing in the way of a more rapid transition from analogue to digitalsensors is the absence of a broadly accepted Standard for the Bus communications at the field level.Some of the leading manufacturers have already made proposals in this direction but it is likely to take afew more years before a universally acceptable standard emerges.

In the meantime, manufacturers of instrumentation and control devices have developed and installedcontrol systems where the communication between supervisory systems and the field controllers is digital,examples are DCS systems and PLC systems. But the field sensors and instrumentation are still largelyincorporated via 4...20mA analogue signals.

There are a number of intelligent digital sensors already available with digital communications capabilityfor most of the traditional applications, such as for measuring temperature, pressure, levels, flow, mass(weight), density, power system parameters, etc. At this stage, these devices are usually connected alongthe lines of RS-485 on a 'Multipoint' bus network in an asynchronous Poll/Response mode. These newintelligent digital sensors are known as 'smart' instrumentation.

The main features that define a 'smart' instrument are: Intelligent, digital, measuring sensor Includes digital data communications as standard Allows connection to a field network (eg multipoint)

There is also an emerging range of intelligent, communicating, digital devices that could be called 'smart'actuators. Examples of these are devices such as Variable Speed Drives, Soft Starters, ProtectionRelays, Switchgear control, etc with digital communication facilities.

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11 MODERN INSTRUMENTATION AND CONTROL SYSTEMS

In the Industrial environment, the main purpose of an Instrumentation and Control System is to take careof the following:

1) To Control The Process And Process AlarmsTraditionally, this was provided by analogue controllers (temperature, flow, etc) operating on standard4...20mA loops. The 4...20mA standard is "open" to equipment from a wide variety of suppliers and itis common for these to be mixed in the same control system. These stand-alone controllers andinstruments have largely been replaced by integrated systems such as DCS (described below).

2) To Control The Sequencing, Interlocking And AlarmsTraditionally, this was provided by relays, timers and other components hardwired in Control Panelsand Motor Control Centres. The sequence control, interlocking and alarm requirements have largelybeen replaced by PLC's (described below).

3) To Provide An Operator Interface For Display And ControlTraditionally, process and manufacturing plants were operated from local control panels by severaloperators, each responsible for a portion of the overall process. Modern plant-wide control systemstend to use a central control room, equipped with computer based graphic operator work-stations thatgather data from the field instrumentation and use it for operator display, to control processes, tomonitor alarms, to control sequencing and interlocking.

4) To Provide Management InformationManagement information was provided by taking readings from meters, chart recorders, counters andtransducers and also from samples taken from the production process. This data is required tomonitor the overall performance of a plant or process and to provide the data necessary to managethe process. Data acquisition is now integrated into the overall control system, which eliminates thetedium of gathering the information and reduces the time that it takes to correlate and use theinformation to remove bottlenecks. This is an area where substantial productivity gains can beachieved through good management of the process.

There is no doubt that Productivity and Quality are the main objectives of any production activity, whetherit be a process or a manufacturing environment. Productivity and Quality are the result of good management. Management can be substantially improved by the availability of accurate and timely data.

The ability of control equipment to fulfil these requirements has depended on the major advances thathave taken place in the fields of integrated electronics, microprocessors and data communications. Thetwo devices that have made the most significant impact on how plants are controlled are:

A) Distributed Control Systems (DCS)Have been developed by the traditional manufacturers of process control equipment, who werefocused mainly on the requirements of the process industries, eg. Petrochemical, Food Processingand Paper. The requirements of DCS users are mainly associated with analogue loops to controlparameters such as temperature, flow, levels, densities, etc. With DCS systems, communications atthe field level are still largely based on the analogue 4...20mA standards and will probably remain thatway for some time to come.

However, DCS systems have for a long time been well integrated at the next higher level with a welldeveloped ability to communicate to computers (VAX, PDP, DEC, etc) and between themselves vianetworks using proprietary protocol. Increasingly, DCS systems are supporting 'open' systemsnetworks providing compatibility with other devices. To provide some facilities for sequence controland interlocking, many DCS systems now have PLC-type digital I/O to enable further integration of thecontrol system.

B) Programmable Logic Controllers (PLC)Were originally developed in the late 1960s to replace electro-magnetic relays and were primarilyused for sequence control and interlocking, using racks of On/Off inputs and outputs now called'digital I/O'.

