Coordination of Generator relay with the downstream motor relay

[EEAM]

There are 4 generators connected to a double-ended switchgear with the tie breaker normally closed. I need to coordinate the downstream motor relay (Multilin 469) with the generator relay (Multilin 489). Do I coordinate the motor relay with one generator, 2 or 4? I'm using ETAP.

 

[rbulsara]

Generator overcurrent protection, typically 51V, may be much different than that of a utility source. The current will split between the generators so you need to consider that too. You need to consider the number of generators that would normally be running.

Sounds like you need help of a professional.

Rafiq Bulsara

http://www.srengineersct.com

 

[electricpete]

I'm not sure which aspect of coordinating you're referring to. In terms of selective tripping - wouldn't you attempt to coordinate with 1 generator and then you are covered for any lineup.

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(2B)+(2B)' ?

 

[EEAM]

Thank you for your response. The generators are sized based on the plant total load. The size of the motor is bigger than the size of one generator (At very low temperatures they are almost equal in size). This system is isolated from the utility grid. I want to coordinate the Overcurrent and Inst and I'm not sure whether to create a motor that's 1/2 or 1/4 of the original size and coordinate one generator relay with that motor relay or coordinate the original size motor relay with 2 or 4 generator relays. Hope this makes sense.