TI NO. 04/2011

VOLTAGE STABLISERS HT/ LT

WORKS DIRECTORATE ENGINEER-IN-CHIEF BRANCH

MILITARY ENGINEER SERVICES MINISTRY OF DEFENCE IHQ (ARMY)

TI NO. 04/2011

TECHNICAL INSTRUCTIONS

ON

VOLTAGE STABLISERS HT/ LT

BY DIRECTORATE OF WORKS

ENGINEER-IN=CHIEF BRANCH MILTARY ENGINEER SERVICES

INTEGRATED HQ OF MINISTRY OF DEFENCE

TTI NO. 04/22011

TI NO. 04/2011

TI NO. 04/2011

INDEX

Content Page No

1. Introduction 1

2. Main Supply Voltage Problems 1

3. Effects of Voltage Variations 4

4. HT/LT Automatic Voltage Stablisers 6

5. Features of Servo Voltage Stablisers 7

6. Technical Specifications 9

7. Comparison with On-Load Tap Changer 10

8. Design 11

9. Installation 17

10. Testing 18

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INTRODUCTION

1. INTRODUCTION Low / High Voltage fluctuation is a common phenomenon in Developing Countries due to the constant increase in demand and huge gap between demand & supply . Automatic Voltage Stabilizer is an equipment meant for obtaining constant voltage from fluctuating mains input supply. It protects valued Plant & Equipments from over and under voltage, resulting in improvement in the efficiency, performance, safety and life of the equipments. Automatic Servo Controlled AC Voltage Stabilizer is a device which controls the voltage variations & gives controlled constant voltage to the connected loads like machines, telecom equipments, married and OTM complex etc just to name a few. Three phase Automatic AC Voltage Stabilizers are specially designed for unbalanced load and unbalanced supply. All the three phases will be corrected individually so that out put voltage will be same in all the Three phases independent from load & supply voltage variations. Automatic Voltage Stabilizer play efficient role in all types of Resistive, Inductive & Capacitive loads, like Resistance Heating, Lighting Equipments, Motors, Rectifier Loads etc. It can be installed any where, may it be an Industrial Plant, Hospital, Hotel, Shopping Mall, Residential Colony /complexes

2. MAINSUPPLY VOLAGE PROBLEMS - SYMPTOMS,CAUSES & SOLUTIONS For electrical systems to function properly, it is necessary to make sure that the quality of the power feeding them is of a sufficient quality to ensure that performance is not impaired or system life expectancy reduced. Without the proper power, an electrical device or load may malfunction, fail prematurely or not operate at all. There are many reasons due to which electric power can be of poor quality and many more causes of such poor quality. Power supply problems are caused by various sources, for example distribution network faults, system switching, weather and environmental conditions, heavy plant and equipment, or simply faulty hardware. Various problems encountered in power supply are:- a) VOLTAGE SAGS

Sags: are short duration decreases in the mains supply voltage which generally last for several cycles.

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Formal Definition – Voltage below 80 to 85% of rated RMS voltage for 2 or more cycles.

Typical symptoms - Sensitive equipment can lock or hang causing data loss and system resets.

Common Causes – Heavy equipment turned on, starting large electrical motors, switching of the mains supply.

Solutions - AC Voltage Stabiliser, AC Power Conditioner & Uninterruptible Power Supply.

b) BROWNOUTS

Brownouts: are long term sags in the mains supply voltage which can last up to several days.

Formal Definition – A steady state of RMS voltage under nominal by a relatively constant percentage.

Typical Symptoms -Equipment can reset or even shutdown. Common Causes – Heavy equipment turned on, starting large electrical

motors, switching of the mains supply or just low voltage output from the generating source.

Solutions - AC Voltage Stabiliser, AC Power Conditioner & Uninterruptible Power Supply.

c) OVER-VOLTAGE & SURGES

Over-Voltage & Surges: are short duration increases in the mains supply voltage which generally last several cycles.

Formal Definition – Voltage above 110% of the rated voltage for 1 or more cycles.

Typical Symptoms - When surges occur equipment can suffer from premature failure. The high voltage causes wear and tear and general component degradation.

This is often unnoticeable until failure occurs. Unusual heat output can be an early sign of problems ahead.

Common Causes – Heavy equipment being turned off.

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Solutions - AC Voltage Stabiliser, AC Power Conditioner & Uninterruptible Power Supply

d) HIGH VOLTAGE SPIKES

High Voltage Spikes: these are very fast high energy surges or spikes in voltage lasting only a few milliseconds.

Formal Definition – Rapid Voltage peak up to 6,000 volts with a duration of 100msec to ½ a cycle.

Typical Symptoms - Equipment can lock or hang, crash and even suffer damage which inevitably causes data loss and corruption.

Common Causes - Switching of equipment, especially heavy inductive loads, arcing faults or atmospheric electrical disturbance, such as lightning strikes and static discharges.

Solutions - AC Voltage Stabilizer, AC Power Conditioner, Isolation Transformer, Uninterruptible Power Supply.

e) ELECTRICAL NOISE

Electrical Noise: this is a high frequency noise either common or normal mode.

Formal Definition – Electrical noise is high frequency interference on the incoming mains supply.

Typical Symptoms - Processing errors, computer lock-up, burned circuit boards, degradation of electrical insulation and equipment damage.

Common Causes – Electric motors, relays, motor control devices, broadcast transmission and microwave radiation.

Solutions - Isolation Transformer, AC Power Conditioner & Online Uninterruptible Power Supply

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f) BLACKOUTS & MAINS FAILURE

Blackout and Mains Failures: when the mains supply fails completely this is known as a total mains failure or blackout.

Formal Definition – Loss of incoming mains supply Typical Symptoms - Complete disruption of equipment operation. A break in

the mains supply of only several milliseconds is sufficient enough to crash, lock or reset many of the components that make up a typical data or voice processing IP network, such as PC, terminal, console, server, PBX, printer, modem, hub or router.

Common Causes - Storms, lightning, wind and utility equipment failure. Typically occurs as a result of loss of power, a mechanical failure, or overloading by consumers.

Solutions - Uninterruptible Power Supply & Diesel Generator

3. EFFECTS OF VOTAGE VARIATIONS ON DIFFERENT TYPES OF EQUIPMENT In cantonments, lighting, air-conditioning and equipments are the main load. Window Air-conditioner, and Air-conditioning plants are having compressors design to work efficiently within +/- 5% of 230 / 400 volts. Current drawn by the Air-conditioner and Air-conditioning plants is minimum at 230 volts single phase and 400 volts three phase, as compared to the current drawn at other voltage. Beyond this they draw heavy current, do less cooling, runs for longer length of time, means more power consumption. When voltage drifts beyond +/- 10% of 230 / 400 volts, these equipment stop working. For natural and brighter outlook, Halogen Lamps, decorative Tubes and CFL are being used and these are rated for 230 Volts. Whenever there is low voltage, lamps does not glow properly and give yellowish tinge. To get a brighter outlook all the time usually higher wattage lamp say of 100 watt is used where normal requirement at normal voltage (i.e. 220/230 Volts) is 60 Watts. Whenever the voltage is higher the Lamps, Tubes and CFL glows much brighter consuming higher power and fails (fuses) normally having 1/3rd of its normal life. By installing voltage stabilizer, one can save 20% to 40% power consumption of lamps and reduce its failure rate up to 80%. Effects of voltage variation are summerised below on various equipments:-

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Load Voltage Reduction

Effects Voltage Increase Effects

Computers

An 8% drop will often cause computer damage, errors and downtime.

A 10% rise will cause computer errors and downtime

Lighting A 10% voltage drop reduces lumen output by over 25% (15% for florescent tubes). Infra Red lamp heat output is reduced by over 20%.

A 10% volt rise reduces life expectancy of incandescent lamps by over 50%.

Radio & TV Transmission

Volt drop will reduce quality of the transmission and coverage range.

Over voltage by 2% will Significantly reduce tube life.

Photographic Processing

A 5% volt drop will increase exposure times by 30% and reduce quality of colour printing significantly.

Voltage rise during printing cycles will cause inferior results

X-Ray Equipment A 1 % change in the filament voltage of an XRay tube will produce an 8% change in the anode current

When used at its maximum rating an XRay tube will be permanently damaged in the case of a 5% volt rise.

Magnetic Equipment

A 10% volt drop can cause relays / contactors to open chatter. Solenoids become sluggish and vibration will cause malfunctions and overheating

Over voltage will cause magnetic core saturation high current and overheating.Wear and distortion is increased.

Induction Heating Heat output is reduced by more than 20% on a 10% volt drop.

Heat output varies approximately with the square of voltage.

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Welding Equipment

A 10% volt drop will increase a welding cycle by 20% if weld quality is to be maintained.

