Question

Explain the types of loss in typical transformer.

Discuss the air gap effect on a magnetic circuit.

Answer 1

1.

Losses in a typical transformer:

In a transformer, there exists two types of losses.

1. The core gets subjected to an alternating flux, causing core losses.

2. The windings carry current when transformer is loaded, causing copper losses.

Core or Iron Losses

Due to alternating flux setup in the magnetic core of the transformer, it undegoes a cycle of magnetisation and demagnetisation. Due to Hysterisis effect, there is a loss of energy in this process which is called hysterisis loss. It is given by -

where, Kh is the hysterisis constant depending upon the material, Bm is the maximum flux density, eta is Steinmetz constant, f is frequency and v is volume of core.

The induced e.m.f in the core tries to set up eddy currents in the core and hence responsible for eddy current losses. The eddy current loss is given by -

where, Ke is the eddy current constant and t is the thickness of the core.

Hence, total core losses in the transformer is -

Copper Losses

The copper losses are due to the power wasted in the form of $I^{2}R$ losses due to the resistances of primary and secondary windings. The copper loss depends upon on the magnitudes of the current flowing through the windings.

Total Cu loss =

2.

Air Gap effect on a magnetic circuit

When a fluc enters into the air gap, it passes through the air gap in terms of parallel flux lines. There exists a force of repulsion between the magnetic lines of force which are parallel and are having same direction. Due to this repulsive force, there is a tendency of the magnetic flux to spread out at the edge of the air gap. This tendency of the flux to spread out at the edge of air gap is called Magnetic Fringing.

It has following two effects:

a) It increases the effective cross sectional area in the air gap.

b) It reduces the flux density in the air gap.