Abstract

HPCL Vishakh refinery was established in 1957 and was subsequently merged with ESSO which was multinational oil company of USA, which was setup in Mumbai and came with a new origin Hindustan Petroleum Corporation of India Limited (HPCL) in 1998. Electrical maintenance is one of the most crucial aspects in the refinery to ensure good productivity, reliability and safety against fire hazards. The industry thus employs one of the most advanced forms of maintenance techniques, i.e., IR Thermography, Vibration Health Analysis, etc… This report of the project shows an overview of the employed maintenance techniques.

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MAINTAINANCE OF POWER IN

HINDUSTHAN PETROLUM COPORATION LIMITED (HPCL)

INDUSTRIAL TRAINING REPORT

SUBMITTED BY

S.YASWANTH VARMA

R.RAVIKANTH SARMA

N.SUDHEER KUMAR

S.K.AVINASH VARMA

In partial fulfillment for the award of the degree of

BACHELOR OF ENGINEERING

in

ELECTRICAL AND ELECTRONICS ENGINEERING

RAGHU ENGINEERING COLLEGE

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JUNE 2011

ACKNOWLEDGEMENT

We would like to thank Mr. S.K.Mishra, Sr. Manager-Training, for accepting our request for industrial training at HPCL, Visakh Refinery.

We express our deep sense of gratitude and respect to Mr. N.Rajarao, Chief Manager, and Maintenance Electrical.

We heartily thank B.Jayanth Rao senior Manager, Planning Electrical for giving us enthusiastic support and guidance.

We express our thanks to Mr. B.J.Benhar Babu, Manager Maintenance, Mr.Rama Chadra Rao Deputy Manager, Mr.nikki Agarwal Deputy manager, Mr. Pritam Majamder Engineer for guiding us with great attention, care and providing vital support at HOCK, Visakh refinery.

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About HPCLHPCL is a fortune 500 company, with annual turnover of Rs 1,16,428 crores and sales-/income from operations Rs 1,31,802 crores ( US $25,618M) during FY 2008-09, having about 20% marketing share in India and is strong market infrastructure. Corresponding figures for FY 2007-08 are is to turnover of Rs 1,03,837 Crores and sales/ income fr4om operations of Rs 1,12,098 Crores ( US $ 25,142M).HPCL operates two major refineries producing a wide variety of petroleum fuels and specialties, one in Mumbai (West coast) of 6.5 million metric tons per annum (MMTPA) capacity and the other in Vishakhapatnam, (East coast) with a capacity of 7.5 MMTPA. HPCL holds an equity state of 16.95% in Mangalore refinery and p0etro chemicals limited, in state-of-the-art refinery at Mangalore with a capacity of 9 MMTPA. In addition, HPCL is constructing a refinery at Bhatinda, in state of Punjab. HPCL also owns and operates the largest lube refinery in the country producing lube based oils of international standards, with a capacity of 335 TMT. This lube refinery accounts for over 40% of India’s total lube base oil production. Presently HPCL produces over 300+ grades of lube, specialties and greases.HOCK ‘s vast marketing network consists of 13 zonal offices in major cities and 90 regional offices facilitated by a supply and distributio0n infrastructure compressing terminals, aviation service station, LPG bottling plants, and an inland relay depots and retail outlets, lube and LPG distributorships . HOCK, over the years has moved from strength to strength on all fronts the refining capacity sturdily increased from 5.5 MMTPA in 1984/85 to 13 MMTPA presently. On the financial fronts, the turnover grew from RS 2687 Crores in 1984-85 to an impressive Rs. 1, 16,428 crores in FY 2008-09. HPCL has an “Excellent” performance for fifteen consecutive years up to 2005-06, since signing of the first MOU with the ministry of petroleum and natural gas. HPCL won the prestigious MOU award for the year 2007-08 for excellent overall performance.

Vishakh refinery:

Rapid worldwide industrialization and scientific advancements has resulted in continuously raising energy requirements in all sectors e.g. industries, transport etc. petroleum being one of the major source of energy there is a pressing need for increasing the production of the crude oil as well as the desire fuel production.

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Concerted efforts are being made for maximizing the crude oil production from oil fields. As a result, quality of crude becomes heavier day by day. A simple distillation of crude oil is not sufficient and economical top meet the demand of the petroleum products esp due to the increasingly heavy nature of crude oil producing using the modern advanced method of crude production. Hence the refineries are required to adopt “Bottom of Barrel Processing Concept” for meeting the product demand.

In the context, vishakh refinery was established in 1957 and was subsequently merged with ESSO which was multinational oil company of USA, which was setup in Mumbai and came with a new origin Hindustan Petroleum Corporation of India Limited (HOCK) in 1978. Over the year the capacity of the refinery was increased to 1.5 MMTPA by de-bottlenecking units.

The major refinery capacity augmentation was taken up in 14985 by commissioning separate streams of 3.0 MMTPA crude distillation units ( CDU-2), fluidized catalytic cracking unit ( FCCU-2), crude oil receiving facilities at high seas ( Offshore tanker terminal ) and associated tankage and product dispatch facilities. Thus the installed capacity has increased to 4.5 MMTPA. The facilities came up in 1985 were the state-of-the art control system for the better and efficient operation.

An order to cater to the increased LPG consumption, the refinery works instrumental in developing first LPG import facilities on the eastern coast in 1987. As a step towards surmounting the frequent power distribution and improve reliability of utilizes a Captive Power Plant (CPP) of 14 MW capacity was widening its product range commissioned Propylene Recovery Unit (PRU) in 1992.

In order to adhere to stringent environment norms the refinery had setup Effluent Treatment Plant (ETP) in 1993 and sulphur recovery unit (SRU) in 1994. With the second major expansion project VREP-2 completed in 1999 crude processing capacity increased from 4.5 MMTPA to 7.5 MMTPA and secondary capacity increased from 1.5-1.6 MMTPA. To meet the stringent diesel fuel specification, Diesel Hydro De Sulphurisation unit (DHDS) was also commissioned in 1999 /2000. To meet additional power requirement of these new units, CPP capacity was augmented by 40 MW in 1999, increasing total power generation capacity to 58 MW.

