Message Board Thread - "138 KV 100 MVAR SF6 breaker"

Title	By	Posted On
138 KV 100 MVAR SF6 breaker	Lerch	10/19/2010
I found the elevated temps in the photo in a substation under about 70% load. The temperatures in three phases of the breaker are about equal but are elevated above anything else in the sub including the power transformer. I found areas on the gas envelopes as high as 124 F, whereas the transformer was at 98 F. There is another 138 KV breaker in parallel with this one with roughly the same load which exhibited no temp rise at all. Breaker gas pressure was normal. High contact resistance is my best guess, but it seems odd that all three phases are at the same temp. Anyone got a better guess?
Re:138 KV 100 MVAR SF6 breaker	Top Gun	10/20/2010
Hello all, I will venture a guess. Lerch said, "There is another 138 KV breaker in parallel with this one with roughly the same load which exhibited no temp rise at all." Therein lies the issue: another system in Parallel with this one. Perhaps the problem lies with the other one which may well have a higher system resistance. That higher system resistance is diverting current over to the one you imaged.
Re:138 KV 100 MVAR SF6 breaker	IRJay	10/20/2010
it looks like band heaters on the right are on and the ones on the left are off.
Re:138 KV 100 MVAR SF6 breaker	Lerch	10/26/2010
Top Gun, thanks, I'll check the bus currents next time I'm out there. IRJay, are you referring to the clamp-on bands seen in the photo below? I had not identified those as heaters (or anything else). Thanks and Regards, Lerch
Re:138 KV 100 MVAR SF6 breaker	Lerch	10/26/2010
Sorry, it doesn't seem to have taken the second image. Lerch
Re:138 KV 100 MVAR SF6 breaker	manuel-thermoimagen	10/29/2010
will be interesting if can upload image of the other parallel breaker, same view angle.
Re:138 KV 100 MVAR SF6 breaker	Lerch	10/29/2010
manuel-thermoimagen wrote: interesting if can upload image of the other parallel breaker, same view angle. Manuel, the parallel breaker was not at all warm. It is of a different design so parts of the SF6 envelopes are obscured. Here's the picture.
Re:138 KV 100 MVAR SF6 breaker	PeterT	11/4/2010
Lerch wrote: Manuel, the parallel breaker was not at all warm. It is of a different design so parts of the SF6 envelopes are obscured. Here's the picture. IRJay is right. The heated areas you see are the breaker's SF6 tank heaters. They are flat resistive elements, held on by the band straps. Only the right ones are turned on, but not the left ones. The circuits for the left should be checked to see if the fuse is blown / breaker tripped. The reason for the heaters is that somewhere below -40C, the SF6 liquifies, which effectively removes the breaker's insulation.
Re:138 KV 100 MVAR SF6 breaker	Lerch	11/5/2010
Thanks to all of you for your quite helpful responses. Regards, John