If you have a transformer with let's say 3x 400 amp fuses protecting its LV outgoing cables how do I calculate its KVA? Do you just time amps by the single phase voltage or by the volts across 2 phases
If you know the rated LV current (I) then for a three-phase transformer it would be I x Vln x 3 where Vln is the phase-neutral current, or I x Ipn x sqrt(3) where Vpn is the phase-phase current so 400A would imply 276kVA....
... But the fuse may or may not be directly related to the rating of the transformer, depending on what it's been put there by the designer for. They might well suggest a higher rating than the transformer actually is if they're only there for fault protection, for example, with overload dealt with by other means.
It should be pretty obvious from the nameplate though, which if you can see the fuses you should be able to see!
If you know the rated LV current (I) then for a three-phase transformer it would be I x Vln x 3 where Vln is the phase-neutral current, or I x Ipn x sqrt(3) where Vpn is the phase-phase current so 400A would imply 276kVA....
... But the fuse may or may not be directly related to the rating of the transformer, depending on what it's been put there by the designer for. They might well suggest a higher rating than the transformer actually is if they're only there for fault protection, for example, with overload dealt with by other means.
It should be pretty obvious from the nameplate though, which if you can see the fuses you should be able to see!
