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My first experience of project has been successful. First of all, I am thankful to my project guide, ER. PRABHAT KATIYAR under whose guideline I was able to complete the project. I am whole heartedly thankful to him for giving me his valuable time & attention. I wish to place heartily thanks to all those who encouraged me throughout the study and provided me the opportunity to learn as a trainee at BHEL Jhansi.

The disciplined environment in BHEL Jhansi has also played a vital role in timely completion of this training.




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Vision, mission and values of BHEL 1

Overview of BHEL 2

Various units of BHEL 4

Activity profile of BHEL 5

BHEL Jhansi (unit) 7

Various department of BHEL Jhansi 10

Health, safety & environment management 20

An Introduction To On Load Tap Changer 22

On-Load Tap-Changers For Power Transformers 24

Design Concept Of On Load Tap Changer 27

Description Of Equipments 29

Installation Of OLTC 35

Test Performed On OLTC 44

Transportation And Operation Of OLTC 46

Supervision And Inspection 47

Conclusion 49

References 50

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VISION A global engineering enterprise providing solutions for a better tomorrow.

MISSIONProviding sustainable business solutions in the fields of Energy, Industry & Infrastructure.


GOVERNANCE: We are stewards of our shareholders investments and we take that responsibility very seriously. We are accountable and responsible for delivering superior results that make a difference in the lives of the people we touch.

RESPECT: We value the unique contribution of each individual. We believe in respect for human dignity and we respect the need to preserve the environment around us.

EXCELLENCE: We are committed to deliver and demonstrate excellence in

whatever we do.

LOYALTY: We are loyal to our customers, to our company and to each other.

ENTEGRITY: We work with highest ethical standards and demonstrate a behaviour that is honest, decent and fair. We are dedicated to the highest levels of personal and institutional integrity.

COMMITMENT: We set high performance standards for ourselves as individuals and our teams. We honour our commitments in a timely manner.

INNOVATION: We constantly support development of newer technologies, products, improved processes, better services and management practices.

TEAM WORK: We work together as a team to provide best solutions & services to our customers. Through quality relationships with all stakeholders we deliver value to our customers.

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BHEL is the largest engineering and manufacturing enterprise in India in the energy/infrastructure sector today. BHEL was established more than 40 years ago when its first plant was set up in Bhopal ushering in the indigenous Heavy Electrical Equipment industry in India, a dream that has been more than realized with a well-recognized track record of performance. BHEL caters to core sectors of the Indian Economy viz., Power Generation & transmission, Industry, Transportation, Telecommunication, Renewable Energy, Defence, etc. The wide network of BHEL’s 17 manufacturing divisions, four Power Sector regional centres, over 100 project sites, eight service centres and 18 regional offices, enables the company to promptly serve its customers and provide them with suitable products, systems and services-efficiently and at competitive prices. BHEL has already attained ISO 9000 certification for quality management, ISO 27000 for Information Technology and ISO 14001 certification for environment management.

POWER GENERATIONPower generation sector comprises thermal, gas, hydro, and nuclear power plant business.


BHEL also caters to Telecommunication Sector by way of small, medium and large switching systems.


BHEL offers wide-ranging products and systems for T&D applications. Products manufactured include: power transformers, instrument transformers, dry type transformers, series &shunt reactors, capacitor banks, vacuum &SF6 circuit breakers, gas-insulated switchgears and insulators.

INDUSTRIESBHEL is a major contributor of equipment and systems to industries, cement, sugar, fertilizer, refineries, petrochemicals, paper, oil and gas, metallurgical and other process industries. The range of systems & equipment supplied includes: captive power plants, co-generation plants, DG power plants, industrial steam turbines, industrial boilers and auxiliaries, waste heat recovery boilers, gas turbines, heat exchangers and pressure vessels, centrifugal compressors, electrical machines, pumps, valves, seamless steel tubes, electrostatic precipitators, fabric filters, reactors, fluidized bed combustion boilers, chemical recovery boilers and process controls.

TRANSPORTATIONBHEL is involved in the development, design, engineering, marketing, production, installation, and maintenance and after-sales service of rolling stock and traction propulsions systems. BHEL manufactures electric locomotives up to 5000 HP, diesel electric locomotives from 350 HP to 3100 HP, both for mainline and shunting duty applications. It also produces

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rolling stock for special applications viz. overhead equipment cars, special well wagons, and Rail-cum road vehicle.RENEWABLE ENERGY Technologies that can be offered by BHEL for exploiting non-conventional and renewable sources of energy include: wind electric generators, solar photovoltaic systems, solar heating systems, solar lanterns and battery-powered road vehicles.

OIL AND GAS BHEL’s products range includes Deep Drilling Oil Rigs, Mobile Rigs, Work Over Rigs, Well Heads and X-Mas Trees, Choke and Kill Manifolds, Full Bore Gate Valves, Mudline Suspension System, Casing Support system Sub-Sea Well Heads, Block valves, Seamless pipes, Motors, Compressor, Heat Exchangers etc.

INTERNATIONAL OPERATIONS BHEL is one of the largest exporters of engineering products & services from India, ranking among the major power plant equipment suppliers in the world.

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FIRST GENERATION UNITSBhopal : Heavy Electrical Plant.

Haridwar : Heavy Electrical Equipment Plant.

Hyderabad: Heavy Electrical Power Equipment Plant.


Tiruchy : High Pressure Boiler Plant.

Jhansi : Transformer and Locomotive Plant.

Haridwar : Central Foundry and Forge Plant.

Tiruchy : Seamless Steel Tube Plant.

UNITS THROUGH ACQUISTION & MERGERBangalore : Electronics Division Electro Porcelain Division.

NEW MANUFACTURING UNITSRanipet : Boiler Auxiliaries Plant.

Jagdishpur: Insulator Plant.

Govindwal : Industrial Valve Plant.

Rudrapur : Component and Fabrication Plant.

Bangalore : Energy Systems Division

BHEL is growing concern to meet the changing needs of the nation has taken it beyond power into the total gamut of energy, industry and transportation BHEL is able to offer a service in each of this fields. Its manufacturing capability is supported by a corporate R&D division at Hyderabad works closely with the research and development cells at various units and Welding Research Institute at Tiruchinapalli.

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Thermal sets and Auxiliaries. Steam generators and Auxiliaries. Industrial fans. Electrostatic precipitators. Air pre heaters. Nuclear power equipments. Hydro sets and Auxiliaries. Motors. Transformers. Rectifiers. Pumps. Heat Exchangers. Capacitors. Porcelain/Ceramics insulators. Seamless steel tubes. Casting and forging.


Turnkey power station. Data acquisition Systems. Power systems. HVDC Commissioning systems. Modernization and Rehabilitation.


