NCEES Problem 109

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Insaf

Electrical Engineer
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If wye-connected source is grounded, is there any difference to determine VBG?

Thanks,

 
I *think* Vbg would then be equal to the line to neutral voltage because the system would be grounded.

 
Insaf said:
If wye-connected source is grounded, is there any difference to determine VBG?

Thanks,
Click to expand...
I do not think there would be any difference. Since this questions is bought up, I will post various phase to ground voltages I calculated for this system. Vag = 0, Vbg= 13.2 @ 180 deg and Vcg = 13.2 @120 deg.

As we can see, this method of grounding creates unequal phase to ground voltages.

Will look forward to any comments.

Thanks,

 
Silkworm said:
I *think* Vbg would then be equal to the line to neutral voltage because the system would be grounded.
Click to expand...
The system is grounded even now.

Well, instead of grounding phase A on supply side ( grounding "A" of supply will keep the grounds at same potential), if point "N" is grounded, then it creates a short circuit on phase A of of the supply. Also, the phase to ground currents of other two phases will be extremely high due to difference in ground potential.

 
My understanding is if the system is UNGROUNDED then the neutral will shift if phase B is connected to ground, which is why the line to line voltage is unchanged. However, if we the system is GROUNDED at the source then you are tying ground to neutral i.e. the neutral is tied to 0V. So Vcb = Vab = Vln.

 

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