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Anonymous Poster #1

Regarding Rotor Earth Fault Relay Problem

05/04/2015 1:37 AM

In our power station, we are using C&S make,mrr1 rotor earth fault relay, in which the value is fluctuating from 75 K-ohms upto 400 K-ohms. 80 K-ohms is alarm setting and 5 K-ohms is Trip setting.

What may be the probable cause for the fluctuation? I already changed the relay with a new one, but still problem persists. Local brush contact, grounding, cable IR value everything checked and found normal. Any suggestions regarding this problem..?
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spades
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Join Date: Aug 2014
Location: Port Macquarie N.S.W. Australia
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#1

Re: Regarding Rotor Earth fault relay problem

05/04/2015 3:56 AM

Have you checked for excessive Carbon deposits on the slip rings?
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SHOCKHISCAN
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Join Date: Nov 2007
Location: Eastern Arizona mountains on Route 666 about a mile from God's country
Posts: 1676
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#2

Re: Regarding Rotor Earth fault relay problem

05/04/2015 9:25 AM

Slip rings not concentric. (Out of round.)

Contaminated/dirty slip rings. (Dirt, oil, paint,?)

Poor brush spring tension. (Fatigued brush springs, improper brush magazine clearance, contaminated.)

Static electrical buildup being discharged through the brushes to ground. (Check for leaking capacitor, shorted inductor, shorted diode, and/or damaged resistor in exciter PS filter.)

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pcchatur
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Join Date: Mar 2010
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#3

Re: Regarding Rotor Earth Fault Relay Problem

05/20/2015 9:19 AM

What is the nature of fluctuation of value? Is it load dependent or speed dependent or totally random? Some times an incipient earth fault which is of flying nature may cause fluctuating values of insulation resistance. If it is load dependent then it has to do something with thermal expansion of the rotor coils. At higher loads when field winding temperature is high, coil expansion may result in reduced clearance / some creep clearance. What is the rating of the generator?
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