STANI MEMORIAL COLLEGE OF ENGG. & TECHNOLOGY,PHAGI JAIPUR -303005

A Ppt Presentation on TRANSFORMER

Submitted byRAKESH RAUSHAN 12ESTEE021

Submitted toAbhishek kr. SharmaH.O.D Electrical Department

What is Transformer ??

• A transformer is a electromagnetic static device which is use to convert high alternating voltage to a low alternating voltage and vice versa, keeping the frequency same.

The main principle of operation of a transformer is mutual inductance between two circuits which is linked by a common magnetic flux. A basic transformer consists of two coils that are electrically separate and inductive, but are magnetically linked through a path of reluctance.

WORKING OF TRANSFORMER

WORKING PRINCIPLE

Construction of Transformer

•Basically a transformer consists of two inductive windings and a laminated steel core. The coils are insulated from each other as well as from the steel core.

•core is constructed by assembling laminated sheets of steel, with minimum air-gap between them (to achieve continuous magnetic path).

•The silicon steel used is to provide high permeability and low hysteresis loss. 

•Laminated sheets of steel are used to reduce eddy current loss. 

Classification of transformer

• As per phase1. Single phase2. Three phase

• As per core1. Core type2. Shell type

• As per cooling system1. Self-cooled2. Air cooled3. Oil cooled

• As per service

1.Power transformer

2.Distribution transformer

Three phase Transformer

Transformer classified as per core

COOLING METHODS OF A TRANSFORMER

For dry type transformers• Air Natural Or Self Air Cooled

Transformer

• Air Blast

For oil immersed tranformers• Oil Natural Air Natural (ONAN)

• Oil Natural Air Forced (ONAF)

• Oil Forced Air Forced (OFAF)

• Oil Forced Water Forced (OFWF)

Air Natural Or Self Air Cooled Transformer

This method of transformer cooling is generally used in small transformers (upto 3

MVA). In this method the transformer is allowed to cool by natural air flow

surrounding it.

Air BlastFor transformers rated more than 3 MVA, cooling by natural air method is

inadequate. In this method, air is forced on the core and windings with the help of

fans or blowers. The air supply must be filtered to prevent the accumulation of dust

particles in ventilation ducts. This method can be used for transformers upto 15

MVA.

This transformer cooling method is generally used for large transformers upto about 60 MVA.

This method can be used for transformers upto about 30 MVA.

ONAF ONAN

Oil Forced Air Forced (OFAF)

This type of cooling is provided for higher rating transformers at substations or power stations.

Oil Forced Water Forced (OFWF) This method is similar to OFAF method, but here forced water flow is

used to dissipate hear from the heat exchangers.

Power Transformer

Power transformers are used in transmission network of higher voltages for step-up and step down application (400 kV, 200 kV, 110 kV, 66 kV, 33kV) and are generally rated above 200MVA.

Power transformer generally operated at full load. Hence it is designed such that copper losses are minimal.

Distribution Transformer• It is used for end user

connectivity. (11kV, 6.6 kV, 3.3 kV, 440V, 230V) and are generally rated less than 200 MVA.

• Distribution transformer is always online and operated at loads less than full load for most of time. Hence, it is designed such that core losses are minimal.

A wide variety of transformer designs are used for different applications.

Auto-transformer

Poly-phase transormer

Leakage transformer

Resonant transformer

Instrument transformers

AUTO-TRANSFORMERS

Autotransformer is a one winding transformer in which a part of the winding is common to both HV & LV sides.

POLY-PHASE TRANSFORMER• Three separate

single phase transformers are suitably connected for 3 phase operation.

• A single three phase transformer in which the cores and windings for all the three phases are combined in a single structure.

INSTRUMENT TRANSFORMERS

A current transformer is a measurement device designed to provide a current in its secondary coil proportional to the current flowing in its primary.

A voltage transformer are designed to have an accurately known transformation ratio in both magnitude and phase, over a range of measuring circuit impedances..

Losses in transformer

(I) Core Losses Or Iron Losses a) Hysteresis loss

b) Eddy current loss

(ii) Copper loss Copper loss is due to ohmic resistance of the transformer windings. 

Copper loss for the primary winding is I12R1 and for secondary winding is

I22R2. Where, I1 and I2 are current in primary and secondary winding

respectively, R1 and R2 are the resistances of primary and secondary

winding respectively.

Hysteresis Loss

The magnetic core of transformer is made of ′Cold Rolled Grain Oriented Silicon Steel . Steel ′is very good ferromagnetic material. That Ferromagnetic substances have numbers of

domains in their structure. The domains are situated randomly in the structure of substance.

Whenever external magnetic field is applied , these randomly directed domains get

arranged themselves in parallel to the axis of applied mmf. After removing this external

mmf, maximum numbers of domains again come to random positions, but some of them

still remain in their changed position. Because of these unchanged domains, the substance

becomes slightly magnetized . To neutralize this magnetism, there will be a consumption of

electrical energy which is known as Hysteresis loss of transformer.

Eddy current loss

In transformer, we supply alternating current in the primary, this alternating current

produces alternating magnetizing flux in the core and as this flux links with secondary

winding, there will be induced voltage in secondary, resulting current to flow through the

load connected with it. Some of the alternating fluxes of transformer; may also link with

other conducting parts like steel core or iron body of transformer etc. As alternating flux

links with these parts of transformer, there would be a locally induced emf. Due to these

emfs, there would be currents which will circulate locally at that parts of the transformer.

These circulating current will not contribute in output of the transformer and dissipated as

heat. This type of energy loss is called eddy current loss of transformer.

Transformer Protection

1.Buchholz Relay

2.Earth Fault Relay

3.Differential Relay

4.Overcurrent Relay

General Faults in Transformer

1.Open circuit fault

2.Overheating or Overloading fault

3.Winding short circuiting fault

4.Faults due to lightning

Protecting Relay

Buchholz Relay Protection

Buchholz relay for transformer protection is only applicable for oil immersed transformer- used mostly for transformers with ratings above 750KVA, it provides protection from all kinds of faults.

The concept of this relay is to utilize Hydrogen producing from fault heat. That is if a fault occurs either slow or fast there will be immense heat and this heat will create hydrogen from transformer oil.

Earth Fault Relay

“Earth fault” means one of the core is being connected or leaked to the earthing or

grounding. This happens when insulation is damaged and coil is in touch with transformer

body and body of transformer is certainly connected to the ground for safety.

Differential protectionDifferential protection is provided in the electrical power transformer rated more than 5MVA.

BushingBushing is an important part of power

transformer. It is used to insulate the

incoming or outgoing conductor into or

out of a grounded barrier, in power

transformer case is the transformer

main tank. The bushings connect the

windings of the transformer to the

supply line and insulate the feed

through conductor from the

transformer main tank.