It is a crude oil processing refinery having a capacity of 7.5 MMTPA. The processing units include crude units, fluidized catalytic cracking units, propylene recovery units and treating units like DHDS and SRU. The total load of the existing refinery is about 39 MW. This load is being met by the HPCL with the help of four gas turbine generators and heat recovery steam generators. The combined power and steam output of steam generating units and the HRSG’s at fight conditioned is about 54 MW and 174 TPH of MP steam respectively. The HPCL’s present power and steam requirements are met by

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following in-house GTG’s and HRSG’s. 2x9MW FRAME-3, GTG 1 and 2 with HRSG’s installed in 1990 2x20MW FRAME-5, GTG 3-6 with HRSG’s installed in 1999. Apart from the captive generators, HPCL has two AP TRANSCO grid incomers at 132 KV level. 11KV supply is derived by two numbers 16/20MVA, 132/KV grid transformers. The present contract demand with APTRANSCO in 13MVA at 0.9pf. HPCL is currently using grid as hot standby and the grid incomers are not paralleled with the GTG’s under normal operating conditions.

The refinery is located at latitude of 17’41”N and longitude of 83’17” E on an area taken on a 99 years lease from Vishakhapatnam port trust.

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Table of contents:

Introduction – About HPCL1

Chapter 1: Electrical Maintenance

What is electrical maintenance? 4

Types of electrical maintenance 5

Breakdown maintenance 5Preventive maintenance 6

Predictive maintenance 6

Methods used in predictive maintenance 7Infrared thermography 7

Motor current signature analysis 8

Equipment health analysis 9

Tan delta test 11

Cable fault locating analysis 12

Surge generator 13

Digital time domain reflectometer 13

Indicator Digipoint 15 Cable route tracer 15

High potential test 17

Chapter 2: captive power plant

Introduction 19

Step-up sequence of CPP 19

CPP facilities 20

Gas turbines 20

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Theory of GTG 20

Generators 22

Generator details 23

Functional description 24

Basic cycle 24 Gas turbine equipments 24 Air inlet equipment 25 Compressor section 25

Rotor assembly 26

Stator 26 Fuel system 28 Diesel system 29 Naphtha valve 29 Brushless generator- basics 29 Automatic voltage regulator 30 Heat recovery steam generator 31

Chapter 3: power distribution in HPCL

Substations 32

Switch gear 33

Bus 34

Power transformers 35

Sub 36

Motor control centre 36

Power control centre 36

Single line diagram of power distribution in HPCL

Direct online starters in SS-50 37

Variable frequency drives 38

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Variable frequency motor 39

Variable frequency controller 39

Dynamic breaking 40

Rectifier in VFD 40

Bibliography 41

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Chapter 1:What is electrical maintenance? Electrical maintenance is the upkeep and preservation of equipment and systems that supply electricity to a residential, industrial or commercial building. It may be performed by the owner or manager of the site or by an outside contractor. The work is commonly performed on a schedule based on the age of the building, the complexity of the electrical system or on an as-needed basis.

The main areas of general electrical maintenance commonly include the power outlets and surge protectors, generators and lighting systems. These supply sources are checked for structural integrity as well as internal stability.

Preventive electrical maintenance is also generally part of a building’s upkeep. This plan ordinarily includes the scheduled inspection of large systems and equipment by a professional electrician. The purpose of these periodic assessments is to fix small problems before they escalate into large ones. Preventive electrical maintenance is particularly important at plants, hospitals and factories that heavily rely on these systems for daily operation. Electrical generators, switches and circuit breakers are regularly checked for solid connections and intact wiring. If flaws are discovered, electricians normally repair the wiring. Depending on the condition of the wiring, the repairs are typically made by splicing wires together. In some situations, the wires are encased in metal tubing called conduit to protect them from wear. Keeping the wiring in good shape ensures a consistent flow of power to heating, ventilation and air conditioning systems.

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Flow chart showing electrical maintenance

Types of electrical maintenance:

Corrective maintenance:

Breakdown maintenance can be defined as a maintenance task performed to identify, isolate, and rectify a fault so that the failed equipment, machine, or system can be restored to an operational condition within the tolerances or limits established for in-service operations. 

Corrective maintenance is the most commonly used maintenance approach but it is easy to see its limitations. When equipment fails, it often leads to downtime in production, and sometimes damages other parts. In most cases, this is expensive. Also, if the equipment needs to be replaced, the cost of replacing it alone can be substantial

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Planned Preventative Maintenance:

('PPM') or more usual just simple Planned Maintenance (PM) or Scheduled Maintenance is any variety of scheduled maintenance to an object or item of equipment. Specifically, Planned Maintenance is a scheduled service visit carried out by a competent and suitable agent, to ensure that an item of equipment is operating correctly and to therefore avoid any unscheduled breakdown and downtime.

Together with Condition Based Maintenance, Planned maintenance comprises preventive maintenance, in which the maintenance event is preplanned, and all future maintenance is preprogrammed. Planned maintenance is created for every item separately according to manufacturers recommendation or legislation. Plan can be based on equipment running hours, date based, or for vehicles distance travelled. Good example of PM program is car maintenance. After so many kilometers or miles oil should be changed, parts renewed.

Planned maintenance has some advantages over Condition Based Maintenance such as:

easier planning of maintenance and ordering spares,

costs are distributed more evenly,

No initial costs for instruments for supervision of equipment.

Disadvantages are:

less reliable than equipment with CBM

More expensive due to more frequent parts change.

Predictive maintenance (PdM):

Predictive maintenance techniques help determine the condition of in-service equipment in order to predict when maintenance should be performed. HPCL mostly uses this type of maintenance. This approach offers cost savings over routine or time-based preventive maintenance, because tasks are performed only when warranted.

