REPORT ON TRANSFORMER MANUFACTURING

INDUSTRIAL TRAINING REPORT ON MANUFACTURING OF POWER AND DISTRIBUTION TRANSFORMER

SUBMITTED BY RAJ MOYAL Roll no.-084022 3rd year B.Sc.Engg(Electrical) Faculty of Engineering Dayalbagh Educational Institute

ACKNOWLEDGEMENT I underwent training program of thirty days from 1st of June 2010 to 5th of July 2010 in Marsons Electrical Industries which is the leading transformer company in India.For this training program I would like to thank Mr.Umasankar Jaiswal,Q.C.Manager of the Marsons Electrical Industries who arranged the training for me .And also I would like to thank the whole staffs of the company for their guidance and kind supervision and who cooperate with us. I am also thankful to Mr.V.P.Pyara ,Head of department(HOD) of electrical engineering and Mr.V Soami Das,Training Incharge ,who filled confidence in me to go ahead in my life and face all difficulties with courage.

(RAJ MOYAL)

2

LAYOUT

3

INTRODUCTION

4

The Company Established in 1973, Marsons is a leading player in the business of manufacturing to Transformers based in India.It is situated at national highway no.2,artoni ,agra (uttar Pradesh). It is an ISO 9001 certified company having an extensive product range of Power & Distribution Transformers from 10 KVA to 20,000 KVA .Almost 400 workers are employed in the industry.Marsons has a sale turnover of about 500 million.it meet the requirement of several state electricity board and it has its client in the foreign countries as U.K,Nigeria,Africa,yemen and Syria.It has well established in the market of Indian power sector. It products are designed to meet the requirement of the global market.

Design and R & D MARSON'S Transformers are designed to meet all the latest national and international standards, including IS, IEC, ANSI, BS, DIN etc. All Marson's Transformers are designed in accordance with customers' specific requirement. High levels of experience and expertise in transformer design and regular investment in research and development has enabled Marson's to ensure excellence and competitiveness in quality, performance, price and delivery. Wide range of Transformers are tested and validated by authorized testing laboratories. All material used are of best quality and of the class most suitable for working under the specified conditions withstanding variations of temperature and atmospheric conditions. Above all, the design incorporates every reasonable precaution and provision for the safety of all those concerned in the operation and maintenance.

The Technology for Manufacturing Oil-immersed Power & Distribution Transformers

5

Marson's corporate thinking is driven by the commitment to quality.The complete in house manufacturing process helps us to ensure optimum quality of the transformer. We have complete testing facility to test and check all the major rawmaterials used in manufacturing the transformer. CRGO laminations are cut and annealed in house to achieve minimum magnetic flux distortion. To ensure the best quality of the Coils of the transformer, winding wires and strips are also manufactured in house.Fabrication section ensure the robustness, quality and fine finish of the tank and radiators of the transformer.Marsons produces several types of transformer as corrugated wall panel,self protected type,ground mounted, hermetically sealed type with gas cushion. e complete test The

manufacturing process of Transformer cover the following      

Fabrication of tanks Core Assembly Coil Winding Core-Coil Assembly Tank-up Transformer Tank Painting & Finishing

.

INTRODUCTION ABOUT TRANSFORMER Transformer is an ac machine that transfers electrical energy from one electrical circuit to another without changing frequency by the principle of electro magnetic induction.Since it’s basic construction requires no moving parts so it is often called the static transformer and it is very rugged machine requiring the minimum amount of repair and maintenance.Owing to the lack of rotating parts there are no friction or winding losses.Further ,the other losses are very low so that the efficiency should be high.The efficiency varies from 97% to 99%.

OPERATING PRINCIPLE 6

The action of a transformer is based on the principle that energy may be efficiently transferred by induction from one set of coils to another by means of varying magnetic flux , provided that both the sets of coils are on a common magnetic circuit.The emfs are induced by the variation in the magnitude of flux with time.It is based on Faradays law of electromagnetic induction.

