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Feeder Relay Setting

Feeder Relay Setting

Feeder Relay Setting

(OP)
From the attach JPEG file with single transformer my understanding as it relates to calculating the relay 50/51 elements are as follows:
1) Determine max transformer FLA, NATURAL COOLING (55deg.C)1mva/  (1.73x3.3kv)=175A.
2) Select phase OC relay(51) pickup in the range 150-300% of transformer OA rating, ie, (1.5xIfl)<(51 pickup)<(3xIfl)--(1.5x175)<(51 pickup)<(3x175)gives; (263A)<(51 pickup)<(525A)---Select pickup setting = 280A, 160% FLA.
3) Select HV CT ratio above Trxf. FLA: 400/5A
4) 51 Pickup in sec. current: 280/(400/5)= 3.5A
5) Assume a max trxf. sec. SC of 30ka.
6) Max. primary infeed to a sec. fault = 30000/(3300x420)=3.8ka
7) Select device 50 setting >1.6x3.8ka=6.1ka
8) Element 50 setting sec. = 6.1/(400/5)=76A delay =0

Finally to my question:
Assuming the the above calculation is correct!!!
1) With two transformers in parallel as in the other JPEG image would line one above be x2?
2) Would we use the max secondary fault current for one transformer or do we add the fault current for both trxf. secondaries.
3) With a configuration of a transformer and motors in parallel as shown in one of the JPEG image; would we add both the trxf. max sec. fault current and the motor bus fault current to determine the infeed max current? In addition, one motor is used as a spare. It only comes on when one of the other motor is being switch. Can we use a factor of say, 25% FLA for this motor to add to the bus total current draw?

I know the question is a bit long but I would love to clarify the points raised.


Regards
JPS

RE: Feeder Relay Setting

(OP)
davidbeach,
You replied to another thread with the same question but that thread was deleted and as such I was not able to read it. If you read the reply, please repeat your reply here if it is not too inconvenient for you.

Please attachment with all three SLD.


Regards

RE: Feeder Relay Setting

I just said that you had already asked the question.  Please don't repeat.   

RE: Feeder Relay Setting

This is a bit involved for an Eng-Tips question.  We are not here to do your work or even check it for you. You really have about 10 questions/issues buried in there

I think if you can break this down into a few separate simple questions in a logical order, you can probably get fairly quick responses.

But most of us don't have time to download and review a large amount of information.  Or at least I don't.

dpc

David Castor
www.cvoes.com

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