Reclosing on 27.6 kV

[UtilityGy]

Hi All,

I am programming a GE relay for a new feeder in a 27 kV station. feeder length is approx. 7 miles. Approx. 3 miles of feeder length is underground cable and rest is overhead line.

Is there a thumb rule that can advise for this feeder not to have reclosing because approx. 50% of feeder length is cable.
Any suggestions ?

 

[dpc]

My suggestion is to not reclose. If there is significant exposure to trees, squirrels, etc on the overhead portion, you might choose to reclose, recognizing that reclosing into UG faults can increase fault damage and perhaps reduce overall safety. I'm not aware of any strong consensus on this issue, however.

In recent years, customers seem much less tolerant of reclosing operations - seeming almost to prefer a longer outage than the brief blips that create problems for all of their electronics.





David Castor

http://www.cvoes.com

 

[Marmite]

Coming at it from a utility perspective, we get penalised for lost customer minutes. Something like 80-90% of overhead line faults are transient which means that most will be successfully reclosed. When the control centre gets an alarm to say that the circuit breaker has tripped, the first thing they will likely do is attempt a manual reclose via scada, so you might as well have the relay try for you. An underground cable fault is a permanent fault in any case, which will require a new piece of cable to replace the faulty section regardless of how many shots have been attempted.
Regards
Marmite

 

[slavag]

Im second with Marmite.

From protection perspective possible do few options for shots, depend on the fault type, etc...

 

[dpc]

If the "underground" fault is in a pad-mounted transformer or a switch cabinet, the reclosing can significantly increase damage and hazards to the public.

It is a arguable point. For a feeder that is 99% underground and 1% overhead, I don't think very many would argue for reclosing. So obviously, there is a tipping point somewhere.



David Castor

http://www.cvoes.com

 

[jghrist]

If the underground portion is at the beginning of the feeder, you could use a line recloser at the UG to OH transition. If the UG portion is after the OH portion, you could put overcurrent protection at the OH to UG transition that is faster than the initial trip on the feeder protection.

 

[dpc]

Good point, jghrist.

David Castor

http://www.cvoes.com

 

[Bramb]

Hi guys,
maybe this can help

http://siemens.siprotec.de/download...1_Protection_of_Combined_Cable_and_OHL_en.pdf

Ciao
Erminio


The difference between overload and short circuit lies in the nature of the fault, not in the value of the current.

 

[desrod]

You might also want to install a fault detector at the UG-OH junction and use the info to decide to manually reclose from SCADA . It is cheaper than a second recloser and it could send the info directly to the operator.