A 10% volt rise will overheat a weld, Reducing quality and causing possible “burn through”.

Transformers At 100 kVA a 10% drop will reduce transformer rating to 90%.

A 10% rise will considerably increase core losses and decrease efficiency proportionally.

AC Motors A 10% volt drop reduces torque by approximately 18% Motor life expectancy Is reduced due to overheating.

A 10% volt rise causes higher starting current and reduces power factor by approximately 5%.

4. H.T/L.T AUTOMATIC VOLTAGE STABILIZER H.T. Automatic Voltage Stabilizers are used to get stable input voltage for individual Distribution Transformer, irrespective of High / Low Voltage being received from Electricity Authority. These are installed on the input side of the Transformers. It also prevents the Transformer from getting overloaded. H.T. Automatic Voltage Stabilizer takes care of wide voltage variation ranges, sleeplessly and in ON LOAD condition, leading to full load utilization of the Transformer installed. L.T. Automatic Voltage Stabilizers holds its potential for units having either L.T. Supply or Low capacity H.T. Connections. The same can be manufactured for Balanced Supply and Unbalanced Loads or Unbalanced Supply and Unbalanced Loads. The range of input supply which the stabilizer is designed for depends upon the voltage condition at the supply point. However some standard ranges for L.T. Stabilizers are as under:- 300V - 460V, 340V - 460V, 360V - 460V

5. SELECTION CRITERIA Over engineer the solution and it can be very expensive. Select a system that does not address all identified power problems, or consider locally available resources, and one can so easily waste money.

Know clearly the requirements Know the right questions to ask Know the advantages and disadvantages of the various design types

When determining the total power rating for the solution required, do not forget to allow for possible future expansion of the load to be protected over the medium to long term. You will need to check the rating of the equipment to be protected. Such ratings are normally quoted in Amps or kVA, and whether single or three phase. You will also need to determine the nominal voltage line to neutral and line to line if three phase, plus the frequency and power factor. Such information is usually shown on the

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rating plate attached to the equipment. It is always recommended that you measure the loads true RMS value. Choosing a stabilizer with the right input variation capability is important because if its input voltage range is exceeded, then its output will increase or decrease by the same amount by which it has gone "out of limit". As a general rule the greater the input voltage swing the stabiliser needs to correct the greater the price. An output voltage to within ± 1% / ±1.5% of the preset output voltage is the norm when specifying a Voltage Stabiliser . However if a lower output voltage accuracy can be accommodated by the load equipment, then the input voltage range can be extended proportionally. As the cost of the stabiliser is linked to the input voltage range it has to handle, accepting a lower output accuracy may prove to be a more economical solution. With most supplies operating on 50 or 60 Hz, your normal mains supply frequency is unlikely to vary more than +/- 2%, and this is well within the capability of most stabilizers . But if the supply is from a local generator it is possible that the frequency could deviate beyond this range and suitable protection should be considered to protect both the load and the power protection system.

6.FEATURES OF SERVO STABILISER Automatic Servo Controlled AC Voltage Stabilizer primarily consists of the following

Linear type continuously variable auto voltage transformer. Double wound bucking & boosting transformer Control motors Electronic control circuits and meter panel Standard fittings

(i) Two Nos. Earthing terminals. (ii) Cable end boxes for incoming and outgoing side for terminating cables (iii) Oil level indicator, filling & drain valve, lifting lugs, wheels.

7. OPTIONAL FEATURES AND PROTECTIONS

Low Voltage Cutoff incase input voltage goes below the range High Voltage Cutoff incase input voltage goes above the range Low / High frequency protection Single phasing prevention Phase reversal prevention Earth fault protection Delay on Circuits Overload / Short circuit Protection Alarm enunciator for auditable indication of above faults Ampere Meter with CTs and Selector Switch. Spikes and surge protection

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Stabilizer bypass system Isolation Transformer on output Outdoor models with canopy Remote control of stabilizer ( with wires )

8. ADVANTAGES 1. REDUCTION IN BREAKDOWN OF ELECTRICAL EQUIPMENTS 2. REDUCTION IN POWER CONSUMPTION 3. IMPROVEMENT IN POWER FACTOR 4. REDUCTION IN MDI 5. UNIFORM QUALITY OF END PRODUCT 6. REDUCTION OF DOWN TIME DUE TO FEWER BREAKDOWN 7. SAVING ON EXPENSIVE MANAGEMENT TIME 8 REDUCTION IN WASTAGE 9. INCREASED EFFICIENCY OF THE PLANT & EQUIPMENTS 10. BETTER WORK & DELIVERY SCHEDULES CAN MAINTAINED

