Relay Settings

[DistCoop]

I've come across a Westinghouse CO-8 relay for a 13.8kV feeder. A testing company has covered up the nameplate of the relay with their test data, but I'm unsure what it means. The paper reads:

120A P.U.
360A -48~
660A -INST


This is fed by a 100:5 CT, so the pickup and the instantaneous makes sense with the settings available to this relay. What does the 360A number correspond to? Is there a way to read the time dial from this information?

Thank you

 

[rcw retired EE]

360 A is 300% of the pickup. That is a typical point for testing the 51 curve timing. The wavy character might mean cycles, so the trip time at 300% is 48 cycles. (I'm guessing). Comparing CO-8 trip curves would get you the TD setting.

Is the Time Dial visible through the front face of the relay? It usually is. That would be another way to confirm the TD setting.

 

[dpc]

Some engineers did not provide the time dial setting for electromechanical relays back in the day. Instead they specified a trip time at a particular current level, feeling this was more accurate than a time dial setting.

 

[DistCoop]

Ahh, of course. I considered that, but was thinking 48ms or 480ms rather than 48 cycles. I should've stared at it longer. A coworker did note that it was 300% of pickup current, which apparently is a common test point.

This test sheet is covering the face of the relay so I can't verify.

Thank you for your comments.