1. There are mainly two kinds of losses in a transformer, namely (i) core loss and (ii) copper loss

Core loss

  1. Core loss consists of two components, hysteresis loss and eddy current loss.
  2. Hysteresis loss depends upon both the applied voltage and frequency.
  3. Eddy current loss is proportional to the square of the applied voltage and independent of frequency f.
  4. For any voltage (v α Bm f), if f decreases B increases correspondingly and if f increases B­m decreases correspondingly. Hence the eddy current loss is independent of frequency f.

Copper loss

  1. When a transformer is loaded, current flows, this results copper loss occurs in both the primary and secondary winding resistances.
  2. Copper loss should be calculated at 750

Dielectric loss

  1. This loss occurs in the insulating materials (such as, in the transformer oil and the solid insulation of h.v. Transformers).

Open circuit and short-circuit Tests

  1. These two tests on a transformer, help to determine (i) the parameter of the equivalent circuit (ii) the voltage regulation and (iii) efficiency.

Open circuit test

  1. This test is carried out to determine (i) core loss at rated voltage and frequency (ii) shunt branch parameters and (iii) turn ratio of the transformer.
  2. The alternating source is connected to the low voltage side of the transformer.
  3. The high voltage side is left open circuited.
  4. 2% to 6% of rated current is required in this test.

Short circuit test

  1. This test is carried out to determine (i) copper loss at rated current and frequency and (ii) the equivalent resistance and equivalent leakage reactance.
  2. The high voltage side of the transformer is connected to alternating source.
  3. The low voltage side of the transformer is short-circuited.
  4. A primary voltage of 2 to 12% of its rated value is sufficient to circulate rated currents in both primary and secondary windings.