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Grounding Riddles No.43 - Selective Earth fault protection in multiple generators
Six No 11kv star connected generators are paralleled with each other on common bus through dedicated bus. Common Low resistor NGR with switched neutral to earth link for all generators will be proposed scheme. Selective relying to identify the faulty source is to be designed.
The earth fault relay 51N with NGR will trip all the generators if the fault occur in only one generator. How can I design the ground fault protection scheme so that only the faulted source will get isolated from the system.
Only one neutral will be connected to the NGR.
Remaining generators neutral will be isolated through Vacuum contactors.
May be 67N along with 51N will do the job but I am not sure theoretically and practically.
Author : Muhammad Waqas - From: Pakistan
 
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