over current device
- Thread starter jbolen
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zog
Senior Member
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- Charlotte, NC
Jonny 5 need more input
If the transformer primary is 11kV, the possibility is that it is on a UK system or one based on it in which case the secondary could be 400V.
On that basis, the rated primary current would be about 66A and the secondary 1804A.
beanland
Senior Member
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- Vancouver, WA
Fuse
Fuse
So, 66A full load current means 65-100A primary fuse. The speed and rating of the fuse needs to be checked against the damage curve and iinrush points to make sure the fuse is not damaged by inrush and provides adequate overload protection for the transformer. Also, at larger transformers, it is often wise to install current limiting fuses because the main fuse cannot interrupt the current for an internal transformer fault.
Fuse
So, 66A full load current means 65-100A primary fuse. The speed and rating of the fuse needs to be checked against the damage curve and iinrush points to make sure the fuse is not damaged by inrush and provides adequate overload protection for the transformer. Also, at larger transformers, it is often wise to install current limiting fuses because the main fuse cannot interrupt the current for an internal transformer fault.
In my orginal question I was trying to keep it simple, but you seem to be on to what i need to know.
What I have is 400 volt generator feeding a step up transformer to 11k volts.
It has a 620 amp high voltage breaker.......this is in Iraq.
I had come up with 66 amps also, but did not understand why? a 620 amp bkr.
thank you
J Bolen
beanland
Senior Member
- Location
- Vancouver, WA
Relay and Damage Curve
Relay and Damage Curve
A 620A rating is the continuous current rating. Most devices in 15kV-class start there and get bigger. So, the 620A is adequate for normal loads but you need to have relay settings that are appropriate for the transformer and generator. Attached shows the damage curve for a transformer and a 100A extremely inverse relay that would trip the 11kV breaker to protect the transformer from damage.
Relay and Damage Curve
A 620A rating is the continuous current rating. Most devices in 15kV-class start there and get bigger. So, the 620A is adequate for normal loads but you need to have relay settings that are appropriate for the transformer and generator. Attached shows the damage curve for a transformer and a 100A extremely inverse relay that would trip the 11kV breaker to protect the transformer from damage.
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