13kv Non segregated bus duct failure prevention

[capnron]

We are dealing with 40 year old insulated tubular aluminum outdoor 13kv bus duct. Over the years my customer has experienced several outages due to faults caused by deteriorating insulation. Repairs are made to clear the fault and the circuit is reenergized. Short of replacing all of the insulating support members is there any method to prevent future failures. All internal heater cicuits are in working order, and they have coated the exterior with a supposed waterproof paint coating. We have never found any obvious leaks but over the years everything is fairly dirty and with approximately 1000ft. of duct there has been some water seepage. Any ideas for fault prevention will be appreciated.

 

[rbulsara]

From your description, only sane idea would be to replace the duct with a new system, either bus duct or cables or cable duct. Anything else is waiting for a disaster.

Rafiq Bulsara

http://www.srengineersct.com

 

[capnron]

I would agree, but it's not my budget. This was a fairly common GE Gas Turbine Power Bank configuration from the 1960's. I was just curious if anyone had dealt with similar vintage equipment with the same faults over time or if this site is better or worse in comparison.

 

[rbulsara]

You can't expect a different result by doing the same thing over and over again, like the repairs in this case.

No good ideas are cheap, no bad idea is ever worth its cost savings. If you are a consultant, all you can do is give the best advice. Let the owner come up with money.

If they insist on just repairing, walk-away from the project or appraise them of the risks.

Rafiq Bulsara

http://www.srengineersct.com

 

[mmt019]

I agree with rbulsara on this subject. I had a bus duct failure last year on some 480V bus duct. It is used outdoors and this bus duct was from the early 70's. Over the years, there were attempts to putty the seams and repaint it to protect the metal parts, but that bought very little time. As rbulsara says, you've done your due diligence by informing them of their options. The owner should bite the bullet and replace it. Otherwise, failure of it is guaranteed. There is my 2 cents worth

 

[ScottyUK]

The big phase isolated ducts used in power plants usually have a low pressure source of dry air bleeding in to the duct. The duct is maintained at a few hundred mBar above ambient so damp air is prevented from entering. If you have holes large enough for liquid water to enter then you need to seal them up.

If the duct or insulator system is already damaged then there may not be much option other than renewal of the dmaaged parts.


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If we learn from our mistakes I'm getting a great education!

 

[capnron]

I agree with everything all of you have said.I have notified the owners and they are considering actions. This is not an isolated phase bus, it is a nonsegregated bus duct with all three phases in one enclosure. Over the years waterproof coatings and additional heaters are probably all that have kept it alive this long. With the flat roofed long horizontal runs there is not really leakage, but enough moisture has crept in to contaminate the fiber board support insulators. Thanks for your input and hopefully they will move forward with replacement.

 

[scottf]

If the current rating is under 7000A, why not put in a modern insulated bus system like this:

http://www.ritzusa.com/common/content.asp?PAGE=383

 

[electricpete]

It sounds like the failures have been related to the insulating supports. You asked for ideas to address the problem without replacing the supports. It seems like the possibilities are limited. Just to throw around a few ideas (brainstorming mode):
[*1] What kind of material are the supports made from ?
[*2] Do the insulators pick up moisture (porous)?
[*3] Can the insulators it be cleaned?
[*4] Perhaps periodic insulation resistance testing can be used as early warning of support degradation?
[*5] Perhaps additional insulation sleeve or tape can be added directly around the conductor at the location of the support (maybe out to 6” on each side of each support so that flashover does not occur even if support degrades).

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(2B)+(2B)' ?