85CO Switch Function 1

[DTR2011]

Generally speaking, I have seen 85CO switches on lines that have a communications based protection scheme.
Is there any general consensus on what exactly placing the 85CO switch in the "Test" position should do, especially to the protection
at the remote end?

My understanding would be that if the local end relaying is being tested / maintained, this would prevent any local permissive / blocking signals. Fairly straightforward for a POTT/Directional comparison scheme. What about an 87L application? What about a mirrored bit application (say the local breaker status).

I've already heard "it depends" from some.

 

[davidbeach]

It does what ever you decide it does. And it's really helpful if it does the same thing at both ends. ;-)

We have a Mirrored Bits Transfer Trip Enable switch. When not enabled the relay does not send any transfer trip bits and it will ignore any received from the remote end(s). We don't consider remote breaker status as "transfer trip" and do not block those bits.

For 87L we use a separate switch. That input is also transmitted to the remote end(s) and each relay's 87L torque equation requires the local input as well as all remote inputs to be asserted for 87L to be enabled.

Pick what you want it to do and implement it. On your own system it can be pretty much anything you want it to be; on tie lines it's really important that both parties understand exactly what's going on.