# NCEES #109 Power



## robertplant22 (Feb 25, 2012)

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!


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## dzdave00 (Mar 1, 2012)

robertplant22 said:


> 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?
> 
> ...


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.


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## kris7o2 (Jun 16, 2021)

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.


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## akyip (Jun 28, 2021)

kris7o2 said:


> 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:









Corner-Grounded Delta System Question


Hello All, What would be the VAG for Corner grounded Delta system with Neutral grounded at WYE connected source ? Please see attached picture. If the WYE Source Neutral is ungrounded, VAG would be Vline-line = 13.2 kV for this example.




engineerboards.com


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