For polarity test on a 11/3.3kV 2.5MVA delta-star Unit
Auxiliary transformer,415V 3-phase supply was applied at
the HV. Connection between Aa was made with a 2.5mm cable.
As soon as power was switched on the cable caught fire and
burnt. This test was then abandoned. It is noteworthy to
say that a similar cable was also used in a similar
transformer for the same. The cable did not burn and test
was successfully completed with good result. What is wrong?
Please, help me out.

Answer Posted / gurucharan singh

When cable burnt, it is clear that there was over current
in the 2.5mm2 cable. That means load connected may faulty,
or oversize then the capacity of 2.5mm2 cable current
carrying.

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