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Cram For The PE

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About Cram For The PE

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    Intern

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  • Engineering Field
    Power eng
  • License
    PE
  • Discipline
    Electrical

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    www.cramforthepe.com

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    www.cramforthepe.com

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  1. It is as Chattaneer PE has stated. I can see why you did what you did though. Perhaps there is a better wording for this. Any suggestions?
  2. Blackburn touches it in his book. However, I do not like the way he describes it. I think my explanation and pictures makes it easier to understand. But I will let you guys decide on that.
  3. Funny story! I do not believe I have ever taken a test that did not penalize you for getting the wrong answer. But I guess that is why I do not understand it. Just answer one question and get a 100%. They should explain further on this point. Anyway in real life and your career you have to figure out answers to questions and problems. You can not just skip it and not be penalized. When you make wrong decisions in life or engineering decisions there are consequences. The philosophy of a test set up like this is not something I personally would agree with.
  4. There is the field current limit. But the question is asking about stability. If you ever look at the generator capibily curve (GCC) you will see the Steady-State Stability Limit (SSSL). This lies in the under-excitation plane. So as you increase field current you get further away from this limit. See below: So with all other things being equal an increase in field current gets you further away from SSSL. As a practical matter, if you think about a generator connected to an infinite system than P=(Vt*Vinf/X)*sin(power angle). The excitation current controls Vt. During a transient condition like a fault a significant reduction in the machine terminal voltage Vt and the ability of the transfer of power occurs. So as Vt is reduced P is also reduced. To prevent this collapse in P requires your excitation system to increase field voltage very very fast to hold Vt to a good value. Also when the fault is removed another violent change in the excitation current is required. So in reality the relationship can be complex. But the question is asking "NOT always used". So your Ie moves up and down to keep stability.
  5. The answer to this question has been published here: http://cramforthepe.com/index.php/2020/02/08/distance-relay-problem-2/
  6. Using vectors is below I just assumed each transformer had a 1:1 ratio to make it easier. I will add to the solution of later book to make it more clear.
  7. Interesting. I did not know about this. So they will probably follow the mechanical and only allow their book in the exam. I will change to my questions to Follow the format of the "alternative questions". It looks like there will still be 80 questions. I don't understand when they say you won't be penalized for wrong answers
  8. I plan to keep the books in print. All I could really do is rely on feedback from people who take the test and tell me how it compares. This fourth volume will probably be my last though. All I know about is the FE transition. I never heard of any PE test yet going this way. My hunch is they will probably still let you come in with as many books as you want.
  9. See image below of capacitor start motor with main, aux and capacitor. I am trying to get them 89° apart. My main is sitting at 31°. In order to put them out by 89° the aux winding w/cap has to be -58°. To move the aux (which is 10+j2) with the capacitor it is going to be minus. Remember inductance is +j and capacitance is -j.
  10. Yes I have fixed this typo in a newer version. The problem should state the voltage is 0.9 (Not 0.95). But to the other question: If a generator has its terminals connected directly to the motor, why would you think they are in series? There is nothing that can be downstream of the motor.
  11. Yes you are correct about no correlation. That is what I will say in the answer key rather than try to confuse about my previous statement.
  12. The correct answer is B. I meant to say that a high voltage line as compared to a low voltage line will have a higher inductance due to the spacing requirements for a high voltage line compared to a lower voltage line. I do not mean to say that raising the voltage raises the inductive reactance. I will get this clarified and re publish. Thank you for brining this to my attention.
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