Distribution Capacitor Bank

[cwhit03]

I retrieved some recloser data yesterday for one of the feeders. The data was showing

Phase A: PF=0.95, kW=258, kvar=85, KVA=269

Phase B: PF=0.56, kW=237, kvar=-346, KVA=421

Phase C: PF=0.51, kW=213, kvar=-356, KVA=416

The power factor on b and c phases were of some concern, and was considering a cap bank. What size cap bank would be ideal for this case. I was thinking of a 300 KVAR bank. I have never dealt with capacitor banks on the distribution feeder level, so any of your input is appreciated.

 

[davidbeach]

First thing I'd do with that data is make sure everything is connected correctly. I find your numbers highly suspect; not that I doubt they were written down correctly, but Garbage In, Garbage Out.

 

[dpc]

The negative kVARs would generally indicate a leading power factor, which is unlikely, but not impossible.

I agree with David Beach that you should verify the connections are correct and the controller is properly configured.

If the pf is truly leading, adding caps is only going to make it worse.

 

[mls1]

It looks like there is a mismatch in your phase B and C currents and voltages. If you take the phase A data and add 120 degrees the power factor comes out about .50 which is nearly what you're reading on phase C and from a simple phasor diagram you can see it will come out leading. I suspect a rolled phase.

 

[rcw retired EE]

Did the recloser give any amp or voltage data to cross check the values? I agree with the other gentlemen, it looks like a rolled phase providing bogus metering data.

 

[wfowfo]

Is it possible that you already have a capacitor bank on this lightly loaded line and one fuse is blown on it? The theory about a rolled phase might explain the bad Kvars, but your Kw would be equally out of wack.

 

[davidbeach]

I like wfowfo's suggestion. But I still say that you need to explain the numbers before doing anything about them (or with them).

 

[LionelHutz]

Wouldn't a rolled phase still provide the same KVA reading on all 3 phases?

A blown fuse on an existing cap bank really does sound like a reasonable problem. Could it be a blown fuse on one of the metering PT's?

In any case, the imbalance of the system measured by the meter would indicate the metering is wrong.