POWER TRANSFORMER The term is used to include all transformers of large sizes(250kva and above) used in generating stations and substations for transforming the voltage at each end of a power transmission line.They may be single or three phase and voltage rating of 220/11kv or in high voltage range.They are put in operation during load hours and disconnected during light load hours or operated on full load.So power transformer are desined to have maximum efficiency at full load(i.e.with iron loss to full load copper loss ratio of 1:1).

DISTRIBUTION TRANSFORMER Transformer of rating upto 200kva,used to step down the distribution voltage to a standard service voltage are known as distribution transformer.They are kept in operation all the 24 hours a day.In such transformer iron loss occur for all the time where copper loss occur only when they are loaded.Therefore,distribution transformers should be designed with iron loss smaller in comparision to full load copper loss(say with iron loss to full load copper loss ratio 1:3)

TRANSFORMER PARTS AND ACCESORIES

7

TECHNICAL PARAMETER OF TRANSFORMER Transformer shall be oil immerged ,hermetically sealed with corrugated tank.The technical parameters of the transformer shall be as below..

8

9

FABRICATION SHOP 10

Transformer tanks are fabricated in this department.Fabrication include cutting of sheets,straightening,bending,welding of sheets and parts of tank. It has three sub shop 1.Sheet cutting 2.Machine shop 3.Welding shop Machine shop has following machines

CNC Hypertherm automation machine

it is used for cutting metal based on design automatically. Gas used methane hydrogen operating plasma system completes an electric circuit between the torch and the workpiece.Specification microprocessor control system Model FINCUT DP Rail length 10000mm Rail garage 3500mm Input voltage 220v ac Total power 5000VA IS NO.10138

Pneumatic Searing machine

This machine is used to cut large sheets and thick sheets but upto certain limit .The machine holds the sheet firmly as pressure is given through compressure chamber.The pressure is being set manually.These are provided with pneumatic clutch brake.

Punch press

This is used to cut different shapes on sheet by using different dies .The dies are made of steel.

Bend hydraulic machine

This machine is used to bend sheets without any distortion.These machines are known for sturdiness,higher efficiency and reliability.They bend the sheets at an angle of 90 degree.

11

Rolling machine

This is used to straightened or to roll the sheets as per requirement.Roll can be at any extent .After cutting of sheets ,they are introduced into it for straightning.

Lathe machine

It is multipurpous machine and is used for giving shape to the fittings of transformer tank like lifting lugs and jacking lugs.

CORE AND CORE ASSEMBLY Core is magnetic link between the two systems connected to the transformer.The core material and it’s construction should be such that the maximum flux is created with minimum magnetizing current and core loss.Steel core cause total flux linking of primary to secondary.The high content of silicon increses the resistivity of the core,hence reduces the eddy current loss.It also has a high permeability at low flux density and narrow hysteresis loop.The steel used for cores may be hot or cold rolled .The cold rolled has more flux density (1.8T) than hot rolled(1.45T) as it has better magnetic properties in the direction of rolling and it also reduces the amount of core material. As the flux in the core is pulsating one,so cores must be laminated.The laminations are put through annealing process.The thickness of lamination varies from 0.35mm to 0.5mm. These laminations are assembled in such a manner that there is no air gap between the joints of two consecutive sheets.The core assembly is done accourding to the weight of the core as the number of plates are decided on the basis of it .

