Circuit breakers are ubiquitous wherever there are electrical circuits that need protection against excess current caused by an overload or short circuit. They range in size and capacity from devices the size of a fingernail used for semiconductor protection to devices as large as a truck designed to protect the high voltage circuits that supply power to cities.
Electrical power is, in most cases, not produced at the same location as it is consumed. The power grid connects power plants with end users and transports the electrical energy from production to consumers.
The power grid is organized into different voltage levels from a few hundred volts (LV), to several 10 kV (MV) up to several 100 kV (HV), depending on the amount of power transportation capacity needed.
The different voltage levels are interconnected by substations which contain voltage transformers, circuit breakers, surge arrestors, isolators etc. as well as other measurement equipment and switchgear.