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Anonymous Poster

Alternator Stator E/F Protection

09/26/2010 11:22 AM

Can you please tell what is the difference between stator 100% E/F protection and 95% E/F protection

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Guru
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#1

Re: Alternator Stator E/F protection

09/26/2010 12:41 PM

5%

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#2

Re: Alternator Stator E/F protection

09/26/2010 3:28 PM

The fault within the 5% winding close to neutral is difficult to measure by the relay as the voltage at that point is close to zero and very less current will flow through the neutral in-case if earth fault. So it is very difficult to sense this fault by current measurement.

This fault close to neutral can be detected either by injection the frequency signal through the neutral transformer (25Hz square wave) or by measuring the 3rd harmonic voltage at the neutral. Any method can be applied.

Regards

Manish

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Active Contributor
Engineering Fields - Power Engineering - Thermal Power Plant Electrical Engineer

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Location: INDIA
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#3
In reply to #2

Re: Alternator Stator E/F protection

09/27/2010 8:08 AM

thank you very much manish sir...

how we can inject 25hz square wave...can you tell me what is first harmonic over voltage and third harmonic under voltage

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Guru

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#4
In reply to #3

Re: Alternator Stator E/F protection

09/28/2010 9:20 AM

I suggest that you attend to our 4-days duration training programme on Protective Realying starting on Oct. 12th at our training centre at Coonoor (near Ooty in Tamilnadu, India). Mail me your ID to send you further details.

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#5
In reply to #3

Re: Alternator Stator E/F protection

10/01/2010 5:08 PM

Yaar the Injection of this low frequency signals is generally done through the grounding transformer of the machine into the stator of the machine which we want to protect. The voltage level of the injection i need to confirm once again.

The method 3rd harmonic is also used to detect the fault close to neutral of the machine. The measurement of voltage for this scheme is done at both neutral and phase side (all 3 phase) by forming an open delta connections across the PT secondary of phase side, and across the grounding resistor at neutral side.

The 3rd harmonic voltage varies with the load, so the setting of this really is really very tough. Incase of fault the voltage level goes down.

The 3rd harmonic voltage varies with the load, so the setting of this really is really very tough. Generally the 3rd harmonic voltage of healthy machine of rating 155MW on base load remains 2V approximately and tries to go below incase of earth fault.

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Engineering Fields - Power Engineering - Thermal Power Plant Electrical Engineer

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#6
In reply to #5

Re: Alternator Stator E/F protection

10/06/2010 8:23 AM

Thanku very much Gautamsir...

you said low frequency signals are send through grounding transformer...is dat NGT...or Resonant grounding(Petersons coil)

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