Loss of Utility Protection
Loss of Utility Protection
(OP)
A quote from an email I recently saw, "The load on this feeder may at some times be less than the capacity of the generator."
The utility is requiring this cogen provider to supply an SEL 700G protective relay. Can anyone help me understand how it's possible to sense loss of utility if the connected load doesn't challenge the overcurrent/underfrequency elements? By sensing a change in Power Factor?
The "At some times" part is somewhat worrisome if the utility is expecting this line to be dead when they open its feeder, and there's still a perfectly happy generator on.
The utility is requiring this cogen provider to supply an SEL 700G protective relay. Can anyone help me understand how it's possible to sense loss of utility if the connected load doesn't challenge the overcurrent/underfrequency elements? By sensing a change in Power Factor?
The "At some times" part is somewhat worrisome if the utility is expecting this line to be dead when they open its feeder, and there's still a perfectly happy generator on.






RE: Loss of Utility Protection
RE: Loss of Utility Protection
G59 is a UK document detailing requirements for detecting loss of utility. The other two are methods of achieving it.
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If we learn from our mistakes I'm getting a great education!
RE: Loss of Utility Protection
I interpret the utility's statement as them requiring reverse power relay. When the gen is capable of producing more power than the load on the feeder, it will back feed the utility, which is not always permitted by utility or may not be in the agreement. It does not have to be dead.
Even all relays need to be utility grade. Many mfr's built-in protection may not cut it.
Yes, talk to the utility co in the end.
Rafiq Bulsara
http://www.srengineersct.com
RE: Loss of Utility Protection
1) 59
2) 27
3) 81O
4) 81U
You may required to have transformer trip if the generation greater than the threshold size specified by the utility.
RE: Loss of Utility Protection
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If we learn from our mistakes I'm getting a great education!
RE: Loss of Utility Protection
ROCOF or df/dt or 81R
vector shift is more...problem,.
posssible use logical functionality, like to 81U or 81O with df/dt.
RE: Loss of Utility Protection
RE: Loss of Utility Protection
It is common utility practice to use automatic reclosing to ensure customers don't have a lengthy outage for a transient fault. This is the real risk to your co-gen. Like David said, transfer trip is recommended.
RE: Loss of Utility Protection
RE: Loss of Utility Protection
RE: Loss of Utility Protection
RE: Loss of Utility Protection
RE: Loss of Utility Protection
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If we learn from our mistakes I'm getting a great education!