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Hot spot in switchgear
6

Hot spot in switchgear

Hot spot in switchgear

(OP)
We had an operator send these pictures from the back of a 13KV switchgear main breaker. Myself and a couple other techs were musisng over what it could be. Our guesses are everything from strip heaters to B phase CT. Any one ever see this before or have any good ideas. Thanks.


RE: Hot spot in switchgear

Assuming those are temps in F and not C, I’d try to rule out a space heater first.

RE: Hot spot in switchgear

75.3C = 167F
Can you rack the breaker out and see what is happening on the other side of the wall?

RE: Hot spot in switchgear

Never mind, probably not cold enough for 24F ambient temperature in the cable compartment. Temps must be in C.

RE: Hot spot in switchgear

2
Hypothesis: a heavily loaded circuit, single conductors through sheet steel encircling the conductor - could it be eddy current heating in the narrowest current-carrying section of the partition?

RE: Hot spot in switchgear

Yeah that sheet looks pretty thin.

RE: Hot spot in switchgear

You could probably track down the heater breaker / fuses for the cubicle and rescan with the IR cam and the heaters off to confirm. The SWGR looks relatively new. Have you checked the manufacturers drawings for heater location?

RE: Hot spot in switchgear

Bad contact in one or more "tulips" due to manufacturing defect?

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

RE: Hot spot in switchgear

A space heater cannot put out that much hest. What happens when the breaker is off?

Muthu
www.edison.co.in

RE: Hot spot in switchgear

Could those be Voltage transformers - may be Bus VTs mounted on withdrawable truck??

RE: Hot spot in switchgear

Induction heating of the ground busses by heavy, adjacent phase currents.
There must be components and/or sheet metal masking the source of the heat for it to be so sharply delineated.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Hot spot in switchgear

davidbeach:


I can't imagine it being anything BUT induction heating. Fits with slight non-symmetry as compared to the other side and they'd never mount anything between those two feed-throughs as there'd be bolt holes if they had.



Keith Cress
kcress - http://www.flaminsystems.com

RE: Hot spot in switchgear

Keith,
Very interesting, I didn't realize inductive heating could be so dramatic.

Here is an article that discusses the effect and includes some photos.

https://www.netaworld.org/sites/default/files/publ...

And another one:
https://www.netaworld.org/sites/default/files/publ...

Quote:

Noncurrent-Carrying Items
Many times other problems can be spotted with ancillary
items which normally do not carry current and, therefore,
(mistakenly) are not part of the normal infrared survey.
Thermographers, experienced in the vastness of potential
problems, will many times glance around in their field of
view and spot other items radiating heat (or not radiating
heat), which will raise their curiosity level to the point of a
closer look. Many times a metallic structural support, cableway,
or cable tray assembly, none of which should be car-
rying current, will indicate heating that is apparently from
electrical current flowing. Field measurements of hundreds
of amperes have been seen numerous times and are most
commonly the result of excessive eddy currents caused by
inductive heating. This heating effect can cause the surface
temperature to rise well beyond the boiling point of water,
potentially presenting a burn hazard to personnel or the
deterioration of other substances in close proximity.
Grounding connections normally do not carry continuous
current; therefore, a ground connection showing any increase
in temperature can indicate a possible problem. Further
investigations of these types of problems have uncovered a
variety of issues, such as ground loops, broken or disconnected
grounds, and high impedance faults.

RE: Hot spot in switchgear

Hi Keith,

That looks the isolated phase bus duct between a generator and it's step-up transformer. The scaffolders at our power station did something similar, making a closed loop around part of the IPB for a 300MW generator with nearly 16kA flowing in the bus. He formed the loop outside of the cross-bonded section where there's no image current cancellation effect. The report was that the tube got hot enough to burn his hand, and when he jolted it there was a blue spark. Poor guy was pretty shaken by the experience. They'd gone a bit higher up than they should have, trying to get ahead on the job.

RE: Hot spot in switchgear

As ScottyUK suggested, a closed loop of steel around a conductor can flow a lot of current - it basically creates a 1-turn transformer. I once measured about 250A flowing through a unistrut completing the circuit around a conductor with 2500A flowing.

Considering that it's likely 1200A or less @ 50Hz or 60Hz just passing by, I would put more belief in the above than in believing the current in the bar is inducing eddy currents that only circulate locally inside that strip of steel. It might contribute, but I find it hard to believe it's solely responsible for that much heat.

It's odd the manufacturer wouldn't know this happens. The similar pass-through location from Schneider has one big insulator for all 3 breaker bus stabs to avoid that exact problem.