12

The entire assembly is done on a frame commonly known as core channel. These frames being used as a clamping support of the core assembly. Three-phase transformer usually employ three-leg core..The sectional areas of the yoke and side leg are 50% of that of the main leg; thus, the core height can be reduced to a large extent compared with the two leg core.For core material, high-grade, grain oriented silicon steel strip is used connected by a core leg tie plate;fore and hind clamps by connecting bars. As a result, the core is so constructed that the actual silicon strip is held in a sturdy frame consisting of clamps and tie plates,which resists both mechanical force during hoisting the core-andcoil assembly and short circuits, keeping the silicon steel strip protected from such force.In large-capacity transformers,which are likely to invite increased leakage flux, nonmagnetic steel is used or slits are provided in steel members to reduce the width for preventing stray loss from increasing on metal parts used to clamp the core and for preventing local

13

overheat.The core interior is provided with many cooling oil ducts parallel to the lamination to which a part of the oil flow forced by an oil pump is introduced to achieve forced cooling.When erecting a core after assembling, a special device shown is used so that no strain due to bending or slip is produced on the silicon steel plate.The steel strip surface is subjected to inorganic insulation treatment.. Yokes are jointed at an angle of 45 degree to utilize the magnetic flux directional characteristic of steel strip.A computer-controlled automatic machine cuts grain-oriented silicon steel strip with high accuracy and free of burrs, so that magnetic characteristics of the grain-oriented silicon steel remains unimpaired.Silicon steel strips are stacked in a circle-section. Each core leg is fitted with tie plates on its front and rear side, with resin-impregnated cotton tape wound around the outer circumference. Sturdy clamps applied to front and rear side of the upper and lower yokes are bound together with tape.And then, the resin undergoes heating for hardening to tighten the band so that the core is evenly clamped .Also, upper and lower clamps are evenly tight.

COIL WINDINGS

14

Windings form another important part of transformers.In a transformer,the high and low voltage windings are so designed that the axial short circuit force is reduced to minimum.Transformer winding are made of copper or aluminium strip conductor.Heavy current capacity needs conductors of large cross section.To reduce eddy current losses in the conductors ,several small wires or parallel straps are preferred to one large strap.This give rise to unequal reactance of the component of the conductors which can be eliminated by transposition of conductors.Instead of placing primary on one limb and secondary on the other limb it is usual practice to wind one half of each winding on each limb.This ensures tight coupling between the two windings.consequently leakage flux is reduced.The positioning of the hv and lv winding with respect to core is also very important from the point of view of insulation requirement.If hv winding were placed next to the core ,it would be necessary to insulate it from the core and lv winding and two layer of hv insulation would be required.By placing hv winding outside and around the lv winding only one layer of hv insulation would be required. The one which is connected to a voltage source and creates the flux is called as a primary winding. The second winding where the voltage is induced by induction is called a secondary.It may be more appropriate to designate the windings as High Voltage (HV) and Low Voltage (LV) windings. The winding with more number of turns will be a HV winding. Continuous Disk Winding The disc coils as the name suggest,consist of number of flat coils or discs connected in series or parallel.The coils are formed with rectangular strips wound spirally from centre outwards in the radial direction.The conductor used is in such length as are sufficient for complete winding or section of winding between tappings.The conductor can be single strip or number of strips in parallel,wound on the flat side.This gives robust construction for each of the discs.The discs are wound on an insulating cylinder spaced from it by

15

strips along the length of cylinder .The discs are separated from each other with press board sectors attached to vertical strips.The vertical and horizontal spacers provide radial and axial ducts for free circulation of oil which comes in contact with every turn.Continuous discs winding are reliable and strong and ,therefore,they are widely employed both as lv and hv windings in large rating transformers. Interleaved disk winding In this winding, electrically isolated turns are brought in contact with each other as shown. Thus, the winding is termed "interleaved disk winding." Since conductors 1 - 4 and conductors 9 - 12 assume a shape similar to a wound capacitor, it is known that these conductors have very large capacitance.This is the most general type applicable to windings of a wide range of voltage and current. This type is applied to windings ranging from 350kV to 1550kV.Rectangular wire is used where current is relatively small, while transposed cable is applied to large current. When voltage is relatively low, a transformer of 100MVA or more capacity handles a large current exceeding 1000A. In this case, the advantage of transposed cable may be fully utilized.Further, since the number of turns is reduced, even conventional continuous disk construction is satisfactory in voltage distribution,thereby ensuring adequate dielectric characteristics. Also,whenever necessary, potential distribution is improved by inserting a shield between turns. Cross over winding. These are made of circular conductors not exceeding 5 to 6 sq mm in cross section. These are used for HV windings of relatively small transformers. These turns are wound in several layers.The length and thickness of each block is made in line with cooling requirements. A number of such blocks can be connected in series, leaving cooling ducts

