Calculator 
Capacity insulator C1
pF
Nominal voltage Un
kV
Calculations:
Uet    =   x.xx kV
Umm =   x.x V
C2    =    x.x nF
The proposed value of the matching capacitanceC2 x.x nF
Terms voltage in the connector for C2
x.x nF
Voltage in the connector atUn = 45 % x.x V
Voltage in the connector atUn = 100 % x.x V
Voltage in the connector atUn = 120 % x.x V