Generator Loss of Excitation Protection (ANSI 40)

N

Thread Starter

niazbibiyana

Hello,

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.

Thanx
 
Hello,

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.

Thanx
Niazbibiyana,

You can have, significant and precious informations, on LOE protection scheme, by reading this powerpoint:
https://fr.slideshare.net/mmuralintpc/loss-of-excitation.

I am sure that it can give you better overview, of the LOE Protection designing and implementation for Generator protection .

Surely that can help you!
Controlsguy25.
 
Niazbibiyana...
You're showing your age! No sweat, I'm probably decades older. However I've graduated from being "old" to being an "Elder"!:giggle:
I'm sure you know that for an L.O.E. condition, the synch-gen'r becomes an induction-gen'r and the reactive energy flowing toward the load, reverses and flows toward the gen'r ! The smart relay guys said "we can't differentiate direction ! What should we do ? They decided to invert the equation related to Z=R+jX having Ohm's or O-H-M's as measuring-units, to equivalent M-H-O's having conductance and susceptance as measuring-units with which direction could be determined ! Q.E.D.
Regards, Phil Corso
Ps1: an update... Mho's are now called "Siemens" ! Ps2: Similar problem for Transmission-Line relaying !
 
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