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PLCs have developed into one of the most effective tools for the automation of manufacturing orprocesses. They are designed and built for the industrial environment and are rugged, reliable, easyto program (ladder diagram) and, most of all, are cost effective. PLC technology has been developedand extended over the years and PLCs have been used in applications traditionally covered by DCS.They now are able to provide computing capability which enables them to process analogue inputs,do calculations, control analogue outputs.

Although originally used as stand-alone units, PLCs now have sophisticated communicationscapability which enables them to communicate with other devices. Initially, PLCs became 'distributed',which means that some of their digital I/O was located some distance away from the CPU and datacommunication techniques were used to transfer the data. They are also capable of communicating'upwards' to higher levels with interfaces to computers (VAX, PDP, DEC, etc) and networks such asEthernet at a process management level.

They can also communicate 'sideways' amongst themselves and other devices at a groupmanagement level, using well known PLC bus networks such as Modicon's Modbus, Allen-Bradley'sData Highway Plus, Square-D's SY/NET, GE's Genius Bus, Texas Instrument's Tiway, Honeywell'sData Hiway, etc. This allows several PLC's to be integrated on a data bus with computers or PC's.

Using various data communication techniques (including 4...20mA standard), these devices collectdata from all parts of a modern plant and deliver it to operator workstations to be used for the followingpurposes: Display of equipment status and process parameters (trends) for operator information and control

purposes To receive and implement commands from the Operator To automatically control the process 'loops' Automatic sequencing to assist the operator Interlocking to supervise operator commands Monitor Alarms and Record Alarms Event Recording for later analysis Management information on all process parameters

In practice, many control systems are well 'integrated' at some levels, while the availability of 'on-line'data at other levels is not often implemented. Direct data communication to the management level, orhigher, is often not used. One of the main reasons is that the data communication at the Plant Controllevel is provided by the DCS or PLC vendors (e.g. Modbus, Data Highway Plus, SY/NET, TIWAY,etc). The users, who are usually responsible for the wider communications requirements, are oftenreluctant to implement this because it presents formidable technical problems both with the datacommunication and the computer programming requirements. A lot of these problems are associatedwith the lack of standardisation of data communications systems and protocols.

At the field instrument level, users have held onto the relative simplicity of the 4...20mA instrumentstandard in spite of the development of digital "smart" instruments. Again, this would be a lot easier ifthere were established standards. From the point of view of many users, the extra hardware cost ofproviding a pair of wires and an analogue input/output from a DCS or PLC appears to be preferable tothe perceived complexities of digital data communications.

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CONTENTS1 INTRODUCTION........................................................................................................................................ 32 RACK AND EXTERNAL INPUT FAULTS................................................................................................. 33 EXTERNAL FAULTS................................................................................................................................. 54 PRISMIC GENERATED ALARMS ............................................................................................................ 5

4.1 Critical Alarm ....................................................................................................................................... 54.2 Excessive Capacity Alarm................................................................................................................... 6

5 FAULT SCENARIOS ................................................................................................................................. 65.1 Power Sharing Faults .......................................................................................................................... 65.2 Load Shedding Faults ......................................................................................................................... 75.3 Set Management Faults ...................................................................................................................... 7

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1 INTRODUCTIONSurface mount technology, solid state electronics, reliable PCB connectors, screw retained inputand output boards, and computer assisted 'pick and place' manufacture ensure that the latestgeneration of PRISMIC Power Management Systems (PMS) provide a high degree of reliability.

PRISMIC PMS systems are designed and manufactured to the highest standards in order to beable to operate without problem in the most arduous of environments.

Internal watchdog circuitry ensures that output signals from the PMS system are disabled and thesystem made 'fail safe' in the unlikely event of either an internal fault within the PRISMIC rack, orif the software detects invalid input configurations on the power system.

Faults within a PRISMIC Power Management System fall within three main categories: Internal failure within the PRISMIC rack assembly. External input status failure resulting in PRISMIC receiving incorrect information from the

field. Failure of external devices controlled by the PRISMIC system e.g. governors AVR's breakers

etc.

2 RACK AND EXTERNAL INPUT FAULTSRack and external input status faults are recognised by the PRISMIC watchdog system providedon the PS-UW card.

Figure 1: Watchdog CardIn the event of a major fault occur within the control rack assembly, the watchdog circuit willnormally 'drop out' thus disabling all digital output signals from the PRISMIC system. With thewatchdog failed the system reverts to manual operation, since all outputs are normally energisedto perform a function.

Any load changes occurring on generation plant operating whilst the PRISMIC is switched off, orwhen the system has failed, will have to be corrected by an operator in manual control, sinceautomatic load shedding control where provided, would be unavailable.

