bursting HID capacitors

[tdexxx]

A string of about five of my customer's pole lights failed recently due to burst capacitors. Assuming the cause of this problem is related to the power supply rather than just faulty capacitors, what power conditions might cause a capacitor to burst, (sustained high voltage, sustained low voltage, spikes..., or what?) These are 24 mfd cylindrical plastic caps on 400 watt metal halide ballasts. Thanks!

Tom

 

[weressl]

A string of about five of my customer's pole lights failed recently due to burst capacitors. Assuming the cause of this problem is related to the power supply rather than just faulty capacitors, what power conditions might cause a capacitor to burst, (sustained high voltage, sustained low voltage, spikes..., or what?) These are 24 mfd cylindrical plastic caps on 400 watt metal halide ballasts. Thanks!

Tom

Two causes I can think of:

1. Age
2. Lightning/transients.(most likely cause of simultaneous failure.)

 

[NJKen]

I had a huge problem with this that ultimatly resulted in the replacing of over 500 of them at one site. The problem was they where not made to endure the high heat inside the fixture. The next round of failures resulted in a second change out to metal caps and that finally resolved the problem and may be the answer to yours as well. This was all paid for by the folks at lithonia lighting. Musco sports lighting also had a major problem with the plastic caps. It seems they are just not made the way they used to be or should be. Thanks a lot Mexico.
Ken

 

[Besoeker]

A string of about five of my customer's pole lights failed recently due to burst capacitors. Assuming the cause of this problem is related to the power supply rather than just faulty capacitors, what power conditions might cause a capacitor to burst, (sustained high voltage, sustained low voltage, spikes..., or what?) These are 24 mfd cylindrical plastic caps on 400 watt metal halide ballasts. Thanks!

Tom

In addition to what Laszlo posted, I can think of one other and that's the quality of the supply. Harmonics generated by non-linear loads, particularly electronics. The harmonics result in an increase in capacitor current above what you would get with a clean supply. I have seen examples of this.
I went to one site to commission a large variable speed drive. Not a single light was working in the switch room. The capacitors had failed in every single one. The site, a zinc mill, had a very large rectifier in the electrolytic part of the process. The harmonics from it distorted the supply resulting in the capacitors being overloaded and their eventual failure.