Impact Of Fuse Blowing Protection Scheme On Live Line Activity 1

[opmgr1]

I am looking to ask our protection people to revised some of the protection scheme currently employed by our utility. The scheme used currently is the fuse saving scheme. To improve MAIFI I am looking to employ the fuse blowing scheme on some feeders. What is the impact if any of this scheme on live line work. Is there any utility experiences where this is concern?
Off the bat one can argue that when the recloser is in the non-auto reclose mode to facilitate live line work if there is any mis-hap then the recloser will operate instantaneously on the fuse saving scheme than against a time delayed operation on the fuse blowing scheme. I believe that this is some what of a pseudo-protection. Any comment?

 

[stevenal]

Initiate instantaneous tripping when reclosing is disabled for live line work. Won't help much for electrical contact, but will decrease arc flash burns should a worker initiate a fault.

 

[davidbeach]

What stevenal said. Also, you will be increasing the through fault damage to your substation transformers by blocking instantaneous on the feeders. If your MAIFI isn't bad enough to be drawing penalties from your state PUC, is the reduction of transformer life worth the benefits derived from a lower MAIFI?

 

[opmgr1]

The penalty is definitely not worth the reduction in the life of the transformer, however each of these transformer have some level of fault/ short-time withstand ability without loss of life IEEE C57.109. What will be ensured is that the reclose interval of the time delayed settings is within the vallues illustated by IEEE bearing in mind that all our transformers were spec. as per C57.12. My concern is that is there any utility that do live line work on feeders that are protected under fuse-blowing scheme?

 

[davidbeach]

In our system, tagging the line both blocks reclose and turns on the normally blocked instantaneous relay element.

 

[opmgr1]

The problem with us is that we have various brands of reclosing relays. In some stations we use the SEL 351 which will allow you to program a separate group for live line settings, however the Cooper Kyle reclosers do not allow you to do this and we have quite a few of these in our stations. davidbeach what brand reclosers do you utilise. Not that there is any promotion taking place but the features you described is interesting and would suit my purpose.

 

[dpc]

What Cooper Recloser control are you talking about? The newer ones (Form 6) should have alternate setting group capability.

 

[davidbeach]

I deal with things at the substation level, outside the fence things get a bit fuzzier. At the substation, reclosing is done by the feeder breaker, either through a separate reclosing relay or through the reclosing logic of the feeder relay. How the tagging switch causes things to happen depends on the devices installed at the station, but in general terms the tagging switch connects the instantaneous relay element to the trip bus and separates the reclosing relay element from the close bus. What might be done with reclosers out on the time, I couldn't say for sure.

 

[opmgr1]

I understand all this. What I am looking for is something like this. I once worked with a line recloser that use the SEL 351 relay. There is a "Live Line Enabled" button, that when activated would disable the reclosing ability of the recloser and automatically switch to a different settings group that is programmed with the live line settings and so even though normally the instantaneous trip would be disabeled, for that particular group it can be enabled. I thought this was what davidbeach was making reference to. dpc is the Form 6 capable of doing this?

 

[tem1234]

Form 4C is capable of doing this. There's an alternate minimum trip and you can desactivate reclosing with switch inside the control panel, so i'm pretty sure that form 6 will do it.

Utility were i am do this kind of stuff often when people are working on line. They desactivate the reclosing option and put a very fast trip curve.

 

[dpc]

opmgr1,

Yes the Form 6 basically does this automagically. When Hot Line Tag is selected it will go to one-shot and switch the protection to the "Hot Line Tag" definite time delay which can be set as low as you want. Actually it shifts to the composite curve of Hot Line Tag Definite Time and TCC1 curve - using the faster of the two for any current. So you can set a specific definite time delay for Hot Line tag condition, based on the minimum pickup settings. These can all be different for Phase and Ground.

If that doesn't float your boat, you can set up an alternate protection group, activated by the Hot Line Tag toggle switch, I believe.

I think the Form 4C can do something similar.

 

[opmgr1]

dpc thanks a million. I will touch base with our protection persons to determine if we use the Form 4C or the Form 6. These definitely have the functions that I am looking for.

 

[dotdognz]

The cooper Form 5 recloser also has this function, if you happen to have those on your network