9.13. Transformer Losses. The losses in a transformer are classified as follows:
- Iron losses (or core losses).
- Copper losses.
- Iron or core losses. It includes hysteresis loss and eddy current loss.
(i) Hysteresis loss. Since the flux in a transformer core is alternating, power is required for the continuous reversals of the elementary magnets of which the iron is composed. This loss is known as hysteresis loss.
Hysteresis loss = khfB1.6max … (32)
where f is the frequency in Hz, Bmax is the maximum flux density in core and Kh is a constant.
(ii) Eddy current loss. This is due to the flow of eddy currents in the core. Thin lamination, insulated from each other, reduce the eddy current loss to small proportion.
Eddy current loss = Kef2B2max … (33)
where Ke is a constant.
Iron or core loss is found from open circuit test. The input of the transformer when on no-load measures the core loss.
- Copper losses. These losses are due to the ohmic resistance of the transformer transformer windings.
Total copper loss = I12R1 + I22R2 = I12R01 = I22R02
These losses, as is evident, are proportional to square of the current (or (kVA)2.
The value of copper losses is found from the short-circuit test.