PFC Capacitor Testing
PFC Capacitor Testing
(OP)
We have an oldish (mid 90's) ABB Power factor correction system that was found in a warehouse and dropped off to us as a freebie. It has 9 50kVAR capacitors + reactors rated at 415V, and an ABB relay to allow for automatic operation or each bank can be switched in manually. The control circuit works exactly as the schematic says it should, all the contactors work and don't look like they have ever actually switched any current (low ducter readings on the contacts), and visual inspection of all connections show that the discharge resistors are intact and in good condition.
My problem is that I haven't actually used much in the way of delta connected capacitors before. According to the IEC standards they require a dielectric test, a visual inspection, electrical operation test and insulation test.
-Dielectric test for 415V is 2500V, so I am assuming that is the 3 phases linked to earth. (We do a lot of MV transformer and switchgear testing, so we have the gear)
-Insulation test is the same I take it? Say 1kV megger to earth.
But...
How do I test if they are functioning AS a capacitor bank? We don't have a large supply here, so I can't just power up a 200kW motor or something (we have plenty of transformers we could energise in the 100-1000kVA range) and I'm a little wary of charging up a big capacitor without being 100% confident in the methods.
Any ideas on how to check their capacitance, and whether I need to remove the shorting resistors to do it?
My problem is that I haven't actually used much in the way of delta connected capacitors before. According to the IEC standards they require a dielectric test, a visual inspection, electrical operation test and insulation test.
-Dielectric test for 415V is 2500V, so I am assuming that is the 3 phases linked to earth. (We do a lot of MV transformer and switchgear testing, so we have the gear)
-Insulation test is the same I take it? Say 1kV megger to earth.
But...
How do I test if they are functioning AS a capacitor bank? We don't have a large supply here, so I can't just power up a 200kW motor or something (we have plenty of transformers we could energise in the 100-1000kVA range) and I'm a little wary of charging up a big capacitor without being 100% confident in the methods.
Any ideas on how to check their capacitance, and whether I need to remove the shorting resistors to do it?






RE: PFC Capacitor Testing
Calculate C from I/(6.28*f*U) and var from U*I. U*I shall reflect rated var at rated voltage, reduce rated var with U squared if lower voltage is used.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: PFC Capacitor Testing
Each 50 KVAR capacitor should draw 59.5 Amps at 415 Volts.
If 50 KVAR @ 415 Volt capacitors are tested at 240 Volts, expect to see about 40 Amps.
This is based on three phase power factor correction capacitors, tested with three phase power.
Other factors apply when testing single phase capacitors and testing three phase capacitors with single phase power.
I am assuming three 16.67 KVAR capacitors in one case, connected in delta with three terminals brought out as a three phase, 50 KVAR unit, as is common in North America.
Bill
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"Why not the best?"
Jimmy Carter
RE: PFC Capacitor Testing
Muthu
www.edison.co.in
RE: PFC Capacitor Testing
After closer inspection, despite the fact the nameplate clearly says 450kVAR in 50 kVAR steps, the actual capacitor modules have 45kVAR written on them... which is a little odd. So presumably they are 3 x 15kVAR units.
We're not going to be using it, Muthu, just want to know if it's a functional unit or if we just bin it.
RE: PFC Capacitor Testing
Muthu
www.edison.co.in
RE: PFC Capacitor Testing
Unfortunately, since clients request that sort of test VERY rarely, there has been no push for us to upgrade our facilities to allow for it. Instead that work is sub contracted out. Not worth doing for this particular case.
RE: PFC Capacitor Testing
Latango, remember that the kVAr ofthe capacitor is going to depend upon the applied voltage. Many PFC capactiors have, on their nameplate, different voltages and different kVAr ratings for each of these voltages.
For an example, if your capacitors were 45 kVAr at 380 volts then they would be 50 kVAr at 400 volts.
RE: PFC Capacitor Testing
Just out of curiousity where does the 6.28 factor come from in your calculation for capacitance?
I know the general form for current through a capacitor is i = C* dv/dt.
RE: PFC Capacitor Testing
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: PFC Capacitor Testing
RE: PFC Capacitor Testing
RE: PFC Capacitor Testing