Capacitor Maintenance Procedure

[gcameron]

I am currently working on a procedure for field inspection and maintenance of medium voltage grounded Y-connected capacitor banks for use on power distribution system (utility). I need some guidance in preparing this procedure especially as it relates to testing the banks for defective units. I am not too clear if the individual units to be tested should be left grounded after they have been de-enrgized and discharged for at least 5 minutes. My problem is that if the phase bushings are grounded (which is normally part of the procedure for de-energizing) then the capacitance meter will record an overload condition because the units will be effectively shorted to ground since the neutral bushings are always grounded.
Please advise accordingly.

 

[RalphChristie]

gcameron:

For normal maintenance procedures we clean each can, check for any visible defects, and tighten connections.
If necessary we disconnect each can totally and measure its capacitance. Faulty cans are replaced. To balance the total capacitance of each phase (for the three phases) we shift some cans to keep the capacitive difference between the phases as small as possible.



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[waross]

A good common sense test for low voltage (480 v) capacitor banks.
1> Whenever you walk past a capacitor bank, drag your hand over the cans. If one is defective, it will be cooler than the others. If so, test further.
2> Check currents with a clamp-on ammeter. This will instantly tell if a capacitor is off spec.
This is more detecting faulty units than maintenance but you may be able to adapt in part to your application.