GE IAC relay as Directional Overcurrent Relay? 2

[dpc]

I'm looking at some one-lines for an old facility that shows several GE IAC relays used as directional overcurrent relays. Since the IAC is non-directional, I'm not quite sure how this is accomplished. I don't doubt the drawing is correct, but I'm curious about the implementation.

Maybe some type of external polarizing relay to block the trip contacts?

Has anyone run across this before?

 

[davidbeach]

Using electromechanical relays, you would likely have a directional element, which has some low minimum magnitude for operation along with the non-directional overcurrent relay. Direction plus overcurrent equals trip.

 

[dpc]

Right, I could understand that - but nothing is listed in the relay setting sheets, and these have generally been pretty complete.

The relay is listed as an IAC51A1CAP, so I'm guessing the "CAP" is making it directional somehow, but I can't find any GE info on a CAP relay or function.

The one-lines do show connections from the PTs to the relay, so maybe it was some special add-on element.

 

[davidbeach]

The GE CAP relay is a 3 phase directional relay. My GE electromechanical relay literature does not seem to indicate an IAC/CAP combination, but there were CAP/IAV combinations in the same case for generator motoring protection. Who knows what kinds of specials there might have been, but the IAC would be doing the overcurrent, without direction, and the CAP would have been doing the direction, without overcurrent. Wire them in series and you have a directional overcurrent relay.

Can you go to the installation and look at the relay(s) in person?

 

[dpc]

I can't go right away, but I will be going there at some point. What you say makes sense. I just didn't have anything on a CAP relay in my old GE stuff.

You're right - there were a lot of "special" relays made back in the old days.

Thanks.

 

[RalphChristie]

David, thats well worth a star.

dpc:
For IAC-overcurrent relays:

http://www.geindustrial.com/cwc/products?pnlid=6&famid=31&catid=222&id=iac&typeId=3

For CAP-relays:

http://www.geindustrial.com/multilin/notes/ger2309a.pdf

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[davidbeach]

Thanks guys.