Clarification regarding 30 Degree Phase shift between Phase to Phase and Phase to ground voltages

[wfg42438]

Hello,

In the sample question from the NCEES PE exam in the solution they consider a 30 Degree Phase shift between Phase to Phase and Phase to ground voltages

From what i recall VAB leads Van by 30 deg which is why they place a -30 deg angle on Van

However this is the first time i see one of there solutions consider the 30 deg phase shift

IS there a general rule of thumb one can follow to not forget when this phase shift is applicable?

 

[akyip]

Hello,

In the sample question from the NCEES PE exam in the solution they consider a 30 Degree Phase shift between Phase to Phase and Phase to ground voltages

From what i recall VAB leads Van by 30 deg which is why they place a -30 deg angle on Van

However this is the first time i see one of there solutions consider the 30 deg phase shift

IS there a general rule of thumb one can follow to not forget when this phase shift is applicable?

View attachment 27165
View attachment 27164

In general, as you said the line-to-line voltages lead the line-to-neutral voltages by 30 degrees. This is assuming a balanced, positive-sequence ABC system.

If the phase angles are not given, usually (arbitrarily) Van is referenced at 0 degrees.

Vab leads Van by 30 degrees.

Vbc leads Vbn by 30 degrees.

Vca leads Vcn by 30 degrees.

So if Van is the reference at 0 degrees, then:

Vac is at 30 degrees.

Vbn is at -120 degrees.
Vbc is at -90 degrees. (-120 + 30 = -90)

Vcn is at +120 degrees.
Vca is at +150 degrees.

Hope this helps. (I am admittedly a bit rusty though.)

 

[wfg42438]

In general, as you said the line-to-line voltages lead the line-to-neutral voltages by 30 degrees. This is assuming a balanced, positive-sequence ABC system.

If the phase angles are not given, usually (arbitrarily) Van is referenced at 0 degrees.

Vab leads Van by 30 degrees.

Vbc leads Vbn by 30 degrees.

Vca leads Vcn by 30 degrees.

So if Van is the reference at 0 degrees, then:

Vac is at 30 degrees.

Vbn is at -120 degrees.
Vbc is at -90 degrees. (-120 + 30 = -90)

Vcn is at +120 degrees.
Vca is at +150 degrees.

Hope this helps. (I am admittedly a bit rusty though.)

Thanks for the feedback this helps!