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Generator Loss of Excitation Protection (ANSI 40)
How to find out impedance locus from active and reactive power?


I know modern generator relays detect field loss of excitation from generator terminal voltage and current. I checked that, in relay, its somehow calculated from P-Q diagram and convert to R-X diagram (For MHO type relay). I want to know, how this conversion take place?

second question, why this type of relay is called MHO relay? as, its calculated on R-X, it should be called impedance relay. But at many place, i noticed, they write it as MHO relay.

Please try to give answer me.