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Indication of the watchdog being 'healthy' is given by a large red LED on the watchdog PS-UWcard which is usually fitted to the bottom left hand side on the PRISMIC rack. This half size cardhas a series of eight diagnostic LED's above the red 'healthy' LED, and a 15 way D-connectorbelow. The connector provides digital, potential free, signals to the external watchdog logic, aswell as an analogue input to measure the integrity of the 24Volt dc supply feeding all of the digitalinput and output channels.

Figure 2: Typical Watchdog Card SchematicFigure 2 shows a typical scheme of connections to the watchdog card (PS-UW). A DIN railmounted module terminates panel wiring and a ribbon cable continues the connections to the PS-UW card within the PRISMIC rack. The 24Volt dc supply, derived from either a battery or powersupply, is connected to cables W1 (positive) W2 (negative). A 'Control Supply Healthy' (CSH)relay, where fitted, provides remote indication to the availability of the 24Volt dc supply. Thissupply is then connected across terminals 1 and 3 on the PS-UW card where it is monitored.

If the voltage drops below a predefined value, there is a possibility that the digital input cards willreceive incorrect status information of the power system which may cause a PMS systemmalfunction. In this case the watchdog will drop out and inhibit further control until the problem isrectified. This situation will be indicated by an extinguished diagnostic LED on the PS-UW card.

A normally open contact across terminals 5 and 9 closes when the PMS system is energised andhealthy, which causes the 'Master Fault Relays' (MFR) to energise when first 'powered up'. Anormally closed contact on timer (RT) will allow the MFR relays to be latched in through their owncontacts. After a few seconds RT timer relay (delay on energise) will energise and open thelatching path to the MFR relays.

If the watchdog now 'drops out' the MFR relays are no longer able to energise, and the watchdogcircuit will need to be reset by depressing the pushbutton on the PS-UW card, or alternativelypowering down the PMS system.

A 'wetting' supply for all the auxiliary digital inputs to the system is provided through wire W1, andwire W3 provides a supply to drive all outgoing interposing relays. It will be noted that the supplyon W3 to the output channels is only present when the watchdog is healthy and, following a shortdelay, after 'powering up' on a system reset. This is to allow the PMS supplies to becomeestablished and to initiate system software.

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The watchdog can fail for a number of reasons, which forces the PMS system into a 'fail safe'condition. Most of the faults other than an internal power supply failure will be shown up by one ofthe diagnostic LED's extinguishing, and the large red LED indicating that the watchdog relay hasswitched off.

Standard functions of the diagnostic LED's are listed below: Loss of 24 Volt control supply. STE bus time out. I/O card address failure. Control software not cycling correctly. Loss of VT voltage sensing. Loss of VT frequency sensing.

In addition, other contract specific functions may be detailed in the Operating & MaintenanceManual.

3 EXTERNAL FAULTSAssuming the watchdog is healthy, it is likely that the fault is a result of one of the following: Field cabling. Terminal connections. Faulty PRISMIC interface cards. Faulty external equipment. Operator error.

Each of the above possibilities should be checked systematically in order to identify and correctthe fault.

4 PRISMIC GENERATED ALARMSA series of alarms are provided by the PRISMIC. The common alarms detailed may not beprovided on all systems and reference should be made to the Operating & Maintenance Manualfor contract specific features.

Critical and Excessive Load Alarms are used to show high and low levels of spinning reservewhich can be an indication the possibility of imminent load shedding, or an indication that toomany machines running on the bars. In the event of these alarms check the following.

4.1 Critical Alarm1) Verify that sufficient machines are on the switchboard to meet the current load requirement.2) Where set management is employed verify that it is functioning correctly, checking that

further machines are available for starting.3) Verify correct operation of system capacity, system load, and spinning reserve metering as

well as on the display system if fitted. Pay particular attention to breaker status signals andmachine master fault relay inputs into the PRISMIC system. Check that sets are not selectedfor manual control since their capacity is deemed equal to their load when in manual thuslowering the spinning reserve. If inputs are found to be incorrect due to a hardware failure,check that a valid 24Volt dc signal is present back to the PRISMIC terminal block. If thesupply is not present check field cabling, If the supply is present replace the faulty digital inputcard, remembering to check links and address selection switches before re-energising.

4) Check if load-shed test has been selected (If fitted). This will cause the spinning reserve tofall to zero. De-select when not in use.