Diesel Electric generators. AC/DC locomotives. DC locomotives and loco shunters. Traction system for railways. Electric trolley buses.


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Boilers. Valves. T.G. sets. Power devices. Solar Cells. Photo Voltaic cells. Gas Turbines. Compressors. Drive Turbines. Oil rigs. Blow out preventers. Wind mills. Control systems for electric devices.


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A BRIEF INTRODUCTIONBy the end of 5th five-year plan, it was envisaged by the planning commission that the demand for power transformer would rise in the coming years. Anticipating the country’s requirement BHEL decided to set up a new plant, which would manufacture power and other types of transformers in addition to the capacity available in BHEL Bhopal. The Bhopal plant was engaged in manufacturing transformers of large ratings and Jhansi unit would concentrate on power transformer upto 50 MVA, 132 KV class and other transformers like Instrument Transformer s, Traction transformers for railway etc.

This unit of Jhansi was established around 14 km from the city on the N.H. No 26 on Jhansi Lalitpur road. It is called second-generation plant of BHEL set up in 1974 at an estimated cost of Rs 16.22 crores inclusive of Rs 2.1 crores for township. Its foundation was laid by late Mrs. Indira Gandhi the prime minister on 9th Jan. 1974. The commercial production of the unit began in 1976-77 with an output of Rs 53 lacs since then there has been no looking back for BHEL Jhansi.

The plant of BHEL is equipped with most modern manufacturing processing and testing facilities for the manufacture of power, special transformer and instrument transformer, Diesel shunting locomotives and AC/DC locomotives. The layout of the plant is well streamlined to enable smooth material flow from the raw material stages to the finished goods. All the feeder bays have been laid perpendicular to the main assembly bay and in each feeder bay raw material smoothly gets converted to sub assemblies, which after inspection are sent to main assembly bay.

The raw material that are produced for manufacture are used only after thorough material testing in the testing lab and with strict quality checks at various stages of productions. This unit of BHEL is basically engaged in the production and manufacturing of various types of transformers and capacities with the growing competition in the transformer section, in 1985-86 it under took the re-powering of DESL, but it took the complete year for the manufacturing to begin. In 1987-88, BHEL has progressed a step further in under taking the production of AC locomotives, and subsequently it manufacturing AC/DC locomotives also.

PRODUCT PROFILE OF BHEL JHANSI UNIT1. Power transformer up to 400 KV class 250 MVA.

2. Special transformer up to 180 KV.

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3. ESP transformer 95 KV, 1400 mA.

4. Freight Loco transformer 3900 to 5400 KVA & 7475 . KVA for 3 phase.

5. ACEMU transformer up to 1000 KVA (1-phase).

1385 KVA (3 phase). .

6. Dry type transformer up to 6300 KVA 33 KV class

7. Instrument transformer VT & CT up to 220 KV class.

8. Diesel electric locomotives up to 2600 HP.

9. AC/DC locomotives 5000 HP.

10. Over Head Equipment cum Test Car

11. Well wagon 200 tone.

12.Rail cum road vehicle

13. Dynamic track stabilizer


PARAMETER 2011 - 12 2012 - 13

Turnover (Rs. /Cr.) 49510 50015

Order Inflow (Rs. /Cr.) 22096 31528

Net Profit (Rs. /Cr.) 7040 6485

Net Worth (Rs. /Cr.) 25373 30315

Megawatts Commissioned 9270 10340

R & D Investment (Rs. /Cr.) 1199 1248

Patents/Copyrights Filed (Nos.) 351 385


DIVISION 2011 – 12


2012 – 13


JHANSI 1300 1365

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HEEP HARDWAR 5415 6375

BAP RANIPET 4210 3703

HPBP TRICHY/SSTP 14571 14970


BHOPAL 4790 4703


BHEL NET 49301 50015


TRANSFORMER COMMERCIAL (TRC)The objective of the department is interaction with the customers. It brings out tenders and notices and also responds to them. It is this department that bags contracts of building

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transformers. After delivery regarding faults, this department does failures and maintenance. All such snags are reported to them and they forward the information to the concerning department.One of the major tasks of this department is to earn decent profits over all negotiations. Transformer industry has become very competitive. The company offering the lowest price gets the contract but this process may continue does the work on very low profits. To avoid such a situation, a body by the name of India Electrical and Electronics Manufacturing Association (IEEMA) was set up. This association helps to maintain a healthy competitive atmosphere in the manufacturing of electrical appliances.


The transformer manufactured in BHEL Jhansi range from 10 MVA to 250 MVA and up to 400 KV. The various transformers manufactured in this unit are:-


a) Generator transformer b) System transformer. c) Auto transformer.

SPECIAL TRANSFORMER a) Freight loco transformer. b) ESP transformer. c) Instrument transformer. d) Dry type transformer.

BAY-00 & 0:

It is a sub part of Fabrication. It is the preparation shop while the other two bays form the assembly shop. This section has the following machines:

Planner machine – To reduce thickness Shearing machine CNC / ANC Flame Cutting machine – To cut Complicated shaft items using Oxy-

Acetylene flame Bending machine Rolling machine Flattening machine Drilling machine Nibbling machine Pantograph flame cutting machine


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It is also a sub part of Fabrication. It is an assembly shop where different parts of tank come from bay 0.Here welding processes are used for assembly, after which a rough surface is obtained Grinder operating at 1200 rpm is used to eliminate the roughness.

BAY-2It is also a sub part of Fabrication It is an assembly shop dealing with making different objects mentioned below.1-Tank assembly 5-cross feed assembly

2-Tank cover assembly 6-core clamp assembly

3-End Frame assembly 7-pin and pad assembly

4-foot assembly

Before assembly, short blasting (firing of small materials i.e., acid pickling) is done on different parts of jobs to clean the surface before painting.


1. Ultrasonic test to detect the welding fault on the CRO at the fault place high amplitude waves are obtained.

2. Die Penetration test Red solution is put at the welding and then cleaned. After some time white solution is mixed. Appearance of a red spot indicates a fault at the welding.

3. Magnetic crack detection Magnetic field is created and then iron powder is put at the welding. Sticking of the iron powder in the welding indicated a fault.

4. X-Ray Test: It is same as human testing and the fault is seen in X-ray film.

BAY-3Here are basically three sections in the bay:

Machine section Copper section Tooling section


It is the winding section.

There are four types of coil fixed in a transformer, they are

1. Low voltage coil (LV)2. High voltage coil (HV)3. Tertiary coil4. Tap coil

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The type of winding depends upon job requirement. Also, the width and thickness of the conductors are designed particulars and are decided by design department. Conductors used for winding is in the form of very long strips wound on a spool, the conductor is covered by cellulose paper for insulation.

