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#122726 - 01/05/06 07:15 PM Surge Arrestor Connection
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Registered: 10/07/00
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 Quote:
I am looking for some input on these pictures.

This is the 12KV secondary of one of two step up transformers on a rush project. I did the terminations last week prior to the transformers being delivered so that when they arrived the men on the job could just bolt them up. (I am on a job 100 miles away) They sent me these pictures today because the surge arrestors you see in the photos were not expected to be there. The concern is two fold.

1. The #6 connecting the arrestor to the HV bushing was factory installed. As you may be able to see it is a 600V THHN insulated conductor. What I have seen in the past is unshielded 15KV cable making this connection inside equipment.

2. The arrestors are mounted directly under the HV bushings and had to be loosened and pushed aside to get the power conductors landed. This moves the top terminal closer to the tank.

My suggestion, since they are owner supplied transformers, was to notify the owner/engineers of or concerns and we are awaiting there direction.

Does everyone else here see this problem??

- Nick



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#122727 - 01/05/06 08:25 PM Re: Surge Arrestor Connection
Radar Offline
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Registered: 04/30/04
Posts: 349
Loc: Los Angeles, CA
The problems you point out are easy to see. Does the owner have a relative in the discount transformer business? I mean, why bother with 600V insulation on a 12KV system, might as well just use bare wire.

Pretty obvious the rope-a-dopes that designed this thing have never bothered to try installing one.

Radar
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#122728 - 01/06/06 05:10 PM Re: Surge Arrestor Connection
Ann Brush Offline
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Registered: 12/27/05
Posts: 155
Loc: Ohia
Definately get someone with oversight to sign-off that you had concerns and that they chose to go with this unorthadox approach. Looks like someone ordered/supplied the wrong unit. Any chance the bushings could feed from the top, then the arrestors could be put back in place and proper straps attached.

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#122729 - 01/06/06 06:44 PM Re: Surge Arrestor Connection
Larry Fine Offline
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Registered: 02/18/05
Posts: 684
Loc: Richmond, VA
"Any chance the bushings could feed from the top, then the arrestors could be put back in place and proper straps attached."

My thoughts, too. Or how about a rectangular plate with 4 bolt holes that could extend the terminals away from the bushings, allowing the arrestors to be swiveled back into position.
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#122730 - 01/06/06 09:32 PM Re: Surge Arrestor Connection
HighPotter Offline
Member

Registered: 08/29/04
Posts: 41
Loc: So. Cal
Actually, I'm pretty sure those are Hubbell MOV style arrestors. The "600v" wiring on the line side is factory provided. The fact that it is 600v wiring is of no consequence. Keeping your distance phase to phase and phase to ground is.

That being said, installing arrestors in a padmount is a horrible design. When the arrestors blow, it is almost always violent. And they can take out the other phases in the process.

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#122731 - 01/07/06 01:17 AM Re: Surge Arrestor Connection
Trumpy Offline

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Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
Ever wondered why they put them rubber boots on HV wires?.
It's so moisture doesn't cause a flash-over problem, it just drips off.
Considering the URD being supplied from this tranny, the feeds to the Surge Diverters looks really sloppy.
600V?, nowhere near it!.
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#122732 - 01/07/06 09:54 AM Re: Surge Arrestor Connection
Nick Offline
Member

Registered: 08/13/01
Posts: 603
Loc: Riverside, CA
"Any chance the bushings could feed from the top"

I have not seen the transformers myself except for the pictures you see. Maybe there would be enough room to form the conductors around the side and connect them at the top but at this point that is a very expensive proposition. The conductors of both transformer would have to be replaced, because I do know they are to short for that. Both ends re terminated and some bracing would have to be added in the enclosures to support the conductors. Extending the bushings with a plate could be an option if that doesn't put them to close to the doors. In fact T&B make a bracket specifically for that.
Like Radar said I don't know what they just didn't use bare wire. It's a live front transformer anyway and as long as all the clearances are met it shouldn't be a problem.
Highpotter, wouldn't the arrestors only blow if they exceeded their rating? How often does this really occur?

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#122733 - 01/07/06 11:41 AM Re: Surge Arrestor Connection
XtheEdgeX Offline
Member

Registered: 04/17/05
Posts: 127
Loc: Florida
"Ever wondered why they put them rubber boots on HV wires?.
It's so moisture doesn't cause a flash-over problem, it just drips off."
And are required on all outdoor HV connections with stress cones, similar to the one shown.

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#122734 - 01/07/06 02:29 PM Re: Surge Arrestor Connection
HighPotter Offline
Member

Registered: 08/29/04
Posts: 41
Loc: So. Cal
"Highpotter, wouldn't the arrestors only blow if they exceeded their rating? How often does this really occur?"

Lightning strike. Phase to phase fault.

Nick, when the right situation happens, they are "designed" to explode. All you find is a hanging tail with some of the arrestor still attached.

Any idea why they didnt spec out elbows, load break or deadbreak? Does the padmount have a oil switch? How is the system fed?

HP


[This message has been edited by HighPotter (edited 01-07-2006).]

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#122735 - 01/07/06 06:58 PM Re: Surge Arrestor Connection
Nick Offline
Member

Registered: 08/13/01
Posts: 603
Loc: Riverside, CA
"Any idea why they didn't spec out elbows, load break or deadbreak? Does the padmount have a oil switch? How is the system fed?"


Well, I am not sure. Like I said this is supposed to be a temporary installation. I did the first phase of this job and the scope that was discussed about this phase and what is really happening is night and day. The job is for a city that a few years ago started its own utility division. The power is feeding a few specific new customers at this site. It does not connect to the are utility grid at all. What I think is happening is politics, budget and time restraints are forcing this temp install so we can go back and build the permanent system under a reasonable construction schedule.

There are a couple 1200KW natural gas generators feeding these transformers at 480V. The transformers step the voltage up to 12.47KV then feed a piece of fused sectionalizing switch gear. From there the feed rises up a pole and runs overhead down the road. Off the pole line the feed runs underground again to a couple of pad mounts that feed the buildings. As I understand it there was supposed to be arrestors on the poles and I am not sure why they are not there. In fact, they have been installed by now. Since I haven't been back I am not sure. (We did not do the overhead work. It was a sub of the GC.)
I do not believe the transformers have oil switches in them, but again I could be wrong. I think this phase is just low budget to get the customers on line and will be gold plated later this year.

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