**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 = k_{h}fB^{1.6}_{max … }(32)

where *f is *the frequency in Hz, *B*_{max}* *is the maximum flux density in core and *K _{h} *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 = *Kef ^{2}B*

^{2}

_{max }… (33)

where K_{e} 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 = I_{1}^{2}R_{1} + I_{2}^{2}R^{2} = I_{1}^{2}R_{01} = I_{2}^{2}R_{02}

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. *

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