Effect of Line-to-Line Fault

[boyaxski]

good day fellow engineers,

i'd like to seek your opinion or know your experience on the effect of a line-to-line fault that occurs on a wye-grounded utility feeder to an open-wye open-delta connected bank. say, the bank was connected to phases A and B of the utility feeder and the same phases of this feeder is faulted (getting in contact when blown by strong winds). we have had damage claims arising from this, apparently due to transient overvoltage, and our analysis is when the lines were faulted the bank in effect is supplied with a single source (in an unknown angular displacement). and, since the secondaries are connected open delta, the output voltages of the two transformers would simply be added thus approximately doubling the phase ca voltage (across the two transformers). we tried some computations using symmetrical components but phase ca does not go high (we probably had it wrong, though). hope you could share with us your computations you may have on this incident. thank you.


boyaxski

 

[waross]

I would expect that the fault would pull the voltage down to less than 50% so that there would be a low voltage condition rather than an over voltage on the open delta.
I would expect any three phase motors to draw excessive current.
If a fuse then disconnected one of the feeders, the other feeder may be able to supply full voltage and double voltage on the open delta could be the result.
respectfully