5) Check if the following preset parameters set correctly, and rectify as necessary: Critical Load Alarm Level Critical Load Alarm Timer Sets Nominal Capacity

6) If the system is in split bus, the critical alarm will work on a `per-bus' basis and the spinningreserve on any bus will `flag up' the critical alarm, even though the overall spinning reserveshown on the system metering indicates sufficient spinning reserve.

7) If an alarm fails to operate, verify output signal is being sent to the interposing output relaysand if necessary check back to the alarm output to verify the integrity of the digital outputcards, interposing relays and cabling.

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4.2 Excessive Capacity Alarm1) Verify that all the on-line machines that are needed to meet the current load requirement are

on the switchboard.2) Where set management is employed verify that it is functioning correctly since sets should be

shut down unless a 'minimum sets to run' selection has been made.3) Verify correct operation of system capacity, system load, and spinning reserve metering as

well as on the display system if fitted. Pay particular attention to breaker status signals andmachine master fault relay inputs into the PRISMIC system. Check that sets are not selectedfor manual control since their capacity is deemed equal to their load when in manual thuslowering the spinning reserve. If inputs are found to be incorrect due to a hardware failure,check that a valid 24Volt dc signal is present back to the PRISMIC terminal block. If thesupply is not present check field cabling, If the supply is present replace the faulty digital inputcard, remembering to check links and address selection switches before re-energising.

4) Check that the following preset parameters set correctly, and rectify as necessary: Excessive Capacity Alarm Level. Excessive Capacity Alarm Timer. Sets Nominal Capacity.

5) If the system is in split bus, the excessive alarm will work on a `per-bus' basis in which theexcessive spinning reserve on any bus will `flag up' should any of the busses spinningreserve exceed the excessive alarm level for the period of the excessive capacity timer,activating the alarm.

6) If an alarm fails to operate, verify output signal is being sent to the interposing output relaysand if necessary check back to the alarm output to verify the integrity of the digital outputcards, interposing relays and cabling.

5 FAULT SCENARIOSThe logical approach to fault finding is to check all relevant inputs. The most accurate way ofchecking inputs is not at the terminal boards, but is best achieved using the PRISMIC HMIsystem which will also check individual card functionality.

If a problem persists following a period of planned maintenance, verify that all interlocks andconnections to the PMS system are returned to normal operation.

In some cases inputs and output signals to the PMS systems may be routed through serialinterfaces, if these fail the PRISMIC may not perform as expected if these signals are lost.

Detailed hereafter are fault scenarios which provide solutions to various common systemmalfunction faults.

5.1 Power Sharing Faultsa) Power Or Reactive Power Sharing Faulty On One Set

With this kind of fault particular attention must be paid to the auxiliary breaker contact inputsinto the system and also the auto/manual selection input. PRISMIC will not control a setunless both of these signals are present.

The auxiliary breaker signal can sometimes be routed through the generator switchgearmaster fault relay where any protection operating on that breaker will also remove the'breaker closed' signal from PRISMIC.

The auto/manual signal is sometimes routed through the excitation system, prime movercontrol system, switchgear and sometimes on offshore applications through the emergencyshutdown system. The route of this signal can be determined by reference to contractdocumentation. If auto/manual is lost, the PRISMIC system will default to Manual control.

1) Check the MW and MVAr values for the faulty set is correct using HMI. Re-calibrate orreplace power transducer card as necessary.

2) Verify the MW capability of the prime mover on the HMI. These may be supplied directlyfrom the governor control panel as an analogue signal or may be set on the HMI and tiedin with fuel selection and air temperature. This is contract specific information which isdetailed in the Operation & Maintenance Manual.

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3) Confirm that the set has not been selected for a special control mode e.g. Base-load,target load or power factor control mode.

4) Confirm correct operation of the governor, AVR, raise/lower relay logic.5) Verify that the PRISMIC is issuing raise/lower signals.6) Verify that the MW or MVAr sharing mismatch is not within the system deadbands.7) Check for an invalid bus configuration.8) Check for a switchgear HV fault.9) Check that no shutdown/offload signals are being given to the PRISMIC from the system

(these are contract specific parameters).10) Verify the correct settings of PRISMIC preset controls.

b) Power Or Reactive Power Sharing Common Faults On All Sets1) Verify voltage and frequency datum's.2) Verify correct operation of AVR and governor control from the PRISMIC panel.3) Verify that all voltage/frequency MW and MVAr analogue inputs are reading correctly on

HMI. Rectify as necessary.4) Check all digital inputs to system, including breaker status/auto/manual selection etc.5) Check preset settings associated with power sharing are correct, i.e. deadbands, pulse

settings etc.

