For a power quality standard, you might also look at IEEE Std 1159 which is aimed at monitoring PQ.
For reliability indices, IEEE Std 1366 covers the material in Desrod2's link from a Naruc presentation. It is a "how to" calculate standard for the different indices like SAIDI and SAIFI. As far as outages being infrequent and limited, I don't think you'll find a standard that deals with this aspect. That's more of a regulatory issue and can be very subjective.
For the three voltages that you've listed, ANSI lists nominal system voltages of 46, 115 and 230 kV. The circuit breaker standards for these voltages assume a +/-5% tolerance with a maximum voltage of 48.3, 121 and 242 kV respectively. You can use the -5% tolerance and get the minimums, but keep in mind that would be based mainly on circuit breakers.