87 - Bus Differential Relay Trip Settings

[MrJLH]

I have a 87 Bus Differential Relay I may need to adjust trip settings on. Is there any guidance out there on determining the trip settings for something like this?

Thanks

 

[EmagSamurai]

I'm not sure I've ever had to set one up from scratch, so maybe someone with more experience will chime in. That said, I believe you need to establish the minimum expected fault current and be sure the relay is sensitive enough to detect and actuate below that. For timing, we typically set ours for fast operation.

 

[NewtonLaw]

Bus diff is usually supplied by using linear couplers and not CTs. These systems are usually set to trip instantaneously for bus fault currents to prevent damage to the equipment supplying the fault current.
Settings are based on the damage curves of the device being protected. Usually I set them to 50% less than the allowed damage levels. You need to know first what it is you are protecting and what other protection schemes that may be applied such as harmonic restraint if a transformer diff scheme was being used.