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Effect of Lost Phase on Ungrounded Wye/Center-Tapped Delta Bank Part-2

Effect of Lost Phase on Ungrounded Wye/Center-Tapped Delta Bank Part-2

Effect of Lost Phase on Ungrounded Wye/Center-Tapped Delta Bank Part-2

(OP)
thread238-255398: Effect of Lost Phase on Ungrounded Wye/Center-Tapped Delta Bank

I'm new to this site and loving it.  I read the above thread and was intrigued.  I've been trying to get my head around this for a while now.  I've attached a graphic from a book that I have.  The part that I'm having trouble understanding is how the neutral on the primary side of the transformer "floats" to one of the phases (C-Phs in the graphic).  I understand that it has to do with only one single phase load on the delta secondary.  I also understand that the voltage over one of the secondary transformers is 173% larger due to line-to-line voltage being applied to primary over the 2 transformers in series.  I just can't figure out how the voltage on the primary from C to N is zero.  Doesn't this mean that the voltage over the single phase load on the secondary should also be zero?  

In the referenced thread "waross" made a statement that may be the piece of the puzzle I need to understand this.  He said:

"For unbalanced loads, the secondary voltages will be in inverse proportion to the loads. The sum of the voltages will be 173% of the normal voltage."

and

"The simple formula says that the voltages across the two transformers will be in inverse proportion to the impedances of the loads and that as one load becomes less in relation to the other the voltage will approach 173% of normal."

Does anybody know this formula or where I can find reference to it?

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