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Anonymous Poster #1

Electrical Protection

03/15/2012 4:33 AM

If differential protection is already provided for a tarnsformer from HV breaker outgoing(HV side) to LV breaker incoming (LV side) wherther Resctricated earth fault protection on LV side is required or not. In my opinion differential protection will take care and RE is not required.What is CR4 members view?
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raghun
Power-User

Join Date: Jan 2010
Location: Hyderabad
Posts: 343
Good Answers: 22
#1

Re: Electrical Protection

03/15/2012 5:03 AM

Differential protection for transformers is not good enough for detecting low current earth faults on star side of the transformer. The REF protection is complimentary to the Differential protection.

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Happy singh
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India - Member - New Member

Join Date: Jul 2010
Location: India
Posts: 162
#2

Re: Electrical Protection

03/15/2012 8:18 AM

Follow link on subject

http://cr4.globalspec.com/thread/62622/Why-to-use-class-PS-CT-s-for-Differential-Protection

Good day KIRE.

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electricalexpert65
Guru

Join Date: Oct 2009
Posts: 2061
Good Answers: 169
#3

Re: Electrical Protection

03/20/2012 11:05 AM

Differential Relay may or may not detect secondary winding earth faults within the transformer. It depends upon the magnitude of the fault current, which again depends upon the mathod of secondary neutral earthing, the distance of fault location from the neutral, etc. Moreover, if the transformer is a Delta/Star Transformer, any secondary earth fault will not be revealed on to the delta side of the transformer. Hence, an REF Relay on the secondary side is a prudent choice to protect the transformer.
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