The main value of Predicted Maintenance is to allow convenient scheduling of corrective maintenance, and to prevent unexpected equipment failures. The key is "the right information in the right time". By knowing which equipment that needs maintenance, the liability. Other values are increased equipment life time, increased plant safety, less accidents with negative impact on environment, an optimized spare parts handling, etc.

The "predictive" component of predictive maintenance stems from the goal of predicting the future trend of the equipment's condition. This approach uses principles of statistical

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process control to determine at what point in the future maintenance activities will be appropriate.

Most PdM inspections are performed while equipment is in service, thereby minimizing disruption of normal system operations. Adoption of PdM can result in substantial cost savings and higher system reliability.

To evaluate equipment condition, predictive maintenance utilizes nondestructive testing technologies such as infrared, acoustic (partial discharge and airborne ultrasonic), corona detection in combination with measurement of process performance, measured by other devices, to trigger maintenance conditions. This is primarily available in Collaborative Process Automation Systems (CPAS). Site measurements are often supported by wireless sensor networks to reduce the wiring cost.

Methods used in predictive maintenance at HPCL:

Infrared thermography:

The most popular and widely used application of infrared thermography is electrical switchgear testing. No other commercial application has achieved the level of interest than that of electrical infrared thermography. Daily, the electrical switchgear in thousands of buildings are checked by thermographers all over the country. Electrical Infrared is now an integral part of any facility manager's preventative/predictive maintenance (P/PM) program.

Infrared thermography is used to perform P/PM inspections on electrical equipment because excess resistance on electrical apparatus indicates electrical faults such as loose connections, , it heats up. Thermography is used to see the excess heat (resistance) so that problems can be found and maintenance personnel can act to correct the problem before the component fails, causing damage to the component, safety hazards and/or production downtime.

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Contacts seen by an Infrathermal camera

Motor current signature analysis:Traditional CSA (Current Signature Analysis) measurements can result in false alarms and/or misdiagnosis of healthy machines due to the presence of current frequency components in the stator current resulting from non-rotor related conditions such as mechanical load fluctuations, gearboxes, etc. more robust and less error prone technology.

The operators of electrical drive systems are under continual pressure to reduce maintenance costs and prevent unscheduled outages that can result in lost production and revenue. The application of condition based maintenance strategies rely on specialized monitors to reliably provide a measure of the health of the drive system. 

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Fig: Motor current signature analysis

Thus, unexpected failures and consequent downtime may be avoided and/or the time between planned shutdowns for planned maintenance may be increased. Maintenance and operational costs are thus reduced. During the past twenty years, there has been a

substantial amount of fundamental research into the creation of condition monitoring and diagnostic techniques for induction motor drives.

Motor Diagnostic technologies have become even more prevalent through the 1990’s and into he new century. The technologies include both Motor Circuit Analysis (MCA)

and Motor Current Signature Analysis (MCSA) applied to both energized and de-energized electric motor systems. The applications appear to be almost endless.

AC Motors and Alternators IDC Motors and Generators Single and Three phase systems Eddy-Current drives Variable Frequency Drives Incoming power quality

Equipment health Analysis:

The emerging trend in the industry and major commercial complexes is Predictive Maintenance. Predictive maintenance helps in improving up time of equipment or a system thereby contributing to increased productivity and avoiding unplanned outages.

Vibration monitoring & analysis is one the important and proven tools in analyzing health of the rotating machines as it can detect 80 to 90% of developing problems.Vibration values are definitely a good parameter to study the current condition of rotating equipment. This value can be captured in varied ways. The interval between these measurements can be optimized through Maintenance Partners for any type of

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machinery. Because of this technique Maintenance Partners offers a powerful tool for detecting damages in early stage.

Fig: Vibration health analysis

Tan delta test:

The tan delta test is a diagnostic procedure to assess the deterioration of the insulation of a medium- or high-voltage cable.

Due to the well known water-tree effect the conductivity of the insulation increases, this reflects in an increase of tan delta values.

So, the interpretation of tan delta test results gives an idea about the aging process in the cable-insulation and hence, allows an assessment of the operational reliability of the cable.

The test engineer is able to distinguish between new, strongly aged and faulty cables and appropriate maintenance and repair measures may be planned.

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Fig: Tan delta test equipment

If however the insulation deteriorates due to moisture the current will also show a resistive component, and the angle between voltage and current will decrease.

By a highly accurate measurement of the phase lag between current and voltage the dissipation factor tan d can be determined.

The dissipation factor tan d is defined as the ratio between active current and ideal capacitive current.

That prevents the device under test from damages during the tan delta test and guarantees damage-free measurement.

Cable fault locating analysis:

The Process of cable fault location comprises of four distinct, but interrelated stages viz.

1. Testing for detection of the nature of fault.2. Conditioning / burning of faults for location.3. Pre-location : Approximate location based on changed electrical relationship due to fault.4. Pin Point location.

Surge Generator:

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Instrument has been primarily designed to produce high voltage surges for pre-location of underground cable fault in combination with inbuilt Reflectometer. LCD Screen for Reflectometer.

Fig: surge generator

The surges produced help in pinpointing the fault and tracing the route of the cable when used with acoustic DIGIPOINT, surge generator generates D.C. high voltage for pressure testing of the underground cables to find out faulty phase and the breakdown voltage with leakage current.

Digital time domain reflectometer:

Reflectometer is a Laptop based Digital Time Domain Reflectometer for pre-location of faults in power Cables. Its state-of-art technology makes it easy to use and yet most reliable for any fault condition. The interactive graphical user interface makes it easy, for even a layman, to pre-locate the fault distance. Serial Port makes the device extremely flexible.

The device has three working modes namely IMPULSE MODE and PULSE ECHO MODE. Pulse echo mode is useful only for open and shot types of faults. The impulse mode when used with surge generator to pre-locate fault distance of almost all types of faults including open, short and intermittent faults by way of ICM, Decay & ARM Method.

