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What is the base value for the generator GREF?

asked 2020-10-08 10:34:18 -0500

bikiran1991 gravatar image

From PSSE's POM manual, it says that the GREF value is a pu value whose base is the turbine rate MW, and if that is not specified by the governor, then its base is the machine MVA (MBASE).

However, when i look at the GREF values, they seem to be very small initially, generally somewhere between 0.03-0.05, where as the PMECH is close to 1 pu, even though both are on MBASE. Also, i tried changing the GREF by 1% and it resulted in 20% change in the power output (with respect to the MBASE). The governor in question is a TGOV1, which doesnt have a TRATE value.

Obviously I am missing something here, and my experiments say the GREF is not on MBASE. Any clarification on this mystery would be appreciated.

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answered 2020-10-09 02:24:41 -0500

perolofl gravatar image

The speed droop value of governor model TGOV1 gives the relation between GREF and PMECH. If PMECH is 0.9 and droop R is 0.05 then GREF = R*PMECH = 0.05*0.9 = 0.045.

Here, the base for GREF is p.u. speed deviation.

GREF is the offset needed in the speed droop control to force the governor to output power PMECH at nominal speed (50/60 Hz).

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Thanks for the answer! Is there some way to get in touch with you? I am asking because your answers regarding PSSE and psspy have been very helpful. My email id is Thanks again!

bikiran1991 gravatar imagebikiran1991 ( 2020-10-10 15:48:38 -0500 )edit

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Asked: 2020-10-08 10:34:18 -0500

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Last updated: Oct 09