Thanks for your comments.
Fuses failed only under steady-state conditions.
Secondary traces from the VT´s at the time of the fuse failure shown a distorted waveform and undervoltage (only one phase)
Repetitive and aleatory faults due to primary fuse blown without apparent cause on instrument voltage transformers, open delta connection. No secondary faults has been reported. Usually, events occur in A and C phases and rarely in B phase. VT's are 4200/120 V, 60 Hz, protected by current...
