Can anyone tell me the formula for converting KvA to amps?

I often need to make these calculations for my job as an event organiser. For examble you have a 500 KvA generator so how many amps 3phase do you have?

I believe to find usable KW you times by 0.8 (as you can only always use 80% of the power for constant supply), but I still can't work out the amps. for examble if you have a 2.5 KvA fridge (2.5 x 0.8 = 2KW) can that be powered safely by a 13 amp plug?

I'm based in England if that makes any difference.

Thanks for your help

Camilla