16

in between the blocks, as required by total voltage requirement. Helical winding One very common cylindrical coil arrangement is the helical winding. For windings of low voltage (20kV or below) and large current, a is helical coil is used which consists of a large number of parallel conductors piled in the radial direction and wound.This is made up of large cross section rectangular conductor wound on its flat side.The coil progresses as a helix. This is commonly used for LV windings. The insulation requirement also is not too high. Between layers no insulation (other than conductor insulation) is needed as the voltage between layers is low. The complexity of this type of winding rapidly increases as the current to be handled becomes more. The conductor cross section becomes too large and difficult to handle. The eddy current losses in the conductor rapidly increases. Hence two or more conductors have to be wound and connected in parallel. The parallel circuits bring in problems of current sharing between the circuits. Transpositions of the parallel paths have to be adopted to reduce unequal current distribution. The modern practice is to use continuously. transposed and bunched conductors

17

Coil assembly 1. High Voltage Coils: H.V. Coils are the components of finished transformers. They are made on automatic layer setting winding machines. A solid cylindrical former of predetermined diameter and length is being used as base over which it is made. 18

Generally round insulated wire of either copper (Cu) or Aluminium (Al) is used as basic raw material. The coils are made in number of layers. The starting and finishing leads of each coil are terminated on either side of the coil. These leads are properly sleeved and locked at number of points. 2. Low Voltage Coils: L.V. Coils are also one of the components of transformer. The procedure of making low voltage coil is generally same as described earlier. The shape of the basic raw-material (Al or Cu) is rectangular. The Test: The "Turn Test" is carried out on the H.V. Coils as per the specifications.

CORE COIL ASSEMBLY The components produced in the coil winding and core assembly stage are then taken into core-coil assembly stage. The core assembly is vertically placed with the foot plate touching the ground. The top yoke of the core is removed. The limbs of the core are tightly wrapped with cotton tape and then varnished. Cylinder made out of insulating press board/ pressphan paper is wrapped on all the three limbs. Low Voltage Coil is placed on the insulated core limbs. Insulating block of specified thickness and number are placed both at the top and bottom of the L.V.Coil. Cylinder made out of corrugated paper or plain cylinder with oil ducts are provided over L.V.Coil. H.V. Coils are placed over the cylinder. Gap between each section of H.V. Coils including top & bottom clearances is maintained with the help of oil ducts, as per the design/drawings. The Top Yoke is refilled. Top core frame including core bolts and tie rods are fixed in position. Primary and secondary windings are connected as per the requirements. Phase barrier between H.V. phases are placed as per requirement. Connections to the tapping switch (if required) are made. Finally, the component is placed in the oven.

19

Transformer Tank Marson’s will have an in-house facility for manufacturing transformer tanks. All tanks are made of high quality steel and can withstand vaccum as specified by the international standards and the customer. All welds are tested, ensuring 100% leak proof of seams and mechanical strength. All transformer tanks are given a smooth finishing by using the "SHOT BLASTING" process. Transformer tanks commonly used are of the following types; 1. Plain sheet steel tank. 2. Sheet steel tank with external cooling tubes. 3. Radiator tanks. 4. Tanks with corrugated wall panels The tank is manufactured by forming and welding steel plate to be used as a container for holding the core and coil assembly together with insulating oil. Transformer tank offers the following features:Subjected to automatic beam welding machine and other special facilities, the tank possesses high quality and strength.Transformers to be transported by ship are structured in a semioval shape on both ends of the tank and provided with reinforcement members rationally arranged, resulting in increased strength and decreased weight.The tank bottom is fitted with a skid base by welding and provided with pull lugs to facilitate rolling in the longitudinal and transverse directions.Capable of withstanding a high vacuum of 0.1 torr or below, the tank can be filled with oil under a vacuum; to thoroughly remove gases and moisture from the insulation.The tank is of completely enclosed,welded construction.Oilproof nitrile rubber gaskets are used on those parts which must be removed from the standpoint of assembly in the field or during maintenance; flanges thereon are provided with

20

machined grooves or gasket retainers to ensure proper tightening of gaskets. Consequently, there is no possibility of oil leakage over an extended period.

