Testing a capacitor bank

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carjam

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Hey guys, I am looking for some info on testing a capacitor bank at 7200 volts. The bank has to be shut down so maintenance can be done on it. I am curious to know can you use a hot stick tester to check it. Obv. i dont want to " wait an hr or so and it should be drained". Any help would be great, thanks in advance
 
carjam said:
... I am curious to know can you use a hot stick tester to check it. Obv. i dont want to " wait an hr or so and it should be drained". ...
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All of the capacitor banks I have seen have an internal bleed resistor - and yes you have to wait the specified time - unless you "know" there is a external impedance (resistive load) on the bank when shut down.

Hot sticks are another issue. Check the specs and see what the DC rating is. Many will not see the DC. Some require a ground wire to see the DC.

Although no longer recognized, I still use a hook stick before I put my hands on cap banks.

carl
 
The code requires capacitors under 600 volts to discharge to less then 50 volts in less then one minute. 460.06

For capacitors over 600 volts 460.28 requires discharge to less then 50 volts in less then 5 minutes.

That said ... don't count on the code alone to protect you.
 
Talked to a guy who works at consumers energy. Actually he took me to a sub station and we looked at one. There is a disconnect to shut the 3 phases down. Once they are down you have to attach a ground to each of the feeders (they look like 1-1/4" hollow tubing) and run them to the earth ground. Then on the back side of the cap bank is a plate that connects all 3 cap banks together and a 4/0 ground runs from that plate to a transformer that steps down the voltage from 7.2k to 120V. (Since the transformer is set to a known value, a relay ties to that and if one of the caps fuses fail the relay will sense the imbalance and will shut the cap bank down. He said that if this didn't happen then there is a potential that the cap bank will burn to the ground).Then you have to ground from the 4/0 going to the transformer, to earth ground, and this will prevent back feed. Once this is complete you go from earth ground to each individual cap and ground it out. He said the reason for this is because if one of the fuses are loose or possibly corroted then there is a possibility that it will not drain. Any ways i thought i would share what i was told. And you are to do all of this with hot stix BTW.
 
Yep, you use a discharge stick, tap and hook is the term to remember. Hubble, AB chance, White safety line, etc all carry them.

You at FES or Delta? Barb B or Tim H (Depending on which plant) at WFG should be able to help you.
 
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