51 Device Coordination
51 Device Coordination
(OP)
So as I understand, the recommended time deference in coordinating electronic relays in series is 0.3 Seconds. I am wondering at what point this time difference should be measure on the TCCs since the delta increases with time due to the log scale. Should it be measure at a particular time?






RE: 51 Device Coordination
Wouldn't it be when fault current is causing the relays to operate quickly?
If that is true, then find the highest short circuit current that is seen by both relays and adjust the settings to achieve the required timing margin at that current.
At all lower currents, the margin between the two trip curves should be greater.
RE: 51 Device Coordination
RE: 51 Device Coordination
If you have a 3-cycle breaker or recloser, that's 50 milliseconds, AFTER the relay decides to trip, that you need to add in.
I have seen that overlooked on many occasions.
RE: 51 Device Coordination
RE: 51 Device Coordination
for DT is usually used from 0.18 up to 0.3sec.
depend on the terminal type and breaker.
For IDMT calculation is another.