TANK UP Assesories - spanner,hammer,plyier,knife,nose plyier,ring snapper,slide ringe,crimping tools,blower,megger instrument,chisel,tape scale,micrometer The core-coil assembly and tank supplied by the fabrication deptt. are taken into tank-up stage. The procedure is: The core-coil assembly is taken out of the oven and the "Megger test" is carried out. Only if the megger value is as per the specification, the assembly may be taken for tank-up. The tanks, supplied by fabrication deptt. are brought to tank-up department duly painted. Fittings like drain valves, HV& LV Bushings, conservator, oil level indicator and explosion vent are fitted in the tanks. The Core-coil assembly is then placed into the tank and properly locked up. Pure filtered transformer oil is filled in the tank to immerse the assembly only. Connections of primary and secondary to the terminal bushings are made. Operating handle for ratio switch is fitted, wherever required. .

OIL FILLING PROCESS The job is put in the tank and the oil is filled into the tank after the clearance checking.The oil is filled from up and the valve is closed when the oil is below 2 inch of the tank. The cover is putted on the tank and after it oil is filled trough conservator and at last conservator is closed trought conservator cap.

TESTING OF TRANSFORMER

21

Marson’s carries away almost all type of routine test .Type test(impulse/voltage) is being done at CPRI Bhopal National Test House,Gaziabad and Government Engineering College,Jabalpur..Testing is done as per IS 2026. Routine test to be carried out on all jobs. 1.Measurement of winding resistance 2.Measurement of insulaion resistance 3.Seperate source voltage withstand test (High Voltage tests on HV & LV) 4.Induced Over voltage Withstand test (DVDF test) 5.Measurement of voltage ratio 6.Measurement of NO LOAD LOSS & current. 7.Measurement of LOAD LOSS & IMPEDENCE.(EFFICIENCY & REGULATION) 8.Vector Group Verification

1.Measurement of winding resistance

This test measures the resistance of the HV & LV winding. The values of resistance should be balance for all three phases and should match the designed values. Equipment used : Digital resistance meter.

2.Measurement of insulation resistance Measures the insulation resistance of HV & LV windings with respect to earth (body) and between LV & HV winding.Recommended Values are 2000Mohms for HV & 500 Mohms for LV and between Primary & Secondary.HV high voltage test : LV winding connected together and earthed. HV winding connected together and given 28 KV ( for 11KV transformer) for 1 minute. INSULATION TESTER OR MEGGER IS USED.

3.LV high Voltage test : HV winding connected together and earthed. LV winding connected together and given 3 KV for 1 minute.Equipment used : High Voltage tester ( 100KV & 3KV)3.Seperate source 22

voltage withstand test (High Voltage tests on HV & LV)- This test checks the insulation property between Primary to earth, Secondary to earth

4.Over voltage Withstand test (DVDF test)This test checks the inter turn insulation.For a 11KV/433V transformer,866 Volts are applied at the 433V winding with the help of a Generator for 1 minute. This induces 22KV on 11KV side. The frequency of the 866V supply is also increased to 100HZ. Equipment used : MOTOR GENERATOR SET

23

5.Measurement of voltage ratio This test measures the voltage ratio as per the customer’s requirement. V1/V2 = N1/N2 The voltage ratio is equal to the turns ratio in a transformer. Using this principle, the turns ratio is measured with the help of a turns ratio meter. If it is correct , then the voltage ratio is assumed to be correct. Equipment used : Turns Ratiometer

6.Measurement of NO LOAD LOSS & current. The iron losses and no load current are measured in this test. The 433V winding is charged at 433V supply & the 11KV winding is left open .The power consumed by the transformer at no load is the no load loss in the transformer. 24

Effect of actual frequency must be taken into account. Equipment used : Wattmeters analyser or power.

