Sequence of Operation of Network Protectors and Feeder CB's

[kartracer087]

What is the usual operation of a feeder protection system supplying secondary networks, is it more typical that the substation circuit breaker will open before the network protector, or the other way around? Reason being, is if you delay the feeder circuit breaker to open a few cycles after the network protector clears, then technically the fault interrupting duty on any device on the primary side of the transformer (such as a SF6 fault interrupter) could be less. This is because the backfeed is elminated before the fault interrupter device can act. However, doing this means you may have a few more cycles of fault current on the high side.

What is typical? Does the feeder MVCB typically beat the network protector? You could set your relaying either way really..

Thanks,

 

[RRaghunath]

Why do you need to delay the feeder protection when all your circuit breakers are rated to the fault level appropriate to the location!

 

[bacon4life]

Network protectors typically only open automatically for reverse flow. Faults in the forward direction do not trigger the network protector to open. The article at

https://en.wikipedia.org/wiki/Network_protector

describes the typical sequence of operation.

Typically network protectors open very fast based on sensitive reverse power. Feeder circuit breakers would rely on much slow time overcurrent relaying.