Recloser by passby protection 2

[gvolley]

To protect faults on our MV long distribution lines we use reclosers to see end of line faults. The questions is what is the protection practice when the reclosers are in the bypass mode for repair or maintenance and the back up protective device cannot see the end of the line fault.. Is exposure acceptable or are temporary fuses installed? If exposure is acceptable is there an acceptable time limit for exposure?

 

[dpc]

Use a fused bypass.

 

[gvolley]

That is done very often. The issue becomes the time, (using line crew), it takes to install temporary fuses versus just using the reclosure bypass blades when the maintenance time for testing the controls is very short. Does anyone accept that kind of exposure.

 

[davidbeach]

Every part of the system should be covered by two different protective devices. So for any given recloser on the line, the upstream recloser or feeder breaker should always reach through the recloser in question and cover the entire line out to the next device beyond the recloser. This may be yet another recloser or may be multiple tap fuses. Having only one device that can sense a fault and trip for it is very risky. The upstream device will generally be slower than the recloser in question, but it may have tagging capabilities that would turn on an instantaneous trip and block reclosing to provide additional protection for the personnel working on the bypassed recloser.

 

[Mbrooke]

Fuses are the best option. good engineering practice is that reclosers that may cause protective issues when bypassed should have a cutout installed instead of a solid blade disconnect. That way a fuse may be inserted in bypass mode. Up to a 200amp T, K, ect fuse may be used as this is what most cutouts max out at. You will lose auto reclose function, but you will not have any high level faults going unnoticed.

 

[pwrtran]

you can also switch some downstream sections to a different feeder and the rest will be covered by breaker protection

 

[gvolley]

Our practice is to have a maximum of 3 sec to clear end of line faults. Keeping in mind no alloweed equipment damage allowed. What no one is sure about is where that number came from. The REA has some comments to allow up to 20 sec to clear end of line faults. What is the practice, i.e. accepted allowed time, to clear end of the line faults by utilities in normal conditions or in the condition when a recloser is being bypassed.

 

[Mbrooke]

On a short line its easy to allow the substation breaker to take over, but long lines especially where the conductor slims down are a challenge. Plus you dont want a fault to trip a main feeder during a re closer bypass. Good point, pwtran, if the feeder has other sources after the recloser in question those can be of help.