7.Measurement of LOAD LOSS & IMPEDENCE. (EFFICIENCY & REGULATION)

25

This test measures the power consumed by the transformer when the 433V winding is short circuited and The rated current is passed through the 11KV winding. Equipment used : Wattmeters or power analyser.

8.Vector Group Verification test This test verifies the Dyn-11 vector group of a distribution transformer.Let the transformer vector group is DYn11; 1.1U 1V 1W-which is primary -Delta Connection 2.2U 2V 2W 2N- Which is secondary-Star connection 3.By connecting terminals 1U& 2U 4.Then three phase Supply is given to 1U-1V-1W 5.By measuring the terminal given below We get a. 1U-1V b. 1V-1w c. 1W-1U d .1W-2W e. 1V-2W f. 1V-2V g. 1W-2V h. 1U-2N i. 1V-2N THE BELOW GIVEN CONDITION IS SATISFIED THEN DYn11 IS CONFIRMED 1.1V-2W=1V-2V 2.1W-2V>1W-2W 3.1U-1V=1V-2N+1U-2N Equipment used : voltmeter.

ACCESSORIES 26

Conservator with drain plug and filling hole : Conservator is normally provided on all ratings of transformers which provides the space for the expansion / contraction of oil on account of the variation of oil temperature during service. It prevents the oil in the tank from coming in direct contact with the atmosphere and protects it from deterioration.Conservator is provided with silicagel breather, oil level gauge, oil filling hole with blanking plate and drain plug for draining/ sampling of oil contaminated by moisture and sludge.

.Magnetic Oil Gauge

This is a dial type gauge, mounted directly on the conservator to indicate oil level. This is supplied with low level alarm contacts and the electrical connections of which are brought out to a terminal box of the oil gauge. Suitable alarm circuit may be connected to these terminals. This oil gauge is not dispatched separately, but is mounted on the conservator, with float arm adjusted to correct length. .

Dehydrating Breather

Regarding moisture absorbent,to display the extent of moisture absorption of the moisture absorbent, it is used.It mixed the kind of moisture absorbent which is blue color under a dry state and changes to pink as moisture absorption progresses. When no breathing is conducted, the breather is isolated from the open air by oil to prevent the moisture absorbent from needlessly absorbing moisture .

MARSHALLING BOX The transformer is provided with certain fittings directly mounted on the transformer at various locations. These fittings are having electrical contacts or terminals which are required to be connected to the protection schemes to give alarm/annunciation under abnormal conditions and if further required to disconnect the transformer from mains. In order 27

to facilitate connections of all such devices to the protective scheme, the cables from all such contacts are wired upto a weather proof terminal box. This box called marshalling box, is also used for housing Oil Temperature Indicator (OTI) and winding Temperature Indicator (WTI)The Marshalling box is made of sheet metal and is provided with a glass window for observing OTI& WTI .Is has a hinged door with locking facility to prevent unauthorised access. The capillaries from OTI& WTI come out from the bottom of the Marshalling box through suitably recessed gland plate thus preventing ingress of dust.

Liquid Temperature Indicator

Liquid temperature indicator is used to measure oil temperature as a standard practice. The dial temperature detector is used to measure maximum oil temperature.The indicating part, provided with an alarm contact and a maximum temperature pointer, is of airtight construction with moisture absorbent contained therein; thus, there is no possibility of the glass interior collecting moisture whereby it would be difficult to observe the indicator.

Winding Temperature Indicator

The winding temperature indicator is a conventional oil temperature indicator supplemented with an electrical heating element.The relay measures the temperature of the hottest part of the transformer winding.The temperature sensing system is filled with a liquid, which changes in volume with varying temperature.The sensing bulb placed in a thermometer well in the transformer tank cover senses the maximum oil temperature.

