For polarity test on a 11/3.3kV 2.5MVA delta-star Unit Auxiliary transformer,4

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.

Question Posted / engr. l. o. osuji

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For polarity test on a 11/3.3kV 2.5MVA delta-star Unit Auxiliary transformer,415V 3-phase supply w..

Answer / jatinder singh

Please do the megger testing of HV winding.May be the
winding was short circuited.

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For polarity test on a 11/3.3kV 2.5MVA delta-star Unit Auxiliary transformer,415V 3-phase supply w..

Answer / 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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For polarity test on a 11/3.3kV 2.5MVA delta-star Unit Auxiliary transformer,415V 3-phase supply w..

Answer / engr. l. o. osuji

Thanks to the respondent.I would like to tell him that no
load was connected besides linking Aa in accordance with
the method for the test. Also, note that similar 2.5mm2
cable has been used on a similar Unit Auxiliary 2.5MVA
11/3.3kV delta-star T/F and 60MVA 132/11kV star-delta T/F
respectively. No burning occurred. Test results were
satisfactory. This piece of information should guide any
contributor. Thanks.

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