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Zach Stone, P.E.

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About Zach Stone, P.E.

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    Lead Instructor for Electrical PE Review INC (EPR)

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    Teaching Electrical Engineering concepts

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    Electrical Power, Industrial Controls, Field Troubleshooting, Construction Management, Turbo Generators and Power Generation, 24hr Production Facilities
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  1. Zach Stone, P.E.

    Oct 18 PE Exam

    Just want to offer some comfort in this thread. We know that according to NCEES, that only 57% of first-time takers and 35% of repeat takers passed the previous April 2018 Electrical PE exam. However, here's some good news that you are free to interpret however you see fit. I speak with a large volume of test takers every year, and guess what? Every single one of them that passes the electrical PE exam is surprised that they did. Every single time. If you are feeling dragged down, or a little burnt out, it's natural. You no doubt put a tremendous amount of effort into studying and NCEES did exactly what they do best: surprise you, challenge you, and test you. Hang in there until the results come out. Depending on how much you studied, you may be pleasantly surprised in a few months when each state releases their results. If you do find out that you did not pass, the best constructive feedback I can offer is to do your best to leverage the negative emotions into focusing even that much harder the next time around. At the very least, try your best to celebrate the hard work you put in, feel positive about your effort, and be pleased with the new knowledge that you have learned that hopefully betters your career by at least a small amount. I find those that are able to do this tend to be more successful than those that are not.
  2. Zach Stone, P.E.

    Preparation for October 2018 Power PE Exam

    Glad you enjoyed it. If you need anything feel free to reach me directly via email at zach@electricalpereview.com
  3. Zach Stone, P.E.

    NCEES Question 530

    Correct. And since Vpu = 1, the per unit short circuit current is equal to the inverse of the equivalent per unit impedance, or: Ipu = 1/Zeq-pu. In my opinion, these type of simple fault problems are easier to solve with the MVA method, including this one. We can use it to verify the solution. For example, the total apparent power at the fault is 15.38MVA: Sf = 40MVA//(1,000kVA/4%) Sf = 15.38MVA The magnitude of the short-circuit current at the faulted 480V bus is 18.5kA: |Isc| = 15.38MVA/(√3·480V) |Isc| = 18.5kA
  4. Zach Stone, P.E.

    Complex Power Current Conjugate S=VI*

    Hi @ellen3720, The first formula uses complex numbers and solves for single phase complex power (both magnitude and angle) as the product of the complex phase voltage and the conjugate of the complex phase current: S1Φ =VpIp* S1Φ = |S1Φ|<θ To solve for three phase power, you can multiply the same formula by three, which also uses complex numbers and the current conjugate: S3Φ = 3•S1Φ S3Φ = 3•VpIp* S3Φ = |S3Φ|<θ The third formula uses magnitudes only, and just solves for three phase apparent power, which by definition is the magnitude of three phase complex power without the angle: |S3Φ| =√3•|VL|•|IL| Typically when using this formula, you'll obtain the power angle from the inverse cosine of power factor: θ = cos-1(PF) S3Φ = √3•|VL|•|IL|<cos-1(PF) The following cheat sheet gives examples to help to avoid similar mistakes with power formulas. You can print it out and take it with you to the PE exam: http://www.electricalpereview.com/biggest-mistake-commonly-made-three-phase-power-formulas/
  5. Zach Stone, P.E.

    What is allowed in exam

    Hi @rmsg, My answer would be the same as the text that you quoted for the same reasons. While I've never personally been asked this before nor read anything specifically stating magnifying glasses I would consult official representation from either NCEES via email or from their documentation. I'd consider contacting them since I do not believe the examine guide mentions magnifying glasses. My best guess is that it would be okay, however, I do not represent nor am I affiliated with NCEES.
  6. I was going over problem 537 of the Pe sample exam . To get a good understanding of this question would this be like the example you had used to describe Icharging current . Which is the line length act as shunt capacitor to ground therefore the line length , the voltage to ground and the radius of the conductor would play a part in Icharging current. If this is the case shouldn't the radius of the conductor be included in this type of problem?

