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hishamageed
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Join Date: Oct 2010
Posts: 2

Double Earthing

10/13/2010 7:57 AM

what happend if we earthed ct secondary in two point in diff protection
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electricalexpert65
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Join Date: Oct 2009
Posts: 2061
Good Answers: 169
#1

Re: Double Earthing

10/13/2010 9:26 AM

Can you ask with a drawing showing the different earthing points?
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hishamageed
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Join Date: Oct 2010
Posts: 2
#3
In reply to #1

Re: Double Earthing

10/14/2010 7:28 AM

I mean by two point that the secondary of LV or HV CT is earthed for examble in the marshalling box and in the protectinon pannel .
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PeterT
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Join Date: May 2010
Location: Liverpool, NY
Posts: 961
Good Answers: 131
#2

Re: Double Earthing

10/13/2010 2:06 PM

Depending on where the ground points are and how long the CT circuit wires are, you may change the amount of current the relay will see in its operating or restraint coils. Consider for example the impact of the grounds as shown in the following illustration (taken from GE's "The Art & Science of Protective Relaying," with my additions of the grounds):

Look to your differential relay's instructions for the manufacturer's recommendations on grounding of the CT circuit.

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