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Thanks for the FYI. This makes the only 2 practice problems I know with corner-grounded deltas a bit misleading, since they had corner-grounded deltas as loads. It also sounds like I shouldn't worry too much about corner-grounded deltas on the exam...

Hey all, Attached is my work and attempt on this problem. I used an equivalent 1-phase circuit diagram to do this problem. I first solved for real power sent using: Psend, 1ph = (Ea,LN * Vt,LN / Xs) * sin(theta), and then multiplied that by 3 to get the 3-phase real power transfer. Then for...

That's nice to know. I didn't think they could actually use a center-tapped open delta. I'm guessing the 57.7% rule for open-delta still applies to center-tapped open delta: the power drawn is only 57.7% of what is normally supplied from a full delta. And that the currents flowing in the phases...

There's one other thing I thought about that further makes me think that Vag will still be 13.2 KV for the case of a grounded source feeding a corner-grounded delta. When a delta becomes an open-delta, its delta phase voltages (which are line-to-line voltages) do not change. So corner-grounding...

The NCEES practice one was an ungrounded source feeding a corner-grounded load. That situation is much simpler: all the corner ground does is make the grounded phase a 0-V reference point. It does not impact the voltages and voltage differences at other points. Line-to-line voltages will still...

Not sure about that question either. I'm not sure how the current flows between the source and load in the case of a Y grounded source feeding a corner-grounded delta. I definitely see your point about the neutral being a short-circuit... Maybe that's why we don't see many problems about a...

Ah, thanks for the shout out! I'm not sure how well I'll do come the exam day, but I'm just gonna do my best. My main concern is that the exam can throw curve balls with unexpected questions...

OneNote. I've been using a tablet (Surface) and a tablet pen to do practice exams. Saves a lot of paper!

I tried to take a shot at this question, because I'm also curious myself and I haven't really seen many examples for a corner-grounded delta. The only 2 practice problems I remember regarding corner-grounded delta are from the NCEES practice exam and PPI practice exam. Both questions had the...

I used the current from the original transformer's 480 V side, because that current corresponded with the 480 V winding. And with how it's drawn and laid out in the autotransformer diagram, that current is the input current for this autotransformer. If you want to calculate the S auto from the...

I'll try to explain as best as I can. With the 600 V/120 V autotransformer configuration, the primary winding of the original regular 1-ph transformer (which has the 93.75 A current) becomes the series winding on the high side of the 600 V/120 V autotransformer, and the primary current 93.75 A...

Revisiting this topic with another example of using Table 430.7 instead of Table 430.251 for induction motor locked-rotor current. See attached from Complex Imaginary (set 4, question 76) Just a friendly FYI.

I see. This line tool, it can be used both horizontally and vertically? I ask because for example: Table 9 Chapter 9 is very long. If for example I had to refer to 750 KCMIL resistance and reactance per unit length...

Hey guys, I have a quick, silly question to those of you guys who have taken the CBT exam. You are able to highlight text in the provided electronic code books (NEC, NESC NFPA, etc.), right? Something like highlighting in the attached screenshot? Just asking this question, because I want to...

Congrats!

Ampera, I hope that my illustrations for this problem help. Also of course, I'll mention that the reason Choice D cannot be made from the given 1-phase standard transformer is because there is no way to add or subtract between 480 V and 120 V to get 240 V.

One more illustration, to answer the apparent power (KVA) problem for the 600 V/120 V step-down autotransformer. Also, I included the note in red about the relation between V1, V2, I1, and I2 at the bottom. This will help visualize how the currents will flow, especially the common current in...

Hey all, I'm revisiting this topic to try to help out on autotransformers. I mentioned earlier in this topic that it helps to visualize the 2 windings to see how you need to connect them. I drew out illustrations for each of the possible choices from the given problem, starting with breaking...

Perhaps, but in my studying and practicing exam problems, I've done many more NEC questions than NESC questions. I guess for me, that's why I am more used to navigating the main common topics of the NEC than the NESC. Just my experience speaking.

Maybe to you it is, but for me the NESC is hard to navigate because it's not as laid out well to me compared to the NEC. Just my two cents LOL I think for NESC questions on the actual CBT exam, I'll probably have to wing it and rely on the power of Ctrl+F... Or hope it's a question about a...