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Fig: time domain reflectometer

The software provides a huge storage capacity so that you may use the Reflectometer test result for future reviews & analysis. The VOP (Velocity of Propagation) control makes it easy to precisely pre-locate the fault distance on cables with different velocity of propagation. The test waveforms can be printed as a hardcopy directly from the software. The fault readings can be transferred over INTERNET for further assistance.

The software is so programmed that it automatically saves all the test results, so that you never miss any important result. All the files are stored on the bases of date and time of the reading taken.

Indicator digipoint:

The DIGIPOINT is an easy to use, dual channel Digital Acoustic Fault Locator. It is used in conjunction with  a Surge Generator  to  determine  the  exact  position  of  faults  in  underground  power  cables. The instrument also indicates the cable by sensing and amplifying the electromagnetic signals produced at the time of surges.

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Fig: Digiphone

The DIGIPOINT consists of two units – the Acoustic transducer or pick–up and the amplifier unit with head phones.The unique feature of DIGIPOINT provides a relative distance indicator with digital coincidence figure readout.This feature is very helpful for the operator in pinpointing the exact location of fault.

Cable route tracer:

The TII Advanced Cable Locator is a microprocessor-based system that incorporates  advanced  digital  signal  processing  techniques to quickly and efficiently trace the path of underground cables, both copper and fiber optic(with metallic trace wire). • Locates cable path• Measures cable or sonde depth with the push of a button.• Measures signal current in the cable.• Identifies cable using toning function.• Locates energized power cable with direct readout   of cable depth.The cable locator provides accurate cable or sonde depth measurements, giving a digital readout in inches, feet and inches, or centimeters (user-selectable).Additionally, when used in conjunction with the EMS Marker Locating Accessory, the locator can:• Pinpoint the exact location of buried EMS markers• Trace a cable path while simultaneously  finding buried markers along the way.

Four modes of operation for accurate locates, even in congested areas:For cable path locating, the receiver uses one of four user selected locating modes – dual peak, dual null, differential or special peak (which increases the sensitivity of the

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receiver for tracing over longer distances). The mode is selected depending on which is most effective under the locating conditions.

The receiver includes four volume settings, including a special “expander” function that makes peaks and nulls more pronounced.The  expander  feature  enhances  the  amplitude  difference  between  two  conductors  carrying  the  same  signal, making  the  unit extremely accurate, even in congested areas. A headphone jack is also included.

The Advanced Cable Locator is easy  to operate and  requires very  little  training. Digital  liquid crystal display (LCD) readout and push-button operation make the unit easy to understand, for more precise locates. A “memory” feature remembers operator set-up from previous use.The system consists of two basic components:• Transmitter with built-in ohmmeter, which also senses and measures the presence of foreign voltage, and tests the continuity of the circuit.• One-piece hand-held receiver with bar graph that indicates received signal and proximity to the cable.The cable  locator  uses  four  active  trace  frequencies - 577  Hz,  8  kHz,  33  kHz  and  200  kHz —  which  can  be  usedindividually or simultaneously  to compensate  for varying  field conditions.

High potential test:

Hipot is an abbreviation for high potential. Traditionally, Hipot is a term given to a class of electrical safety testing instruments used to verify electrical insulation in finished appliances, cables or other wired assemblies, printed circuit boards, electric motors, and transformers.

Under normal conditions, the insulation in a product can break down, resulting in excessive leakage current flow. This failure condition can cause shock or death to anyone that comes into contact with the faulty product.

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Fig: Hipot test equipment

A Hipot test (also called a Dielectric Withstand test) verifies that the insulation of a product or component is sufficient to protect the operator from electrical shock. In a typical Hipot test, high voltage is applied between a product's current-carrying conductors and its metallic shielding. The resulting current that flows through the insulation, known as leakage current, is monitored by the hipot tester. The theory behind the test is that if a deliberate over-application of test voltage does not cause the insulation to break down, the product will be safe to use under normal operating conditions—hence the name, Dielectric Withstand test. Environmental factors such as humidity, dirt, vibration, shock and contaminants can close these small gaps and allow current to flow. This condition can create a shock hazard if the defects are not corrected at the factory. No other test can uncover this type of defect as well as the Dielectric Withstand test.

Three types of Hipot tests are commonly used. These three tests differ in the amount of voltage applied and the amount (or nature) of acceptable current flow:

Dielectric breakdown Test::

 The test voltage is increased until the dielectric fails, or breaks down, allowing too much current to flow. The dielectric is often destroyed by this test so this test is used on a random sample basis. This test allows designers to estimate the breakdown voltage of a product's design.

Dielectric Withstand Test:

 A standard test voltage is applied (below the established Breakdown Voltage) and the resulting leakage current is monitored. The leakage current must be below a preset limit or the test is considered to have failed. This test is non-destructive and is usually

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required by safety agencies to be performed as a 100% production line test on all products before they leave the factory.

Insulation Resistance Test

 This test is used to provide a quantifiable resistance value for all of a product's insulation. The test voltage is applied in the same fashion as a standard Hipot test, but is specified to be Direct Current (DC). The voltage and measured current value are used to calculate the resistance of the insulation.

Chapter 2

Captive power plant:

The power requirement of HPCL–VR was earlier being met from APSEB. However frequent interruption in power supply were observed which causes crude through put loss, damage to equipment, fire hazard and unscheduled shutdown. With the above in view APSEB permitted HPCL, to install CPP. The CPP commissioned in 1991 is bussed on cogeneration of power and steam, leading to more energy efficient use of fuels as compared to a conventional power plant. The project step-up includes number of 9 MW

Capacities (ISO) gas turbines generators (GTG’s) along with two numbers heat recovery steam generators (HRSG) of 2.94 T/HR at 15 at 256 Centigrade in unfired condition at GTG base load. For that in view of VR expansion process from 4.5 MMTPA to 7.5 MMTPA and to meet the power requirement of refinery another set to GTG’s of generating capacity to 25MW (ISO) each along with two number of HRSG of 60 T/HR at 15 at 280 centigrade in unfire3d condition at GTG base load another auxiliary equipment are installed on a part of VREP-H during 1999-2000 at a cost of RS.150 crore approximately.

