Transformer

Definition :-A Transformer is static electrical machine which is used to change or transform the voltage and current of alternating current system with same frequency and constant power. It has no rotating parts, hence it is called a static transformer.

There are two principle on which a transformer works ;

• Faraday’s Law of Electromagnetic Induction :- When the magnetic flux linking the coil or conductor changes, and EMF is induced in it. The magnitude of that induced EMF is directly proportional to the rate of change of flux linkage.
• Mutual Induction :- When EMF is induced into an adjacent coil located within the same magnetic field, the EMF is said to be induced in the coils according to their turns(N).

Basic Construction of Transformer

• Magnetic Circuit :- Consisting of core, limb and damping structure.
• Electric Circuit :- Consists of primary and secondary winding.
• Dielectric Circuit :- Consisting of insulation in different forms and used at different places.
• Tank and Accessories :- consists of conservator, breather, cooling tube, bushings etc.

Operation

When primary winding is energized by a sinusoidal voltage. The secondary winding feeds the load. The alternating current is primary sets up an alternating flux in the main core. The secondary winding is linked by most of this flowing flux and according to the law the EMF is induced across secondary winding. Then, the induced EMF supplies the current to the load proportionally. This transfer of energy from primary to secondary is done without changing frequency. In this operation power remains same.So it is also know as frequency and power constant device. A transformer is rated in VA,KVA (Kilo Volt-Amp) OR MVA( Mega Volt-Amp).

Transformation Ratio (K) :- It is defined as the ratio of secondary voltage to the primary voltage or in the same manner it is defined as the ratio of number of turns in secondary winding to the primary winding.

Transformation Ratio (K) = V₂/V₁ = N₂ /N₁

*V₁ – Primary Voltage

V₂ – Secondary Voltage

N₁ – No. of turns in primary Winding.

N₂ – No. of turns in secondary winding

Types of Transformer :-

1.Position of winding concerning the core

a) Core Type b) Shell Type

2.According to number of turns or Transformation Ratio

a) Step up ( N₂ > N₁ ) b) Step Down ( N2 < N₁ ) c) Isolation ( N₁ = N₂ )

3.Type of service

• Power Transformer
• Distribution Transformer
• Instrument Transformer :-
  • Current Transformer
  • Potential Transformer
  • Auto Transformer

4.On the basis of supply

a) Single Phase b) Three Phase

5.On the Basis of cooling

• Air natural (AN) or self cooled or Dry type
• Air Forced (AF) or Air Blast Type
• Oil Natural Air Natural (ONAN)
• Oil Nature Air Forced (ONAF)
• Oil Forced Air Forced (OFAF)
• Oil Natural Water Forced (ONWF)
• Oil Forced Water Forced (OFWF)

Losses in Transformer

a) Core or Iron loss

i) Hysteresis Loss ii) Eddy current Loss

b) Copper Loss

c) Stray Loss

Application of Transformer

There are lots of application of a transformer due to its tremendous property, some of them are mentioned below;

1.As we know that high voltage transmission is done because it makes system more efficient, to bring the generated voltage (i.e. 11Kv or 33kv) at higher voltage (i.e. 132KV, 220KV, 400KV, 500KV and 765KV) transformers are used.

2.At secondary distribution or at consumer’s end Transformers are used to reduce the voltage level to a usable and safe level of 440/220V for domestic and offices etc uses.

3.Transformer are used for measurements purposes called instrument transformers.

4.In electric communication transformers are used for variety of purposes. For example, For maximum power transfer we need a transformer.

5.Transformers are also used in telephone circuits, control circuits, Heating circuits, radio engineering etc.