SWBD cable insulation deterioration
SWBD cable insulation deterioration
(OP)
During a recent cleaning, we found some internal cabling that had insulation issues (see file). The cabling is from the load cables to the contactors (Cutler-Hammer), voltage level is 6.6 kV, the conactors are pretty much closed all the time so no frequent load spikes to speak of, and loading is well below capacity of these conductors. Initial assesment is low energy electrical arcing, corona discharge, and tracking as a reasult of no outer
semi conducting shield. These cables intended use is listed as temporary installation around damaged cables or for temporary power sources. They come with the cubicles, so I never gave them a second thought. Until now!
semi conducting shield. These cables intended use is listed as temporary installation around damaged cables or for temporary power sources. They come with the cubicles, so I never gave them a second thought. Until now!






RE: SWBD cable insulation deterioration
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If we learn from our mistakes I'm getting a great education!
RE: SWBD cable insulation deterioration
old field guy
RE: SWBD cable insulation deterioration
RE: SWBD cable insulation deterioration
That probably ranks amongst one of the worst MV starter panels I've ever seen. As well as what the others are saying with regard to the P.D. problem, I would also be looking very carefully at the routing and fixing of the LV wiring. In your 3rd photo, the CT secondary wiring looks dangerously close to the 6.6kV terminations.
At 6.6kV, I would expect to see separated busbars on insulated pillars (not zip tied rubber insulated cable) and would also expect to see Low Voltage insulation level CTs mounted on earthed bushings.
It's almost amusing to see the MV cabling held together with zip ties. As well as the discharge between the conductors, I can also envisage that under fault there will be plenty of cables flailing around in that cubicle! Sack the company who built it. You are lucky it's lasted this long.
RE: SWBD cable insulation deterioration
It's ok, it's 60Hz electricity in that panel. Not as dangerous as 50Hz.
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If we learn from our mistakes I'm getting a great education!
RE: SWBD cable insulation deterioration
Out of curiosity, how long have those cables been in service at that location? I'm curious how long that corona has been attacking the insulation because that cracked piece is pretty scary looking.
Regards,
Jim
RE: SWBD cable insulation deterioration
Good point about the LV wire near the termination, but know that the insulating boots have been removed from the 6.6 kV terminations as shown laying down in the first photo.
RE: SWBD cable insulation deterioration
RE: SWBD cable insulation deterioration
I spotted that the red shrouds were off the terminations, but they look equally as naff as the wiring and I wouldn't trust them not to fall off. Interesting to hear the OEM's response, I wish I had £1 for every time i've heard that one, I wouldn't be sat here now! Even the big boys make some iffy gear from time to time.
Just out of curiosity, is this just the cable termination chamber shown in your photos? If so, is there an earthing truck or something that goes in there? How is the cable earthed in that gear?
Scotty,
What's that 60Hz business? Sounds like science fiction. It'll never catch on!
RE: SWBD cable insulation deterioration
That disconnect has an earthed position, and once earthed the contactor is closed to short and earth the load side. Now the part that really gets me going. The path to earth from the disconnect which is now shorted, is from the disconnect shorting bar to the panel side sheet via sheet metal screws that just happen to be there to hold the works together! And the same from that point all the way thru the switchgear structure! Unbelievable. I raised hell for so long about that (and I am sure I wasn't the only one) they finally changed that in the new configuration and have a dedicated ground wire at that shorting bar.
60 Hz just makes the work day go faster, since I use 50Hz master clocks.
RE: SWBD cable insulation deterioration
Remind me to never, ever, buy anything made by Cutler-Hammer. I'd had about enough of Eaton's sh¡t when they owned Ottermill in England, probably the worst motor control centres in British history but this stuff looks just as bad and it is working at MV.
I wonder if we have 60Hz clocks here?
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If we learn from our mistakes I'm getting a great education!
RE: SWBD cable insulation deterioration
If control power is lost, I would not be able to close the contactor to earth. If it is already earthed its OK (contactor latched).
A minor related nuisance is in the control room mimic I can't tell the difference between a contractor closed normally to the load and one closed to earth. It really doesn't matter much in my installation, but it could in other applications.
