95 or 110kV?

[odlanor]

A typical hydro power plant consist of some block generator-stepup transformer . Generator are 13,8kV and transformer are 13,8kV-delta/138 or 230 or 525kV star grounded.
Neutral Generator are grounded by high impedance (resistor or singlephase transformer with resistor at secondary.)
Auxiliary transformers are 13,8kV-delta/460V-star grounded.
All 13,8kV equipments, (not generator) are 15kV class.
Question:
What BIL to choose: 95kV or 110kV ?.
note:IEC adopts 95kV.

.

 

[cranky108]

I perfer to use 110kV for the major equipment, and 95kV for insulators, that way flash overs don't happen on the major equipment.

 

[magoo2]

I agree with cranky. Most utilities opt for the power class BIL in the stations and the distribution BIL outside the stations. Line transformers are used in such large quantities that economics dictate going with the lower (distribution) BIL. Station equipment is used in much smaller quantities and it is worth spending a little more for enhanced reliability.

 

[odlanor]

It seems ANSI std power transformer estabilish 110kV for transformer with class II : including winding >= 121kV
and
95kV for for transformer with class I : including winding <= 72,5kV.

So we could use 110kV for 13,8kV-stepup transformer and
95 kV for auxliary transformers, CT , PT,switching equipment.
I dont know about bus duct.

 

[inpran]

Odlanor,
I didn't get a reference standard to suggest you exactly what voltage class to use, but ABB'S T&D reference book made a mention of the fact that 95 kV is used for distribution class and 110 kV for Power class.

 

[odlanor]

I formulated my question very bad.
Generation system has rated voltage of 13,8kV. So equipaments are:
By ANSI you chose 15kV class - BIL 95 or 110kV.
By IEC you chose 17,5kV class - BIL 75 or 95kV because in Europe there is rated voltage 15kV for generation.
Manufacture chosen equipments of 17,5kV-95kV.
I prefer 15kV-110kV but I do not know how to justify!