question on fault analysis

dregan

Joined Apr 3, 2008
6
I'm trying to learn about fault analysis and I have a question about an example phasor diagram from a fault that I have been looking at. I'm pretty sure that it is a A-B phase to phase fault (high currents on lines A and B in opposite phase as well as low voltages). I've also calculated what I believe to be the fault current and fault voltage phasors by adding the respective phasor of the two lines together. Now I'm trying to determine whether the fault is close or far from where the phasor diagram was measured. Here is my thinking: Since the fault votage phasor is high and the fault current phasor is low, this would imply a high impedence suggesting that the fault exists far away from where the measurement was taken. Anyone think this is a valid assumption? Thanks for your input!

Dave

edit: here is the diagram.

Last edited:

subtech

Joined Nov 21, 2006
123
This is a "classic" diagram of an A-B phase fault. The A & B voltage phasors have reduced in magnitude and the angular difference between the two is relatively small . I've no idea of the current scale here, but if the phase C current phasor shows normal load current, then your assumption that the fault is a goodly distance from the source makes sense in that the fault current for phases A and B seem to be roughly 3 times the load current. Thus far, I'd say your analysis is correct. Good job!

What is your assessment of the source impedance behind this fault??