For winding first the mould of diameter equal to inner dia meter of required coil is made .The specification of coil are given in drawing. The diameter of mould is adjustable as its body is made up of wooden sections that interlock with each other. This interlocking can be increased or decreased to adjust the inner diameter of coil.

The moulds are of following types

1. Belly types2. Link types3. Cone type

BAY-5It is core and punch section. The lamination used in power, dry, ESP transformer etc for making core is cut in this section.

CRGO (cold rolled grain oriented) silicon steel is used for lamination, which is imported in India from Japan, U.K. Germany. It is available in 0.27 and 0.28 mm thick sheets, 1mt wide and measured in Kg. .The sheet s are coated with very thin layer of insulating material called “carlites”.

For the purpose of cutting and punching the core three machines are installed in shop

BAY-6Single-phase traction transformer for AC locomotives is assembled in this section. This Freight locomotive transformers are used where there is frequent change in speed. In this bay core winding and all the assembly and testing of traction transformer is done.

Three-phase transformers for ACEMU are also manufactured in this section. The supply lines for this transformer are of 25 KV and power of the transformer is 6500 KVA. The tap changer of rectifier transformer is also assembled in this bay. Rectified transformer is used in big furnace like the thermal power stations / plants (TPP).


1. This is the insulation shop. Various types of insulations are2. AWWW - All Wood Water Washed press paper.3. The paper is 0.2-0.5mm thick cellulose paper and is wound on the

conductors for insulation.4. PRE COMPRESSED BOARD: This is widely used for general insulation &

separation of conductors in the forms of blocks.5. PRESS BOARD: This is used for separation of coils e.g. L.V. from H.V. It is up to

38 mm thick.

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6. UDEL(Un Demnified Electrical Laminated) wood or Permawood7. This is special type of plywood made for insulation purposes.8. FIBRE GLASS: This is a resin material and is used in fire pron areas.9. BAKELLITE10. GASKET- It is used for protection against leakage.11. SILICON RUBBER SHEET- It is used for dry type transformer.

BAY 8It is the instrument transformer and ESP transformer manufacturing section.


These are used for measurement. Actual measurement is done by measuring instruments but these transformers serve the purpose of stepping down the voltage to protect the measuring instrument. They are used in AC system for measurement of current voltage and energy and can also be used for measuring power factor, frequency and for indication of synchronism. They find application in protection of power system and for the operation of over voltage, over current, earth fault and various other types of relays.


The Electrostatic Precipitator transformer is used for environmental application. It is used to filter in a suspended charge particle in the waste gases of an industry. They are of particular use in thermal power stations and cement industry.

The ESP is a single-phase transformer. It has a primary and secondary. The core is laminated and is made up of CRGOS. It is a step up transformer. An AC reactor is connected in series with primary coil. The output of the transformer must be DC this is obtained by rectifying AC using a bridge rectifier (bridge rectifier is a combination of several hundred diodes). A radio frequency choke (RF choke) is connected in series with the DC output for the protection of the secondary circuit and filter circuit. The output is chosen negative because the particles are positively charged. The DC output from the secondary is given to a set of plates arrange one after the others. Impurity particles being positively charged stick to these plates, which can be jerked off. For this a network of plates has to be setup all across the plant. This is very costly process in comparison with the transformer cost. A relive vent is also provided to prevent the transformer from bursting it higher pressure develops, inside it. It is the weakest point in the transformer body. An oil temperature indicator and the secondary supply spark detector are also provided.

One side of the transformer output is taken and other side has a ‘marshalling box’ which is the control box of the transformer.


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In this bay power transformer are assembled. After taking different input from different bays 0-9 assembly is done Power transformer is used to step and step down voltages at generating and sub-stations. There are various ratings –11KV, 22KV, manufactured, they are

1. Generating transformer2. System 3. Autotransformer.

A transformer in a process of assemblage is called a job. The design of the transformer is done by the design deptt. & is unique of each job; depends on the requirement of customer. The design department provides drawing to the assembly shop, which assembles it accordingly.

The steps involved in assembly are:

1. Core building2. Core Lifting.3. Unlacing.4. Unlacing and end-frame mounting.5. High voltage terminal gear and low volt terminal gear mounting6. Vapour phasing and oil soaking7. Final servicing and tanking.8. Case fitting.


There are three sections in store:

1. Control Receiving Section2. Custody Section3. Scrap Disposal Section

LOCOMOTIVE PRODUCTION (LMP)There are following products are manufactured at Loco shops

Alternating Current Locomotive (ac Loco) WAG-5H AC./D.C. Loco WCAM-2P WCAM-3

W-broad gauge A-running in AC mode

C-running in DC mode G-hauling goods train

P-hauling passenger train M-hauling passenger

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& goods train

Diesel Electric Locomotive Shunting (DESL) 350 HP 700 HP Single Power Pack (SPP): One 700 HP m/c is made as a single

Unit. It is a meter gauge locomotive

Twin Power Pack (TPP): 2 350HP m/cs are combined in 1 engine & can be operated individually or in combination depending on


450 HP 1400 HP 1150 HP 1350 HP 2600 HP1150 HP and 1350 HP DESL s are non-standard locomotives and are modified versions of 1400 HP DESL based on requirement of customer.

Under mention are the new non-conventional products designed and developed for Indian Railways based on their requirement. OHE (Overhead electric) recording and testing cars UTV(Utility vehicle ) RRV(Rail cum road vehicle) DETV( Diesel electric tower car) BPRV(Battery power road vehicle) BCM(Blast cleaning machine) 200 T Well wagon for BHEL Haridwar Metro Rake-Kolkata Metro Railways

LOCOMOTIVE MANUFACTURING (LMM)This section deals with manufacturing of locomotives. The main parts of the locomotive are

Under frame: The frame on which a locomotive is built

Super structure: The body of locomotive is called superstructure or Shell and is made of sheet of Mild steel

DC motor




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Static Rectifier-MSR

Static Converter-SC


Bogie-The wheel arrangement of a loco is called a bogie. A bogie essentially contains

1-wheel axle arrangement


3-Brake rigging

Traction transformer: It is fixed on under frame and gets supply from an overhead line by equipment called pantograph. The type of pantograph depends on supply. This transformer steps down voltage and is fitted with a tap changer. Different taps are taken from it for operating different equipment. One tap is taken and is rectified into DC using MSR and is fed to the DC motor.

Railways has two types of power supplies – 25 KV, 1 Phase, 50 Hz AC

1500 V DC

An AC/DC loco is able to work on both of these supplies. For e.g. WCAM-3.


This department looks after the commissioning and maintenance of all the machinery used in the factory. It also has 3 two-stage air compressors for supplying compressed air to the various bays.