5.2 Load Shedding FaultsThe loads to be shed are divided into non-monitored, where their value is preset in software, andmonitored, where transducers monitor their MW values.

1) Check load shed test is not selected (if fitted).2) Check bus section breaker auxiliary inputs, load breaker auxiliaries and generator breaker

auxiliary inputs are working. Correct as necessary or replace the digital input card.3) Check generator breaker/master trip relay auxiliary inputs. Correct as necessary or replace

the digital input card.4) Check relay and contactor logic associated with load shedding. Correct or replace as

necessary.5) Check preset settings associated with load shedding.6) Check that the load priority selections are as required and are valid.7) Check for correct kW signal levels of the generators on the power transducer card. Correct

CT, PT or wiring as required, or replace the power transducer card.8) Check that the load shed guard relay is operating correctly.

5.3 Set Management FaultsSet management includes the starting and stopping of sets on either load demand, faulty on-lineset or after being manually instigated. Normally, faulty set management can be attributed to thefailure of external plant e.g. a diesel engine failing to start. In general the 'set failed to synch'alarm or the 'incorrect duty selection' alarm will be present if such a problem exists.

The set management functions detailed may not be provided on all systems and reference shouldbe made to the Operating & Maintenance Manual for contract specific features.

a) Checks For Set(s) Not Being Started1) Verify the correct operation of system capacity, system load, and spinning reserve

metering as well as on the display system if fitted. Pay particular attention to stopping andtrip logic including the PRISMIC stop and start guard relay.

2) Verify that set(s) have been selected for automatic operation. Check field cabling externalswitches and interlocks including switchgear, governor AVR etc. Rectify as necessary.

3) Verify that the set(s) have been selected for a valid duty selection. Check field cabling,external switches and interlocks. Rectify as necessary.

4) Check whether any set(s) have failed to synchronise. Check external plant operationincluding cabling, external switches and interlocks. Check starting logic including thesynchronising scheme. Re-prime the system by switching the erroneous set(s) back intomanual control and then re-select auto operation.

5) If the system is in split bus, set management will control on a 'per-bus' basis, which oftenoverrides the duty selection.

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6) Check if an 'unable to start' signal is present with the erroneous set(s) i.e. set critical oremergency shutdown system.

7) Check if the following preset parameters are set correctly, and rectify as necessary: Set Start Margin. Start Timer. Sets Nominal Capacity. Fail to Synch Timer.

8) Check if load-shed test been selected (if fitted). De-select when not in use.

b) Checks For Set(s) Not Being Stopped Or Offloaded CorrectlyThe standard system when offloading a set is to lower the governor and AVR datum's tooffload both active and reactive load from the set. After a predefined 'cool down period', abreaker trip signal is then issued followed by a prime mover stop signal. Often PRISMIC onlyissues a stop command to the prime mover control system.

1) Verify correct operation of system capacity, system load, and spinning reserve meteringas well as on the display system (if fitted). Pay particular attention to stopping and triplogic including the PRISMIC stop and start guard relay. Rectify as necessary.

2) Verify set(s) been selected for automatic operation. Check field cabling, external switchesand interlocks including switchgear, governor, AVR etc. Rectify as necessary.

3) Verify that set(s) have been selected for valid duty selection. Check field cabling, externalswitches and interlocks. Rectify as necessary.

4) Check if the set(s) have failed to synchronise. Check external plant operation includingcabling, external switches and interlocks. Check starting logic including the synchronisingscheme. Re-prime the system by switching the erroneous set(s) back into manual controland then re-select auto operation.

5) If the system in is in split bus, set management will control on a 'per-bus' basis, whichoften overrides the duty selection. Check that there is a valid reason within the systemthat the set is not stopped i.e. last set on the bars.

6) Check that there is no 'minimum sets to run' type signal present with the erroneous set(s).7) Check that the following preset parameters set correctly, and rectify as necessary:

Set Stop Margin. Stop Timer. Sets Nominal Capacity

8) Where PRISMIC offloads the reactive and active power, check that the pulse lengths aresufficiently long to offload the set. Rectify as necessary.

9) Check if load-shed test been selected (if fitted). De-select when not in use.

