SOLUTION

Short circuit or Impedance test

The short-circuit test is carried out at very low voltage and at the rated full load current. Therefore, the iron loss at that voltage is very low. Short-circuit test is performed to determine the leakage reactance.

The short-circuit test on the transformer is performed to determine the equivalent resistance and leakage reactance either referred to the primary side or referred to the secondary side. Thus for the performance calculation of a transformer, there is no necessity of determination of the individual parameters of the primary and secondary windings once the equivalent resistance and equivalent leakage reactance are known.

Short circuit test or Impedance test is performed to determine
⇒ Copper loss at full load
⇒ Equivalent impedance (Z_o1 or Z_o2)
⇒ Leakage reactance (X_o1 or X_o2)

• In the short-circuit test, the secondary terminals are short-circuited by a thick conductor, and a reduced voltage is applied until the rated primary current flows. From the measured voltage and current, we can calculate the leakage inductance.
• A short circuit test is performed on the HV side of the transformer.
• Low voltage (5 to 10%) is applied to the primary and slowly increases till full load current is flowing both in primary and secondary.
• The ammeter reading gives full load current I_L.
• Since applied voltage is small so flux (Φ) is also small therefore core loss is small hence core loss can be neglected.