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Blown Fuse on Capacitor Bank and Unbalanced Voltages

Blown Fuse on Capacitor Bank and Unbalanced Voltages

Blown Fuse on Capacitor Bank and Unbalanced Voltages

(OP)
I recently asked some questions about capacitors in general and got some answers to really help clear things up but I have another question. I was told by a linecrew putting up a new transformer that the secondary seemed high, was between 126 to 127V. It is normally a blown fuse or stuck switch on a capcitor bank so I went out to check a 3 phase 600 kvar cap bank nearby and two of the oil switches are in and one has the handle hanging down. I take the bank out of service, recheck the voltage and it is down around 122 volts. I was just curious what causes this large unbalance if one of the phases is opened and the other two phases are online. Normally this bank would give a 2 maybe 3 volt rise but since one of the oil swithces was stuck open the rise was higher. If anyone doesn't feel like answering and just has some reading material I have no problem trying to read through and figure it out on my own but it seems the only thing I find when searching is how to protect cap banks or how they should be wired, not what happens when one fails. I appreciate any help.

RE: Blown Fuse on Capacitor Bank and Unbalanced Voltages

Are the capacitors connected grounded wye, ungrounded wye, or delta?

RE: Blown Fuse on Capacitor Bank and Unbalanced Voltages

What is upstream of this bank? Voltage regulators, single phase or three phase? What sort of regulator(s)? How far away?

RE: Blown Fuse on Capacitor Bank and Unbalanced Voltages

(OP)
It is a grounded wye bank and I forgot to mention this is the first step of a 3 step bank all 600kvar grounded wye. The step with the blown fuse was the first step and im not sure why but a lot of our cap banks with several steps have the second step then first then third. So upstream there is a cap bank about 200 ft and downstream there is a cap bank about 400 ft. There are no voltage regulators on this feeder and this is fairly close to end of the feeder.

RE: Blown Fuse on Capacitor Bank and Unbalanced Voltages

Its possible that the kVAR imbalance on the circuit could be interacting with the line's zero sequence reactance to shift the neutral point. This would cause a voltage rise on one or two phases and a drop on the others.

The other possible cause would be a delta tertiary in the substation transformer circulating the kVAR imbalance and causing a rise on all phases.

How (on which phases) was the voltage rise measured?

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