What is a Transformer? EMF Equation & Efficiency of Transformer

Updated: Jun 25

Transformer is a static piece of equipment which does not have any moving part in it. The transformer transforms higher voltage to lower voltage or vice versa without changing the frequency. The input power and output power remains the same, ignoring the small losses in the transformer.

The transformer functions on the principle of Farady's law of electromagnetic induction. The voltage induced in the primary and secondary winding is directly proportional to the rate of change of flux.


Why Transformer is required?

The power generation plant is usually located near the source of fuel availability point and usually very far from the power power utilization ends. The transmission of power at low voltage level cause voltage drop and the line loss. The increased transmission voltage leads to lower losses and good voltage regulation. Therefore, the generation voltage is boosted to high voltage through step up transformer at generating station end for transmission purpose. The voltage is stepped up using a step up transformer.

Step-up Transformer

In a step-up transformer, Vs>Vp and Ns>Np.Examples of step-up transformer is 11/132 KV,11/220KV,6.6/132 KV transformer.

The voltage at utilization level is stepped down by transformer. Thus, the main equipment used for stepping up and stepping down of the voltage is transformer.

Step-down Transformer

In a step down transformer Vs < Vp and Ns<Np. Examples of step down transformers are 132/6.6 KV, 132/11 KV, 6.6/0.440 KV, 11/6.6 KV,11/3.3 KV etc.

Construction of Transformer

Main Parts of Transformer

Transformer has following parts;

  1. Winding - Primary and secondary winding made of copper

  2. Conservator Tank - It is used to take care of for expansion and contraction of transformer oil.

  3. Breather with silica gel - It is used to remove the moisture from the air entering in the transformer

  4. CRGO Magnetic core - Laminated steel CRGO core is used for providing low permeability path to flux

  5. Pressure Release device - Used to protect the transformer in the case of major fault inside the transformer

  6. Buccholtz Relay - Used as a protective equipment in the case of fault in the transformer

  7. Dielectric Materials - The insulating materials used to insulate live parts from non conducting parts of the transformer

  8. Mineral Oil - Used for insulation and cooling Purpose

  9. On load Tap Changer - Used to increase/decrease the voltage under on condition of transformer

  10. OFF load Tap Changer - To increase /decrease the voltage under off condition of transformer

  11. Bushings ( LV and HV) - Used for Connection for HV and LV side

  12. Radiator or Cooling tubes - Used for cooling of transformer

  13. External Cooling Fans - Used for force cooling of the radiator tubes

  14. Main Tank - Used for to in house the transformer winding and core

Types of Transformer

Transformer can be classified into different categories on the basis of following factors.

  1. Position of the winding around the magnetic core

  • Core Type

  • Shell Type

2. According to turn Ratio or transformation ratio

  • Step-up

  • step- down

3. Types of service

  • Power Transformer

  • Distribution Transformer

  • Instrument Transformer

- Potential Transformer

- Current Transformer

- Auto Transformer

4. On the basis of supply

  • Single Phase

  • Three Phase

5. On the basis of Cooling

  • Air Natural (AN) or Self cooled

  • Air Force(AF)

  • Oil Natural Air Natural(ONAN)

  • OIl Natural Air Force (ONAF)

  • OIl Force Air Force (OFAF)

  • Oil Natural Water Force (ONWF)

  • Oil Force Water Force ( OFWF)

EMF Equation of Transformer

Voltage induced in the primary is;

Voltage Induced in the secondary is;

Dividing equation(2 ) by Equation(1)

emf equation of transformer

Losses in Transformer

Following types of losses occur in a transformer.

1. Core or Iron loss

  • Hysteresis loss

  • Eddy current loss

2. Copper losses

3. Stray losses

Efficiency of Transformer

The ratio of output power to input power is known as efficiency of a transformer.

Transformer efficiency formula

Related Articles

  1. Working principle of transformer, turn ratio & transformation ratio

  2. Percentage impedance of transformer and its calculation

  3. Leakage Reactance of Transformer

  4. Transformer winding Resistance

  5. Difference between power and distribution transformer

  6. Cooling classes of transformer

  7. Difference between an ideal and practical transformer

  8. What is step-up and step-down transformer?

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