power transformer in dpl

12-08-2014 Abhishek Roy 1

DPL Power Transformer(Unit-

4)

12-08-2014 2Abhishek Roy

Transformer Ratings In

DPL


KVA Rating 37500KVA

HV/LV (KV) 132/6 KV

Impedance Voltage at 75 c 11.10% at above ratings

Connection Symbol Ydelta1

Frequency 50Hz

Total Weight 66tones

Quantity of Oil(gallons) 4048

Manufactured by English Electric Co Ltd

Generating transformer for Unit(1&2)


MVA Rating(MVA) 42.5 59.5 85

HV/LV Rating 132/11 KV

HV/LV(line current) 372.22/4679.3(amps)


Frequency 50Hz

Temp Rise Oil(deg Celsius) 40

Temp Rise Winding(deg

Celsius)

55

Manufactured By BHEL

Generating Transformer For Unit (3&5)


KVA Rating (KVA) 85000

HV/LV(KV) 132/11

HV/LV(line current) 372/4680 amps


Frequency 50Hz

Generating Transformer for Unit 4

What is a

Transformer???

A transformer is a static Device which

consists of two or more stationary

electric circuits whose

main purpose of transferring

electrical power by

magnetically link without

changing the frequency.

The Transformer consists of

several parts:-

1. Core

2. Coil

3. Bushings

4. Tap Changer


Transformer Equation


The 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 Transformer


Step 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 fluxi.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 laminatedin 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% silicon


Transformer Windings

The conducting material used 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 braided Litz wire to 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.


Transformer Bushing

The non-faded portion in

the picture on the left

hand side is the

bushings. In electric

power, a bushing is

an insulated device that

allows an electrical

conductor to pass safely

through a (usually)

earthed conducting

barrier such as the wall of

a transformer or circuit

breaker.


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.12-08-2014 12Abhishek Roy


Transformer Tap-Changer

Tap changer is

connection point

selection mechanism

along power

transformer winding that

allows a variable number

of turns to be selected in

discrete steps. A

transformer with a

variable turns ratio is

produced, enabling

stepped voltage regulati

on of the output. The tap

selection may be made

via an automatic or

manual tap

changer mechanism.

Transformer Construction


Core Type Transformer Shell Type

Transformer

Core Type Transformer


In 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 Φ.

Shell Type Transformer


In 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 Φ/2.

Transformer Protection


In the field of electric power

distribution and

transmission, a Buchholz

relay is a safety device

mounted on some oil-filled

power transformers

and reactors, equipped with

an external overhead oil

reservoir called

a conservator. The

Buchholz Relay is used as

a protective device

sensitive to the effects

of dielectric failure inside

the equipment.

Silica Gel Container


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?


When 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.

power transformer in dpl

Engineering