NCEES Power Sample Exam #107

[Dodgeviper1017]

I am confused why they divide 65 kV by the sqrt of 3 and the MVA by 3. I get that they are converting to a single phase approach to solving the problem and I get the answer but the problem never states whether the line is in a delta or wye configuration. Would this not make a difference? So how do they know to divide by 3 to find phase unless they tell you its delta or wye?

 

[allgood]

You might want to look at the thread below.

 

[Dodgeviper1017]

Thanks for the reply, I have checked out that thread. However I am confused on to how they knew that it was wye instead of delta? I get they converted it to single phase for easy analysis but why in the way they did it. If this was delta sqrt of 3 would not have been used right?

 

[allgood]

I don't have my book with me so I'll take a look at it once I get home.

 

[TWJ PE]

If you aren't told, you are to assume given voltages are line-to-line.

 

[knight1fox3]

If you aren't told, you are to assume given voltages are line-to-line.

This also tends to apply to most EE practical applications as well. :thumbs:

 

[Dodgeviper1017]

Yeah that is what I assumed thanks for the answers. So basically if they don't specify delta or wye I assume line to line and wye? This seems to be the common pattern and was confirmed by you guys. Thanks for all the help.

 

[Phatso86]

I am confused why they divide 65 kV by the sqrt of 3 and the MVA by 3. I get that they are converting to a single phase approach to solving the problem and I get the answer but the problem never states whether the line is in a delta or wye configuration. Would this not make a difference? So how do they know to divide by 3 to find phase unless they tell you its delta or wye?

these are the same issues I have regarding the sqrt(2) factor and sqrt(3) factor. You always seem to make an assumption

What I've been explained previously is that transmission lines are always assumed to be wye connected unless stated otherwise. (Doesn't really help, but looks like that's what we have to go by - assume wye for transmission lines))

 

[Dodgeviper1017]

Thanks that helps I did not know to assume wye for transmission.

 

[cupojoe PE PMP]

Thanks that helps I did not know to assume wye for transmission.

It is generally understood that the voltage given is line to line unless state otherwise. Just want to make sure you realize that it doesn't matter how it is connected on either end. It is still the same line to line voltage.