GENERATOR AND TRANSFORMER

[binwork91]

When we size generator, do we consider inrush of the transformer?

I have 250KW 480v 3p generator with 450A breaker feed 300KVA 480v step down 208V transformer.
Will the generator work due to transformer inrush current?
I size primary breaker to protect the transformer, but will it protect generator?

 

[augie47]

Can't address inrush but IMO the breaker is oversized for generator protection.

 

[binwork91]

Can't address inrush but IMO the breaker is oversized for generator protection.

Yes, it should go 300KW generator.

I still worry about transformer inrush current.

 

[synchro]

It might be possible to minimize inrush if you can keep the transformer connected to the generator (but with no load on the transformer) and bring up the excitation relatively slowly after the generator has got up to speed. It might not be a problem, but if the generator's excitation is active when it's ramping up to speed then it might be possible to saturate the transformer with a higher V/Hz than it can handle and therefore cause some inrush current. Perhaps you could contact the manufacturer about having the transformer connected at startup vs. the inrush current you will have if the transformer is connected later.