The department has 03 different divisions:

Electrical Engg. Electronics Engg. Mechanical Engg.


This division looks after all the electrical machinery and power distribution of the factory. Snags detected in the system are immediately reported to this dept by the concerning dept.WE&S takes prompt action to rectify it.

The factory has a feeder of 11KV .The total load sanctioned for the factory is 2500MVA but the maximum demand reaches the range of 1700-2000 MVA.

Here are various sub-stations (SS) inside the factory, for distribution of power to different sections.

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SS -1 Supplies Bay-6 to Bay –9

SS -3 Supplies Bay 1to Bay-4

SS -4 Supplies Boiler and loco plant

SS -5 Supplies Bay -5

SS -6 Supplies Administrative building

TECHNOLOGYThis department analyses the changes taking place in the world and suggest changes accordingly. This is very important because the products must not get obsolete in the market otherwise they will be rejected by the customer.

FUNCTIONS: Technology functions can be classified as:

Processing Sequence - The sequence of process of manufacturing is decided for timely and economic completion of the job.

Operation time estimate - It includes incentive scheme management Allowed operation time - It includes incentive amount Facilities identification - It includes looking for new equipment or plant or tools

to increase productivity Special process certification - Special processes are the ones requiring expertise

for example identifying errors, cracks, air bubbles in welding Special tools requirement - Special tools are allotted, if possible, when required

else the design has to be reconsider. Productivity projects compilation - It includes the initial analysis of the problem

and their appropriate solution to enhance productivity.The principle of working is that “IF YOU DO NOT MAKE THE CHANGES IN YOUR COMPANY, THE CUSTOMER WILL CHANGE YOU”.

CENTRAL QUALITY SERVICE First we get acquainted with a few terms concerning this department.

QUALITYIt is the extent to which products and services satisfy the customer needs.

QUALITY ASSURANCEAll those plants and systematic action necessary to provide adequate confidence that a product or service will satisfy the given requirement is called quality assurance.

QUALITY CONTROLThe operational technique and activities that are used to fulfill requirement for quality are

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quality control.

QUALITY INSPECTIONActivities such as measuring, testing, gauging one or more characteristics of a product or service and comparing these with specified requirement to determine conformity are termed quality inspection.


FINANCIAL (In Rs. /Crore)

PRODUCT 2011 – 12


2012 – 13


Growth %

Power Transformer 564 457 –19

Non Power Transformer 304 376 24

Loco 430 532 24

Total 1300 1365 5


PRODUCT Unit 2011 – 12


2012 – 13



MVA 9585 10101

ESP TRFR NOS 1280 1745





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DESL NOS 15 10




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BHEL, as an integral part of business performance and in its endeavor to becoming a world class organization and sharing the growth global concern on issues related to Environment, Occupational Health and Safety, is committed to protecting Environment in and around its own establishment, and providing safe and healthy working environment to all its employees. For fulfilling these obligations, Corporate Policies have been formulated as:

ENVIRONMENTAL POLICY Compliance with applicable Environmental Legislation/Regulation; Continual Improvement in Environment Management Systems to protect our natural

environment and control pollution; Promotion of activities for conservation of resources by Environmental Management. Enhancement of Environmental awareness amongst employees, customers and


OCCUPATIONAL HEALTH AND SAFETY POLICY Compliance with applicable Legislation and Regulations. Setting objectives and targets to eliminate/control/minimize risks due to Occupational

and Safety Hazards. Appropriate structured training of employees on Occupational Health and Safety

(OH&S) aspects. Formulation and maintenance of OH&S Management programmes for continual

improvement; Periodic review of OH&S Management System to ensure its continuing suitability,

adequacy and effectiveness; Communication of OH&S Policy to all employees and interested parties.

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Fig. Tap Changer



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A tap changer is a connection point selection mechanism along a power transformer winding that allows a variable number of turns to be selected in discrete steps. A transformer with a variable turn ratio is produced, enabling stepped voltage regulation of the output. The tap selection may be made via an automatic or manual tap changer mechanism.


If only one tap changer is required, manually operated tap points are usually made on the

high voltage (primary) or lower current winding of the transformer to minimize the current

handling requirements of the contacts. However, a transformer may include a tap changer on

each winding if there are advantages to do so. For example, in power distribution networks, a

large step-down transformer may have an off-load tap changer on the primary winding and

an on-load automatic tap changer on the secondary winding or windings. The high voltage

tap is set to match long term system profile on the high voltage network (typically supply

voltage averages) and is rarely changed. The low voltage tap may be requested to change

positions multiple times each day, without interrupting the power delivery, to follow loading

conditions on the low-voltage (secondary winding) network.

To minimize the number of winding taps and thus reduce the physical size of a tap changing

transformer, a 'reversing' tap changer winding may be used, which is a portion of the main

winding able to be connected in its opposite direction (buck) and thus oppose the voltage.



Also called No-Load Tap Changer (NLTC), off-circuit tap changer, or De-Energized Tap

Changer (DETC).

In low power, low voltage transformers, the tap point can take the form of a connection

terminal, requiring a power lead to be disconnected by hand and connected to the new

terminal. Alternatively, the process may be assisted by means of a rotary or slider switch.

Since the different tap points are at different voltages, the two connections cannot be made

simultaneously, as this would short circuit a number of turns in the winding and produce

excessive circulating current. Consequently, the power to the device must be interrupted

during the switchover event. Off-circuit or de-energized tap changing (DETC) is sometimes

employed in high voltage transformer designs, although for regular use, it is only applicable

to installations in which the loss of supply can be tolerated. In power distribution networks,

transformers commonly include an off-circuit tap changer on the primary winding to

accommodate system variations within a narrow band around the nominal rating. The tap

changer will often be set just once, at the time -of installation, although it may be changed

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later during a scheduled outage to accommodate a long-term change in the system voltage



Also called on circuit tap changer or On Load Tap Changer (OLTC).

For many power transformer applications, a supply interruption during a tap change is

unacceptable, and the transformer is often fitted with a more expensive and complex on-load

tap-changing (OLTC, sometimes LTC) mechanism. On-load tap changers may be generally

classified as either mechanical, electronically assisted, or fully electronic.

Fig. On Load Tap Changer

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Power transformers equipped with on-load tap- changers (OLTCs) have been the main components of electrical networks and industrial applications for nearly 90 years. OLTCs enable voltage regulation and/or phase shifting by varying the transformer ratio under load without interruption.

From the start of tap-changer development, two switching principles have been used for load transfer operation – the high-speed resistor-type OLTCs and the reactor-type OLTCs.

Over the decades both principles have been developed into reliable transformer components which are available in a broad range of current and voltage applications. These components cover the needs of today’s network and industrial process transformers and ensure optimal system and process control.

