When the mill is tied to the power company,operate the turbine in back-pressure control and operate the generator in the kVAr mode with automatic switching of the governor to isochronous control and the exciter to voltage control on loss of tie.
Implement an automatic under/over frequency relay and load-shed scheme with four
set points. Settings other than the first (59.7 Hz) are suggestions and need to be studied further for verification. The underfrequency trip relay (81) for generator protection should be set at 58.5 Hz. Steam turbines normally should not operate below this frequency.
— At 59.7 Hz, trip the tie, woodyard, and wastewater 15 kV breakers.
— At 59.5 Hz, trip the O2 plant 15 kV circuit breaker.
— At 59.3 Hz, trip the digesters, chemical plant 15 kV circuit breaker.
— At 59.0 Hz, trip the product 15 kV circuit breaker.
Check the V/Hz relay protection on the exciter.While this device has been working, a
verification of proper operation is in order.