Two types of fault currents can appear on power systems: ground and phase-to-phase. The more important when it comes to surge arresters is the first, which is basically the current that flows through the circuit when there is a short to ground.

American Transmission Company (ATC) own and operates transmission lines in the States of Wisconsin, Michigan, Minnesota and Illinois. The system originally belonged to local utilities that had different standards and this resulted in a variety of different line surge arrester installations at 69 kV and 138 kV.

Bushings are key components of HV substation equipment such as transformers and switchgear, allowing conductors to transfer energy from one insulating medium to another. Most typically, this is from an oil or SF6 insulation environment to air.

Not long ago, a HV cable termination operating in a Mediterranean country experienced catastrophic failure, sending high velocity porcelain shards in all directions.

There are a variety of reasons why an arrester might reach such a state.