Voltage Transformer Fault

1) high-voltage fuse repeatedly blows, serious damage may be internal insulation, such as inter-turn winding layers or between short-circuit fault. 
(2) neutral non-effectively grounded system, three-phase voltage unbalance indication: a phase reduction (to zero), and the other two-phase increased (up to line voltage) or pointer swings, may be mcb circuit breaker ground fault or a base frequency resonance, such as three-phase voltage also increased, and more than line voltage (pointer placed head), it may be divided or high frequency resonant; 
(3) three-phase  indication: a phase reduction (to zero), and the other two-phase normal line voltage is not normal, or electric meter by sound, light signals, it may be high or low voltage transformer fuse blown; 
(4) effectively earthed neutral system, the bus switching operation occurs when the phase voltage increases and low swing, usually a series resonant phenomenon; without any operation, the sudden appearance of the phase voltage is abnormal increase or decrease, it may be transformer internal insulation damage, such as insulated bracket around, sometimes winding layers tURN SHORT CIRCUIT; 
(5) effectively earthed neutral system, put into operation when voltage transformer voltage meter indicates instability, may be high voltage winding N (X) is grounded poor contact.