What topics need to be understood for NCEES Power problem 514?

[R2KBA]

This problem seems to be a fault analysis problem, however I don't feel that I have the knowledge yet to solve it. I generally solve short circuit problems using the MVA method outlined by Moon H. Yuen ("learn it in an hour, use it anywhere, memorize no formula" available through IEEE industry applications) which has always provedn to be extremely quick and easy. I really like this method and I would like to use it for this problem if possible.

Can someone help point me in the right direction in terms of what I need to study and understand for this type of problem? I currently have the Camara EPRM and other PPI materials, the GA Tech binder (about to start the couse in a week), the Grainger Power Systems Analysis book, and the Wildi Electrical Machines, Drives and Power Systems book, and all the IEEE color books.

Thanks.

 

[Complex Imaginary]

R2KBA,

This is not an issue of using the MVA method versus the per-unit method. There is no real per-unit work to be done since no actual impedances were given, only the proportion of impedances to each other. This is done to make the problem easier to solve; they are basically giving you the information to solve the problem so you don't have to do any per-unit conversions.

So what is this problem really testing? It's testing your knowledge of the different sequence network diagrams. Each kind of fault has its own sequence circuit diagram; double line to ground; 3-phase fault; and in this case: the single phase to ground fault. That diagram shown in the solution is the standard diagram for a single phase to ground fault. To understand this better, you need to study symmetrical components and sequence network diagrams. A really good online (free) relatively short explanation is here (and it's a pdf you can download):

Sequence Networks

After you understand how to get that diagram, the rest is simple circuit analysis with Kirchhoff's laws and all that.

That's a good start. If you need more in-depth information, you will probably need a legitimate college textbook covering this stuff. Books about fault analysis, or power systems and power engineering should cover it. This, by the way, is a great example of how the PE exam can ask questions involving symmetrical components without requiring long, complex mathematical procedures.

I hope that helps.

Josh

Complex Imaginary

 

[R2KBA]

Thanks, this certainly helps.

 

[EEVA PE]

This problem seems to be a fault analysis problem, however I don't feel that I have the knowledge yet to solve it. I generally solve short circuit problems using the MVA method outlined by Moon H. Yuen ("learn it in an hour, use it anywhere, memorize no formula" available through IEEE industry applications) which has always provedn to be extremely quick and easy. I really like this method and I would like to use it for this problem if possible.
Can someone help point me in the right direction in terms of what I need to study and understand for this type of problem? I currently have the Camara EPRM and other PPI materials, the GA Tech binder (about to start the couse in a week), the Grainger Power Systems Analysis book, and the Wildi Electrical Machines, Drives and Power Systems book, and all the IEEE color books.

Thanks.

The GA Tech Binder section 11 has all the patterns for the faults. Just be able to recognize which fault it is and match it to the pattern and just do simple circuit analysis. Problem 514 is just the Line-To-Ground pattern. Then write 2 equations Va1 = 1 - (Zo/10)Ifault and Ifault = 1/ ((Zo/10) + (Zo/10) + Zo. Then solve the 2 unknowns with the two equations and your answer for Va1 pops out.

These fault problems are all cook book problems, just need to recognize which fault and match it.

 

[R2KBA]

Thanks EEVA. I am almost to that section in the lectures.

 

[ElecPwrPEOct11]

Thanks for the help all. I thought I understood non-symmetrical faults (from EERM & Complex Imaginary video), but was completely baffled by this question. I had never seen the diagrams for the various sequence networks before. I'll be studying that link by Josh @ CI. Any other resources people have found particularly helpful?

 

[ElecPwrPEOct11]

I've been studying this topic and feel like I have a fairly good understanding of it now. My one question is on a three phase fault. I understand the each of the sequence network diagrams is separated from each other (not interconnected). If you use the same parameters as are given in problem #514, I0 and I2=0. Wouldn't the positive sequence voltage V1 also =0 since there is no fault impedance in this problem description? Please let me know if I'm not understanding this correctly. Thanks.

 

[R2KBA]

Oh, yeah, and thanks Josh for the info and link. Sorry ElecPwrPEOct11 I don't know how to answer your question yet. This is one of the last areas I am still trying to understand.

 

[ElecPwrPEOct11]

OK, please let me know what you come up with. It seems like three phase fault should be pretty straightforward and could be an easy point on the exam.

 

[ElecPwrPEOct11]

Can anyone answer this three phase fault question from above?

Summarized- With a three phase fault and no fault impedance I see the positive sequence voltage as being = 0. This makes intuitive sense to me since your line voltages would drop to 0 with a true 3 phase fault and no fault/line impedance. Please let me know if I'm thinking about this wrong.