The majority of resistor-type OLTCs are installed in- side the transformer tank (in-tank OLTCs) whereas the reactor-type OLTCs are in a separate compartment which is normally welded to the transformer tank.

This paper mainly refers to OLTCs immersed in trans- former mineral oil. The use of other insulating fluids or gas insulation requires the approval of the OLTC manufacturer and may lead to a different OLTC de- sign, as shown in chapter.


The OLTC changes the ratio of a transformer by adding or subtracting to and turns from either the primary or the secondary winding. The transformer is therefore equipped with a regulating or tap winding which is connected to the OLTC.

The principle winding arrangement of a 3-phase regulating transformer, with the OLTC located at the wye-delta-connection in the high volt- age winding. Simple changing of taps during an energized status is unacceptable due to momentary loss of system load during the switching operation. The “make (2) before break (1) contact concept”, shown in Figure 4, is therefore the basic design for all OLTCs. The transition impedance in the form of a resistor or reactor consists of one or more units that bridge adjacent taps for the purpose of transferring load from one tap to the other without interruption or appreciable change in the load current. At the same time they limit the circulating current (IC) for the period when both taps are used. Normally, reactor-type OLTCs use the bridging position as a service position and the re- actor is therefore designed for continuous loading. The voltage between the taps mentioned above is the step voltage, which normally lies between 0.8 % and 2.5 % of the rated voltage of the transformer

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Fig switching sequence of OLTC

With a reversing change-over selector the tap winding is added to or subtracted from the

main winding so that the regulating range can be doubled or the number of taps reduced.

During this operation, the tap winding is disconnected from the main winding. The greatest

copper losses occur, however, in the position with the minimum number of effective turns.

This reversing operation is realized using a change-over selector which is part of the tap

selector or of the selector switch (arcing tap switch). The rated position is normally the mid

position or neutral position.

Fig. Switching sequence of tap selector – diverter switch (arcing switch)

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The double reversing change-over selector avoids the disconnection of tap winding during the

change-over operation. In phase-shifting transformers this apparatus called the advance-retard


Which of these basic winding arrangements is used in each individual case depends on the

system and operating requirements. These arrangements are applicable to two winding

transformers as well as to autotransformers and to phase-shifting transformers where the tap

winding and therefore the OLTC is inserted in the windings (high-voltage or low- voltage

side) depends on the transformer design and customer specifications. For regulated

autotransformers, fig. 8 shows various circuits. The most appropriate scheme is chosen with

regard to regulating range, system conditions and/or requirements, as well as weight and size

restrictions during transportation. Autotransformers are always wye-connected.

a) Three pole line-end arrangement

b) One and two pole line-end arrangement

c) Three pole mid-winding arrangement

I neutral end regulation (fig. 8 a) may be applied with a ratio above 1 : 2 and a moderate

regulating range up to 15 %. This operates with variable flux. a scheme shown in fig. 8 c is

used for regulating high voltage for low voltage U2 regulation, the circuits fig. 8 b, 8 d, 8 e

and 8 f are applicable. The arrangements fig. 8 e and 8 f are two core solutions. Circuit

fig. 8 f operates with variable flux in the series transformer, but it has the advantage that a

neutral end OLTC can be used. In the case of arrangement according to fig. 8 e, the main and

regulating transformers are often placed in separate tanks to reduce transport weight. At the

same time, this solution allows some degree of phase shifting by changing the excitation

connections within the intermediate circuit. Over the last few years, the importance of phase-

shifting transformers used to control the power flow on transmission lines in meshed

networks has been steadily increasing .The fact that IEEE provides a “guide for the

Application, specification and Testing of Phase-shifting Transformers“ proves the demand

for These transformers often require regulating ranges which exceed those normally used. To

achieve such regulating ranges, special circuit arrangements are necessary. Two examples are

given shows a circuit with direct line-end regulation, fig. 10 an intermediate circuit

arrangement illustrates very clearly how the phase-angle between the voltages of the source

and load systems can be varied by the OLTC position. Various other circuit arrangements

have been implemented.


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Apart from tap selection, the most important task of an OLTC is the break function or current

(load) transferring action. After transferring the current, the contact which “breaks” must be

capable of withstanding the recovery voltage. The required switching capacity (the product of

switched current and recovery voltage) for a specific contact in an OLTC is based on the

relevant step voltage and cur- rent but is also determined by the design and circuit of the

OLTC. The switching capacity itself is primarily a function of the contact design, contact

speed and arc-quenching agent.

Historically, most power transformers use mineral oil as a cooling and insulation medium.

The development of OLTCs toward the present “state of the art” de- signs also focused on

transformer oil. Apart from the insulation properties of the transformer oil, the arc- quenching

behavior of the switching contacts deter- mined the design and size of “oil-type” OLTCs.

In an oil-type OLTC, the OLTC is immersed in trans- former oil and switching contacts make

and break current under oil. This conventional OLTC technology has reached a very high

level and is capable of meeting most of the transformer manufacturers’ requirements. This

applies for all the voltage and power fields today, which will probably remain unchanged in

the foreseeable future.

Along with the increase in demand for electrical energy in metropolitan areas, the necessity

for installing transformers in buildings creates a need for regulating transformers with

reduced fire hazards. In addition to this and with respect to the prevention of water pollution,

regulating transformers that do not require conventional mineral oil as an insulating or

switching medium are preferable.

Apart from gas-immersed transformers, which are mainly used in Japan, dry-type

transformers and trans- formers with alternative insulating fluids meet these requirements,

which are increasingly being requested.

Conventional tap-changers are not really suitable for this kind of regulating transformers,

because the use of mineral oil as a switching medium is – for the rea- sons mentioned above –

not desirable and would also require technically complex and expensive overall solutions.

In addition, worldwide deregulation in the electric industry is still a concern. As part of this

market, mechanisms have been encouraged to price transmission services and encourage both

generation and trans- mission investment.


The OLTC design that is normally used for higher ratings and higher voltages comprises a diverter switch (arcing switch) and a tap selector. For lower ratings, OLTC designs in which

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the functions of the diverter switch (arcing switch) and the tap selector are combined in a selector switch (arcing tap switch) are used.

With an OLTC comprising a diverter switch (arcing switch) and a tap selector, the tap-change operation takes place in two steps. The next tap is first preselected by the tap selector at no load. The diverter switch then transfers the load current from the tap in operation to the preselected tap. The OLTC is operated by means of a drive mechanism. The tap selector is operated by a gearing directly from the drive mechanism. At the same time, a spring energy accumulator is tensioned, which operates the diverter switch – after release at a very short time interval – independently of the motion of the drive mechanism. The gearing ensures that this diverter switch operation always takes place after the tap preselection operation has finished. The switching time of a diverter switch is between 40 and 60 Ms with today’s designs. During diverter switch operation, transition resistors are inserted which are loaded for 20–30 Ms, i.e. the resistors can be designed for short-term loading. The amount of resistor material required is therefore relatively small. The total operation time of an OLTC is between 3 and 10 seconds, depending on the respective design.

