4000 Amp Bus Failure

[IndustrialElect]

Hi All,
Has anyone had any issues with 4000 amp (Spectra) bus Duct failures? The plant I am working at has had two failures in the past year. One failure occurred just outside the mcc rm., and the other occurred just inside the mcc rm. wall. The faults seem to have occurred in the same general location on the bus duct. The issues seems to be with the 3/8" insulated bolt nearest the end of a buss section. I'm am curious, if there were any other incidents with the same issues in the recent past. The Bus Duct is only about two years old, and the Plant E/I engineer has a lot of concern about personal safety. Thanks for any feed back.

 

[Zogzog]

I would think installation issues would be the culplit, what type pf maintenence do you do on these?

 

[rcw retired EE]

If this bus is runing horizontal in the picture, I don't see any supports around this joint and horizontal jog. Could the weight of the duct cause some deformation leading to a joint failure? I am not that familiar with Spectra duct but have seen support issues with other busducts.

 

[desertfox]

Hi

Have you contacted the manufacturer?

 

[IndustrialElect]

Hi All; Thanks for the response;

Zogzog: The two buses which failed, were installed in the same manner by two different contractors. The PF maintenance is IR scans at the joints.
Rcwilson: The buses which failed were both installed in a horizontal manner and the support is just out of the pic frame. We thought the support issue may be a cause on the first failure but there were not any signs of twisting of the bus with either failure.
Desertfox: We did contact the manufacturer, they stated since the bus was purchased in 2010 and was not installed for 2 years, and now only being in service for about a year and a half, they would not be liable for warranty. They also said the extent of the arc flash would make it impossible to determine a cause for the failure.

I did see a thread on this site stating, a possible cause may have been the shifting of the bus bars inside the housing due to shipping issues. I do know this bus was shipped in a vertical manner (standing on its side). If the bus bar did shift inside the housing it could have rubbed a wear spot on the insulated pass through bolt. This could have caused the bolt in question to cause a fault to ground. Any thoughts on this??

 

[John2025]

Nice. You'd think the manufacturer might actually give hoot about such a massive failure. Granted there are plenty of possibilities beyond an error on their end, but how do they know? Do you know the SCCR rating of the bus and the available fault current feeding it?

 

[desertfox]

Hi IndustrialElect

I have had a look at the Spectra site and looked at some of the installation manuals (link added) you mention about the 3/8 insulated bolts, I cannot see any sleeve insulated bolts in their instructions assuming of course that I have the correct manual.

http://www.geindustrial.com/publibr...selectedCategory=General&selectedPubType=null

Its the bottom one on this link which mentions blue expoxy.
Can you confirm that the installation was carried out correctly with the manual.

 

[IndustrialElect]

Hi Desertfox;
The bolt I am referring to is the factory installed bolt nearest the end of the bus section. I will include another pic. Thanks

 

[IndustrialElect]

Hi All;
Here are the pics of the two failures, the faults appear very similar in location. Please let me know what you think.

 

[IndustrialElect]

Another Pic of the failures.

 

[IndustrialElect]

One more Pic.

 

[LionelHutz]

To me, it looks like it failed between the bus bars and the side structure.

 

[desertfox]

Hi IndustrialElec

I wonder if moisture is getting inside the bus duct and then onto the conductors?
There appears to be rust on some of those pictures which suggest there is condensation around.
Is the bus duct subject to vibration which might loosen the bolts?
I think you need to replace what's damaged and ensure you follow the installation manual to the letter and monitor it very closely, that way if you have no problems then its down to installation, on the other hand if you do have an issue then your looking for a different cause.

 

[IndustrialElect]

The rust is from the bus setting outside after the failure occurred. The failure with the rust is from an outside installation but the other on was installed just inside the building in a MCC Rm.. We did consider it being an installation issue but I find it difficult to believe two different contractor crews installed the bus in two different environments, one inside and one outside, with the exact same failure, at the same corner of the bus. Still looking for anyone with the same issue at another plant. Thanks for all the input.

 

[meeko]

install bus duct. Megger bus duct. bus duct fails megger test. re assemble and test again, fails again then don't put in service or you are asking for trouble. and contact Schneider or eaton ect.

 

[electricpete]

you lost me meeko. Who said anything about megger failure?

=====================================
(2B)+(2B)' ?

 

[desertfox]

Hi Industrialelec

In your post you mention the factory installed insulated bolts, so they are untouched bolts as far as installation goes.
In that case I have to agree with your earlier comments about it not being an installation fault.
This insulated bolt then I presume it passes through the conductors although applies no tension on them.
What exactly does this bolt hold on? I am wondering if this bolt wasn't tightened up correctly at the manufacturer's or works loose in service what the outcome might be.

 

[collies99]

What may I ask is the voltage class of the bus duct ?

How long was each bus operating before failure ?

We do both megger, hipot (some dc / some ac) and ductor test for acceptance/maintenance various plants. Was any tests ever done ?

 

[IndustrialElect]

The bolt in question passes through the buss bars and simply attaches the two exterior body sections together. The voltage on the bus is 480v and both buses had been megger tested and in service for 12 and 18 months, before their respective failures. We still can't get a satisfactory response from the manufacture. They seem to have washed their hands of the whole situation.

 

[collies99]

I tend to agree with LionelHutz that the pictures tend to suggest a fault with the outside structure.

Also the pictures has similar evidence of the fault occurring at the joints. (this may be a weakness in the total system and may bear a close scrutiny at all buss bar joints whether of the straight-thru type of the angular type.

It is possible that the joint cover bolts are too close to the bus bars once installed whether it is the wrong length bolts, shifting of the buss bars inside its housing or exposed bars when the sliding contacts make as in its penetration of male/female joints is not at 100%.

I read in the manual that the insulation system is testet at 5kv hi-pot, this may merit a hipot test of the system at 60-75% of fatory test voltage to see if there are any weakness in the existing system.

Haver a Merry Christmas and a Happy New Year.