Earth Fault Relay Acting Source or Load

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madhu_rtpp Participant Join Date: Jul 2013 Posts: 1	Earth Fault Relay Acting Source or Load 07/09/2013 12:11 PM
	in the below circuit diagram left side is the source from a 132/33 KV transformer and a radial feeder is seen which feeds the load through 33/6.6 KV bus. There are two motor loads of of 1080 KW each. There are two breakers one at source side and the other at the load side. Earth fault protection is given for both source and load side breakers. The source side ct ratio is 400/1 A and load side CT ratio is 75/1 A. the residual CT setting at both load and source side is 20% ( 80 A at source side and 15 A at load side). Now my question is that if a earth fault occurs in the radial feeder, whether both the source breaker and load breaker trips or not. If the fault occurs near the load side which breaker trips first source or load?
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TonyS Guru Join Date: Aug 2010 Location: Resting under the Major Oak Posts: 4347 Good Answers: 181	#1 Re: Earth Fault Relay Acting Source or Load 07/09/2013 3:53 PM
	Is this a homework question? Looks like it to me. __________________ The reports of my death are greatly exaggerated.
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Ritz11 Active Contributor Join Date: Jul 2013 Posts: 11	#2 Re: Earth Fault Relay Acting Source or Load 07/10/2013 7:37 AM
	Obviously if fault occurs after the CT location in load side then Load side breaker must be tripped first. but fault occur just befor CT location then source side breaker will be tripped. There are many things which needed to be considered here, like other load details connected to the source, this system is earthed system or floating system, etc.
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electricalexpert65 Guru Join Date: Oct 2009 Posts: 2061 Good Answers: 169	#3 Re: Earth Fault Relay Acting Source or Load 07/14/2013 11:46 AM
	That depends upon the type of earthfault protection (time delayed or instantaneous or residual, etc.) and the co-ordination between the load side & source side relays. Assuming time delayed protection with proper co-ordination, then for a fault at the load side (near the motors), then first only the 33kV CB must trip and of it does not trip in the rqeuired time, then the 33kV upstream CB would trip. Whereas if the earth fault is at the location shown in the picture, then only the upstream 33kV CB will trip as the down stream 33kV CB protection relays would not see this fault.
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