RE: Hot spot in switchgear

It doesn't have to be encirclement or a closed loop. In Keiths top left picture, the intruding bar or pipe is hottest in the area of the strongest flux. This suggests local eddy currents. This effect may also be present in non-ferrous material. An AC flux will induce a potential with the resulting eddy currents in any conductive material. It is, of course, a much stronger effect with a ferrous material forming a magnetic core.
If the current was caused by a closed loop the same current would circulate in the loop and the entire loop would be hot.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Hot spot in switchgear

I would expect the bus in Keith's first pictures flows A LOT more current than the bus in the OP's enclosure so I could believe local induction there more so than the OP's picture. However, without seeing the whole structure it's hard to know if that bar forms a closed loop or not. Structure that acts as a heat sink at each end of that bar can explain why its the hotter in the middle. Same with the enclosure picture, no-one can say if there is a loop around a single phase or 2 phases of bus from the picture.

RE: Hot spot in switchgear

I ScottyUK's hypothesis above regarding the OP's pictures. I suspect the design called for a stainless steel plate here, but a steel plate was mistakenly used during assembly.

RE: Hot spot in switchgear

(OP)
Thanks for all the input guys, I haven't heard back any word on this as of yet. I am currently at another substation for metering upgrades but will try and get some more info and answers to post back here.

RE: Hot spot in switchgear

I looked at this again and I have to agree with Scotty's suggestion.
Magnetic encirclement.
An excerpt from the Canadian Electrical Code:
Rule 12-106 (5)

Quote (CEC)

(5) A single-conductor cable carrying a current over 200 A shall be run and supported in such a manner that
the cable is not encircled by magnetic material.
Aluminum, Stainless, Micarta or, my favorite for field builds, a hacksaw cut between the openings. Quick, cheap and easily done in the field.
Despite the intense colour, 73 degrees C is probably not enough to burn the paint off or cause rapid heat corrosion of parts.
In severe instances I have seen the paint burned off of an enclosure and have seen rapid heat damage of equipment. eg: A 400 Amp rated disconnect carrying less than 200 Amps with unbalanced loading in the multiple steel conduits feeding the switch. The steel conduits became very hot and the copper conductors conducted the heat to the switch blades. Heat corrosion destroyed the switch blades.
This case is not nearly that hot.
But if the current increases close to or above around 200 Amps, you may have problems.
With a ferrous material the heating is from a combination of magnetic hysteresis, eddy currents and the ferrous core.
With a non ferrous material there will still be eddy currents but with the absence of a ferrous core the effect will be orders of magnitude less.
Inductive heating does not only work with ferrous material.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Hot spot in switchgear

(OP)
Hello all,
Sorry it has taken me so long to get back to this. Here is the statement from one of our engineers in coordination with the metal clad provider:

Please read the email below from Company X regarding the substation WR1 switchgear. Their assessment of the hotspots in the wall steel in the substation switchgear is consistent with the preliminary evaluation by the Substation Maintenance Engineering team and others. Heat is being generated in ferrous steel that is surrounding current-carrying conductors due to magnetic flux, which in turn generates eddy currents. Magnetic flux and eddy currents increase with current magnitude, so as the current goes up, so do the eddy currents and hotspot temperatures. Generally, magnetic flux heating and eddy currents can be reduced or eliminated in the switchgear design before manufacturing by using non-ferrous metal around current-carrying conductors, such as aluminum or stainless steel. I asked Company X for details of their magnetic and thermal modeling as a visual aid in understanding the physics, and they are working on something they can share with customers.

Since this heating is within the design & construction standards of metal-clad switchgear, and does not approach the 110°C limit set forth in IEEE 37.20.2-1999 section 5.5.6.c (reaffirmed in 2005 [see excerpt below] and unchanged in 2015 revision), this unit is operating under normal conditions. Accordingly, there is no increased possibility of failure of this switchgear compared to any other switchgear in our substations. All switchgear has different loading due to differences in fundamental frequency and harmonic current levels. Company X switchgear of similar design and vintage on our system have less loading, different load characteristics, and subsequently, no abnormal heating has been observed.

Thanks for all your help!

RE: Hot spot in switchgear

Thanks poulin76 for the follow-up.

Next the company will tell you it was done this way on purpose to provide "component-less enclosure heating". wink

Keith Cress
kcress - http://www.flaminsystems.com

RE: Hot spot in switchgear

OSHA requires hot surface touch protection.

RE: Hot spot in switchgear

It seems like the temperature under the red insulation boots may be even hotter. How much load was on switchgear during the photo compared to the nameplate rating?

RE: Hot spot in switchgear

I think the temperature of all those external surfaces accessible shall not exceed 70degC (just from my memory, to verify).

RE: Hot spot in switchgear

I think I recognize the design, that surface isn't accessible while energized and the time it requires to take a clearance will probably allow much more cooling than just from 75.3C to 70C. Manufacturer probably should have slit that plate between phases to interrupt the eddy currents; above 2000A they go to a non-ferrous plate. I'll wager a guess that it was running at 1000A + at the time of the scan and that C phase had the most load of any of the phases, say by 60-70A. winky smile

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