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CONTENTS1 INTRODUCTION........................................................................................................................................ 32 GENERAL MAINTENANCE ...................................................................................................................... 33 ROUTINE CHECKS ................................................................................................................................... 34 CALIBRATION OF GENERATORS/GRID FEEDERS .............................................................................. 35 CALIBRATION OF LOAD FEEDERS ....................................................................................................... 46 LOAD INHIBITS......................................................................................................................................... 47 SPINNING RESERVE ALARMS ............................................................................................................... 58 SET MANAGEMENT MAINTENANCE...................................................................................................... 59 LOAD SHEDDING MAINTENANCE.......................................................................................................... 5

9.1 General................................................................................................................................................ 59.2 Gradual Overload Load Shedding....................................................................................................... 59.3 Fast Acting Load Shedding ................................................................................................................. 69.4 Under-Frequency Load Shedding ....................................................................................................... 6

10 PRINTERS AND HMI SYSTEMS............................................................................................................... 711 RECORDS.................................................................................................................................................. 7

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1 INTRODUCTIONRegular planned maintenance can detect early signs of failures or problems in the PRISMICSystem. Most features, e.g. load shedding, might remain unused for extended periods and ageneral malfunction will not be detected until it has failed to operate. The PRISMIC PowerManagement System has a dependable record in the field although it relies on the externalhardware performing correctly.

Due to the diversity of equipment on the Customer site, the trend these days is to arrange servicecontracts with the supplier of the equipment. Brush offers a rapid response service on all Brushequipment, including machines, should a problem arise on site.

2 GENERAL MAINTENANCEAmong the most common causes of failure within an electrical control room are: Loose Connections. Dirty or Oxidised Contacts. Insufficient Contact Pressure. Pitted Surfaces.

Thus, equipment should be maintained in a clean condition, and panel doors should be keptclosed whenever possible.

Equipment should be checked for mechanical soundness to ensure that components are secure,particularly those with moving parts such as relays and switches etc. Caution must be observedwhilst checking relays as certain relays can trip and close switchgear.

Maintenance of auxiliary equipment such as synchronisers etc. fitted in the PRISMIC panel isimportant and guidance is given in the appropriate Instruction Manual/Handbook.

Where the PRISMIC panel is in close proximity to a diesel engine, it is worthwhile checking thepanel for ingress of carbon deposits. If the PRISMIC cards have become coated, switch off andcarefully remove one card at a time and dust down with a soft brush. Avoid touching the card'sedge connectors. Do not remove or replace cards while the rack is powered-up. Take care withPower Transducer cards, as 50V ac is present at all times sets are on line.

3 ROUTINE CHECKS Verify correct operation of the lamp test facility, if provided (Panels fitted with LED indication

do not require this facility). Verify that the master fault relay is energised within the panel. Verify all cards being cycled correctly by checking the card 'access' LED is illuminated on all

I/O cards. Check all cards are positively located in the I/O slots. Check for charring and hot components, especially relays that are continually energised. Generally check security of connection links etc. Check tightness of all ribbon cables and panel terminals.

4 CALIBRATION OF GENERATORS/GRID FEEDERSConfirm the accurate calibration of inputs to the Power Transducer cards by checking thePRISMIC MW readings against a known accurate source. If a HMI system is present thisinformation can be read off the screen.

Note: Ensure when calibrating or trimming these cards to revert to MANUAL selection beforeproceeding with card tests.

The offset controls can be verified by using the CT shorting links commonly found in PRISMICpanels.

Verify calibration of the bus voltage measurements. These are normally fed into an analogueinput on an analogue input card. Calibration is through potentiometers on the AI card front panel.

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5 CALIBRATION OF LOAD FEEDERSWhen each load feeder is monitored for load shedding it is important that the calibration iscorrect, else too much or too little load will be shed during a load shedding situation. Normally,the Analogue Input card is used for this function. Verify the correct operation of each channelusing an 'in-line' watt meter where possible.

The analogue card will normally be fed from a 4-20mA transducer, either in the panel orexternally in the switchgear. Offset and gains are available on each channel to trim anyinaccuracies within the system.

Where possible verify all digital input channels. This may be impossible on a 'on-line' system.Ensure that no sequences are initiated as the result of certain inputs being energised.

Where the PRISMIC drives analogue meters, use the data module to check calibration byreferring to the card function sheets found in the Operating & Maintenance Manual. Checksystem capacity, system load and spinning reserve values on meters (if fitted) and on the HMIsystem.

The following tests involve placing voltage and frequency fluctuation on the system, as well aspower and VAr swings between sets: Ensure this will have no detrimental effect on on-line systems. Ensure no electrical protection relays will operate as a result of the tests before commencing. Where possible, run extra generators to improve system security.