9. RATING PLATE Each corrector is provided with a rating plate of weather- proof material fitted in a visible position. The entries on the rating plate should be indelibly marked (for example, by etching, engraving or stamping). The information to be given on the rating plate shall be as under:

a) Type of line voltage corrector b) Manufacturer’s name; c) Manufacturer’s serial number; d) Number of phases: e) Year of manufacture; f) Rated kVA; g) Rated frequency; h) Rated input voltage range; i) Rated output voltage; j) Rated output current; k) Type of cooling; and l) Class of insulation.

In addition, the following information relevant to servo- motor shall also be given on the rating plate of the motor:

a) Rated torque, b) Rated voltage, c) Type of supply, and d) Rated watts

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10.TECHNICAL SPECIFICATIONS Following information be furnished to the vendors while ordering a voltage stabiliser:- Rating : Input Voltage Range : Output Voltage : Output Voltage Stabilization : Within + 1% Wave Form Distortion : Nil Response Time : Less than 10 ms Correction Speed : Up to 70 V per sec Suitability : Suitable for all power factor load Cooling : Air Cooled / Oil Cooled Additional Facility : Manual operation Type of load : Unbalanced/Balanced Load. Installation : Indoor / out door Degree of Protection : IP – 30 No Load Loss : Less then 0.5% Efficiency : 98–99% Winding Material : Input/Output Termination : Transformer Oil : New insulating oil ISI 335 marked.

11. PAYBACK PERIOD Owing to stabilizer’s efficiency and associated benefits, the payback period of Automatic AC Voltage Stabilizers is within 6-12 months and depends upon the input variation and the number of working hours. In today’s world the machines are very sophisticated, voltage sensitive and costs millions & millions, any breakdown due to voltage variations will cost a lot . Input Voltage % of reduction in Appx. Power Saving Variation breakdown Possible Possible 380-420 Volts No reduction in breakdown No saving & No Of electrical equipments Stabilizer required 380-440 Volts Up to 20% reduction in Up to 5% breakdown of electrical equipments. 360-460 Volts Up to 60% reduction in Up to 7% breakdown of electrical equipments. Below 340 & Up to 80% reduction in Up to 10% Above 460 volts breakdown of electrical equipments.

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12. OTHER IMPORTANT FACTORS a) STABILIZER WITH INDIVIDUAL PHASE CORRECTION The price of stabilizer suitable for unbalanced input voltage is hardly 10% higher then a balance type of stabilizer and is suitable for balanced or 100% unbalanced load , balanced or 100% unbalanced voltages, and voltage correction is very high upto 70 volts per second. Balanced type of stabilizers are suitable only for 100% balanced voltage and at least 90% balanced load and they are very slow in voltage correction with speed merely 4-6 volts per second. All imbalances of supply voltage are passed to the system and therefore are not economical.. b) HIGH SPEED OF CORRECTION The correction speed of stabilizers is up to 70 Volts / Sec. depending upon the range of voltage variation and capacity of voltage stabilizer. High correction speed is required in case of residential and commercial loads where the voltage varies very fast on account of the voltage drops or rises as the transmission lines are of light duty. In industries lot of jerk load keep coming and if the stabilizer is slow in correction then the output voltage will never be stabilized. c) STABILIZER ON GENSETS Automatic Voltage Controller is not required on Gensets. The stabilizer is effective on the generator set but there is no need of stabilizer to be run on generator as there is inbuilt Automatic Voltage Controlling system in the generator. If the Automatic Voltage Controlling system is not working properly, then you can run the stabilizer with the generator. Moreover with the variation of frequency and the wave shape, the output voltage of the stabilizer may vary by 1 to 3%. d) DISTRIBUTION TRANSFORMER HAVING ON LOAD TAP CHANGER Distribution transformer having on load tap changer also require stabilizer because the tapping of OLTC is not changed frequently. It is changed only when the problem of very high or very low voltage is felt. The stabilizer continuously monitors the output voltage level. However the range of stabilizer can be kept low where OLTC is installed.

13. COMPARISON OF STABILIZER AND ON LOAD TAP CHANGER AUTOMATIC VOLTAGE CONTROLLER ON LOAD TAP CHANGER Voltage Control is entirely step less thereby providing a close tolerance on the output.

