Motor capacitor failures

[rmore]

We have a problem with capacitor failures in the field.
Some key information:
* The problem occurs at 220V 50/hz locations. No complaints at 120V/60Hz locations. (different manufacturers for 50hz vs 60Hz motor).
* This is happening at a number of sites.
* Failures occur after running about a year.
* Our OEM customer assures us that supply and environmental conditions are clean and well regulated. (Medical application).

What are the most likely causes under these circumstances?

 

[electricpete]

I'm not sure I'll be able to answer but no doubt a lot more info is needed.

Is it a run cap or a start cap or some other cap?

Do you have more details about the cap (part number).

In what way does it fail? Electrical short? Do you see anything when looking at the failed cap (signs of overheating, puffing up etc)?

 

[waross]

Possible reasons.
Poor quality.
Poor assembly. For instance, an improper setting on the tool used to crimp the spade connectors to the leads may be generating heat which conducts to the capacitor terminal and damages the end of the capacitor.
Too many close rapidly repeated starts. Starting capacitors are not rated for continuous duty. Rapidly repeated starts may overheat the capacitors.
Transient overvoltages. In a combined inductive/capacitive circuit the voltage across the capacitor may exceed the applied voltage. This is not an issue with motor starting capacitors, but it may be a capacitor quality issue. The capacitors may have less ability to withstand transient overvoltages than is needed.
Are these motors driving high inertia loads? Extended start times may be overheating the capacitors.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[edison123]

Medical facilities are generally clean and supply is well regulated.

Given that 120 V/60 Hz caps from one OEM are working fine, I am going with poor product quality/poor design from the other 220 V, 50 Hz OEM. Replace all 220 V caps with the first OEM caps.

Muthu

http://www.edison.co.in

 

[electricpete]

> The capacitors may have less ability to withstand transient overvoltages than is needed.

No doubt. It reminds me that power system voltage harmonics can cause heating of caps, so electronics connected to the power system nearby could cause a problem. Probably less likely in a hospital as edison mentioned but there are no doubt a wide variety of environments within hospitals.

I feel like it's a guessing game, though. All we know is some kind of caps associated with a motor fail after a year. We don't know what kind of caps or what is the application or anything about the power system or the capacitor appearance / test results after failure.