Feeder protection relay settings
Feeder protection relay settings
(OP)
Hi
Does any one have some guidance/standards on the criteria of relay settings for distribution feeder protection (27.6kV and below), espacially for those breakers that do not have reclose function and the feeder protection relay does not have both low-set inst. and the hi-set inst.? My concern is how much percent in terms of the total feeder length that the inst. overcurrent pick-up setting should cover, do you want inst. overcurrent to see the end of line fault or you want it only to see the fault at the first tapping pole and the rest will trip on time delayed overcurrent? I think that is a trade-off between fuse-saving and the reduction of SAIDI and SAIFI, but I don't have clear mind on the criteria, so I appreciate any helpful thought!
Thanks in advance?
Does any one have some guidance/standards on the criteria of relay settings for distribution feeder protection (27.6kV and below), espacially for those breakers that do not have reclose function and the feeder protection relay does not have both low-set inst. and the hi-set inst.? My concern is how much percent in terms of the total feeder length that the inst. overcurrent pick-up setting should cover, do you want inst. overcurrent to see the end of line fault or you want it only to see the fault at the first tapping pole and the rest will trip on time delayed overcurrent? I think that is a trade-off between fuse-saving and the reduction of SAIDI and SAIFI, but I don't have clear mind on the criteria, so I appreciate any helpful thought!
Thanks in advance?






RE: Feeder protection relay settings
RE: Feeder protection relay settings
200% max load current < the inst. pickup < 50% of the end of line 3Ph fault.
But the problem is most faults will cause the feeder breaker to trip. So any good practice can make trade-off?
RE: Feeder protection relay settings
RE: Feeder protection relay settings
Your orignal post did not specify overhead or underground so reclosing maybe an option if you have overhead.
Coordination is an art, and less of a science.
RE: Feeder protection relay settings
RE: Feeder protection relay settings
The high set over current is useful for fast clearing for close in big faults. Problem is that so often there is a coordination point so close to the substation that it can't be used (A slight delay some times helps with fuse coordination).
For everything else there is time over current, which must be set to see the end of line faults (phase to phase, or phase to ground). There is a little debate on how much lower to go to cover fault impedance.
RE: Feeder protection relay settings
RE: Feeder protection relay settings
And that's the answer: Do the best with what you have, or replace it.
I've seen it many times where when I describe the problem to my boss, and we don't have the money. But a year or two later they find the money to fix the problem because someone better politicly connected complained.
RE: Feeder protection relay settings
RE: Feeder protection relay settings
david, I like your correction. I meant the breaker was not wired to have reclose feature.
However, for the existing relays, my thought is to set the hi-set inst. to see about 1/3 of the line instead of the end of line fault, any comments?
RE: Feeder protection relay settings
Time-overcurrent should cover the entire line. Instantaneous should cover about 85% of the way to the first set of fuses. If you have no main line fuses, why not run the instantaneous all the way out and let the time-overcurrent back up the tap fuses?
RE: Feeder protection relay settings
did you mean the inst. setting should see all the way out to the end of line?
RE: Feeder protection relay settings
RE: Feeder protection relay settings
RE: Feeder protection relay settings
RE: Feeder protection relay settings