Answer Posted / m.b.parthasarathy

1. You've not mentioned clearly that the short occurred either in transformer or control board.
2. There my be many reasons.
3. In rush voltage may be higher.
4. The device(IGBT) used in the UPS, would be lower value. say 150A/400/600V
5. for ex, the above said UPS, 200kva/480v dc, due to improper maintenance of battery, weakness or prone to ageing the DC may be very low. Instead of 480V Dc it works only in 444V dc. Two or Three batteries may be getting weak.
6. Insulation of the transformer may be worn out

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