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Power TransformerDPL Power Transformer(Unit-4)

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Transformer Ratings In DPL12-08-2014Abhishek Roy3KVA Rating37500KVAHV/LV (KV)132/6 KVImpedance Voltage at 75 c11.10% at above ratingsConnection Symbol Ydelta1Frequency50HzTotal Weight66tonesQuantity of Oil(gallons)4048Manufactured byEnglish Electric Co Ltd Generating transformer for Unit(1&2)

12-08-2014Abhishek Roy4MVA Rating(MVA)42.5 59.5 85HV/LV Rating132/11 KVHV/LV(line current)372.22/4679.3(amps)Connection SymbolYdelta1Frequency50HzTemp Rise Oil(deg Celsius)40Temp Rise Winding(deg Celsius)55Manufactured ByBHELGenerating Transformer For Unit (3&5)

12-08-2014Abhishek Roy5KVA Rating (KVA)85000HV/LV(KV)132/11HV/LV(line current)372/4680 ampsConnection SymbolYdelta1Frequency 50Hz Generating Transformer for Unit 4

What is a Transformer???A transformer is a static Device which consists of two or more stationaryelectric circuits whose main purpose of transferringelectrical power by magnetically link without changing the frequency.The Transformer consists of several parts:- 1. Core 2. Coil 3. Bushings 4. Tap Changer

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Transformer Equation

12-08-2014Abhishek Roy7The Simple Transformer Equation states:-

V2/V1=N2/N1=I1/I2

Where V2,N2 And V1,N1 are the terminal potential difference and number of turns in secondary and primary sides respectively. Whereas I1 and I2 are the current flowing in primary and secondary sides of the transformer.

Types of Transformer12-08-2014Abhishek Roy8Step UP Transformer : A transformer in which N2>N1 and which converts low voltage to high voltage.

Step DOWN Transformer : A transformer in which N1>N2 and which converts high voltage to low voltage.

Transformer Core

Transformer core is a closed magnetic circuit through the mutual flux i.e. the flux which links with both the winding passes.

The core material and the construction of the core will be such that magnetizing current and core losses are minimum.

The core of the transformers are laminated in order to reduce eddy current losses.

The laminations are 0.33-0.5mm thick.

These laminations are made of transformer graded steel containing 3-5% silicon12-08-20149Abhishek Roy

Transformer Windings

Theconducting materialused for the windings depends upon the application, but in all cases the individual turns must be electrically insulated from each other to ensure that the current travels throughout every turn.

High-frequency transformers operating in the tens to hundreds of kilohertz often have windings made of braidedLitz wireto minimize the skin-effect and proximity effect losses.

Large power transformers use multiple-stranded conductorsas well, since even at low power frequencies non-uniform distributionof current would otherwiseexist in high-current windings.12-08-201410Abhishek Roy

Transformer Bushing

The non-faded portion in the picture on the left hand side is the bushings. Inelectric power, abushingis aninsulateddevice that allows an electrical conductor to pass safely through a (usually) earthed conducting barrier such as the wall of a transformer or circuit breaker.12-08-201411Abhishek Roy

A bushing must be designed to withstand the electrical field strength produced in the insulation, when any earthed material is present. As the strength of the electrical field increases, leakage paths may develop within the insulation. If the energy of the leakage path overcomes the dielectric strength of the insulation, it may puncture the insulation and allow the electrical energy to conduct to the nearest earthed material causing burning and arcing.

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Transformer Tap-ChangerTap changeris connection point selection mechanism along powertransformerwinding that allows a variable number of turns to be selected in discrete steps. A transformer with a variable turns ratio is produced, enabling steppedvoltageregulation of the output. The tap selection may be made via an automatic or manualtap changermechanism.

Transformer Construction

12-08-2014Abhishek Roy14Core Type TransformerShell Type Transformer

Core Type Transformer12-08-2014Abhishek Roy15In the core type of transformer, the primary and secondary windings are wound outside and surround the core ring. In the core type transformer construction, one half of each winding is wrapped around each leg (or limb) of the transformers magnetic circuit. In the core type transformer flux flowing through the frame is .

15 Shell Type Transformer12-08-2014Abhishek Roy16In the shell type transforme, primary and secondary windings are wound on the same centre leg or limb which has twice the cross-section of the other two legs. The advantage here is that the magnetic flux has two closed magnetic paths to flow around external to the coils on both left and right hand sides before returning back to the central coils.This means that the magnetic flux circulating around the outer limbs of this type of transformer construction is equal to/2.

Transformer Protection12-08-2014Abhishek Roy17In the field ofelectric power distributionand transmission, aBuchholz relayis a safety device mounted on some oil-filled powertransformers andreactors, equipped with an external overhead oil reservoir called aconservator. The Buchholz Relay is used as a protective device sensitive to the effects ofdielectricfailure inside the equipment.

Silica Gel Container12-08-2014Abhishek Roy18

Most of the power generation companies use silica gel breathers fitted to the conservator of oil filled transformers. The purpose of these silica gel breathers is to absorb the moisture in the air sucked in by the transformer during the breathing process.

What is Transformer Breathing?12-08-2014Abhishek Roy19When load on transformer increases or when the transformer under full load, the insulating oil of the transformer gets heated up, expands and gets expel out in to the conservator tank present at the top of the power transformer and subsequently pushes the dry air out of the conservator tank through the silica gel breather. This process is called breathing out of the transformer.

12-08-2014Abhishek Roy20Thank UAnd now the PresentationWill be Continued byChandan Singha