How do you test a 3 phase capacitor?

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nuckythompson

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Nova Scotia
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Electrical
I have a 3 phase capacitor for a 4160V motor that I am not sure how to test. Here are my thoughts..

- Find a datasheet that has measured uF values and measure capacitance with a meter to compare. No datasheet found yet. Picture of nameplate attached (sorry the picture isn't great).
- As you can see the nameplate has a uF rating and kVAR rating. Is this a phase to phase value? I could also calculate uF from the kVAR - (kvar/2*pi*f*V^2). I measured across the phases and got values close to the uF nameplate rating.
- Measure resistance to ground and phase to phase to find any shorts. Got high readings for these but wasn't sure exactly how to analyze.

If anyone has experience with this I would greatly appreciate any insight.

Thanks,
:)
 

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@Besoeker3 - do you mean find a spare capacitor to compare?
@ptonsparky - cannot measure current. Unit is offline.

From the phase-to-phase capacitance readings being close to nameplate, and GΩ readings phase-to-ground and phase-to-phase via a megger test, I am thinking this capacitor is OK, but I am not really sure how to properly test it. You can also see the capacitor charge up, but I am really not 100% sure what to look for.
 
nuckythompson said:
You can also see the capacitor charge up, but I am really not 100% sure what to look for.
Click to expand...

I've never done one as big as you describe. For a smaller capacitor of the size found in residential air conditioning units, you can see it charge up by using an ohmmeter and it'll read a low resistance at first, then higher as it charges. Then you can transpose the leads and see it again as you charge it to the other polarity.
 
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