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Topic Title: Sizing Transformer Fuse For compact Substation Unit
Topic Summary: Compact Substation
Created On: 29 November 2012 06:43 AM
Status: Read Only
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 29 November 2012 06:43 AM
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jackdaniel

Posts: 69
Joined: 29 November 2012

Hi Guys,

Im confuse in sizing the HRC fuse of the RMU for transformer protection, From IEC 60787 Table, the fuse for 1250KVA transformer rated 12KV,the fuse rating is 100A per pole.But if we use the circuit breaker, the rating is 2000A. why it's different?
 29 November 2012 11:09 AM
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ArthurHall

Posts: 735
Joined: 25 July 2008

A circuit breaker may be rated at 2000A but the protection relay can be set down to what ever you want.
2000A is probably the standard size for that unit.
 30 November 2012 12:55 AM
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jackdaniel

Posts: 69
Joined: 29 November 2012

Thanks, i got it..
 01 December 2012 06:49 PM
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JonathanHill

Posts: 225
Joined: 09 September 2002

I wonder if there is some confusion here - it would be very unusual for an RMU feeding a 1250kVA transformer to be rated above 200A. If a 2,000A device were used, then the protection would need to be set at <5% of rating which is a big ask for accuracy.

A 2000A CB rating would, however, be consistent with the LV side of the transformer.

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Jonno
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