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So one of my books says that the turns ratio of a three phase transformer bank of a 13 kV delta - 138 kV wye transformer is 13/ (138/sqrt 3). Is that the single phase transformer ratio of one of the three transformer making up the bank, or is that the total three phase turns ratio?

Is anyone bringing any of the IEEE books with you to the exam? I have all of them in a pdf format so I'm not sure I want to go spend all this $$ to print them out, especially since mostly all of them are hundreds of pages...and that'd be a lot log lug around in addition to all the other books...

This is an easy points question that might trip me up on the test if I think about it too much. I got it right, but when I start thinking about it, I get confused. So they are asking for the relay tap setting, which in an 800:5 CT, that 5A is the tap setting, isn't it? Or is the questions...

Since when is dividing amps by impedance give you amps? The way I did it was to take 1pu (volts) / total Z to get the Ipu. Then multiply that by the Ibase. I just assumed a 1pu volts, I'm not sure that was even correct. But nonetheless, I still don't understand how they got real amps by...

If all we are looking for is the turns ratio, then are these the basic rules: 1. For 3 phase transformers, use line to line ratios. 2. For 1 phase transformers, use line to neutral ratios. This question comes in reference to NCEES #506, where they use the line to neutral ratios. But in...

How can you use the effective Z to find the voltage drop and still get the same answer? it specifically says that it is an approximation of the answer, but when I do it (400 amps with angle corresponding to 0.8, times the effective Z), I get 473.xxx, which is closer to the 475 answer than the 471.

Why do they divide 12.5 by sqrt 3 for doing the single phase equivalent of Van? It is a delta load, where there isn't even a neutral to consider. I know I am wrong, just don't get why at all.

For NEC Table 9 for impedance values, why do they give the ohms/neutral? what does the neutral have to do with the impedance of a phase line? And what if it is a 3 wire system with no neutral? Also, to use the table for voltage drop calcs, what pf do you use to calculate the effective Z, is...

You cannot just subtract phasor quantities by their magnitude, correct? In the Chelapati book, page 3-54, they subtract 1036 angle -6.9 kVA from 1135.5 kVA to get 117.4 kVA. That's an error, correct? Does anyone know if there is an errate available from the Chelapati books anywhere? I'm sure...

Anyone can answer this, but for anyone who's got the Chelapati book, this is on page 3-48, why do they divide the 208 by sqrt 3 to transfer the l-n voltage on the low side to the l-n voltage on the high side?? The high side is delta, so the single phase equivalent would still just be the 2400V...

Where do they get the -30 and +30 degrees in the answer? And do the * dots in the wattmeters have anything to do with how they are read?

I got a question i'm trying to solve. There is a 3 phase system with a delta motor load and three single phase loads. Part of the question asks to find the line current (so the line current of one of the phase motors plus the current from one of the single phase loads). To find the single...

Do you think we will need to include the DC component in any fault calculations? I don't exactly have the grasp on this concept as it is, but a couple of my books discuss it. I think that you use include it for subtransient calculations only, which the exam could very well have, but I haven't...

Can someone explain this to me? I understand the 2370-460 part, because you want to know how much copper losses were added since you got to 50% load. But where does the 4 multiplier come from to get from there to 100%? Hopefully the answer to this question will help me solve #526 also.

"A single phase transformer rated 11/7.2 kV has an impedance of 10.0%. During a factory short circuit test done at rated current, the voltage (kV) applied to the HV terminals will be most nearly:" Answer: 10% of 100 kV = 10 kV. Do you multiply by 10% because of the impedance or because 10%...

Why do they divide the transmission system voltage of 60 by square root of 3 when dividing by the impedances to find the fault current? How do they know if that transmission system is not a delta and then the line-line voltage just equals the phase voltage (so that it would be just 60/Z)??

If they are doing the single phase equivalent calculation and divide 480 by square root of 3, then why don't they divide the total balanced load of 400A by 3 to get the equivalent 133.33A per phase?

The load is a balanced delta, so when they do the single phase analysis to find the line-line source voltage, they divide the line-line load voltage of 12.5 kV by square root of 3. How do they know to do this, because you don't know if the source is delta or wye (or do you? it's not shown on...

Anyone have any good online resources for these topics (especially the first four listed)?? Nothing too much in depth, as I assume the questions for these topics will be general (well, maybe SC will be more in depth). I just can't find anything that provides information relevant to test...