The function of the circuit breaker is to cut off and close the load circuit, and cut off the fault circuit to prevent accidents from expanding and ensure safe operation. The high-voltage circuit breaker is to break 1500V, the current is 1500-2000A arc, these arcs can be extended to 2m and continue to burn without extinguishing. Therefore, arc extinguishing is a problem that must be solved by high voltage circuit breakers.
The principle of arc-extinguishing arc is mainly to cool the arc to attenuate the heat release. On the other hand, the arc is used to stretch the arc to enhance the recombination and diffusion of the charged particles, and at the same time, the charged particles in the arc gap are blown off, and the dielectric strength of the medium is quickly restored.
Circuit breaker selection
The selection of the circuit breaker must be selected according to normal operating conditions, and its thermal stability and dynamic stability should be verified according to the open circuit condition. In addition, environmental conditions such as temperature, wind speed, temperature, pollution level, altitude, seismic intensity, and ice thickness should be considered.
When the general electrical conditions are exceeded, effective measures should be taken.
There are several requirements for high voltage circuit breakers, which are reflected in the basic technical parameters of the circuit breaker.
(1) The circuit breaker can work for a long time under rated conditions (rated voltage, rated current).
(2) It should have sufficient breaking capacity and ensure sufficient thermal stability and dynamic stability (breaking current, rated closing current, ultimate passing current, heat)
Stable current).
(3) It has the shortest breaking time, which is beneficial to reduce the fault time of the power grid, reduce the damage of the faulty equipment , and improve the stability of the system.
of.
(4) The structure is simple, the price is low, the volume is small, the weight is light, and the installation is convenient.
The following are the characteristics of several common circuit breakers:
1. Multi-oil circuit breakers are simple to implement and inexpensive, but they are not used under normal circumstances due to their large amount of oil, large volume, large maintenance workload, and prone to explosion and fire.
2. The oil-less circuit breaker uses less oil, the fuel tank structure is small and firm, and has the characteristics of saving materials, explosion-proof and fireproof. The safety of the oil-less circuit breaker makes the power distribution device greatly simplified, small in size, easy to transport, and is currently being widely used.
3. The air circuit breaker has large breaking capacity, fast action time, small size, light weight and no fire hazard, but the structure is complicated, the price is expensive, and the compressed air system needs to be installed. It is mainly used for electrical parameters and disconnection time of 110KV and above. In systems with higher requirements.
4. SF6 has good electrical performance and high fracture voltage. The operation and maintenance of the equipment are very convenient, the maintenance period is long, and its breaking performance is good, the floor space is small, and in particular, the development of the SF6 closed combination electric appliance can greatly reduce the footprint of the substation. SF6 circuit breakers are widely used in the 1990s. At present, China has successfully produced and developed 220, 330, 500KV SF6 circuit breakers .
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