Symmetrical Components for Cross-Country Fault 6

[davidbeach]

I am working on a paper, for one of the relay conferences, that is looking at protection of ungrounded/high impedance grounded systems for the condition where there is already one ground fault on the system and a second fault occurs elsewhere on the system.

I have calculations using SKM, that appear reasonable, but I would like to be able to include a symmetrical components analysis of the fault currents. I have many books in my library with information about LLG faults where the fault happens in one location. What I would really like to find is a reference that deals with a phase to ground in one part of the system simultaneously with a different phase to ground elsewhere in the system.

When a relay sees both faulted phases, the sequence components are quite different than when a relay sees only one of the faulted phases.

References would be greatly appreciated.

Thanks,

David Beach.

 

[stevenal]

Anaylsis of Faulted Power Systems by Paul Anderson has a chapter on simultaneous faults.

 

[davidbeach]

stevenal, yes, he does. The problem, at least without a thorough reread of the chapter, is that it deals with two-port networks and I have two one-port networks. The problem, as I see it with a quick skim through, is that his system of solutions has a source at each fault location and a network of impedances between the two faults. What I'm looking at is a radial system with a single source and two networks in parallel.

Thanks for the reference though.

 

[jghrist]

Westinghouse T&D Reference Book has several sequence diagrams for multiple unbalances including simultaneous single line-to-ground faults on phases A and B at different locations. Figure 22 of Chapter 2 in the 4th Edition.

 

[davidbeach]

jghrist, thanks. That diagram (at least in the 5th edition & it doesn't appear to have been revised) works for the case where the two faults are in the same circuit, separated by an impedance. That is one of the cases I am looking at, but the one I'm most interested in is the case where there is one source (the T&D example seems to be for two sources, although one could be left open) and two independent paths from the source to the two faults.

 

[mykh]

Power System by Behic Gungor has a chapter on generalized study of all types of faults including multiple and simultaneous faults.

http://www.arcadvisor.com/index.html

has online fault current calculator with detailed description and calculation examples of conventional fault analyses.

 

[davidbeach]

Well, between a bit of the T&D book, a bit of Anderson (but the chapter on Changes in Symmetry) along with a bit of Blackburn thrown in for good measure, I think I have a solution. UGLY, but it works; and I'm so glad for MathCAD, it takes 15 equations to solve the 15 unknowns, although not all 15 are independent. It would be an absolute bear to have to reduce all of those equations to get a smaller set of truly independent equations. Come to WPRC in October if you want to see the results.

Thanks again to stevenal and jghrist.

mykh, I do not have a copy of Gungor, and that fault current calculator doesn't look like it would give me anymore information than what I have from SKM. I was looking to understand how & why it produced the results it did, I have the calculated fault currents, including sequence components. But, thanks anyway.

 

[RalphChristie]

David

In Power System Protection Vol.1, (Principles and components) edited by the Electricity Training Association are a few pages that deal with cross-country earth faults. (Condition A being a single-phase-to-earth fault on phase b and condition B a similar fault, but on phase c) They refer to Edith Clarke's book Circuit analysis of a.c. power systems for more information on simultaneous fault conditions. I do not have a copy of Edith Clarke's book, but could try to scan some pages from the first mentioned book, and then send it to you if you would like it.

Another book I think that can have some info on this subject is Conrad St Pierre's Book, A Practical Guide to Short-Circuit Calculations. Unfortunately I do not have a copy at home, but I'll check when I get back to work again.

Regards



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[davidbeach]

RalphChristie, thank you very much, that is exactly what I was looking for. One more favor to ask, could you please send a copy of the title page so I can cite it as a reference?

 

[stevenal]

Congrats on your well researched presentation and paper. For everyone else, here's a link to the paper:

http://www.basler.com/downloads/NegSeq.pdf

Although mia from eng-tips, Busbar made it to the conference. He had some favorable comments on the presentation.

 

[davidbeach]

Thanks stevenal.

 

[RalphChristie]

Excellent David!
Congratulations

 

[rcw retired EE]

I liked David's presentation also. Just got to figure out how to apply it now.