Start-up sequence of CPP:

Auxiliary lube oil pump starter. Auxiliary hydraulic pump starts. Jaw clutch of torque converter accessory gear box engages. Diesel engine starts and warms up for 120secs. When the timer T2 DW times

out, and the DE speed is 1000rpm Ace. Solenoid picks up. Diesel engine speed goes to 2000rpm and HP shaft rotates.

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The lock up- solenoid 20DA-2 energies and the DE speed is held constant at 1800 rpm.

At 18% of HP speed, cranking status is displayed on mark-IV up to 25% of HP speed is cranking.

Purging timer T2TVSC starts when cranking is displaced and times out after 60 seconds.

Diesel stop value opens and firing timer T2F starts and time allow for flame detection in 60 seconds (if within 60secs. No flame is established machine go back to cranking).

The turbine warms up for 60seconds (T2W). At about 52% HP speed jaw clutch disengages and LP shaft starts rotating. After 5mins diesel engine stops. From 80% HP and LP shaft speed exceeds HP.

CPP facilities:

The major facilities implemented in CPP are as follows

Gas turbines:

1&2

These are complete package units with enclosure for whether protection, thermal and acoustic insulation. The individual unit houses gas turbine, load gears box and electrical generator. The operating speed of a gas turbine is 6000rpm and the trip speed is 7150rpm.

3, 4, 5&6

The operating speed is 5100rpm. When the turbine starting system is actuated and the clutch is engaged, ambient air is drawn through the air inlet assembly, filtered aand compressed in 17 stage axial flow compressor. Compressed air from the compressor flows into the annular space surrounding ten combustion chambers, from which it flows into the space between the outer combustion gasing. In the combustion liners and enters the combustion zone through the metering poles in each of the combustion liners.

Theory of GTG:

Gasses passing through an ideal a gas turbine undergo

three thermodynamic processes. These are isentropic compression, isobaric (constant

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pressure) combustion and isentropic expansion. Together these make up the Brayton

cycle.

In a practical gas turbine, gasses are first accelerated in either a centrifugal or

radial compressor. These gasses are then slowed using a diverging nozzle known as

a diffuser; these processes increase the pressure and temperature of the flow. In an

ideal system this is isentropic. However, in practice energy is lost to heat, due to friction

and turbulence. Gasses then pass from the diffuser to a combustion chamber, or similar

device, where heat is added. In an ideal system this occurs at constant pressure

(isobaric heat addition). As there is no change in pressure the specific volume of the

gasses increases. In practical situations this process is usually accompanied by a slight

loss in pressure, due to friction. Finally, this larger volume of gasses is expanded and

accelerated by nozzle guide vanes before energy is extracted by a turbine. In an ideal

system these are gasses expanded isentropically and leave the turbine at their original

pressure. In practice this process is not isentropic as energy is once again lost to friction

and turbulence.

If the device has been designed to power to a shaft as with an industrial generator or

a turboprop, the exit pressure will be as close to the entry pressure as possible. In

practice it is necessary that some pressure remains at the outlet in order to fully expel

the exhaust gasses. In the case of a jet engine only enough pressure and energy is

extracted from the flow to drive the compressor and other components. The remaining

high pressure gasses are accelerated to provide a jet that can, for example, be used to

propel an aircraft.

Fig: Brayton cycle

As with all cyclic heat engines, higher combustion temperatures can allow for

greater efficiencies. However, temperatures are limited by ability of the steel, nickel,

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ceramic, or other materials that make up the engine to withstand high temperatures and

stresses. To combat this many turbines feature complex blade cooling systems.

As a general rule, the smaller the engine the higher the rotation rate of the shaft(s) must

be to maintain tip speed. Blade tip speed determines the maximum pressure ratios that

can be obtained by the turbine and the compressor. This in turn limits the maximum

power and efficiency that can be obtained by the engine. In order for tip speed to remain

constant, if the diameter of a rotor is reduced by half, the rotational speed must double.

For example large Jet engines operate around 10,000 rpm, while micro turbines spin as

fast as 500,000 rpm.

Mechanically, gas turbines can be considerably less complex than internal

combustion piston engines. Simple turbines might have one moving part: the

shaft/compressor/turbine/alternative-rotor assembly (see image above), not counting

the fuel system. However, the required precision manufacturing for components and

temperature resistant alloys necessary for high efficiency often makes the construction

of a simple turbine more complicated than piston engines.

More sophisticated turbines (such as those found in modern jet engines) may have

multiple shafts (spools), hundreds of turbine blades, movable stator blades, and a vast

system of complex piping, combustors and heat exchangers.

Thrust bearings and journal bearings are a critical part of design. Traditionally, they

have been hydrodynamic oil bearings, or oil-cooled ball bearings. These bearings are

being surpassed by foil bearings, which have been successfully used in micro turbines

and auxiliary power units.

Fig: Turbo shaft engine

Generators:

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1&2:

Generators which converts mechanical energy is rated for 11.2MVA at 0.8,11kv,3-phase ,50hz , 4-pole machine which runs at a speed of 1500rpm . the generator is coupled with the gas turbine through the load gear box which reduces gas turbine of 6500rpmto 1500rpm. Dc excitation current is fed to generator rotor winding

Using brushless excitation system. Automatic voltage regulation keeps the output voltage constant. The generator is protected by appropriated relays against over current, short-circuits and earth faults etc. the generator winding is cooled externally using forced air cooling system. the generator is enclosed within a metal using forced air cooling systems . the generator is enclosed within a metal enclosure which is protected by co2 extinguishing system against possible electrical fires.

