Synch Check Relay requirements on a double ended sub

[JBUDA54]

I am working on a project where we have a 2000kVA double ended sub that normally pulls power from the utility from two different ckts. Occasionally the utility source is swapped to local generator power. This swap-over from utility to local generator power is done upstream from my double ended substation. This different location has synch checks engaged to allow this swap over. I am getting a request from an engineer stating that he would like synch check relays on the two main 480V 3200A CBs and the 3200A tie. Is this an over kill or is it good engineering practice? The 15KV ckts will always be in synch based on the synch check relays that are preformed up stream of my double ended sub. I am caught in a battle between two engineers. One saying a synch check is required on the 480V load. He states that occasionally they hook up smaller generators to provide power during certain outages. The other engineer states that all the power synching is done at the upstream location and he does want to spend the money to add this relay to his project. Are there any requirements for synch check relays on the secondary of a double ended sub? I have done some google searches on these keywords and have not come up with anything substantial. Thanks in advance.

 

[racobb]

Since you are fed from 2 circuits, and probably only 1 will be on generator, sounds like the possiblity of an out of phase tie does exist if you do not have sync checks on the switchgear.

Alan

 

[rbulsara]

I would not rely on upstream or remote sync check in any case. It is a necessary and cheap insurance. A good practice.

Moreover, in your case how there generator is supposed to be in sync with A, if say only B side utility is lost?

When in doubt, err on the side of conservative approach, although this is not a matter of preference, imho.

Rafiq Bulsara

http://www.srengineersct.com

 

[davidbeach]

If you never do make before break switching the sync check is unnecessary; but if there is any chance of make before break switching, then you really should have some form of sync check. Once you have a sync check relay you will also have the capability of blocking close to a dead line and that should be implemented also.

 

[JBUDA54]

Clarification:

The utility enters a substation upstream of mine at 15kV and is step down to 4160V. The 4160V bus is synch checked prior to the 4160V generators being paralleled with the utility. Once the generators are on line in parallel and carrying the load the utility is disconnected. When the local generators are carrying the load the two ckts into my sub are in synched. When the utility is carrying the load with the generators off line it is my understanding that they are supposed to be in synch (keep reading).

I do argee with the responses that have come in that this is cheap insurance. The engineer arguing to have this feature also stated that if a circuit was modified where a phase was swapped that it could cause a fault if the secondary of my swgr is paralleled.

Thanks to all that have provided input. It is always nice to have experts offering their advise at this site. I work at an engineering office full of senior electrical engineers that could have provided the same response, but I am currently in a construction trailer away from my colleagues. Thanks for helping me in this situation!!!

 

[alehman]

I agree with the others. "Supposed" to be in sync isn't good enough. The sync check relay is a must-have if closed transition operation is possible.

Alan
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"It’s always fun to do the impossible." - Walt Disney