Size of existing capacitors

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Red Wiggler

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I have a situation where there are existing Power Factor Correction capacitors installed on a 3 phase service. The customer wants to verify that these capacitors are the correct size. (and that they are doing their job) The trouble is that there is no identifiy information on the capacitors to indicate what size they are.

Is there someway that you can measure the capacitance of the system or figure out what size of capacitors they are using. The system is up and running, and I was wondering if we installed some sort of recorder and developed a base line while the capacitors were in the cirucuit, and then disconnect the capacitors, and see what changes on the recorder. I would assume if the data is correct, a person could make calculations to discover what size the capacitors are.

Any thoughts?
 
Red Wiggler said:
I have a situation where there are existing Power Factor Correction capacitors installed on a 3 phase service. The customer wants to verify that these capacitors are the correct size. (and that they are doing their job) The trouble is that there is no identifiy information on the capacitors to indicate what size they are.

Is there someway that you can measure the capacitance of the system or figure out what size of capacitors they are using. The system is up and running, and I was wondering if we installed some sort of recorder and developed a base line while the capacitors were in the cirucuit, and then disconnect the capacitors, and see what changes on the recorder. I would assume if the data is correct, a person could make calculations to discover what size the capacitors are.

Any thoughts?
Click to expand...
Why don't you just measure the current?
Unless the supply is very dirty, that should give you a fairly good indication.
 
kvar = I_c*V_LL*1.732

I_c is the line current flowing from the capacitor bank, measure with clamp-on at the cap breaker or fuse, V_LL is the line to line voltage. No need to put a recorder on and shut off the cap...on second thought, I wonder if there is a way to tell if any of the phases have caps that are failed? Are there indicator lights telling you if any caps have failed?
 
wirenut1980 said:
kvar = I_c*V_LL*1.732
Click to expand...
That gives you VAr, of course. You need to divide by 1,000 to get kVAr.

wirenut1980 said:
I_c is the line current flowing from the capacitor bank, measure with clamp-on at the cap breaker or fuse, V_LL is the line to line voltage. No need to put a recorder on and shut off the cap...on second thought, I wonder if there is a way to tell if any of the phases have caps that are failed? Are there indicator lights telling you if any caps have failed?
Click to expand...
The current in each of the three phases should be balanced. If it isn't, that would indicate a problem.
 
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