1) AVR Control - Voltage Control, Islanded ControlPlace all sets under MANUAL control, manually reduce AVR datums on all sets. Switch backto AUTO and verify that the line volts on the bus-bar return to nominal setting. Verify that noinstability is present. Adjust volts stabilising control if instability is found. Repeat, this timetaking the datums above nominal volts.

2) AVR Control - VAr Sharing, Islanded ControlBy placing one set under MANUAL control, reduce the AVR datum on that machine. Switchback to AUTO and verify that the PRISMIC matches the machines VArs to the othermachines. Repeat, this time increasing the AVR datum. Repeat on remaining sets. Resetstability settings if necessary.

3) Governor Control - Frequency, Islanded ControlPlace all sets under MANUAL control, manually reduce the governor datum so the busfrequency falls below nominal. Return all sets to AUTO operation and check all governordatums are raised to obtain the nominal system frequency. Repeat, increasing the governordatums above nominal. Reset stability setting if necessary.

4) Governor Control - Power Sharing, Islanded ControlBy placing one set under MANUAL control, reduce the governor datum on that machine.Switch back to AUTO and verify PRISMIC returns the machine's MW to match with otherinterconnected machines. Repeat, this time increasing the governor datum. Repeat inremaining sets. Reset stability settings if necessary.

5) Grid Controls (When Utilised)Perform a similar exercise as above on the AVR and governor settings, but check the MWand VArs are returned to their target valves. Reset stability settings if instability occurs.

6 LOAD INHIBITSTo prove this mode of operation the spinning reserve has to be reduced sufficiently to initiate loadinhibit signals. It is important to know that if this reduces below zero then load shedding canoccur.

By carefully reducing the nominal MW capacity of each of the sets, the load inhibit signals shouldbe initiated when the spinning reserve falls below the preset restart MW value, assuming thebreaker is open. Verify that this happens and check the preset settings when using this function.

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Placing low loaded sets under MANUAL control can also reduce the spinning reserve, reducingMW on a manually selected set will also perform the same function.

7 SPINNING RESERVE ALARMSTo verify correct operation of the critical spinning reserve alarm, the spinning reserve has to fallbelow the critical spinning reserve set level for the duration of the critical spinning reserve timer.This can be achieved in the same way as for the testing of the load inhibits above.

To verify correct operation of the excessive spinning reserve alarm, the spinning reserve has torise above the excessive spinning reserve set level for the duration of the excessive spinningreserve timer. This can be achieved by either bringing extra sets on-line or by temporarilyincreasing each of the on-line sets' capacity. Take particular care not to decrease the capacitysuch that load shedding operates. Record spinning reserve levels and timers.

8 SET MANAGEMENT MAINTENANCEVerify where possible the correct operation and sequence of the starting and stopping of setsfeature. Check for correct operation of the incorrect duty selection alarm by selecting an invalidselection.

The 'Fail to Synch' alarm may be checked by isolating the switchgear closing fuse associated withthe set being started. Verify 'Minimum Sets to Run' feature if fitted. Record preset valuesassociated with the set management feature including levels and timers.

9 LOAD SHEDDING MAINTENANCE

9.1 GeneralTo perform a test on a system will require running the system with the output trip relays isolated.It is recommended that extra generating plant is put on-line during this period if the system isbeing utilised for production. Isolating the 'load shed guard relay' will inhibit the trip relays. Caremust be taken with removing individual trip relays, as often, the trip circuit is 'open to trip'.

Tripping breakers on a HV scheme is of prime importance as often it is the 'last ditch' attempt toprotect electrical plant under fault conditions other than the manual trip button on the switchgearmechanism.

Tripping a breaker either locally, via protection schemes, or from a remote location, normallyelectrically energises a trip coil which releases the switchgear mechanism.

Two schools of thought exist on the tripping philosophy, often based on voltage rating andreliability of the system:

1) Open To TripWhilst this ensures that the breaker trips should any trip circuit cabling fail, it reduces thereliability of the system as well as reducing the integrity of the trip coil as it is permanentlyenergised.

2) Close To TripSystems using this method of tripping often use trip circuit supervision protection relays toverify any cable breaks, trip fuse failure, loss of dc tripping supply or trip coil failures withinthe switchgear panel. Should a fault be detected an alarm will 'flag up' rather than the breakertrip. Trip circuit cabling is often doubled up to improve the tripping circuit integrity.

9.2 Gradual Overload Load Shedding It is recommended that extra generating plant is put on-line during this period if the system is

being utilised for production. By isolating the 'load shed guard relay' this will inhibit the trip relays, care must be taken with

removing individual trip relays as often the trip circuit is 'open to trip'.

