Generator Differential Relay 87 Setting

[Parsons]

I will appreciate any help in setting the ABB differential relay (87M). The following are the available information:

(1) There are 3 ABB 419M relays (Model 419M, IB 7.6.1.7-1). They are used for differential protection (87M) of a 2250KW, 0.8 PF, 4.16KV, standby diesel generator. The two sets of CTs have a 600/5 ratio.

(2) The instruction I downloaded from ABB Website gives me only limited application information. This relay has a non-linear percent differential characteristic with a operation pick-up current of 0.1 to 0.5 Amp. The instruction didn't give a good example on how this relay should be set.

(3) Generally, we try to set the diffential relay to the minimum setting. How do I make a calculation to determine the minimum in this case. Is 0.1 Amp setting the suitable setting?

Regards,

 

[peebee]

There's a little information on a similar Basler relay at

http://basler.com/downloads/genprotguidC.pdf

.

I'd also suggest calling your ABB rep, they're usually pretty good with those kinds of questions, or at least know someone with the answers.

 

[busbar]

Don't usually drop names but call Cliff Downs in ABB's Allentown PA operation.

And, if it's the same relay, don’t forget to install that weird little 3ø outboard reactor that is shipped with the relay, or false trips may drive you bananas.

I apologize for stating the obvious, but especially for the low-end settings of the I-T-E 87M, insist that all six CTs are identical and field proven to have the very same kneepoint.

 

[Parsons]

Thanks for the quick reply from (Peebee) and (Busbar). I will follow up with the ABB contact provided by Busbar on Monday. They are located back East and have already left for today. Hopefully, I will get some recommendation from them.

Finding the right person to talk to is a challenge. Most companies are spread too thin and we are losing the technical capability very fast.

Appriciate all your help!

Regards,

 

[peebee]

"Most companies are spread too thin and we are losing the technical capability very fast."

You can say that again.

 

[riteshbharat]

always remember, the best way to protect a generator winding is by use of high impedance differential protection and not by biased differential, as the setting keeps on increasing with fault current.

cheers