Selection Of Highest System Voltage for 34.5 kV Swgr.

[PNK]

This refers to a 60 Hz HV system based on IEC standard which has been specified with the following voltage and insulation ratings :-
- Nominal or Operating system voltage = 34.5 kV rms (L-L)
- Highest or Rated System Voltage = 36.0 kV rms (L-L)
- 1 Minute PF voltage withstand = 70 kV rms
- Basic Lightning Impulse - 170 kV Crest or peak.

I am not sure a 36.0 kV Rated voltage is adequate here. The right voltage should have been :-
- Nominal or Operating system voltage = 34.5 kV rms (L-L)
- Highest or Rated System Voltage = 38.0 kV rms (L-L)
- 1 Minute PF voltage withstand = 80 kV rms
- Basic Lightning Impulse - 200 kV Crest or peak

Although in a controlled or well confined installation within control of a single company, a 36 kV can be accepted, but in general this allows only 5.0 % upper range, where as it would be more appropriate to at least retain a + 10 % margin and selected switchgear with 38.0 kV rms highest rated voltage.

Would appreciate if any one could throw more light on the right standard guideline for selection of the HV switcgear for the above application in terms of the margin required to be applied between Nominal or Operating Voltage and the Rated Equipment Voltage to be selected..

 

[busbar]

Not sure this will help… the C37 stuff probably references C84 w.r.t. nominal/maximum voltage, and—ANSI C84.1-1995 "60Hz Voltage Rating" lists 34500Y/19920: Nominal, and 36510Y/21080: Maximum Utilization and Service Voltage.

Maybe that will buy you some rounds. These numbers seem to mesh better with 38 over 36.