Operating challenge associated with of 34,500 volts?

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mbrooke said:
Then why do so many POCOs want a wye primary? T and delta connected 15kv pigs are everywhere for sale on the net, but 25 and 35kv are exclusively wye.

In my mind 200Es on a station transformer will not be much of a risk due to customer load dampening ferro out. Just drop the unit via some SF6 load breaks.
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I think that is because of ferroresonance. Chances of FR increase with ungrounded primaries and higher voltages.
 

The potential for ferroresonance has caused nearly all utilities in the U.S. to apply grounded wye-wye transformers at 25 and 35 kV classes. However, many utilities continue to use delta-connected primaries on underground transformers at 12.47 kV for decades with no known difficulties. There may be a perception that ferroresonance cannot happen in 15 kV class systems. While it is less likely, it is still possible. One factor is the proportion of losses. Newer, low-loss transformer designs are making it more likely than previously.
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electrofelon said:
I think that is because of ferroresonance. Chances of FR increase with ungrounded primaries and higher voltages.
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My understanding is that load above a certain % of the kva will dampen it out. Typically in the IEC world where most everything is delta a 500kva pole pig has several hundred customers meaning little or no load is not an issue with a blown cutout as I understand it.
 
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