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Join Date: Sep 2011
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Capacitor Testing

06/21/2014 12:25 PM

Sir,

Please let me know How to test the capacitors of a capacitor panel.(1KVAr,5KVAr,20KVAr)

Thanks

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Guru

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#1

Re: capacitors

06/21/2014 12:41 PM

Easy. Pick up the phone and ring the capacitors' supplier.

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#2

Re: capacitors

06/21/2014 4:02 PM

Discharge the entire panel. Disconnect each capacitor. Recharge each one and then short the leads. If you get a spark, it's good. No spark, no good.

Replace defective caps, reconnect, re-energize.

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#9
In reply to #2

Re: capacitors

06/22/2014 7:36 AM

If you want to do it that way, give me chance to get clear.

Last time I had a PFC panel go wrong it blew the end caps off two 200A HRC fuses. I wanted to be 110% certain it was OK before I switched it back in to service.

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#3

Re: capacitors

06/21/2014 5:39 PM

The newest nominee for the Darwin's Awards

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#10
In reply to #3

Re: capacitors

06/22/2014 9:31 AM

I agree wholeheartedly.

I think as far as electrical systems go this photograph sums it up:

..........so if you know nothing about it, leave it alone and get a qualified person to look at!!

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#4

Re: capacitors

06/21/2014 5:40 PM

This could be potentially dangerous if the person asking doesn't know.

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#5
In reply to #4

Re: capacitors

06/21/2014 7:23 PM

That's why I nominated them for Darwin's award!

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#6

Re: capacitors

06/21/2014 10:17 PM

Really. Anyone incapable of searching for a tool to measure a parameter should not ever attempt to measure that parameter. At the same time I must honor your recognition of ignorance, particularly when you presumably also recognize the dangers of a novice working outside of their competence.

Without knowing one iota of information about how these capacitors are used, I cannot help. A true, "ideal" capacitor will only need one metric to describe it, the capacitance value. Unfortunately, ideal capacitors do not exist in our real world. Most of the time a good electrical engineer will specify one of a variety of real world capacitors so that the parasitic, "non-ideal" attributes of a real capacitor will not matter in the actual circuit that it will be used.

To be brief, ask the designer how to test these capacitors or come back to us only with an understanding of the difference between ideal and real capacitors. If you come back to us, be prepared to explain how these capacitors will be used.

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#7
In reply to #6

Re: capacitors

06/22/2014 2:13 AM

We have at least one iota.

OP's kVAr figures suggest that these are in a power factor correction application.

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#13
In reply to #7

Re: capacitors

06/22/2014 11:57 AM

Sorry but you cannot say you know something and then say that information is suggested. Your only lying to yourself.

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#8

Re: capacitors

06/22/2014 2:33 AM

Test them very carefully after first disconnecting them with even more care.

Prior to that take extra care to short them to make sure they are fully discharged.

Now, before you do any of the above, apply extra extra care that your PFC panel is totally disassociated from any external energy sources and that you have very carefully placed the lock out key(s) in your pocket.

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#11
In reply to #8

Re: capacitors

06/22/2014 11:17 AM

Sorry to say but that's not a "good" answer, it's an irresponsible one, as are all those giving any kind of instructions to assist in this lunacy. Clearly this Darwin Award nominee is clueless about what he is trying to do and faces the real possibility of electrocution or serious physical injury.

In reality throwing a solid short on a fully charged 20kVAR capacitor is not a test of anything but the potential destructive capacity of the ensuing arcflash. Shunt capacitors need to be tested for voltage withstand, capacity, dielectric strength, etc., just like any other piece of equipment to be sure that they are fit for the duty that they will be exposed to.

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#12
In reply to #11

Re: capacitors

06/22/2014 11:53 AM

Yes! Safe discharging of a capacitor requires a circuit that can withstand the release of the maximum amount of Joules of energy the capacitor might hold. Far too many laymen think that the shorting sticks used on a capacitor bank discharge the capacitors. They do not! The shorting sticks prevent static charge from recharging the capacitors. Shorting out a charged capacitor can be lethal to the one holding the stick.

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