Corner grounded delta and power system analysis programs

[ijl]

I am trying to compare the short circuit currents in a partial network "fed" by
1) the secondary (or tertiary) of a transformer connected in delta with one phase grounded ("corner grounded delta")
2) the secondary (or tertiary) of a transformer connected in a grounded wye (Yn)
There may be different types of faults, and the fault may be anywhere in the partial network, not necessarily at the transformer secondary.
It seems that the fault currents may be different in the two cases.

My question is, which of the well known power system analysis programs (SKM, EDSA, DigSilent, ETAP, etc) cover the case of the corner grounded delta?

 

[JensenDrive]

All I can speak of with recent experience is SKM's software. SKM does not directly cover corner grounded systems. However, it seems if you solidly ground, for instance, B phase, an A phase to ground fault would be the same as a phase to phase fault on a Wye-G system. If you wanted the phase to ground voltage on the unfaulted hird phase, I suppose you could somehow monkey with the Wye-G phase to phase results to figure the voltage out, but SKM does not make it easy for you.

 

[davidbeach]

If you really want to get into the detail of something like this, I'd suggest an EMTP type of program. That will allow you model what ever you want.

 

[jghrist]

However, it seems if you solidly ground, for instance, B phase, an A phase to ground fault would be the same as a phase to phase fault on a Wye-G system.

Except that in a Ø-Ø fault, the current will flow in the phase conductors, but in a Ø-grd fault the current will flow in one phase conductor and in the equipment grounding conductor and other parallel ground paths. The impedance will be different.

 

[ijl]

Davidbeach, I am using ATP, but I thought that there should be some simpler way.

 

[JensenDrive]

jghrist
Wow, thanks; that was a notable oversight on my part.

I wonder if you could estimate the fault by treating it as single phase to ground fault at the end of a cable fed by a single phase xfmr? I mean if you have a 480delta:208Vdelta corner ground, I wonder how close you would be if you told SKM that you have a 480V(A-B) to 208 single phase xfmr, and the faulted the end of your 208V cable. Of course, now you have to spend more $ to get the SKM single phase analysis module.

A related issue is that ground fault impedance for cable is largely a guesstimation. The typical impedance tables such as in the NEC and the IEEE Red book are for balanced three phase current (Z1). A few resources will list Zo for cable, but they are all over the map; there are just so many variables.

 

[jghrist]

I wonder if you could estimate the fault by treating it as single phase to ground fault at the end of a cable fed by a single phase xfmr?

I don't see why this wouldn't work. You will only have current in the faulted phase and in the winding between the faulted phase and the grounded phase. This seems identical to the situation of a faulted single phase circuit.