Utility distribution feeder reclosing timing 2

[apowerengr]

Questions were started in previous threads. Can anyone discuss their reclosing scheme for a utility distribution feeder including target reset (manual or automatic upon successful reclose), reclosing open interval timing (how long do you leave the feeder off before attempting reclosing?), how many reclose attempts do you take before lockout and how long to you let the reclose relay (79 device) be shot advanced before you reset it to it's first shot? I'd also ask you to denote if you're using reclosers or breakers w/relays. If breakers, what about the breaker duty cycle as it relates to the reclose interval and number of attempts.

Thanks!

 

[davidbeach]

There are as many answers to this as there utilities doing reclosing. It just depends on many different things. There aren't necessarily any right answers, just some that work better in some situations than others.

 

[dewone]

Typical reclose times are like 7-10 seconds after trip. 3 Shots then lockout. Schemes I've seen anyway.

 

[jghrist]

Some factors to consider in the initial reclosing interval:

1. Arc deionizing time.
2. Possibility of multiple lightning strokes.
3. Effect on customer equipment.
4. Breaker duty cycle.
5. Reset time of upstream overcurrent relays.

I like to make the first interval 2 seconds for the second factor. This conflicts with the third factor, however. An immediate reclose may keep customers' computers from tripping off. Breakers usually require at least a 0.3 second interval which will make most computers trip off anyway.

 

[tinfoil]

it can also depend on the nature of the feeders themselves.

Long rural overhead feeders are going to experience more 'transient' faults from branches/squirrels/lightning/etc, and we therefore may use 3 shots to lockout (i.e. 2 recloses) to maximize the chances of an automatic restoration.

Dense urban underground feeders tend to have only 'sustained' faults, and we use only 2 shots to lockout ( 1 reclose), since faults tend not to go away, and you don't want to beat up your system any more than you have to.

 

[davidbeach]

Reclosing on underground feeders? Do you ever find transient faults on underground feeders?

 

[apowerengr]

I've seen transient faults on underground feeders usually at termination points or pad-mounted switchgear. Mice, snakes and even an occasional skunk. I agree with one reclose on totally underground feeders as I've experienced multiple recloses on underground damaging the cable to the point that we could not "thump" it to locate the fault. As for reclosing intervals on feeders using breakers, I like to purchase breakers with 2x the interrupting rating required, then use 5-5-5 or 5-10-10 second reclose open intervals. This stays within the duty cycle of the breaker but keeps the wires sparking so if you have the general public involved (car-kill for example)they stay away. Some reclosing intervals with 30-45 second open intervals allow too much time in my opinion.

 

[dpc]

For a strictly underground feeder, we do not recommend reclosing to our clients. Even one reclose into a cable fault would seem to be asking for a lot of unnecessary trouble. For feeders that are a combination of OH and UG, we generally reclose, but try to size the UG fuses to clear quickly, or use a pad-mount interrupter to protect the UG portion.

For overhead feeders we generally go with one fast trip with high-speed reclose (2 or 3 cycle delay) and then two slow curves with 5 to 10 sec delay. I've never seen much point in delaying beyond 10 sec, but a lot of people use greater delay times.

 

[wfowfo]

We used to use longer reset times when we had to coordinate with induyction disc transformer relaying. We're getting away from that now.
What I want to know is; what "reset" time do you use after a successful reclose for the 79 circuits to go back to a "normal" mode?

 

[stevenal]

180s reset. Regardless of the presence of induction disk relays, too short a reset can ensure lots of operations. Incident 1:
Two feeders exited a station on double circuit structures. A tree through both lines caused a circuit to circuit fault. Recloser A would operate a few times, then recloser B would operate while A reset, and so on. High side fuses eventually cleared the fault after way too many recloser operations. Incident 2: On a cold winter morning, a coworker complained of all the blinks he saw at home prior to coming to work. I went to the station in question, and watched the recloser bang away. It would stop just long enough so it could reset, then it would start banging away again on the overload.

 

[jnims]

To get an overview of what some utilities are doing, go to

http://www.pes-psrc.org/i/

Click on the "Published Reports" link then scroll down to the Working Group Report "Results of the 2002 Distribution Protection Survey".