3, 4, 5&6:

The generator is rated at 27.388mva at 0.8pf, 11kv, 3-phase, 50 Hz. The generator is 2pole machine running at a synchronous speed of3000rpm. The turbine speed is reduced from 5100rpm to 3000rpm through a load gear box. The generators is provided with open air ventilation system consisting of air filter unit by 2 axial flow fans located on the rotor aft one at either end. The generator rotor is supported on 2 journal bearings lubricants by the turbine oil system

Fig: cut-section of an alternator

Generator – Details

1. Make - Bharat Heavy Electrical Limited 2. output rating - 11,250KVA3. rated frequency -50hz4. full load current -590A5. P.F -0.86. rated speed -1500rpm

The generators are provided with a brushless excitation which eliminates the provision of slip rings and brushes.

Functional Description:

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Definition of gas turbine: A gas turbine is machine or engine in which mechanical power in the form of shaft is produced when a steam of air rushes on the blades r by buckets of a wheel it turn round .

Basic Cycle:

A gas turbine operates by

Continuously drawing in fresh air . Compressing thin air through a higher pressure Adding and burning fuel in the compressed air to increase its energy level. Directing the high pressure and temperature air to an expansion turbine

converts the gas energy to mechanical energy of a rotating shaft. The resulting low pressure, low temperature gases are discharged to atmosphere

Gas Turbine Equipments

Air inlet equipment:

The air supply for the turbine flows through a duct assembly prior to entering compressor the duct contains a air silencer and trash screen. The air silencer consisting of a number of acoustical panels from a section of duct assembly and attenuates the high frequency sounds created by compressor blades.

Compressor section:

The axial flow 15 stage compressor section consists of compressor rotor casing, and to exit guide vanes. In the compressor the air is confined to the space between the rotor

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and the stator blades where it is compressed in stages by an alternate series of rotting blades which supply the force needed to compress the air in each stage and the stator blades guide the air so that it enters the following rotor stage at proper angle. The compressed air exists through the compressor discharge casing through the combustion chamber. Air is also extracted from the compressor for the turbine cooling and for lube oil sealing at the bearings of the turbine.

Rotor assembly:

The compressor rotor is an assembly of 15 wheels two stub shafts assemblies, tie bolts and the compressor rotor blades and shafts are assembled by mating rabbets and secured by 12 tie bolts arranged concentrically around the rotor axis. The forward stub shaft contains the journal and the thrust number for the number one runner and the thrust bearing assembly, sealing surfaces for the bearing oil deflectors and compressor flow pressure air deflectors. The aft stub shaft contains for no.2 journal and thrust bearing assembly, the sealing surfaces for the bearing oil deflectors compressor high-pressure air seal. The shaft wheel portion of the stub haft contains the first stage compressor rotor blades. The compressor rotor assembly is dynamically balanced before it is assembled to the unbalanced turbine rotor assembly. This complete assembly is then dynamically balanced.

Stator:

The stator (compressor casing) enclosed the compressor portion of the rotor and is

divided into 4 sections; inlet casing, forward compressor, aft compressor and discharge

casing. The inner section, which directs the flow of outside air from the inlet equipment

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to the compressor blades, contains no 1 bearing assembly and low pressure air seals.

The forward section of the compressor casing is downstream of the inlet section

contains the stator for stages 0 through 3. the aft section downstream of the forward

section contains the stator blades for stages 4 through 9.

Combustion section:

The combustion section consists of 10 combustion chambers, fuel nozzles, cross fire tubes and transition pieces.

The combustion chambers are arranged concentrically around the axial fuel compressor and are bolted to the compressor discharge section bulkhead. Air for combustion is supplied directly to the compressor to the combustion chambers. This arrangement is called a reverse flow system since the compressor discharge air flows forward around the liners and then enters and flow back towards the turbine. Fuel is fed into the chambers of the turbine section.

Figure showing combustion section

Turbine section:

In the turbine, high temperatures gases from the combustion section are converted shaft horse power. This section comprises of the following components

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1. Turbine casing2. First stage nozzle3. Second stage nozzle4. First stage turbine wheel(hp turbine)5. Second stage turbine wheel(lp turbine)6. Diaphragm assembly7. Inter stage gas parts

Diesel engine:

The diesel engine starting motor (10hp, 125v dc) starts the diesel engine during startup procedures. The diesel engine lube oil pressure should be sufficient enough for startup. Diesel engine minimum speed sensed by pressure switch accelerating solenoid .The accelerating speed of the engine is nearly 2100rpm. The cooling for this engine is provided by CWM line.

Hydraulic torque converter:

This is a single stage hydraulic device coupled to the starting diesel engine. It transmits the DE output torque to the turbine accessory gear; all moving parts of the torque converter are lubricated with the system lubricating oil. The torque converted housing is bolted directly to DE flywheel housing. Converter operating temperature will vary with sum temperature and converter speed ration.

Fuel system:

The turbine can use a variety of liquid and gaseous fuels, which may vary substantially in hydrocarbon composition, physical properties and levels of contamination. High pressure fuel pumps how dividers have substantially improved the reliability of these critical fuels. Naphtha fuel to the GTG’s is from the two fixed cum floating roof tanks 183 A and 183 B each approximately. 2600KJL diesel system is from tanks 181, 182A each of approx 300KL. The fuel is pumped from the tank by fuel forwarding pumps. A

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pneumatic control bypass valve is provided in discharge of the pump for recirculation of fuel back to maintain discharge pressure. The fuel travels to the pressure controller where the pressure is controlled by pressure control valve (5.5-6 Kg/sqcm) with bypass valve from where it goes to the filter skid

Diesel System:

From the 25 micron dual filter skid, diesel goes through the trip oil operated stop value to reach main fuel pump. The servo controlled bypass value in the discharge line of the main fuel pump enters a 0.5 micron filter and then goes through the filter.

The flow divided as six output ports each connected to a combustion chamber. The flow divider which is driven by input pressure itself distributes diesel at equal pressure to all combustion chambers through check values calibrated at 7kg/sqcm pop pressure.

