# NCEES Power Sample Exam #514



## madblur (Mar 20, 2014)

Symmetrical Components is not one of my stronger topics, especially when it comes to drawing the zero sequence diagrams. I think there is something very basic that I am not understanding with the solution for problem number 514.

1. Is the T1 configuration (wye-wye, delta-wye, delta-'grounded wye', etc) irrelevant? If so, why? Is the '1 pu' voltage source not the source on the primary side of T1?

2. If only T2 is relevant, I'm still confused on the zero-sequence connection shown in the solution. Based on my references, the zero-sequence circuit for a grounded-wye to ungrounded-wye transformer has a disconnect between the primary and secondary phases...I don't see any disconnects shown. I assume this is because they simply didn't show the entire sequence circuit diagram, but it's confusing me about how they arrived at their solution.

Any help/advice/useful resources would be appreciated.

Thanks


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## madblur (Mar 23, 2014)

Ok, I just realized that they are actually giving the thevenin equivalent sequence impedances so there is no need to work out the sequence networks. Really, all you need to do is know how to connect the positive, negative, and zero sequence networks for a single-phase to ground fault.


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