Circuit Breaker Working Principle and Selection

    First, the function of a circuit breaker is to cut off and connect load circuits, as well as to disconnect fault circuits to prevent accidents from expanding and ensure safe operation. High-voltage circuit breakers must interrupt arcs with voltages of 1500V and currents of 1500-2000A, which can be stretched to 2m and still continue to burn without extinguishing. Therefore, arc extinction is a problem that high-voltage circuit breakers must solve. The control box is auxiliary equipment for light high-voltage test transformers, used together with the test transformer for withstand voltage and leakage tests. The control box features beautiful appearance, small size, light weight, simple operation, and convenient maintenance.

Second, the principle of arc blowing and extinguishing mainly involves cooling the arc to weaken thermal ionization, and on the other hand, lengthening the arc through blowing to enhance recombination and diffusion of charged particles, while blowing away charged particles in the arc gap to quickly restore the insulation strength of the medium.

Third, selection of circuit breakers

The selection of circuit breakers must be based on normal working conditions, and their thermal and dynamic stability must be verified under short-circuit conditions. In addition, the environmental conditions of the installation site should be considered. When environmental conditions such as temperature, wind speed, humidity, pollution level, altitude, seismic intensity, and ice thickness exceed the general service conditions of electrical equipment, 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 operate for a long time under rated conditions (rated voltage, rated current).

(2) It should have sufficient breaking capacity and ensure adequate thermal and dynamic stability (breaking current, rated closing current, ultimate through current, thermal stability current).

(3) It should have the shortest possible breaking time, which is beneficial for reducing the fault time of the power grid, mitigating damage to faulty equipment, and improving system stability.

(4) It should have a simple structure, low cost, small size, light weight, and be easy to install.

Fourth, the following are the characteristics of several common circuit breakers:

1. Bulk-oil circuit breakers are simple to implement and inexpensive, but due to large oil consumption, large size, heavy maintenance workload, and susceptibility to explosion and fire, they are generally not used.

2. Minimum-oil circuit breakers use less oil, have a small and sturdy oil tank structure, and feature material savings, explosion-proof and fire-proof characteristics. Minimum-oil circuit breakers are safe to use, greatly simplify power distribution devices, are small in size, and easy to transport; they are currently widely used.

3. Air circuit breakers have large breaking capacity, fast operation time, small size, light weight, and no fire hazard, but they have complex structures, high prices, and require compressed air systems; they are mainly used in systems of 110KV and above where high electrical parameters and short breaking times are required.

4. SF6 has good electrical performance and can withstand higher breaking voltages. The equipment is convenient to operate, maintain, and repair, with a long maintenance cycle, good breaking performance, and small footprint. In particular, the development of SF6 gas-insulated switchgear can greatly reduce the footprint of substations. SF6 circuit breakers were widely used in the 1990s, and China has successfully produced and developed 220, 330, and 500KV SF6 circuit breakers.