HV vacuum circuit breaker is the indoor switching equipment of three-phase AC 50Hz rated voltage 12kV power system. HV vacuum circuit breaker is used as the protection and control unit of power grid equipment and power equipment of industrial and mining enterprises. It is suitable for frequent operation under rated working current or short circuit current.
Vacuum circuit breaker consists of conductive circuit, separable contact, arc extinguishing device, insulating parts, base, transmission mechanism, operating mechanism and so on. The conducting loop is used to carry the current; Separable contacts are the actuators for connecting or breaking a circuit. The arc extinguishing device is used to quickly and reliably extinguish the arc, so that the circuit is finally disconnected. Compared with other switches, the arc extinguishing device of vacuum circuit breaker has the strongest ability of extinguishing arc, and its structure is also more complex. The split and close movement of the contact is driven by the work of the operating mechanism and the transmission mechanism. Its operation mode can be divided into manual, electric, pneumatic and hydraulic. Some circuit breakers (such as oil circuit breakers, sulfur hexafluoride circuit breakers, etc.) operating mechanism is not included in the body of the circuit breaker, but as an independent product to provide circuit breakers with optional use.
The vacuum circuit breaker includes eight main parameters as below:
(1) Rated voltage: nominal voltage, phase (i.e. line) voltage for three-phase systems, the value is specified in national standards.
(2) Working voltage: the high voltage that the circuit breaker allows to work for a long time. The value is usually 10 ~ 15% above the rated voltage. This high voltage is referred to as the rated voltage in the IEC standard.
(3) Rated current: refers to the circuit breaker at the rated frequency, long-term through the current without damage, and each part of the heating does not lead to more than the long-term working temperature rise.
(4) Rated short-circuit breaking current: under specified conditions, the circuit breaker can ensure normal short-circuit breaking current.
(5) Rated short-circuit current: under rated voltage, specified operating conditions and performance conditions, the circuit breaker can ensure normal short-circuit current (peak value).
(6) Rated short-time withstand current: in the specified use and performance conditions, as well as in a certain short time (such as 2 seconds), the circuit breaker in the closed position can carry the current effective value. This value is usually the same as the rated short-circuit breaking current.
(7) Rated peak tolerance current: in the specified use and performance conditions, the circuit breaker in the closed position can withstand the rated short-time tolerance current a half wave peak current.
(8) off time: from the breaker to disconnect instruction from the moment to the end of the arc time of the time interval.
There are many kinds of circuit breakers, their applicable conditions and places, arc extinguishing principles are different, and there are also great differences in structure. Therefore, there are many ways to classify circuit breakers. The main classification methods are:
(1) According to the applicable appliances are divided into AC circuit breakers and DC circuit breakers.
(2) According to the use of voltage is divided into low-voltage circuit breakers and high-voltage circuit breakers. The rated ac voltage of the former is not greater than 1200V or the rated dc voltage is not greater than 1500V. The latter is rated at 3000V and above.
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