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With the load shedding output relays isolated reduce the spinning reserve below zero byplacing several in manual and reducing the MW on the sets selected manual onto the autoselected sets verify that the gradual overload timer store on the diagnostic unit starts tointegrate up until the first load `trips' (as indicated on the HMI or on an annunciator) and thenas the load has not physically been tripped off the switchboard further trips will emanate fromthe PRISMIC system as there is still a simulated overload condition.

The duration of the distance between trip signals is referred to as the 'retrip timer'. Verify correct operation of the gradual overload Load shedding feature and record the

settings of the gradual overload timer, retrip timer, trip pulse length. Re-adjust if necessary. Re-install any equipment that has been isolated or by-passed.

Should this feature not operate correctly refer to the contract documentation for any contractspecific variants and if not refer to PRISMIC PMS Fault Finding section.

9.3 Fast Acting Load Shedding It is recommended that extra generating plant is put on-line during this period if the system is

being utilised for production. By isolating the 'load shed guard relay' this will inhibit the trip relays, care must be taken with

removing individual trip relays as often the trip circuit is 'open to trip'. With the load shedding output relays isolated simulate a generator having been tripped off the

board either by removing the breaker auxiliary input or the master fault relay contacts into thePRISMIC system. Assuming this has caused the spinning reserve to go negative instant loadshedding will be instigated (as indicated on the HMI or on an annunciator) and then as theload has not physically been tripped off the switchboard further trips will emanate from thePRISMIC system as there is still a simulated overload condition.

The duration of the distance between trip signals is referred to as the 'retrip timer'. Verifycorrect operation of the fast acting Load shedding feature and record the settings of the retriptimer, trip pulse length. Re-adjust if necessary.

Re-install any equipment that has been isolated or by-passed.

Should this feature not operate correctly refer to the contract documentation for any contractspecific variants and if not refer to the PRISMIC PMS Fault finding section.

9.4 Under-Frequency Load Shedding It is recommended that extra generating plant is put on-line during this period if the system is

being utilised for production. To verify the correct operation of this PRISMIC feature it is required that the busbar frequency

be lowered. Normally this will not cause the switchgear to trip out as the protection scheme isnormally set lower than the PRISMIC under-frequency trip levels but can cause UPS systemsto produce under-frequency alarms.

By isolating the 'load shed guard relay' this will inhibit the trip relays, care must be taken withremoving individual trip relays as often the trip circuit is 'open to trip'.

With the load shedding output relays isolated place all sets into manual control and physicallyisolate all the PRISMIC raise governor relays.

Reduce all the governors manually so that the bus frequency falls below the under-frequencytrip level and switch all sets back into PRISMIC control.

After the under-frequency timer has timed out load shedding will be instigated (as indicatedon the HMI or on an annunciator although trips electrically isolated). One load will then beshed, further tripping of single loads will then proceed the time between these trips are thesetting of the re-trip timer. Although in the real world PRISMIC would have corrected thegovernors to increase the bus frequency to nominal tripping would be halted when the busfrequency rose above the under-frequency recovery level.

Verify correct operation of the under-frequency load shedding feature and record the settingsof the following: Under-frequency trip level Under-frequency recovery level Under-frequency trip timer Under-frequency recovery timer

Re-adjust if necessary. Re-install any equipment that has been isolated or by-passed.

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Should this feature not operate correctly refer to the contract documentation for any contractspecific variants and if not refer to the PRISMIC PMS Fault Finding section.

Various systems have a stage two under-frequency load shedding system where should thesystem receive a severe under frequency condition blocks of loads are shed. This can be provedout in the same way as the stage one under-frequency although the trip levels are normally setlower and could possibly clash with the switchgear under-frequency protection relays. In this casemove the trip set point temporarily higher and verify at a different setting.

10 PRINTERS AND HMI SYSTEMSAlthough covered by suppliers manuals/handbooks, generally ensure the monitors and printersare clean. The screen may be cleaned with a proprietary anti-static foam cleaner whilst the printer

mechanism may be cleaned with a soft brush. Check printer ribbons are serviceable and an adequate supply of paper is available. Most

printers have test modes to check the mechanisms, refer to the suppliers manual/handbookfor more details.

Verify condition of all cables and connectors where applicable to the Health and Safety atWork guidelines for mains portable and transportable equipment.

11 RECORDSRecord all preset parameters including load shedding tables.

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