It depends on the market, but in the US - IEEE/ANSI world, CCVTs have the same BIL rating as most equipment up to 161 kV.
The following are the CCVT BIL ratings above 161 kV, according to ANSIC93.1:
230 kV - 1050 kV BIL
345 kV - 1550 kV BIL
500 kV - 1800 kV BIL
765 kV - 2425 kV BIL
I understand the rationale to have the CCVT BIL ratings higher than most other equipment is 2 fold:
1) CCVTs commonly sit out on the transmission side of the substation outside of the arrestor protection zone, i.e. when used for power-line carrier.
2) Due to the inherent, almost perfect, voltage gradient of a CCVT (capacitor voltage divider) it's not very hard to build CCVTs with higher BIL ratings. More importantly than the BIL rating is the associated PFWV rating, which is also higher than most other equipment. This higher PFWV level helps to 'weed out' substandard capacitor elements. This was a reaction to some of the less reliable paper/paper capacitor rolls used in older vintage CCVTs.
Marmite-
The higher BIL ratings do not have anything to do with ferroresonance. Ferroresonance, as it applies to CCVTs, is an internal resonance and not system ferroresonance.
This is so far the best explanation about this subject. You well deserve a star.
Considering the overvoltage (OV) effect at the line entrance of the substation produced by the reflective traveling wave in particular during open breaker conditions. Do you think this OV effect also play a role in the rational to increase the BIL?
Is it not the practice in US to have Surge Arresters at the line entrance (to substation)! If so, the CCVT is protected against the incoming surges, isn't it!