Voltage Control in discreet steps and the available output would be dependent on the desired step voltage.

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The mechanical movement of the Regulator is very simple and consists of a Pinion & main gear only which moves the armor. Hence no periodic maintenance required.

The mechanical movement is relatively complex comprising of chain, gear trains, operating mechanism spring changing system and armor of contact, so on Maintenance is complicated and can be done by trained technicians only.

Preventive maintenance require only to change the carbon contacts, this being the component under-going wear and tear. Replacement cost is low and is easy, the material being light and compact.

The number of moving parts are more and hence wear and tear occur in moving contacts, fixed contacts, gear trains, transition resistors and so on. Replacement cost are high and cannot be attended by normal operating staff

The movement of the contact on the Windings of the Regulator which is at low Voltage and does not cause sparking and Hence there is no contamination in the Transformer oil

The mechanical movement causes sparking at each change of tapping as OLTC is fitted on high voltage winding thereby causing the oil to carbonize and entire oil has to be replaced in due course.

14. DESIGN The various technologies employed in voltage stabilization can often be a daunting task and it is not always clear as to which technology is best for a particular application. a) ELECTRONIC SERVO / ELECTRO- MECHANCAL DESIGN For most applications Servo Electronic -Electro Mechanical have proved to be a very reliable and cost-efficient voltage stabilization solution, being able to accommodate an input voltage swing of in excess of 40% whilst still delivering an accuracy of 1% on the output. Comprising a transformer having its secondary winding connected between the mains supply and the load, the primary voltage is automatically controlled through a motor driven variable transformer - ensuring a continuous, smooth and very stable output voltage.

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High Voltage / Transient Spikes are normally limited by the inclusion of ‘Spike Clippers’. Such clippers typically limit transients to twice the peak voltage of the supply. While Electronic Servo stabilizers do contain some moving parts, the most demanding power conditions has proved the design to be a very reliable The long-life expectancy, compact size and low cost of ownership makes servo electro mechanical stabilizers economical solutions. DESIGN ADVANTAGES

DESIGN DISADVANTAGES

Size and weight advantages over other methods of stabilization

Moving parts requiring limited maintenance

Fast speed of response to voltage changes – ideal for most applications

Lower speed of response compared to solid state designs

Very competitively priced

Negligible output waveform distortion Not Frequency dependent

Will attenuate voltage spikes if required

Unaffected by load or power factor changes

Low cost of ownership with ease of serviceability

Endurable, with long life expectancy b) SOLID STATE SATURABLE REACTOR DESIGN

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With no moving parts, solid state design based systems utilise the latest control circuitry delivering a very high speed of response and output accuracy maintained to ±0.5%. Since all components are of electronic design, they are virtually maintenance- free

Solid state based systems are ideal solutions for equipment that must have output voltage accuracy better than 1%. DESIGN ADVANTAGES DESIGN DISADVANTAGES High speed of response to voltage changes

Usually less price competitive when compared to Servo Electronic design

Output voltage accuracy better than 1 %, typically 0.5%

High weight to kVA ratio compared to electronic servo designs

No Moving parts – virtually Maintenance Free

High efficiency

Not Frequency dependent

Output voltage does not collapse on overload or severe input voltage drop

Low output waveform distortion

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Unaffected by load or power factor changes

Will attenuate voltage spikes if required c) MAGNETIC INDUCTION SOLID STATE DESIGN The design technology utilises a simple, yet highly reliable, rotor and stator design principle to increase or decrease the magnitude of the voltage in a series transformer winding, which thereby delivers and maintains a constant voltage.

Unlike the Servo-Electro Mechanical design, this technology does not require carbon brushes and there is no contact wear. As a result Magnetic Induction based stabilizers are highly reliable and can be viewed as virtually maintenance free solutions.

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DESIGN ADVANTAGES DESIGN DISADVANTAGES High output voltage accuracy Less price competitive when compared to

Servo Electronic design

High reliability

Virtually Maintenance Free with no contact wear or requirement for carbon brush replacement

d) FERRO-RESONANT-SUPER ISOLATION SOLID STATE DESIGN Based around a highly reliable and endurable Constant Voltage Transformer (CVT), super isolation design based systems are able to tolerate very wide input fluctuations, even when the input voltage drops as low as 40%, the output voltage will be maintained at nominal voltage ±5%. . With no moving parts and no electronic control circuitry there is no need for maintenance and is virtually an install and forgets solution. The design can withstand high instantaneous overloads and is able to suppress lightning induced spikes and surges. Compact in size and quiet in operation, this design has the inherent ability to withstand a ride-through even when there is a very short power failure, maintaining voltage for 3msecs. This feature is exceptionally useful for sensitive electronic equipment when there are frequent short breaks or severe voltage dips.

