Auto reclose initiation in 33kV OHLs

[RRaghunath]

This is regarding the 33kV OHL that has no. of tap offs catering to various field installations along the run.

There is a Pole mounted Auto Reclosure (PMR), with electronic protection module for setting OC and EF protection, in each of the tap-offs.

There is also a Auto reclose relay in the beginning of the OHL in the 33kV SWBD and the OC & EF protective relays.

The auto reclose in the individual tap offs is initiated by the operation of instantaneous OC / EF elements in the protection module of the PMR. Whereas, if the instantaneous elements in the protective relays in upstream 33kV SWBD are set to initiate the auto reclose for the main OHL, the grading with the protection in tap offs is lost and if the time delayed elements initiate the reclose, then the tripping of the main OH line for faults in the main line section is delayed and can mean unsuccessful reclose as well.

Could any one please advise. I would appreciate if some one can tell me what is the practice followed under such situations.

Thank you in anticipation.

 

[wbd]

For this situation, you have to look at the TCC's and conductor burn down curves and see if you can delay the breaker operation to give the side tap reclosers a chance to operate.
You may also have to put in a very fast recloser operation on the first indication of a fault with a close delay to give the fault time to clear. Remeber that 80 - 90% of OHL faults are temporary (tree contact, animals, etc.)
I guess the bottom line is can you live with allowing the main bkr to hold back until the reclosers can cycle thru all their operations until lockout. This would keep the rest of the circuit energized.
If you're going to try to let the main ckt bkr hang in until the reclosers operate, you need to be careful on the TCC. If your main bkr is using electro-mechanical relays, the disks may not have time to fully reset prior to the recloser operating, therefor your relay TCC has shifted. You might experience some co-ordination problems.

 

[stevenal]

The practice is to use a relay that has sequence coordination capability upstream from the recloser. This type of relay can sense if the recloser has operated and skip the instantaneous trip when needed. Most microproccessor relays have this feature. Look around

http://www.selinc.com

for more info.

 

[jbartos]

Suggestion: It may be a good idea to adhere to some industry standards, e.g.

http://standards.ieee.org/reading/ieee/interp/C37.60-1981.html

Also, if there are any short circuit calculation results available.