When to Use 30 Degree Phase Shift

[Dodgeviper1017]

So I know it is to be used in phasor calculations, and not in magnitude. However, it seems to me that sometimes they elect to use and sometimes not. For example in NCEES Problem 129 they don't use it when converting from 480 Volts, but in NCEES Problem 111 they do. Why is this?

 

[Dodgeviper1017]

Wonder if it has to do with a selta being used on 1 and not told on the other? Really this is confusing to me if anyone has any information it would be greatly appreciated.

 

[knight1fox3]

Have a look at this and see if it helps any:  

 

[Dodgeviper1017]

This will help quite a bit. I cant look at my book until I get home but this seems to clear up what I remember.

 

[Phatso86]

I was just about to make a post about this problem. Hopefully someone will respond to my question.

Here it is:

Why do I get different voltage angles (same magnitude) if I do KVL around loop aABb (-17deg) vs doing KVL around loop aANn (5.7deg)

Obviously n and N are the fictitious neutral nodes. Still got the right answer, but the angles are killing me

 

[Dodgeviper1017]

Here is what I did

Vab = 70angle-20(5+j10)+12500angle0-(5+j10)70angle-120

When input to calc I get 

Vab = 70angle-20×(11.18angle63.43)+12500angle0-(11.18angle63.43)70angle-140

782.6angle43.43+12500angle0-782.6angle-76.57 = 12693.199angle5.7

Vab=12.95 kV which is C

I think it might be because you would be finding Vba not Vab.

 

[Dodgeviper1017]

Just worked it out the other way. I see what you mean I get the same. My best guess is still above. Good news still get right answer if its only magnitudes but might help to know for test.