Transformer

Transformer is a static electric device that transfers electrical energy from one circuit to another circuit by generally changing the voltage and current level at same frequency.

Transformer works on the principle of Electromagnetic Induction.

Core of the transformer is made of ferromagnetic material that provides low reluctance path for magnetic flux.

EMF Equation in Transformer

Hence, induced emf leads flux by 90 ^o in transformer

Properties of Ideal Transformer

1. No losses.
2. No leakage flux.
3. Infinite permeability i.e. zero reluctance.

Hence, at no load,

Phasor Diagram of Ideal Transformer on No Load

From mmf balance,

Phasor Diagram of Ideal Transformer on Lagging P.F Load

Practical Transformer on No Load

It draws a small current I ₀ (2 to 5% of full load current) on no load, called No Load Current or Exciting Current. It has two components

1. Core loss component I _C .
2. Magnetizing component I _m .

MMF Balance

Equivalent Circuit of Practical Transformer

Phasor Diagram of Electrical Transformer on Lagging Power Factor Load

Phasor Diagram of Electrical Transformer on Leading Power Factor Load

Equivalent Circuit of Transformer Referred to Primary

5. On neglecting shunt branch, equivalent impedance of transformer referred to primary side

Applications of Transformers

1. To Step-up / step-down voltage in power system network.
2. For impedance matching in electronic circuitry.
3. Step-down transformer in designing small power supplies and laptop/mobile chargers.
4. Electrical Isolation.

Note

Transformer has more efficiency as compared to motors and generators because transformer is a static device. It does not have any rotating part.

Transformer is always rated in kVA or MVA, not in kW or MW.

In all the phasor diagrams drawn above, step don transformer has been considered.