We replace a lot of older 100 kVA 3Ø transformers with 200 kVA or 300 kVA after dataloggers were installed.
The tranny's have been taking hughe overloads for years without any major problems. Last week we had a 100kVA blow up and loose all its oil after been running at 384 Amps almost continuous on 3 Ø. ( Inom is 139 Amps Ø )
We found that out when the temp. 200 kVA generator stalled about 3 times and needed to be replaced with a 325 kVA genny.
HT fuses are usually overrated, because they need to supply the backfeed line if a fault occurs via the open point. Often a
56 Amps 11kV HRC fuse is the 11 kV protection fuse for the primary side of the tranny ( Inom 5.5 Amps ) LT fuses non existent or double 200 Amps NZI's or 5 way 160 Amps DIN panels.
This is for 11000/230/400volts system.
