NCEES Power #525 and #535

[snerts50]

See I thought I had these down...

Could someone with a moment help me clarify these two problems? Are there differences? I found the right answer on 525, but when I applied the same thought process to 535, i found the wrong answer.

They appear, to me at least to be similar.

Any help would be appreciated.

 

[Flyer_PE]

The key to both of these is in the direction of the currents in the windings. They both come down to simple node analysis but you have to have the relative direction of the currents correct.

 

[EEVA PE]

See I thought I had these down...
Could someone with a moment help me clarify these two problems? Are there differences? I found the right answer on 525, but when I applied the same thought process to 535, i found the wrong answer.

They appear, to me at least to be similar.

Any help would be appreciated.

Problem 535 has a twist to it which threw me initially that may be confusing as you compare 525 to 535. In 535, they are looking for "each phase". I initially read the problem too fast and overlooked this and selected 49.5 MVA. For a answer that is a 1/3 of it @ 16.5 MVA. I am trying to read the questions slowly and make it a habit so I do the same on the real exam.

 

[knight1fox3]

One thing I did during my exam to help eliminate the possibility of mis-reading the problem was to read each question slowly and then circle or underline exactly what the question was asking. This helped me to not read the problem too fast and assume I knew what the question was asking. Just a tip.

 

[snerts50]

See I thought I had these down...
Could someone with a moment help me clarify these two problems? Are there differences? I found the right answer on 525, but when I applied the same thought process to 535, i found the wrong answer.

They appear, to me at least to be similar.

Any help would be appreciated.

Problem 535 has a twist to it which threw me initially that may be confusing as you compare 525 to 535. In 535, they are looking for "each phase". I initially read the problem too fast and overlooked this and selected 49.5 MVA. For a answer that is a 1/3 of it @ 16.5 MVA. I am trying to read the questions slowly and make it a habit so I do the same on the real exam.

I picked up on the single phase transformer fine, using the correct VA rating and V rating, but for some reason I cannot wrap my head around the differences between these two problems, I see that the polarity of the winding connections matters, which in turn dictates the movement of the current, as Flyer said...but I cant get to it. I am trying to make some diagrams and digging through Wildi at the moment, I hope it comes to me. This is annoying...

But true reading slowly is KEY for these questions.