CVT used in 110kV radial feeder (feeder from generating station 110 kV bus to 110kV substation directly) will loose its ability of 0.2 class accuracy with repeated fault tripping of 15 times in a period of 2.5 years.
110 kV feeder has 3 CVT but the failed CVT is in c phase and the repeated line faults were also in c phase. Other 2 CVT are fine, no error in accuracy. All the time the fault current usually depends on the distance it is 3.5 to 4.2 kA and fault is cleared off in 0.12 sec from the instant of fault detected by the distance relay.
would be glad provide any more details if required.