Naphtha Valve:

The fuel from control valve travels two stages. Filtration consists of 25 microns and 6micron dual filter skid. Accumulated pressurized with nitrogen are provided upstream of a Naphtha control valve to take care of the pressure fluctuations in the system . Naphtha passes through the three way transfer valve and reached the PFD skid before naphtha change out takes place, diesel has to enter or pass through naphtha skid to chamber. the fuel after six micro naphtha filters enters naphtha PFD consists of a trip oil operated stop valve a screw pump with discharge of which is controlled by a servo operated by pass valve.

Brushless Generator-Basics:

The permanent magnet generator (PMG) is coupled to shaft of the generator. The PMG has a permanent magnet on its rotor. The stator has winding after star up of the turbine; the PMG is also rotating at the same speed as that of generator. The permanent magnet causes a magnetic flux in the air gap between stator and rotor in the PMG. The stator windings cut in this flux (on rotation) and thus an emf is reduced in the stator windings. This is at 220v, 75 Hz.

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The variable dc current output of the AVR is brought to the stator winding of the main exciter .This winding then induces a magnetic flux in the air gap of the exciter. The rotor winding as it is rotating at the speed of the generator cuts flux and thus there is an induced emf (ac) in the rotor. this rotor current is rectified by the diodes and the consequents direct current(dc) is then fed through cables which run inside the hallow shaft the generator to the main field winding of the generators since the diodes are mounted on the rotor of the exciter of the regular maintence of carbon brushes etc.

Fig: brushless generator connected to turbo shaft

Automatic Voltage Regulator:

The AVR is intended for excitation and control of generators equipped with alternator exciter employing rotating non control rectifier.

Main parts of the regulator equipment are:

1. The closed loop control system including a separate gate control set and thyristor set each. Field discharge circuit.

2. An open loop control system for exchanging signal between regulator equipment and control room in power supply in power supply circuits.

Generator voltage control. Un-delayed limiting control for the output current of the thyristor set. Limiting control for under excited range. Delay limiting control for the over excited range. Automatic field suppression during shutdown of the generator. Delayed limiting control for stator over current.

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V/Hz limiter

Heat recovery steam generators:

A Heat Recovery Steam Generator (HRSG) is a steam boiler that uses hot exhaust gases from the gas turbines or reciprocating engines in a CHP plant to heat up water and generate steam. This steam in turn drives a steam turbine and/or is used in industrial processes that require heat.

HRSGs used in the CHP industry are distinguished from conventional steam generators by the following main features:

The HRSG is designed based upon the specific features of the gas turbine or reciprocating engine that it will be coupled to.

Since the exhaust gas temperature is relatively low, heat transmission is accomplished mainly through convection.

The exhaust gas velocity is limited by the need to keep head losses down. Thus, the transmission coefficient is low, which calls for a large heating surface area.

Since the temperature difference between the hot gases and the fluid to be heated (steam or water) is low, and with the heat transmission coefficient being low as well, the evaporator and economizer are designed with plate fin heat exchangers.

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Fig: Heat recovery steam generator

Chapter-3

Power distribution system in HPCL:

The modern distribution system begins as the primary circuit leaves the sub-station and ends as the secondary service enters the utilities. A variety of methods, materials, and equipment are used among the various utility companies, but the end result is similar. First, the energy leaves the sub-station in a primary circuit, usually with all three phases. Most areas provide three phase industrial service. There is no substitute for three-phase service to run heavy industrial equipment. A ground is normally provided, connected to conductive cases and other safety equipment, to keep current away from equipment and people.

Substations:

A substation is a part of an electrical generation, transmission, and distribution system. Substations transform voltage from high to low, or the reverse, or perform any of several

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other important functions. Electric power may flow through several substations between generating plant and consumer, and its voltage may change in several steps.

Fig: Substation

A substation that has a step-up transformer increases the voltage while decreasing

the current, while a step-down transformer decreases the voltage while increasing the

current for domestic and commercial distribution. The word substation comes from the

days before the distribution system became a grid. The first substations were connected

to only one power station, where the generators were housed, and were subsidiaries of

that power station.

Switch gear:

The term switchgear, used in association with the electric power system, or grid, refers to the combination of electrical disconnects, fusesand/or circuit breakers used to isolate electrical equipment. Switchgear is used both to de-energize equipment to allow work to be done and to clear faults downstream. This type of equipment is important because it is directly linked to the reliability of the electricity supply.

Fig: switch gears

The very earliest central power stations used simple open knife switches, mounted on

insulating panels of marble or asbestos. Power levels and voltages rapidly escalated,

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making open manually-operated switches too dangerous to use for anything other than

isolation of a de-energized circuit. Oil-filled equipment allowed arc energy to be

contained and safely controlled. By the early 20th century, a switchgear line-up would

be a metal-enclosed structure with electrically-operated switching elements, using oil

circuit breakers. Today, oil-filled equipment has largely been replaced by air-blast,

vacuum, or SF6 equipment, allowing large currents and power levels to be safely

controlled by automatic equipment incorporating digital controls, protection, metering

and communications. The technology has been improved over time and can be used

with voltages up to 1,100 kV.

Bus bar system:

In electrical power distribution, a bulbar is a strip of copper or aluminum that conducts electricity within a switchboard, distribution board, substation or other electrical apparatus.

Fig: Bus bars

The size of the bus bar determines the maximum amount of current that can be safely carried. Bus bars can have a cross-sectional area of as little as 10 mm² but electrical substations may use metal tubes of 50 mm in diameter (1,963 mm²) or more as bus bars, and an aluminum smelter will have very large bus bars used to carry tens of thousands of amperes to the electrochemical cells that produce aluminum from molten salts.

