Power factor correction unit totally blown up 2

[BigBill53]

Hi all,
I have a bit of an unusual one here, and I was wondering if anybody has come across something like it (or maybe a PFC expert could point me in the right direction).

I recently took a look at a power factor correction unit that had pretty much totally blown up. All of the capacitors have failed (either burst open or are short circuited). Some of the resistors on the contactors are burnt. In many places there are burn marks on the busbar - very strange for a 415V system where the busbar is spaced at around 40mm apart.

Some other relevant facts:
[ul]
[li]It wasn't a lightning strike - it was during the middle of the day and clear weather[/li]
[li]The harmonics on this site are practically zero - probably the only source of harmonics is the fluoro lights in the offices. Because of the remoteness of the site and the lack of competent electricians, the management stipulated that the entire plant be run on star/delta and autotransformer starters. All they have is electric motors.[/li]
[li]No other equipment was damaged at the time[/li]
[li]The PFC unit was second hand. The last owner used it for around 2 months and then it sat unused for 5 years[/li]
[li]The ambient temperature at the time was not excessive for this area (maybe 30 degrees celsius)[/li]
[/ul]

I have no idea what has happened here. The customer needs this to run their entire plant at the same time (their current transformer is too small) but I don't want to recommend they install another one if this is going to happen again. Any help would be greatly appreciated.

 

[LionelHutz]

What you're describing on the bus sounds fairly typical of a fault that occurs (failed capacitor rupturing) which starts phase-to-phase arcing in the panel. Once that happens, the damage level is proportional to the time it takes the protection to clear. I've seen busbar and other components which completely dissappeared when the protection didn't clear the fault quickly.

 

[Skogsgurra]

This is a case I had a few years ago.

There had been a water damage to a plant and the insurance company didn't want to pay. Instead they said that they should send a company to clean up everything and then pay for any damage that could be attributed to the water. When that damage occured a few months later, they said it wasn't caused by water but by overvoltage. Which is rather ridiculous.

I was hired to do an investigation and found this:

http://www.gke.org/pub/files/Copper bar with low energy arc 1.jpg

This is where it started. A low energy arc had started inside a hollow stand-off insulator where water had stayed after the cleaning. The inner surface had carbonized and then the arc started. It was a new 500 V system with insulated neutral. So currents were kept low. But, of course, when ionized air propagated into the panel - the real arcing started.

Is this something similar to what you saw?

Gunnar Englund

http://www.gke.org

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