[Amps] HV transformer and Variac

[Steve Bookout]

Hello all.

Question for the experts.

How does using a Variac to control the output of a HV transformer affect 
things like efficiency?

I think it would be reasonable to think that a transformer operated at 
less than rated input voltage would be less efficient than one run at 
full primary voltage.  I mean, it cost 'something' just to make a 
transformer act like a transformer.

I ask because I have a perfectly fine 'pole pig' transformer rated at 5 
KVA.  7200 AC volts on the output (reversed) is a bit much for my needs, 
so was wondering what the trade-off would be if it were run at 
considerably less than 220 input.

I can see this is a better xformer for a 4cx10000, than anything I would 
be using, but I have what I have.

73 de Steve, NR4M