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DESIGN ADVANTAGES DESIGN DISADVANTAGES High speed of response to voltage changes

Not generally competitive in ratings above 10 kVA

Output voltage does not collapse on overload or severe input voltage drop

High weight to kVA ratio compared to other stabilisation methods

Attenuates voltage spikes Frequency dependent – not ideal for where severe frequency variations are an issue

Competitively priced AC Power Conditioning solution for ratings of 5 kVA or below

Highly reliable with extremely high MTBF performance

Inherent ride-through ability

Endurable, with long life expectancy

No moving parts-virtually majntence free e) ELECTRONIC TAP CHANGING SOLID STATE DESIGN The Electronic Tap Changer design principle operates by automatically selecting one of a series of taps on an auto transformer.

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DESIGN ADVANTAGES DESIGN DISADVANTAGES Most competitive in price for 2 kVA and below

Poor output voltage accuracy – typically no better than ± 5%

High Efficiency Generally / Historically deliver a low MTBF (Mean Time Between Failure)

Negligible output waveform distortion

No Moving parts – virtually Maintenance Free

15. INSTALLATION As stabilizers are suitable for 100% continuous duty cycle, the stabilizer can be installed as per actual running load taking into consideration the future expansions. In small installations, stabilizer can be installed near the particular machine for which the stabilizer is meant for. In bigger installations, the stabilizer can be installed at the mains or section wise after the LT ACB / OCB. Installation needs cables of suitable capacity to input from ACB / OCB and from output to Distribution panel. Over voltage / Under voltage signal is provided which can be used for tripping ACB / OCB in case voltage goes beyond specified level.

A) Install the stabilizer in a dry, cool and well ventilated place. B) Switch off the power supply before making any connection. C) Connect the input terminals to main supply. D) Mode selection switch should be kept towards manual position. E) Switch on the stabilizer (through the MCB/ ON-OFF Switch, whichever is

provided) keeping the voltmeter switch to output position. F) Press the manual switch towards boost side. The output voltage will increase

till the low limit indicator glows. G) Press the manual switch towards buck side. The output Voltage will decrease

till the high limit indicator glows. H) Change the mode selection switch to auto position. The output voltage will

automatically get set at specified output Voltage. I) By rotating the output voltage adjust control; the output voltage can be

adjusted by +/- 6% of the specified output voltage. J) Repeat the above operations for all phases in case of three phase unit. K) Switch off the mains and connect the load and again switch it on.

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16. TESTING Following test should be carried out after installation:-

A) INSULATION RESISTANCE TEST :- The insulation resistance between the terminals and body of the corrector shall be measured and recorded. It shall not be less than 5 mega ohms when measured at 500 V dc at room temperature not exceeding 45 degree C.

B) HIGH VOLTAGE TEST :- The test voltage of 1.5 kV (rms) shall be applied at rated frequency for one minute between the winding and the body of the corrector which shall be earthed. There shall be no disruptive discharge or collapse of test voltage.

C) OUTPUT VOLTAGE TEST: - For this test voltmeter of accuracy class index better than 0.5 shall be connected across the output terminals. The output voltage for different input voltage shall be recorded for different input voltages both at full-load and at no-load covering specified input voltage, not less than five voltage reading at approximately equal intervals shall be taken at corrector input and output points excluding the mains lead the voltage shall not differ by more than 1% of the rated output voltage.

D) NO –LOAD CURRENT TEST:- The no load current shall be measured at rated frequency with the rated lowest and highest input voltage applied to the input terminals, the output terminals being kept open –circuited.

E) NO-LOAD LOSS RUN METHOD:- Method for carrying out no-load loss test shall be same as for carrying out no-load current .This test may be combined with the no-load current test.

F) LOAD LOSS TEST AND EFFICIENCY:- The corrector shall be set at different positions corresponding to the input voltage range and the values of load losses checked at these positions. The point where the load loss is maximum, shall be the highest loss position and the value obtained at this point shall be taken load for the purpose of this test. The losses are to be computed at 75 degree c. .