Pressure Relief Device

28

When the gauge pressure in the tank reaches abnormally to

0.35 0.7kg/cm2 the pressure relief device starts automatically to discharge the oil. When the pressure in the tank has dropped beyond the limit through discharging, the device is automatically reset to prevent more oil than required from being discharged.

Protective Relays The following protective devices are used so that, upon a fault development inside a transformer, an alarm is set off or the transformer is disconnected from the circuit. In the event of a fault, oil or insulations decomposes by heat, producing gas or developing an impulse oil flow.To detect these phenomena, a Buchholtz relay is installed

Buchholtz Relay The Buchholtz relay is installed at the middle of the connection pipe

29

between the transformer tank and the conservator. There are a 1st stage contact and a 2nd stage contact as shown.

The 1st stage contact is used to detect minor faults. When gas produced in the tank due to a minor fault surfaces to accumulate in the relay chamber within a certain amount, the float lowers and closes the contact, thereby actuating the alarm device.The 2nd stage contact is used to detect major faults. In the event of a major fault, abrupt gas production causes pressure in the tank to flow oil into the conservator. In this case,the float is lowered to close the contact, thereby causing the circuit breaker to trip or actuating the alarm device.

Off-circuit Tap Changer The transformer is fitted with an off-circuit tap changing switch to obtain required tap voltage. It can be hand operated by a switch handle mounted on the tank. Locking device is fitted to the handle to padlock it on any tap 30

position and also to prevent any unauthorized operation of switch. The switch mechanism is such that it can be locked only when it is bridging two contacts on any particulars tapping position and cannot be locked in any intermediate position.It is important that the transformer should be isolated from the live lines, before moving the switch. Operating the switch when transformer is energized, will damage the switch contacts due to severe arcing between the contacts, and may damage windings also.

ON load Tap Changer

The on-load tap changer is employed for changing the turn ratio of the transformer to regulate the system voltage while the transformer is delivering load.The tappings are provided at the neutral end of hv windings of a generator transformer.The changer is operated by a motor operated driving mechanism by local or remote control and a handle is also fitted for manual operation in case of an emergency.All type of on load tap changing circuit are provided with an impedence.The impedence may be either a resistor or centre tapped reactor.

Temperature gauges

A Temperature Gauge is a common safety device installed on transformers, regulators and other electrical equipment when filled with liquid insulating fluids for dielectric insulation and cooling.. A temperature gauge is installed to measure the changes in the temperature of the liquid insulating fluids.Temperature gauges provide a positive system to measure and indicate the insulating fluids temperature in transformers, regulators and other electrical equipment.

Pressure vacuum gauge Pressure-Vacuum Gauges are commonly installed as safety devices on liquid insulating fluid(s) filled transformers, regulators and other electrical equipment that provides a gas space above the oil.

31

Liquid level gauge This type of gauge is a common safety device installed on transformers, regulators and other electrical equipment when filled with liquid insulating fluids for dielectric insulation and cooling.

Radiators The function of radiators is to limit the temperature of oil and winding by dissipating heat that is generated due to losses within the transformer while in service. The number of sections per radiator and the number of radiators per transformer will depend upon the losses and permissible temperature rise.Distribution Transformers are normally provided with Radiators welded to tank. Each radiator consists of number of "Sections made from pressed sheets forming channels for oil flow. These "Sections" are welded to Header Pipes at Top & Bottom.

Circuit breaker Circuit Breakers provide short circuit and thermal protection for both pad mounted and overhead distribution transformers. These are applied immersed in the transformer oil on the low voltage side to protect the transformer against secondary faults and excessive overloads.

