Possible overheating of factory installed conductors in equipment

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kush_ee

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Hi everyone. This is a solar equipment related question. These pictures are of the internal cables (factory installed) inside a string inverter – 1500 VDC, 600 VAC. Some inverters had catastrophic failures which led the client to shut down the entire site and perform detailed inspections of all units. During inspections, this type of discoloration/sweating/condensation was observed in these cables in almost all inverters. In some instances, more damage was observed where one of the cables had completely burned up. Any insights into what exactly might be causing this? Have you seen this type of discoloration/ sweating on conductors in any other application?

Our initial suspicion is on moisture entry into this cable area which may have caused oxidation/corrosion over time, which increased resistance and caused an overheating. Another possible cause might be a manufacturing defect where the factory installed undersized cables.
Full load AC current - 127 A at 600 VAC
Full load DC current - 178 A at 1500 VDC
IMG_1834.jpginv.jpgIMG_1497.jpg
 
kush_ee said:
Hi everyone. This is a solar equipment related question. These pictures are of the internal cables (factory installed) inside a string inverter – 1500 VDC, 600 VAC. Some inverters had catastrophic failures which led the client to shut down the entire site and perform detailed inspections of all units. During inspections, this type of discoloration/sweating/condensation was observed in these cables in almost all inverters. In some instances, more damage was observed where one of the cables had completely burned up. Any insights into what exactly might be causing this? Have you seen this type of discoloration/ sweating on conductors in any other application?

Our initial suspicion is on moisture entry into this cable area which may have caused oxidation/corrosion over time, which increased resistance and caused an overheating. Another possible cause might be a manufacturing defect where the factory installed undersized cables.
Full load AC current - 127 A at 600 VAC
Full load DC current - 178 A at 1500 VDC
View attachment 2557521View attachment 2557523View attachment 2557520
Click to expand...

That’s definitely moisture ingress. Not sure what came first. The high resistance connection and heating effects or the corrosion due to moisture. Any way to seal off the unit/raceway or even install condensation heaters?
 
Xptpcrewx said:
That’s definitely moisture ingress. Not sure what came first. The high resistance connection and heating effects or the corrosion due to moisture.
Click to expand...
hi @Xptpcrewx and thanks for your reply. Question: if it's moisture ingress, then why is it only accumulated/ visible on one of the conductors? The other conductors right next to it look completely dry.

Also, can't this "sweating" occur due to overheating/ overload as well?
 
kush_ee said:
hi @Xptpcrewx and thanks for your reply. Question: if it's moisture ingress, then why is it only accumulated/ visible on one of the conductors? The other conductors right next to it look completely dry.
Click to expand...

Heat and the due point. I’m betting that one terminal has a poor connection and runs a bit hotter. Be it mechanically or because of the corrosion. You can take a thermal scan and confirm.
 
Xptpcrewx said:
Heat and the due point. I’m betting that one terminal has a poor connection and runs a bit hotter. Be it mechanically or because of the corrosion. You can take a thermal scan and confirm.
Click to expand...
thermal scans were performed. all results looked normal. in other words, all conductors had similar temperatures.
 
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kush_ee said:
we did perform thermal scans. all results looked normal. in other words, all conductors had similar temperatures.
Click to expand...

I don’t know what to say. There’s no way similar temperatures are involved with that last picture. Clearly one terminal was hot enough to destroy the insulation.
 
yes, what you are saying makes sense. I meant that prior to the insulation damage, like months before this was discovered, routine thermal scans were performed and they all looked normal. It is definitely a possibility that they did not perform the scan properly and failed to focus on these conductors.
 
kush_ee said:
yes, what you are saying makes sense. I meant that prior to the insulation damage, like months before this was discovered, routine thermal scans were performed and they all looked normal. It is definitely a possibility that they did not perform the scan properly and failed to focus on these conductors.
Click to expand...

Is the sweating occurring on the same middle conductor in every unit?

Note: That insulation is rated 105*C. That’s a decent amount of temperature rise.
 
No, unfortunately, there is no pattern on the sweating. In some units, it is on just one conductor, while in some it is on three other conductors.
 
It's not water. It's some type of oily, sticky substance, so yes it can very well be the "chemicals driven out of the sleeves by heat".
Question then becomes - what's causing overheating of these cables that are factory installed?
It's a UL listed product so we were assuming that the cables are tested for the rated current. Should we not assume that?
 
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