Insulators for an overhead power line (OHL), in many substation applications and on the overhead electrification systems of railways, must, primarily, support the conductors. Also important, as already mentioned, is the need to avoid frequent flashover events from occurring.
Although the total mechanical failure of such an insulator is, fortunately, a rare event, its occurrence may be very serious. For example, should a vertical insulator of an OHL (often referred to as a suspension unit) break, then its conductor could be supported by the insulators of the neighboring support structures (often called towers) at either side. Then, it is possible that this conductor could be reenergized but with little ground clearance!
The consequences of a flashover vary from being annoying to being very costly. For example, the damage resulting from the external flashover of the insulating housing of a high power circuit breaker during a synchronizing operation, when the voltage across the polluted surface can increase to twice the normal value, could be extremely large.
Although the total mechanical failure of such an insulator is, fortunately, a rare event, its occurrence may be very serious. For example, should a vertical insulator of an OHL (often referred to as a suspension unit) break, then its conductor could be supported by the insulators of the neighboring support structures (often called towers) at either side. Then, it is possible that this conductor could be reenergized but with little ground clearance!
The consequences of a flashover vary from being annoying to being very costly. For example, the damage resulting from the external flashover of the insulating housing of a high power circuit breaker during a synchronizing operation, when the voltage across the polluted surface can increase to twice the normal value, could be extremely large.