SR750 MUTILIN RELAY

[swiminelectricity]

Hi,

I have a question regarding GE relay SR-750-003.
What do Ins_OC=1.29, OC_PU=2 stand for? Ins_OC should be larger than OC_PU? Is that right?

Thank you in advance.

 

[rbulsara]

Yes to the last part of your question in general. Where are you reading the settings? What is it protecting? I beleive SR-750 is a feeder relay.

 

[swiminelectricity]

HI,

I read this in SKM project file.

 

[alehman]

The SR750 is a feeder relay. I don't see that exact nomenclature in the documentation, but I would guess that Ins_OC is instantaneous overcurrent pickup and OC_PU is time overcurrent pickup. Instantaneous would normally be set higher than time overcurrent.

http://geindustrial.com/products/manuals/750/750-a4_5.pdf

pg. 37-39.

 

[davidbeach]

I'm not familiar with the details of that particular relay, but it is not at all uncommon to find a utility feeder relay set with its instantaneous (50) pickup set lower than its time-overcurrent (51) setting. On a fault, the 50 would pickup and trip first, the recloser would close the breaker again after its set time, either blocking the 50 or allowing it one more shot, after which the 51 element will have one or two shots. This type of scheme is often referred to as a fuse saving scheme, the instantaneous shots are an attempt to let the fault self clear without operating any fuses, the longer shots are timed to allow a downstream fuse to clear a permanent fault.

 

[alehman]

Didn't think about a recloser. To further clarify, recloser operation is normally used on overhead circuits where faults may clear themselves.

 

[Bung]

If reclosing was involved, it would more likely be a SR760 (which is a 750 with built-in reclose facility).


Bung
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