  7. I read a lot of electrical engineering books. Wildi's is by far one of my favorites, and in my opinion, one of the best reference books you can take with you to the exam. The best way to get the most out of any reference book specifically for the PE exam, is to get familiar with it ahead of time. The order that material appears in each chapter is very intuitive and builds on each other. The best thing to do is skim every chapter that is a subject on the exam and note the headings, subheadings, formulas, and diagrams so that you'll have a general sense of the information laid out in each the chapter. When you come across pain points like areas you've struggled with, or particular points of interest as it applies to the PE exam, stop and tab the page and read a little more indepth. You could probably skim the entire book in about two hours and have a general sense of what's in it so that you know where to look. "This is a tough question but I remember a similar one in Wildi's book. This is a sync. generator question, let me start in the sync generator chapter and flip quickly until I find the heading that fits the problem."
  8. These are my sentiments exactly. The book is essentially his Magnus opus and life's work. It's everything he figured out along the way when all of this stuff was new. Imagine that. Think about how old induction motors are. In his career, it was all groundbreaking and state of the art technology that was being figured out by trial and error. Think mad scientists and crazy laboratories. It's pretty crazy when you stop and think about it. Now, all this is just part of our modern everyday life that no one ever even gives a second thought to except for engineers who apply it towards practical problems.
  9. Hi @jnspark, the equation for reactive power that you're trying to use (quoted above) calculates the reactive sending power. NCEES is asking for the reactive power dissipated (lost) in the line reactance when the sending active power is at it's maximum. Slight but important difference. "When the sending power is at its maximum" tells you what angle to use for your complex voltages. NCEES was even (surprisingly) kind enough to tip you in the right direction of what angle to use for delta if you are unfamiliar with max power conditions (sin(90º) = 1). To calculate the power lost in the line reactance just treat it like a two terminal device. If you know the voltage across a two terminal device and the impedance of the two terminal device, then you can calculate the complex power consumed by the impedance (or supplied by it if the device is a source): S = V^2/Z (O+jQ) = V^2/(0+jX) Q = (VA-VB)^2/X Where VA and VB are the line-to-line complex voltages with VA leading VB by 90º, X is the per phase line reactance, and Q is the three phase reactive power consumed by the per phase line reactance. Alternatively, you could plug in the line-to-neutral complex voltages VA_1ø and VB_1ø with the same angular displacement of VA_1ø leading VB_1ø by 90 degrees to solve for the per phase reactive power loss, then multiply by three to calculate the total three phase reactive power loss since it is a three phase transmission system: Q_1ø = (VA_1ø-VB_1ø)^2/X Q_3ø =3·Q_1ø Q_3ø = 3·(VA_1ø-VB_1ø)^2/X Or you could solve by calculating the current first using Ohm's law then solve for reactive power like others have pointed out in this thread similar to the NCEES solution. All roads lead to Rome.
  10. Zach Stone, P.E.

    NFPA 70E

    Hi @rmsg, NCEES tests on codebooks the year after they have been updated. That means that the 2018 NFPA 70E will not be tested on until 2019. For the Oct 2018 PE exam the 2015 edition of the NFPA 70E is the correct book.
  11. Zach Stone, P.E.

    What is allowed in exam

    Glad it helps. It's fun to speculate, but it's always nice to know what the official rules are.
  12. Zach Stone, P.E.

    What is allowed in exam

    This is a question that pops up often. Your best resource to answer what is/is not allowed will always be the official examinee guide by NCEES. Otherwise, rumors and hearsay may confuse or mislead you. Here is an official link to the examine guide: https://ncees.org/wp-content/uploads/ExamineeGuide_June-2018.pdf
  13. Zach Stone, P.E.

    Delt Configuration

    Hi @kduff70, The trick is realizing that it is actually complex number (or vector) addition and not just adding magnitudes. The surprising thing when you do this is that the longest leg of the center tapped delta is not the connection with the greatest voltage magnitude. Here is a cheat sheet PDF of the center tapped delta directly from our online course from our chapter on Transformer Connections. It has the diagram, proper labeling, formulas, phasor diagram, and an example of a 240V/208V/120V center tapped delta. Feel free to print it out and take it with you to the exam: Center Tapped Delta - Electrical PE Review.pdf It's a large PDF. When you open it don't forget to zoom in to see the details. Also, if you need help with the open delta connection which is even more confusing, here is a detailed free article that will be a HUGE help (you can also print this out and take it with you to the exam): Electrical PE Review - Open Delta Transformer Connection Hope this helps!
  14. Zach Stone, P.E.

    Question For Those Who Have Taken Exam in TN

    That is my understanding. Post it notes already used for book tabs are okay, blank "new" or "unused" post-it notes are a no go. I'd be in trouble. I NEVER use standard book tabs. Too expensive and I can never keep enough around (I read voraciously and tab A LOT!). I have a custom way of making book tabs using post-it notes. I've considered making a video demonstration of it since it is such a money saver and you never run out of book tabs.
  15. Zach Stone, P.E.

    Preparation for October 2018 Power PE Exam

    Thanks for the kind words and the mention. Glad you enjoyed your time with us!