BUSHING a) Bare bushing :

i) Draw through bushing (oil flood type) :-Winding lead is soldered to the stem of bushings which is drawn through the hole in porcelain and is fixed outside the porcelain with leak proof gasket. Oil is flooded through the hole of the porcelain which acts as an insulation between the lead and earth in addition to the porcelain insulation. 32

ii) Solid Bushing (through stem type) Through stem protruding out of porcelain on either side is provided with nuts and washers to take windings lead on one side and supply cable on the other side. Bushing is completely sealed on one end for oil tightness. b) Outdoor through stem type porcelain bushings. c) Cable box type porcelain bushings. d) Cable box type epoxy bushings.

COOLING OF TRANSFORMER . Cooling of the transformer is the most important for it’s durability.As the rating increases better cooling techniques are needed. Simple air cooling of the transformers is adopted in dry type transformers. The limit for this is reached by the time the rating is a few kVA.This method of cooling is termed as AN(Air Natural). Air Blast(AB) method improves on the above by directing the blast of air at the core and windings. ON (Oil Natural) This method permits the increase in the surface available for the cooling further by the use of ducts, radiators etc.OB(Oil Blast) method is an improvement over the ON-type .and it directs a blast of air on the cooling surface. In the above two cases the flow of oil is by natural convective forces. OFN (Oil Forced Natural)in this a forced blast of oil is employed.When there is blast of air,the cooling method become OFB(Oil Forced Blast). A forced circulation of oil through a radiator is done with a blast of air over the radiator surface. Next comes OFW which is similar to OFB except that instead of blast of air a forced circulation of cool water in the radiator is used in this.

Cooling System Capacity Cooling equipment 33

Self-cooling type (ONAN) 30,000kVA or below Panel-type radiators Forced-air-cooled type (ONAF) 30,000kVA~150.000kVA Panel-type radiators and cooling fans Forced-oil, forced-aircooled type (OFAF) 150,000kVA or more Unit cooler or panel-type radiator, and Installation of cooling fans and pumps

PROPERTIES OF TRANSFORMER OIL Even though the basic functions of the oil used in transformers are a) heat conduction and b) electrical insulation, there are many other properties which make a particular oil eminently suitable. Organic oils of vegetative or animal origin are good insulators but tend to decompose giving rise to acidic by-products which attack the paper or cloth insulation around the conductors. Mineral oils are suitable from the point of electrical properties but tend to form sludge.The properties that are required to be looked into before selecting an oil for transformer application are as follows:Insulting property.Viscosity Purity Sludge formation.Flash point And Fire point Flash point of an oil is the temperature at which the oil ignites spontaneously. This must be as high as possible (not less than 160◦C from the point of safety). Fire point is the temperature at which the oil flashes and continuously burns. This must be very high for the chosen oil (not less than 200◦.

PAINTING AND FITTINGS : The entire procedure of painting is done under two stages: 1. Cleaning of tanks The cleaning of tank is done normally by chipping/grinding. The outside surface of the tank is short blasted to achieve a very fine and smooth finish. 34

2. Painting of tanks After cleaning the tanks, a coat of hot oil resistence paint is applied on the internal surface of the tank. The outside surface is painted with a coat of Red Oxide primer and subsequently with one coat of enamel paint as per customer's requirement.

Fittings and accessories as per customer's specification and drawing are checked. Air Pressure test is subjected to avoid any leakage and seepage on all transformer.Transformers are filled with oil upto the minimum level marking, wherever necessary.

Summary At last I would like to say that this training was a success for me,as I learned a lot about the manufacturing ,design and other aspects of transformer which could not have been learned otherwise.As I have already mentioned that Marsons Electrical Industries is the leading transformer company of 35

India.Company designed the transformer by well defined quality policy accourding to the ISO-9001:1994 standard.The company acquired quality system certificate from Det Norske Veritas,vide Certificate No. RIN 350-AQ-1746 dated 14.06.2001. Company not only supply their products in India but also in foreign countries like U.K,Nigeria,Seria,etc.There products are of very good quality and process is carried out in required environment.The staffs are very experienced and guide with interest.

36