RE: SWBD cable insulation deterioration
RE: SWBD cable insulation deterioration
Older MV MCC's were less compact and did have more clearances, buswork instead of flexible cables, and separate cabling and contactor compartments. The push for smaller and cheaper resulted in these minimal space designs. (Other supplier's are worse.) An "advantage" is the equipment is front access only and can go against a wall to save valuable space.
It is unusual for ANSI equipment to have any grounding means for the outgoing cables to the motor or load as is common on IEC or BS equipment.
RE: SWBD cable insulation deterioration
I hoped you were going to say that. I just wasn't confident.
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If we learn from our mistakes I'm getting a great education!
RE: SWBD cable insulation deterioration
You are right in that we are using this gear because we can place two sections back-to-back in the same depth as one breaker section.
jghrist,
I don't see that tie down to a bus, but it may be an illusion in the pic that I am seeing thru?
RE: SWBD cable insulation deterioration
rovineye
Thanks for clearing that up. That gear really is vile stuff! When I asked the question about the earthing, I did think it looked like the cables were terminated in the starter cubicle, but I hoped I was wrong. And earthing via a contactor...........not great, even if mechanically latched! An earthing device in our 50Hz world generally has to be capable of making onto a full power fault and that generally rules out earthing via contactors!
At least the cables are secured properly in the cubicle in your last photo, but I would imagine you might still get P.D. problems even in that cubicle at the point where the cables come together through the core balance CT.
Stop talking about 60Hz, I told you, it'll never catch on!
RE: SWBD cable insulation deterioration
Yes, the load cables are terminated there as well! In the 3rd photo of my first upload, you can see the black load cables terminating to the red "jumpers" just below the CTs. The only thing not in the cubicle is the supply bus, which is joind by the disconnect thru those shutters in the top.
RE: SWBD cable insulation deterioration
RE: SWBD cable insulation deterioration
A survey of all the switchgear in question showed that we had these cables installed produced by up to 5 different manufacturers. I say up to, because one set had no manufacturers marks at all. All had the same basic construction and ratings. 3 of the manufacturers cables were deteriorated as previously shown. The other two looked brand new.
Testing showed that the deteriorated cables had not lost any insulating capacity as compared to the brand new cable samples. That was the best news. The cracking had only occurred on the outer jacket.
PD testing did not show a difference between new and old cables from the same manufacturer. But, the point at which pd developed and extinguished was radically different between brands. We use these at 6.6kV, and the 'bad' cables developed pd at voltages as low as 3.9kV, and the good as high as 12kV! Results were consistent across manufacturers batches.
Eaton/Cutler Hammer traveled to my locations and changed out the cables even tho they were out of warranty. They sent large groups of engineers (including the original designer of these contactors), techs and mechanics, obviously very concerned. They now have processes in place to measure pd inception and extinction levels of every cable batch that goes into these products. Last I heard from their engineer he was on the way to Saudi Arabia to check on installations there. Good for them!
RE: SWBD cable insulation deterioration
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If we learn from our mistakes I'm getting a great education!
RE: SWBD cable insulation deterioration
I have to say however, that cables I classify as "bad" may not be bad in other applications. The primary use of these type cables are as a temporary bypass of damaged cables, not permanent as we are using them, and all caution that they should be installed with separation phase to phase and to earth. Installed that way, all these manufacturers' cables may be fine. But we use them long term, tightly bundled and laying on earth, hence the damage resulting from the pd/corona/ozone in all but those least susceptible to pd development.
I wouldn't have any problem pointing out the "bad" manufacturers, but I still have not figured out who made them. They are marked with the cable broker's name, or nothing, but not an actual manufacturers name. Very unusual.
RE: SWBD cable insulation deterioration
I've seen similar, but not as bad, situations in genset terminal compartments from major manufacturers.
Alan
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"It's always fun to do the impossible." - Walt Disney
RE: SWBD cable insulation deterioration
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If we learn from our mistakes I'm getting a great education!
RE: SWBD cable insulation deterioration