2400V startup of long idle motors

[bentov]

A customer needs to start using some pumps that have been offline for several years, typical unit is 900hp 2400V with 200kVar power factor correction capacitors connected on load side of contactor. We'll test the motor windings from the panel with our Baker ADX12 (Resistance, IR/PI, Surge, etc. - DC Hipot at reduced level, only if desired by customer).

How to test the old Westinghouse capacitors prior to energizing though? Might they need reforming? Do we need to figure out how to energize them separate from the motors?

 

[waross]

This is one of the few decisions that I have never had to make in the field.
But disclaimer aside. I would consider one of two courses of action.
Disconnect from the motor in any event.
1. Test with a rising DC voltage that is current limited (Series resistor?) to see if reforming is needed.
2. Just set-up and reform all capacitors.
You may wish to check the cost of replacement capacitors against the cost of testing to help with your decision.
I would also consider flooding any ball or roller bearings with grease until new grease is discharged and then letting the bearings drain when the motors are started.

 

[Gr8blu]

If you're going to be testing the machine windings from the panel, you're going to have to disconnect the caps anyway. So, they are already a separate entity.
Test caps (in groups, or as individuals) per the steps outlined by Bill (waross). And regrease the bearings.

If these machines have basically been sitting outside on the pump stand all this time, unprotected from weather and local pests (and probably without anticondensation heaters wired up and powered), get them into a reliable local shop for a once-over.

Also ensure that whoever is responsible checks the condition of the pumps and impellers as well.

 

[PHovnanian]

How to test the old Westinghouse capacitors prior to energizing though? Might they need reforming? Do we need to figure out how to energize them separate from the motors?

Testing the caps might be a good idea. A capacitance bridge can be used to see if the nominal values and loss factors have changed from their spec (if the latter is even published somewhere). I'm not sure about reforming. That's usually an issue for electrolytics (polarized caps). And those would be unusual for power factor correction.

If you are going to use a capacitance bridge, they will need to be taken out of circuit.