×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Loss of Utility Protection

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.

RE: Loss of Utility Protection

As the utility I'd be requiring transfer trip in that case. Probably best to talk to utility.  

RE: Loss of Utility Protection

Google the one or more of the following: "G59 relay"; "ROCOF relay"; "vector shift relay".

G59 is a UK document detailing requirements for detecting loss of utility. The other two are methods of achieving it.
  

----------------------------------
  
If we learn from our mistakes I'm getting a great education!
 

RE: Loss of Utility Protection

This is a common interconnect requirement for synchronous generators. (by most utility co. in the USA).

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

Even there is a load match but the frequency may more or less slip away.  So the basic anti-islanding protection shall have the following elements:
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

Normally those functions are too slow to prevent a prime mover stall under gross overload, which is why a vector shift or rate-of-change-of-frequency relay is used instead. It detects the slowing of the set before it reaches the point of no return.
  

----------------------------------
  
If we learn from our mistakes I'm getting a great education!
 

RE: Loss of Utility Protection

What Scotty say.
ROCOF or df/dt or 81R smile.
vector shift is more...problem,.
posssible use logical functionality, like to 81U or 81O with df/dt.
 

RE: Loss of Utility Protection

btw, G59 is great document, one of the best on the LOM ( loss of main) issue.

RE: Loss of Utility Protection

As far as "expecting the line to be dead", I would hope the utility would use lockout tagout on all sources and personal safety grounding to ensure the line is dead when needed for work.

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

Its not simple provide transfer trip in the distribution network

RE: Loss of Utility Protection

No, it is simple enough, just not inexpensive.

RE: Loss of Utility Protection

Yep, David, you are right.

RE: Loss of Utility Protection

where can i find G59 document?

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources