In most cases, overhead lines are built with bare wires. These accidents are sometimes caused by wind, sleet and damage to trees, cranes, airplanes or supporting structures. Lightning or operating overvoltage may cause flashover between brackets or conductors. Even under normal voltage conditions, contaminated insulators sometimes flash.
The conductor of underground cable is separated from the ground and insulated by solid, which can be oil-impregnated paper or plastic, such as polyethylene. Over time, these materials have undergone some degradation, especially when the cable is overloaded at its high working temperature. ! ! Any small gap in the insulating material of the insulator will lead to the ionization of the contained gas, which will adversely affect the insulation performance, and short-circuit products will be formed between cable conductors. If lightning or switching produces abnormally high values between transient voltage conductors, the possibility of cable failure will increase.
Transformer faults may be caused by insulation degradation caused by lightning or switching transient overvoltage. The insulation fault between adjacent turns of the same winding caused by sudden overvoltage may lead to short circuit. The main insulation material may fail, resulting in arcing between the primary and secondary windings, and between the windings and grounded metal parts (such as iron core or oil tank).
The generator may fail because of insulation breakdown between adjacent turns in the same slot, resulting in a single turn short circuit to ground. Insulation breakdown may also occur when winding and grounding coil are embedded between steel structures. In the same slot, the short circuit of the machine is extensive, which leads to breakdown between different windings.
Balancing three-phase faults, such as balancing three-phase loads, can be handled according to line-to-line neutrality or equivalent single phase. The problem can be solved, volts, amperes, ohms. Of course, the handover of single-phase line fault and three-phase fault are the same on the basis of equivalent single phase.