PROTECTION COORDINATION
PROTECTION COORDINATION
(OP)
Which fault current is to be used for coordination of IDMT overcurrent relays - 1/2 cycle symmetrical or interrupting current (4-5 cycles, 50Hz). I am using the IEC 60909 method of determining scct currents (EDSA software).
I have been through many standards (IEEE color books) and cannot find a definitive reference to this.
In depth discussion would be welcomed.
I have been through many standards (IEEE color books) and cannot find a definitive reference to this.
In depth discussion would be welcomed.






RE: PROTECTION COORDINATION
The interrupting value, while it is based on the symmetrical fault current, usually takes into account the manufacturer's test procedure for the interrupting rating of the C/B, among other factors. This results in a value that is usually greater than the symmetrical fault current. The important thing about relay curve coordination is the time difference at the high current end of the curve, usually required to be a minimum of 0.3-0.4s for electromechanical relays(per IEEE 242). You might be able to cut this time in half for electronic relays, but this is a good rule-of-thumb.
RE: PROTECTION COORDINATION
RE: PROTECTION COORDINATION
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