NCEES #109 Power

[robertplant22]

A 3-pahse, 3-wire, ungrounded, 13.2kV (phase-to-phase) wye-connected source is connected to a balanced delta load that is grounded on corner A. The voltage measured between corner B and ground is most nearly:

The answer to the problem is 13.2kV. but what I want to know is, what would be the difference if the wye-connected source was grounded?

My reasoning say it would be VAG = 13.2kV/sqrt(3) = 7.62kV can someone confirm? Also can someone expand on this topic of delta corner grounded system with un ungrounded source?

Thanks!

 

[dzdave00]

A 3-pahse, 3-wire, ungrounded, 13.2kV (phase-to-phase) wye-connected source is connected to a balanced delta load that is grounded on corner A. The voltage measured between corner B and ground is most nearly:

The answer to the problem is 13.2kV. but what I want to know is, what would be the difference if the wye-connected source was grounded?

My reasoning say it would be VAG = 13.2kV/sqrt(3) = 7.62kV can someone confirm? Also can someone expand on this topic of delta corner grounded system with un ungrounded source?

Thanks!

The wording of this question does not really make sense. In the real world, to go from an ungrounded wye source to a corner grounded delta, I believe you would need a transformer. Your thinking is correct if the source was grounded wye. Seems like the point of the question was to show that on a corner grounded system, the phase to ground voltage on the ungrounded phases is equal to the phase to phase voltage. The question seems unnecessarilly confusing.

 

[kris7o2]

Hi all, I am still struggling to understand this question. I'm not sure I understand what a 3-phase, 3-wire, ungrounded wye connected system vs. a 3-phase, 3-wire grounded system looks like. Does anyone have a diagram of these, and how they would be connected to the corner of a balanced delta load that is grounded? I think that is the reason I can't understand this problem is that I do not know what difference(s) a grounded wye and a non-grounded wye make.

 

[akyip]

Hi all, I am still struggling to understand this question. I'm not sure I understand what a 3-phase, 3-wire, ungrounded wye connected system vs. a 3-phase, 3-wire grounded system looks like. Does anyone have a diagram of these, and how they would be connected to the corner of a balanced delta load that is grounded? I think that is the reason I can't understand this problem is that I do not know what difference(s) a grounded wye and a non-grounded wye make.

There was another topic on the Power Exam forum about this that you may want to check out:

https://engineerboards.com/threads/corner-grounded-delta-system-question.36261/