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Supply of Reactive Power through Generator/Exciter
We are planning to provide ancillary service to the grid by means of reactive power support by raising or lowering the excitation of our turbo generator.

Hi,

Our grid code mandates that all generators must have the capability to supply/absorb MVar within the range of 0.85 lagging to 0.9 leading. Supplying/absorbing MVar beyond these power factor limit can be subject to remuneration thus we want to operate our generators beyond these power factor as long as we will operate with the capability curve. However during testing, when we raise the AVR voltage setter to raise to supply of MVar, the generator terminal voltage also increases from 14 kV to 14.4 kV. We stop at 14.4 kV because the standard says that the safe operation for generator should be 95%-105% of terminal voltage (100% Rated = 13.8 kV). But when the our voltage is 14.4 kV the power factor is 0.95 lagging which means it is still inside the "free zone" and our objective is to operate lower than 0.85 lagging but the 105% limit hindered us from doing this.

Can someone provide me recommendations on how are we going to operate lower than the 0.85 lagging or 0.9 leading power factor without hitting the 95%/105% generator terminal voltage limit. Can reconfiguring the AVR solve this concern? Our AVR is ABB Unitrol F. Or will changing the generator stepup transformer tap changer have an effect? Our off load tap changer is set at tap 2 (224.25/13.8 kV). Our grid voltage is maintained at 230 kV.

Thank you in advance.

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In our plant the voltage control range was 22kV+/-7.5%. As part of AVR function tests during commissioning, the AVR vendor increase the limits of upper and lower to test the maximum and minimum VAR values, but he only touched the max/min VAR value only for seconds by step jumps, because he don't want to mess with grid stability, generator heating etc.

But during normal operation, we are also getting limited with these upper and lower limits. Me also searching how I can operate the machine on the max/min VAR region.