The most convenient power source of a Laboratory addressed to perform short-circuit withstand tests on transformers is a line coming from a HV substation with suitable short-circuit power. This because a short-circuit withstand tests of a transformer last at most 500 ms, so the impact on HV network is very limited in time. Moreover the apparent power of a HV power grid is significantly higher than the short-circuit power of one generator, in so allowing to test power transformers of rated power much higher.

According to the IEC Standard 60076-5, three phase transformers can be tested adopting the following test circuits:

• three phase test circuit in a pre-set or post-set configuration,
• single-phase equivalent test circuit.

The three phase tests circuit has to be preferred when testing a three phase transformer. In the pre-set method the transformer under test is fed at the higher rated voltage windings, being the other winding already in short-circuit conditions. Conversely in the post-set method the transformer under test is at first fed at one side  and the short-circuit is closed lather on the opposite side.

The three phase tests circuit has to be preferred when testing a three phase transformer. In the pre-set method the transformer under test is fed at the higher rated voltage windings, being the other winding already in short-circuit conditions. Conversely in the post-set method the transformer under test is at first fed at one side  and the short-circuit is closed lather on the opposite side.