Roger Dugan

For just a simple transformer with 2 windings (H and L) the short circuit impedance from H to L in percent is %R(H) + %R(L) + j XHL. When there are more than 2 windings, it can seem more complicated. The required impedances are the winding resistances (in percent) and the short circuit reactance (in percent) between each pair of windings. Some power system analysis programs will want you to specify an X for L and and X for H. But there is actually no such thing for this analysis. A short circuit,...

Specifically, what problems are you encountering?

%R and XHL etc. come from the transformer test report. OpenDSS is not computing these values. There is an explanation somewhere how the transformer model values are computed. If I can't find it promptly, there is an IEEE paper from 2003 PES General Meeting that explains the model. Just search IEEE Xplore for my name.

This is not a function we anticipated when OpenDSS was originally developed. The COM interface was implemented to allow users to add their own features by writing some computer code in a language of their choice. So that's basically what you have to do for functions like you are wanting that are not part of the OpenDSS design. You can try exploiting the Zsc command to return the impedance matrices at two different buses in the system that have only one path between them. The difference might be what...

The Newton-Raphson method should work in actual quantities as well as per units, although the Jacobian may be more difficult to determine. In some cases, I have used the Y matrix as a stand-in for the Jacobian with some success. But it all depends .... As for converting the transformer Yprim back to per units, it may be possible, but I have never done it so I don't know what to recommend. As OpenDSS develops the Yprim for a transformer, it comes through a step where it is essentially per unit (or...

I was involved in the 34-node model but I have no memory of why we did it the way we did. Maybe we got a tip from Kersting or found that there was an assumption made and adjusted the OpenDSS model accordingly. I had more of an input into Mod2 version because I knew what it would take to match the version in Kersting's program. But I do not recall how specific decisions were made.

I just ran Mod1 and did not get any errors. What errors do you get? I think the difference between Mod1 and Mod2 is that Mod2 adds nodes in the middle of the line sections to better match Kersting's results. Bill's program assumes the distributed load is located at the center of the line. The connection of the Load elements is intended to match the way Kersting defined the test feeder. The 1-phase Delta loads are suspicious. It could be an error by the person who made up the test case. The computed...

Usually the 11/0.415 transformers are Dyn11 which is a 3-phase connection. I'd be interested to know how they cut off one phase. Is there automatic switching somewhere? Do they open up two of the transformers in a 3-phase bank? A little more explanation is needed, but I am thinking it is unlikely they are Y-y transformers.