Help - 130kV OHL Disturbance

[marco1966]

Hi,
I received from a colleague the attached disturbance " 130kV OHL short circuit".

My question is :
Why during the short circuit the phase A and B and C currents are in phase ?!?!

Any idea ???

Thank you for your support.

Marco

 

[davidbeach]

If A, B, and C are all in phase you are looking at the results of a ground fault.

 

[PHovnanian]

The voltage traces appear to be due to a fault between line 1 (red) and ground. But the current traces show some odd current reading on line 3 (green). For a line to line fault, I'd expect to see the two line currents out of phase by approximately 180 degrees. Which is not the case here.

I'd need to take a close look at how the CTs are connected to understand whether this is an actual reading or some artifact of the wiring scheme.

 

[slavag]

Marco.
Could youy please send us Comtrade file, intresting see vektor diagrams before--after fault.
Best Regards.
Slava

 

[davidbeach]

Like I said, it is a line to ground fault as seen from a location on a network. If you're used to looking at faults on radial systems it will seem very weird to have all three phases line up, but in networked systems it is not at all uncommon. Draw out your sequence diagrams and you will see that (+), (-), and (0) are all approximately in phase and can be of similar magnitudes, resulting in all phases being of similar phase and magnitudes. Pick the right impedances in front of, and behind, the fault and you can get most any set of currents you can dream up.

 

[jghrist]

This is probably one of two or more sources of the fault current.

If this was the only source to a Ø-grd fault, there would be current only in the faulted phase. If it was measuring the current coming from a grounding transformer, it would show all zero-sequence current and all phases would be in phase and equal.

You can get some screwy looking currents in each source when you have multiple sources feeding a fault.

 

[PHovnanian]

Hmm. Grounding transformer. Any change its something like a zig zag configuration? And where are these measurements being made w.r.t this transformer (if it exists)?