GSU Transformer Impedance

[boze2210]

Failure of a GSU Transformer with Z%= 8.725. We have found a rental trasformer but with a Z%= 12.24. Will the difference make the rental transformer not fit to the application?

boze2210

 

[waross]

Expect a lower available fault current level on the secondary.
Your voltage regulation will probably be a little greater. It is a function of resistance, reactance, current and power factor. However, if you are able to monitor the secondary voltage you should be able to compensate with excitation adjustments. You may want to re-evaluate some of your protection settings to address the higher impedance and possible lower fault levels.
A lot depends on the complexity of the system and on the length of time the odd transformer will be in service.
Is this transformer-generator unit paralleled with other generators on the same site?
Is the rental the same KVA rating and if not have you adjusted the Z% accordingly?
For example, if a 10 MVA at Z=8% transformer is replaced with a 15 MVA transformer at Z=12% the 15 KVA unit may be rerated to 10 MVA with an Z of 8%.
respectfully

 

[ScottyUK]

Does the rental transformer have an OLTC? It would be preferable to have a greater tapping range than the lower impedance transformer has otherwise the reactive load on the generator may be awkward to control under certain conditions.


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