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Transformers:

HPCL uses a wide range of transformers which are very important in the power distribution system. A transformer is a device that transfers electrical energy from one circuit to another through coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field through the secondary winding. This varying magnetic field induces a varying electromotive force (EMF), or "voltage", in the secondary winding. This effect is called mutual induction. HPCL is having approximately 79 transformers in the entire refinery with the ratings like 10MVA/11KVA, 11/3.3KVA, 3.3/1.1KVA, 1.1KVA/415VA and etc.

Fig: 10 MVA power transformer

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Substation-50:

Substation-50 is one of the most peculiar and important substation in the HPCL’s power distribution system. In this substation there will be two incomers from the captive power plant (CPP) which bears 11KV. The panels in this substation are of two kinds, they are Power Control Centre (PCC) and Motor Control Centre (MCC). The 111KV is first stepped down into 5 divisions, in this process the outgoing lines are fed to two types of motors like High Tension motors (HT) and Low Tension motors (LT). then the remaining lines will fed the 6 Motor Control Centre (MCC) (for motors) and 1 Light Distribution Board (LDB) panels.

Meter control centre (MCC):

Duly wired with ACB/MCCB/SFU/DOL/STAR-DELTA/ATS Starters. Various designs provided like single/double front, fixed type, with Marshaling terminations. Cubicle type extensible on each side. Require Control voltage facilities with control. All starters are provided with type 2 co-ordination where required. Separate bus bar chamber for vertical droppers. Can be operating by remote on/off

Fig: MCC panel

Power control centre (PCC):

Main LT Panel, PCC With single, Multiple incomer, bus couplers with proper interlocking, Required protection, fault indications, interlocking is provided. Various designs are offered in PCC like top, Middle, Bottom Horizontal bus chamber, panel with aluminum/copper bus bars, top/bottom/front/rear cable termination, combinations of APFC Part with PCC.

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Required facilities like DG Incomer with AMF Functions, Cut-off of nonessential feeders at the event of failure of mains power.

Panel with provision to connect bus duct at main incomer side.

Fig: PCC panel

Direct on-line starters in SS-50:

A direct on line (DOL) or across the line starter starts electric motors by applying the full

line voltage to the motor terminals. This is the simplest type of motor starter. larger sizes

use an electromechanical contactor (relay) to switch the motor circuit. Solid-state direct

on line starters also exist.

Fig: DOL starter

A direct on line starter can be used if the high inrush current of the motor does not

cause excessive voltage drop in the supply circuit. The maximum size of a motor

allowed on a direct on line starter may be limited by the supply utility for this reason. For

example, a utility may require rural customers to use reduced-voltage starters for

motors larger than 10 kW.

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DOL starter is sometimes used to start small water pumps, compressors, fans and conveyor belts. In the case of an asynchronous motor, such as the 3-phase squirrel-cage motor, the motor will draw a high starting current until it has run up to full speed. This starting current is commonly around six times the full load current, but may be as high as 6 to 7 times the full load current.

Variable frequency drives:

A variable-frequency drive (VFD) is a system for controlling the rotational speed of

an alternating current (AC) electric motor by controlling the frequency of the electrical

power supplied to the motor.[1][2][3] A variable frequency drive is a specific type

of adjustable-speed drive. Variable-frequency drives are also known as adjustable-

frequency drives (AFD), variable-speed drives (VSD), AC drives, microdrives or inverter

drives. Since the voltage is varied along with frequency, these are sometimes also

called VVVF (variable voltage variable frequency) drives.

Variable-frequency drives are widely used. In ventilation systems for large buildings,

variable-frequency motors on fans save energy by allowing the volume of air moved to

match the system demand. They are also used on pumps, elevator, conveyor and

machine tool drives.

VFD motor:The motor used in a VFD system is usually a three-phase induction motor. Some types

of single motors can be used, but three-phase motors are usually preferred. Various

types of synchronous motors offer advantages in some situations, but induction motors

are suitable for most purposes and are generally the most economical choice. Motors

that are designed for fixed-speed operation are often used. Certain enhancements to

the standard motor designs offer higher reliability and better VFD performance, such as

MG-31 rated motors.

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Variable frequency controller:

The usual design first converts AC input power to DC intermediate power using

a rectifier or converter bridge. The rectifier is usually a three-phase, full-wave-

diode bridge. The DC intermediate power is then converted to quasi-sinusoidal AC

power using an inverter switching circuit.

VFD system

The inverter circuit is probably the most important section of the VFD, changing DC

energy into three channels of AC energy that can be used by an AC motor. These units

provide improved power factor, less harmonic distortion, and low sensitivity to the

incoming phase sequencing than older phase controlled converter VFD's. Since

incoming power is converted to DC, many units will accept single-phase as well as

three-phase input power (acting as a phase converter as well as a speed controller);

however the unit must be de-rated when using single phase input as only part of the

rectifier bridge is carrying the connected load.

Dynamic breaking:

Using the motor as a generator to absorb energy from the system is called dynamic

braking. Dynamic braking stops the system more quickly than coasting. Since dynamic

braking requires relative motion of the motor's parts, it becomes less effective at low

speed and cannot be used to hold a load at a stopped position. During normal braking

of an electric motor the electrical energy produced by the motor is dissipated as heat

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inside of the rotor, which increases the likelihood of damage and eventual failure.

Therefore, some systems transfer this energy to an outside bank of resistors. Cooling

fans may be used to protect the resistors from damage. Modern systems have thermal

monitoring, so if the temperature of the bank becomes excessive, it will be switched off.

Rectifier in VFD:

A rectifier is an electrical device that converts alternating current (AC), which

periodically reverses direction, to direct current (DC), which is in only one direction, a

process known as rectification. Rectifiers have many uses including as components

of power supplies and as detectors of radio signals. Rectifiers may be made of solid

state diodes, silicon-controlled rectifiers, vacuum tube diodes, mercury arc valves, and

other components.

Bibliography

HPCL official website Wikipedia.com Network protection and automation guide Google.books.com Google.images.com Power systems – J.B.Gupta Electrical machines – P.S.Bhimbhra

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