Electrical power transmission networks are protected and controlled by high-voltage breakers. The definition of high voltage varies but in power transmission work is usually thought to be 72.5 kV / 110 kV / 220kV/ 400kV or higher. High-voltage circuit breakers used on transmission systems may be arranged to allow a single pole of a three-phase line to trip,
instead of tripping all three poles; for some classes of faults this improves the system stability and availability.
As the voltage level is high the arcing produced during switching operation is also very high. So, special care to be taken during designing of high voltage switchgear. special features for safe and reliable operation. Faulty tripping and switching operation of high voltage circuit are very rear.
High voltage circuit breaker, is the main component of HV switchgear, hence high voltage circuit breaker should have Most of the time these circuit breakers remain, at ON condition, and may be operated after a long period of time. So CBs must be reliable enough to ensure safe operation, as when required.