A selector switch (arcing tap switch) as shown in carries out the tap-change in one step from the tap in service to the adjacent tap. The spring energy accumulator, wound up by the drive mechanism actuates the selector switch sharply after releasing.

Fig. oil type OLTC



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The OILTAP® M on-load tap-changer is used to vary the ratio of oil-immersed transformers under load. In general it is designed for network transformer as well as industrial transformer applications. The tap-changers comprise a diverter switch and a tap selector in a single column design and represent the most recent state of technology. The tap-changers offer both transformer manufacturer and user a great number of essential advantages.

Fig. OLTC type M


– three-pole design for neutral application at 350 A, 500 A and 600 A ratings for three-phase wye-connected windings

– single-pole designs at 350 A, 500 A, 600 A, 800 A, 1200 A and 1500 A ratings for auto connected windings or single-phase transformers

– available with ±9, ±11, ±13, ±15, ±17 steps – insulation to ground and tap selector size can be selected independently of one another

– convenient for bell-type tank installation – additional devices for potential tie-in of tap winding during change-over operation of the change-over selector (tie-in resistors, potential contact)


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– high speed transition resistor type diverter switch with arc extinction at the first current zero

– diverter switch uses snap-action mechanics by energy accumulator mounted directly on the diverter switch

– minimum possible tap selector dimensions because four available sizes ensure matched impulse voltage with stand ability

– radial dimensions of the tap selector are reduced by special shaping of all parts on high potential, distances between tap selector bars determined by actual voltage stress – optimised integration of the change-over selector into the fine selector contact circle


– rapid tap change operation, low thermal stress on the transition resistors– diverter switch arcing contacts made of tungsten-copper alloy at 500 A and

above– –simple tap selector design, effective contact cooling, high short-circuit with

stand ability– tap selector gear with steady torque during the tap changer operation


– oil-immersed installation of the entire tap-changer in the transformer main tank

– simple to connect– drive shaft and pipe connections easy to orientate– straight forward coupling to motor drive unit


– long contact life– quick and easy to disassemble diverter switch insert– simple to adjust and control– oil suction pipe built-in– diverter switch contacts easy to replace


An on-load tap-changer is normally used in power transformers in an electric grid, where its function primarily is to keep a constant voltage out from the transformer. Some on-load tap-

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chargers are used in transformers where their function is to control the power of the transformer by regulating the voltage. The on-load tap-changer can be described as a mechanical switching device that will change the turn ratio in the transformer without interrupting the load current. This makes it possible to keep a constant voltage out from the transformer and to compensate for variations in the load.

A common on-load tap-changer generally consists of a motor drive unit, an axis system, a diverter switch with a housing, and a selector mounted under the diverter switch. Such an on-load tap-changer is named a diverter switch type. Another on-load tap-changer, wherein the selector and the diverter switch are merged into the same unit is named a selector switch type.

The main objective of an electric motor drive unit is to drive the connected on-load tap-changer to a higher or a lower tap of a transformer. Electric motor drive units for tap changers are rather complex and the cost for their production and assembly- is considerable. Further, electric motor drive units are to a large extent order designed, with a customer requirement as basis, which further increases cost for their production and assembly.

Fig. Motor assembly for OLTC


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An object of the present invention is to provide an electric motor drive unit for tap-changers which is adaptable to different customer requirements.

The invention is based on the realization that by providing an on-load tap-changer with an electric motor drive unit at a minimum the following advantages are achieved:

• Reduced lead time in production

• Flexibility for late order changes

• Service friendly design

• Reduced tap-changer motor drive cost


A relay is automatic device which senses an abnormal condition of electrical circuit and closes its contacts. These contacts in turns close and complete the circuit breaker trip coil circuit hence make the circuit breaker tripped for disconnecting the faulty portion of the electrical circuit from rest of the healthy circuit. The protective relay is designed to protect the on-load tap-changer and the transformer during a malfunction within the on-load tap-changer or the selector switch oil compartment. It trips when the specified oil flow speed between the on-load tap-changer head and the oil conservator is exceeded. The protective relay must be connected so that the transformer is immediately isolated from the power when the protective relay trips.

Fig Protective Relay


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Due to the special arrangement of the tap-changer phases in three columns, the horizontal drive shaft must be mounted between the three tap-changer heads above the tank cover. Since a swivelling of the upper gear unit will initiate a switching action, make sure that the adjustment position of the diverter switch is re- gained after the alignment of the gear units.

Fig Drive Shaft and Bebel Gear


Check that the operating positions of all columns are identical (tap-changer head, inspection window). Each one of the one-phase OLTCs must be in the adjustment position.

Turn the upper gear unit of the tap-changer heads into the desired installation position and fix them there (tighten thrust collars and tab-lock the screws).

Take note of the arrow on the drive shaft flange below the punched serial number. The direction of the arrow indicates the rotation sense when crank- ing the motor drive clockwise and must be identical on all gear units.

Operate the tap-changer poles separately by one step by rotating the trunnions counter-clockwise until the diverter switch operates once. Check coincidence of operating positions of all tap-changer heads.

Mount the horizontal drive shaft between the tap- changer heads. Return the OLTC set that is all tap-changer poles together, into the adjustment

position. The adjustment position is reached by turning the drive shaft in clockwise direction. Check simultaneous operation of all diverter switches. Check coincidence of position of all tap- changer heads and the motor drive unit.

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Mount the vertical drive shaft.

Make sure that bevel gear serial number and on-load tap-changer serial number are identical. The horizontal drive shaft must be in proper alignment with the trunnion in the tap-changer head. After loosening the thrust collar (6 bolts M8, was. 13) the upper gear unit can be swivelled (fig. 39). After adjusting the upper gear unit, the thrust collar must be re-tightened (max. torque 15 Nm). Tab-lock the screws. In case of bevel gears in special design and intermediate bearings of the vertical or horizontal drive shaft above instructions apply analogously.

Square shafts, coupling brackets, coupling bolts, screws, nuts and lock tabs are made of corrosion-proof steel. We recommend, however, to apply the same outside coating here as to the transformer tank. The square shafts and the guard plate for the footstep protection for the horizontal drive shaft at the trans- former cover are supplied in oversize (various standard lengths). These parts must be cut to the required size before mounting. Finally equalize the rotation lag between on-load tap- changer and motor drive unit will be completed.

