generator step-up transformer high voltage

[bxny]

Why are generator step up transformers sometimes specified with a high voltage winding rating higher than the nominal system voltage they are connected to? For example, a generator step up transformer connecting to a 400kV system is specified with a high voltage winding rating of 420kV.

 

[dpc]

Transmission line voltages at large generating stations can run a little high if they are exporting a lot of reactive power.



David Castor

http://www.cvoes.com

 

[rcw retired EE]

When the generator is supplying reactive power the 5% boost in voltage allows the generator to supply the MVARs without exceedign its +/-5% voltage range. The 5% increase compensates for the voltage drop through the transformer.

 

[m3ntosan]

You’ll find this situation for system transformers (400/275 kV) as well, not only for GSU. Most systems operate at +/- 5% at 400 kV, so you can get 420 kV often during nights and weekends. It’s the same with all 400 kV equipments, look at circuit breakers, and disconnectors for instance; it’s the same 420 kV rating.

May you grow up to be righteous, may you grow up to be true...

 

[bxny]

Thankyou, all, for your input.