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  1. So not a relay problem so much as a transformer problem? I guess what got me was the Vng part. Thanks.
  2. Can anyone provide an explanation for this problem? I presume it's something to do with the ratio, but what is Vng? Is this simply asking for what voltage (line to neutral) is necessary, in KV, on the primary to trip? Gotta say, stuff like this is not making me look forward to Friday.
  3. I agree too. the equation for capacitance is Which has radius in the equation. I think it plays a tiny role in the equation compared to length and voltage, but still proportional. What are we missing?
  4. Check out the following link Triplen Harmonics as it will give a good overview. I will not present math or equations as I don't know them, but with 3rd harmonics, a triplen harmonic, you need to also think in terms of symmetrical components and KCL. The third harmonic is zero sequence current, also known as ground fault current. It is what is sometimes called circulating current and is a simple summing of all the currents. As far as I understand it, and I am not a PE yet just someone dealing with protection and grounding banks, the major problem with ground fault current and triplen harmonics occurs in a system with a grounding connection. So the key part of the NCEES question will be the mention of a 3-phase 4-wire system. If this was a 3-phase 3-wire system, meaning floating-wye or Delta, then there is no source of ground fault current and I believe the answer would be zero, unless KCL is a myth and the world is really flat. There are tons of links out there, just search "triplen harmonics" . Good luck to all of us in October!
  5. I talked to a co-worker, who took the April test, and he explained to me the "j" that is dropped in the NCEES equation makes it purely reactive and therefore the I^2 * R equation becomes the reactive power. All that confusion for the lack of the "j" in the denominator. Thanks BirdGrave, but per chance did you forget the root 3 in the Current equation since these are line-to-line?
  6. I am working on problem 531 and I personally do not agree with the NCEES answer. Help! The question is asking for the Var losses in a transmission line during the transfer. I used the equations I found to calculate the active power transmitted, done to simply verify that the system did in fact 5,000 MW from System A to System B, using the equation ONE below. Next I calculated the var losses using equation TWO below. Based on the equation to find vars transmitted from A to B I calculate Yet NCEES says the answer is (D) 10,000 MVARS. So what am I missing? It does not seem like we find the vars transmitted from System A to System B as well as from System B to System A which would double. I say this because the problem states 5,000 MW transmitted from A to B. Any help is greatly appreciated. FYI-> I just found a similar equation to the one I used on the NERC website and I would hope they get it correct.
  7. I purchased the cheaper international edition of the Wildi book and am extremely frustrated with the horrible index. I was wondering if anybody on the board and who has the US edition can tell me if the index in that copy is useful? For example, looking at transformers in the int'l edition simply returns a ton of page numbers and no sub categories like ideal transformer model, equations, loses, etc. Throughout the whole book it's like this and I have decided the book is useless since I can't just pick a topic to look up and read on, which translate to the test as not being able to find an obscure tidbit when needed on a hard question. If the US edition is better, is it possible to get a scan of that and hope the page numbers are the same? Thanks Neil
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