Fig. Bebel Gear Assembly


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To mount the tap-changer head to the transformer cover a mounting flange is necessary. This mounting flange should meet the requirements of the tap-changer head gasket surface.

Fig. Drawing for mounting tap changer

To position the thread studs (M12, max. length = 45 mm) we recommend the use of a drilling template. If requested, the drilling template will be supplied without charge with the first on-load tap-changer type R.

Fig. Drilling template


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The diverter switch oil compartment is lowered through the cover aperture (= mounting flange) of the trans- former. The tap-changer head is attached to the mount- ing flange by means of bolts. Then, the tap selector is fastened to the diverter switch oil compartment.


Place the diverter switch oil compartment on a level surface. Clean sealing surfaces of mounting flange and tap- changer head. Put an oil-proof gasket on the mounting flange of the transformer cover. Lift the diverter switch oil compartment by hooking up the tap-changer head. Lower

the oil compartment cautiously into the mounting flange. Take care of screening rings (with Um ≥ 170 kV only). 5. Check position of tap changer head.

Attach the tap-changer head to the mounting flange with bolts.


Remove the blocking plate from the coupling (shown in figure below) of the oil compartment bottom.

Fig Removal the blocking plate


Raise the tap selector to the oil compartment and attach. At the same time the mechanical coupling for the tap selector drive has to be performed. Finally, connect the tap selector connecting leads to the diverter switch oil compartment.


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Put the tap selector down on a level surface. Get ready 4 lock nuts M12 with washers.


Remove the blocking strip from the tap selector coupling. The coupling must not be displaced afterwards

Fig. Removal of blocking strip

2. Put the tap selector on an appropriate lifting device. Remove the ring nuts. Raise the tap selector to the diverter switch oil compartment. Be sure that tap selector

connecting leads clear the diverter switch oil compartment and remain undamaged. Position coupling parts and attachment points of tap selector and oil compartment to

match properly. Raise the tap selector to its final height.

Fig. Raising of tap selector Bolt tap selector attachment points to the oil compartment bottom: 4 lock nuts M

12/w.s.19, washers, maximum torque 65 Nm. Remove the wooden support from the laterally attached change-over selector.

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OLTCs R III 1200 and R I 3000/3600:

6 connecting leads to oil compartment terminals according to Each one attached by 1 bolt M12 (w.s.19) lock nut and screening cap, torque 80 Nm.

Fig. 6 connecting leads to oil compartment terminals

OLTC R I 2002/2402:

4 connecting leads to oil compartment terminals according to Each one attached by 1 bolt M12, lock nut and screening cap, torque 80 Nm.

Fig. 4 connecting leads to oil compartment terminals


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Firstly, lift the on-load tap-changer into the supporting structure and connect it to the tap winding. The OLTC must be attached to the supporting structure in such a way that it cannot be displaced. The supporting flange is provided with through-holes which allow it to be fixed to the supporting structure. It is advisable to put spacer blocks temporarily between supporting structure and supporting flange and to remove them before the bell type cover is set up.


The assembly of diverter switch oil compartment and tap selector as well as the connection of tap selector connecting leads has to be carried out according to section Lift the assembled on-load tap-changer, into the supporting structure. Make sure that the on-load tap-changer is in proper mounting position and fasten it there safely.

Prior to setting up the bell-type tank the tap-changer head must be removed from the on-load tap-changer.

1. For this purpose, open the tap-changer head cover (24 hexagonal head screws M10, w.s.17, with lock washers).

2. Take care of the cover gasket.

3. Remove the position indicator dial.

Fig. Removal the clip from the shaft end

4. Take note of the red-marked area not covered by the supporting plate of the diverter switch unit.

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Fig. -marked area not covered by the supporting plate

5. Remove the fixing nuts of the supporting plate (4 nuts M8, w.s.13, lock washers,

Fig. Remove the fixing nuts of the supporting plate

6. Withdraw the diverter switch unit carefully from the oil compartment. Keep the diverter switch unit in a vertical position.

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Fig. Withdrawing of the diverter switch unit

7. Remove the suction pipe. The pipe connection has to be withdrawn from within the tap-changer head. Take care of O-rings.

Fig. withdrawing of pipe connection

8. Unscrew the remaining nuts in the tap-changer head, 17 nuts M8, w.s.13. lock washers. Lift off the tap-changer head from the supporting flange. Take care of the gasket.

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Fig. Unscrewing of the remaining nuts in the tap-changer


1. Before mounting the bell-type transformer cover clean the sealing surface of the oil compartment supporting flange. Place the gasket onto the flange. Withdraw the spacer blocks.

Fig. Placing of the gasket onto the flange

2. Lift the bell-type cover over the transformer active part and lower it to its final position.

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3. Before mounting the tap-changer head clean the sealing surfaces (bottom of tap-changer head, mounting flange). Put an oil-resistant gasket on the mounting flange.

4. Place the tap-changer head on the mounting flange. Check the mounting position of the tap-changer head by means of 2 adjusting bolts and the marks of the supporting flange and tap-changer head which allow assembly in the correct position only. Depending on the final height adjustment leave a clearance of 5 to 20 mm between tap-changer head and supporting flange.

Fig. Place the tap-changer head on the mounting flange

5. Lift the on-load tap-changer slightly by means of the lifting traverse. Make sure that all supporting flange studs easily slide through the fixing holes of the tap- changer head.

Fig. lifting of tap changer

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We recommend to ratio-meter the transformer with a low AC voltage before drying. To operate the drive shaft in the tap-changer head a short tube of nominal width 25 mm with an insert coupling bolt of 12 mm dia. together with a hand wheel or a hand crank may be used.

In case of OLTC set 3 x RI2002 ... 3600 all three tap- changer heads have to be coupled by the horizontal drive shafts.

When using an ED, 16.5 drive shaft revolutions of the tap-changer drive shaft are required for one tap-change operation. The diverter switch action can be heard distinctly.

Fig. Tap changer head cover

To operate the change-over selector a higher torque is necessary. The end positions shown on the connection diagram supplied with the delivery must never be overrun. It is therefore necessary to check the operating position through the inspection glass in the tap-changer head cover. Keep the number of tap-change operations to a minimum as long as the on-load tap-changer has not been immersed in oil. After the transformer ratio test the on-load tap-changer has to be set back to the adjustment position in which it was delivered by MR. The position is indicated in the connection diagram delivered with the equipment.


If the transformer is to be vapour phase dried in its own tank, open the kerosene drain plug.

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Before applying voltage to the transformer check the mechanical operation of on-load tap-changer and motor drive.

For these test operations the on-load tap-changer has to be run through the complete operating cycle. Make sure that in each operating position the indicators of motor drive and on-load tap-changer (tap- changer head) read the same position. Make sure that in both end positions the electrical and mechanical limit stops function automatically.

