Transformer Inrush

[jimmy2times]

I guess this is a lot more complex than the simple question I ask but is there a simple rule of thumb for assessing transformer inrush currents on islanded generators?

I have a line up of 4x8MVA generators (11kV) and a 20MVA transformer (33/11kV) which needs to be energised from the secondary, with the minimum amount of 11kV generators on line.

(I have EDSA power system tool but I do not have the dynamics part of the package which includes a transformer model part apparently. The only way I can assess this in the package at the moment is to substitute the transformer with a motor model of the same rating and set the starting current to be the equivalent of In x 12. This gives an initial bus-voltage drop of 33% with 3 generators on line.)

 

[dpc]

You might want to search this forum - this topic has come up a few times. Inrush will be limited somewhat by the internal impedance of the generators.

I don't think it is worth the trouble to attempt a transient analysis.

You might be able to energize the transformer as you are bringing up the generator field. This is commonly done on large generators with unit transformers.