pad mount transformers, underground feeders question

[in the bucket]

We have a 5 kv distribution line dead ended on a dip pole. There are three solid blade/porcelain "chocolate box" type disconnects feeding one set of 3 phase undergrounds. There's about a quarter mile of underground feeding three 500 kva pad mounts for various commercial properties.

A few months back, I got sent out to pull these disconnects so a contractor could work on a service. It was 5 am and pitch dark out. I pull the first one, when I pulled the second, it drew an arc fully open. I remembered some old time telling me if that happens, wave the stick through the arc to kill it. That didn't work and this thing was blazing. Now I can't see sh*t with the ball of fire to get the hot stick into the hole to try to close it. I get it closed. Second try, I get it open without an arc. The third one opens fine.

OK, so now I know that these solid blade switches are not made to break a load and there is no means to put a load buster on them.

I can't kill this whole circuit in the future because it feeds a couple of neighborhoods too.

If I have to get these transformers off in the future, would you pull the elbows off of the bushings with a hot stick live? I've never done this or seen it done. What about re-energizing it? Would you only do it if you had access to the building to kill the load on the secondaries? I know if the elbows have white bands they are load break elbows, but I have no training on practical methods involving UG and pad mounts, any tips would be greatly appreciated.

Maybe the best thing would be to change out the chocolate boxes to some decent switches, but in the meantime, I'm stuck with what is there.

[Lineman North Florida]

We break load with load break elbows all the time and I wouldn't hesitate going that route knowing what you do about the non load break switches, but rather than set up at 3 different pad mount transformers each time I believe I would push hard to change out the switches at the dip pole. One final thought, are the padmounts feed-thru type? if so do they have an internal switch?

[Orgnizdlbr]

I wouldn't make or break three phase load with an elbow, number one its prohibited on our property, number two you have the feroresonance possibility. Sounds to me like your engineers need to find a spot to cut in switches with load break capability.

[lewy]

I am on the same page as LNF I would pull the elbows and park them, then go back and change the switches out to new . Also like LNF said if the transformer has an internal switch use it first then open the switches then park your elbows for a visual open, but either way I would be getting rid of those old switches. Not likely feroresonance at that voltage.

[in the bucket]

We break load with load break elbows all the time and I wouldn't hesitate going that route knowing what you do about the non load break switches, but rather than set up at 3 different pad mount transformers each time I believe I would push hard to change out the switches at the dip pole. One final thought, are the padmounts feed-thru type? if so do they have an internal switch?

Next time we do infrared scanning and have everything open for inspection I'm going to check for the internal switches. They are feed through, that I know. I'd be hesitant to pull an elbow on the first one, that would be pulling the load on all three transformers. Then, the second elbow would have a huge load on it as everything is single phasing now. I guess the best way to do it if I had no choice would be to work the end of the line forward to the dip pole. Thanks to everyone that had input. I'm going to try to get the switches changed out, but, unfortunately, I have little say in the matter.

[lewy]

Take an amp check first, they are good up to 200 amps. I would be telling them I will be changing them the next time it is out. As far as an internal switch you would be able to see it when you open the door.

[in the bucket]

Take an amp check first, they are good up to 200 amps. I would be telling them I will be changing them the next time it is out. As far as an internal switch you would be able to see it when you open the door.

I pulled an elbow kit off the shelf the other day and read all the nomenclature. If I recall, inside the pad mount there are slots for parking stands, I'm pretty sure we don't have these stands. They would be a separate piece that slides into the slot. Some of our transformers have the red bushing covers sitting in those slots if there is anything there at all.

I have to look into this or I'll end up with three hot cables flopping around someday. All our other locations have a dip pole for every transformer, there's no other location with multiple transformers on one run. I've never had to pull an elbow. We just pull the cutouts at the pole. I replaced concentric neutral cables once and did the terminations myself but I just put the elbows on the transformer by hand before I heated it up. If I ever get the opportunity with a de-energized transformer, I'm going to grab a shotgun stick and practice pulling and installing elbows.

[lewy]

You have to have parking stands as well as caps that go on the live bushings. You should give the elbows a slight twist to the right to break the seal, if they have never been pulled before can be quite difficult. I was reluctant to give advise on pulling a live elbow online.

[Lineman North Florida]

I pulled an elbow kit off the shelf the other day and read all the nomenclature. If I recall, inside the pad mount there are slots for parking stands, I'm pretty sure we don't have these stands. They would be a separate piece that slides into the slot. Some of our transformers have the red bushing covers sitting in those slots if there is anything there at all.

I have to look into this or I'll end up with three hot cables flopping around someday. All our other locations have a dip pole for every transformer, there's no other location with multiple transformers on one run. I've never had to pull an elbow. We just pull the cutouts at the pole. I replaced concentric neutral cables once and did the terminations myself but I just put the elbows on the transformer by hand before I heated it up. If I ever get the opportunity with a de-energized transformer, I'm going to grab a shotgun stick and practice pulling and installing elbows.
A company has to furnish you a few basic things, parking stands and joy caps and proper training on how to pull a live elbow just to name a few, after seeing the spot that they have put you in I would change out the switches and nothing more. Good luck. Charlie.

[rob8210]

Just tell the boss those old chocolate boxes are cracked , and need to be replaced before they fail, causing an outage!

[busman]

This is probably obvious, but remember that parking stands come in both insulated and grounded versions.

Mark

[LAMartin.CVEC]

I wouldn't make or break three phase load with an elbow, number one its prohibited on our property, number two you have the feroresonance possibility. Sounds to me like your engineers need to find a spot to cut in switches with load break capability.

Normally Labour, I'd agree with you on this but he did state it was 5kv. I am assuming 4800 or 4160. Very unlikely that either one of those voltages are victims of ferorenance, how ever depending on the amp load flash over and catastrophic failure are very possible. I'd go to the elbows--but only if they were load break--if that can't be done safely then blink the circuit and do exactly what you recommended. Cut in a GOAB or triple single do the work safely or continue to bat the stick around in the air and continue to pray as the fire rains down.

Reading back on this OGB, I guess I actually agreed with you.

Work Safely,

L.A. Martin
Journeyman/Retired
Electric System Operator
CVEC

[rob8210]

If the company won't change the switches, I would use the elbows too, as long as they are load break. They are designed to withstand it!

[in the bucket]

Just tell the boss those old chocolate boxes are cracked , and need to be replaced before they fail, causing an outage!

We do this when ever we can. Sometimes they fall great distances out of the bucket, (by accident of course) and shatter (unfortunately) so that they don't get used on another job.

Working for a small muni is very different from the situations that most of you guys seem to be from. The good news is, that our new substation is 98% complete and will be on line soon. It replaces a very old and neglected one. Thanks all for the advise!

[Gale19XX]

Unless I missed a comment I was kinda curious if this was loop fed with a normal open anywhere? Also whats the line protection before the blades? If I understand it correctly the OH dead ends URD takes off feeding 3 commercial, and a few neighborhoods? If this isn't looped, that means any bad spot from the pole to the first tub would have everyone out. I would assume being even a small muni those commercial customers are a must to have on line. You'd think if they invested what they have in URD they would spring for somethin other than those blades or something to keep the meters spinning for those specific customers.

On another note, I agree with working from the end back towards the line but I don't see a problem with pulling the elbows on any of these provided they are load break. Feroressonance is more likely to occur if you got little to no load coming out, and a lot more likely to occur at the dip than it is at the elbow. Given your voltage as well would lead me to believe you shouldn't be facing any.