Misalignment between on-load tap-changer and motor drive unit exists, if on-load tap-changer and motor drive unit show different operating positions. Misalignment of coupling between on-load tap- changer and motor drive unit leads to severe damage of on-load tap-changer and transformer, if operation is continued. The transformer must not be taken in operation.

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If the transformer is to be transported without the motor drive unit, set the motor drive to the adjustment position and uncouple. To remount the motor drive unit follow the instructions.

Install this by-pass tube between pipe connections E2 and Q of the tap-changer head. For short time conditions of 2 to 4 weeks without oil conservator, lower the oil level by approx. 5 litres.

If the transformer is to be transported or stored without oil filling, drain the oil of the on-load tap-changer completely.

The interior of the on-load tap-changer should be conserved and protected in the same way as the transformer itself (nitrogen-sealing).

If a prolonged stand-by period is expected, the heater of the motor drive unit must be connected to the suitable power supply.


If the transformer is filled with oil but stored or trans- ported without oil conservator, a bypass tube must be installed between the interior of the tap changer and the transformer tank to compensate the static pressure caused by expansion of oil.


Do not operate the motor drive unit while the on-load tap-changer is uncouple.


Before putting the transformer into service, operational tests of on-load tap-changer and motor drive have to be performed. At the same time check the function of the protective relay. Loop in signalling contact for undershooting the minimum oil level in the on-load tap-changer oil conservator in the on-load tap-changer tripping circuit. Make sure that the circuit breakers switching off the transformer operate when the test push button »OFF« is pressed. Be sure that they energize the transformer only after push button »IN SERVICE« of the protective relay has been pressed. After the transformer has been energized, tap-change operations under load can be performed. Gas accumulating under the cover of the tap-changer head will cause minor oil displacement and/or escape via the oil conservator.


The protective relay has to be inserted into the trip- ping circuit of the circuit breakers so that energization of the protective relay switches off the trans- former immediately (see Operating Instructions No. 59 for protective relay RS 2001).

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It is only necessary to inspect the tap-changer head, the protective relay and the motor drive unit occasionally.


•oil tightness of sealings of the tap-changer head, the protective relay and the pipe connections,

•sealings at the motor drive housing,

•proper function of the electrical space heater inside the motor drive unit,

•the condition of the control devices in the motor drive unit.


Damage to the on-load tap-changer due to not enough oil in the oil conservator of the on-load tap- changer! Actuation of the on-load tap-changer with too little oil in the on-load tap-changer’s oil conservator may cause damage to the on-load tap-changer! Make sure that the contact for signaling the falling below the minimum oil level in the on-load tap- changer’s oil conservator was looped through to the tripping circuit of the circuit-breaker and that the circuit-breaker will immediately de-energize the transformer when the oil has fallen below this minimum oil level in the oil conservator.


If the protective relay operates, do not reset until the on-load tap-changer and the transformer have been checked. For this purpose also withdraw the diverter switch unit and check it according to our Inspection Instructions. Proceed in detail according to our Operating Instructions No. 59 for the protective relay RS 2001.

Before returning to energized operation, make sure that the cause of the trouble has been corrected and that the on-load tap-changer and the transformer are free of damage.

Never reconnect the transformer without prior checking. Continued operation of the on-load tap changer can result in severe damage of on-load tap- changer and transformer.


In general, the inspection can be carried out by qualified and MR-trained personnel within one day, provided it is well prepared and organized.

We strongly recommend to have inspections performed by our Technical Service. This guarantees a professional performance including all the latest updating measures.

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Inquire for spare parts when preparing an inspection which will not be carried out by MR personnel (please indicate OLTC number and number of operations).

The number of tap-change operations determining the inspection intervals indicated in table II and table III are figures based on experience with oil qualities normally used.

The tap selector of the on-load tap-changer is generally maintenance-free. In special cases, however, if OLTCs are used in industrial transformers where high operating numbers are to be expected, our technical service department must be contacted after about 1,000,000 operations. The diverter switch insert of the OLTC is to be replaced after 800,000 operations.

If the number of operations per year is 15,000 or higher, the use of our oil filter plant type OF100 with paper filter insert is recommended. The use of our oil filter plant type OF100 with combination filter insert is obligatory for OLTC type R with insulation to ground Um < 245 kV. Filtering of switching oil allows to extend the inspection intervals.

The user should regularly test the transformer insulating oil according to the relevant standards.

If inspection has not been performed by MR-personnel, please give us your report for data collecting purposes.


The tap-changing equipment must be inspected at regular intervals to maintain a high level of operating reliability.


Inspections of the tap-changer equipment are obligatory. Disregarding the inspection intervals endangers the trouble-free operation of on-load tap- changer and transformer.

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This report clearly replicates the tremendous growth of a company which continuously renovated its technology to contribute not only in the infrastructure building in India but also of the world.

It is an asset for our country to have such a public sctor industry which has fulfilled the dream of our first Prime Minister Sh. Jawaharlal Nehru by operating in 65 countries and making it to global.

The vision and mission of this company are successful can be adjudged with the faith of the stake holders in this company.

BHEL Jhansi although a smaller unit in comparision to otherunits of BHEL, is a very productive one with the manufacturing of the electric locomotives, power transformers etc.

The work load here can be accessed from the fact that the order of the locomotives has forced the company to shift its Bus Duct section to other unit of BHEL.

In future also the company is having orders of metro coaches and this clearly shows why this company is still recession proof.

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Dr. Dieter Dohnal, Electrical Machines

G. Spence, A. C. Hall, “On-load Tap-changers Current Experience and Future Development; Users Experience and Perspective,” IEEE European Seminar on Developments On-Load Tap Changers: Current Experience and Future, 9 November 1995.

M. Runde et al, “Acoustic Diagnosis of high voltage circuit-breakers,” IEEE Transactions on Power delivery, Vol.7, No.3, July 1992.

V. Demjanenko et al, “A noninvasive diagnostic instrument for power circuit breakers,” IEEE Transactions on Power delivery, Vol.7, No.2, April 1992.

S. Tenbohlen, M. Stach et al., “Experience-Based Evaluation of Benefits of On-line Monitoring Systems for Power Transformers”, CIGRE Session 2002, paper 12-110, Paris, 2002.

A case study Rupali Vibhute" ,R.M.Holmukhe2 Mr.P.S. Chaudhari", Mr.T.S.Hasarmani4 1.4postGraduate Student, Electrical Engineering Department, 2Assistant Professor, Electrical Engineering Department, Bharati Vidyapeeth Deemed University, College of Engineering, Pune, India 3Scientist ,DRDO, Pune

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