Currently, oil and SF6 circuit breakers are being replaced everywhere with vacuum circuit breakers. This type of switching equipment is designed to protect power circuits from short circuit currents and overloads at various voltage levels from 10 kV to 220 kV. The reasons for replacing equipment are caused not only by operational wear and obsolescence. Oil circuit breakers have a fairly short shutdown resource, it is necessary to control the oil level, as well as install powerful electric drives to ensure the required response speed. In addition, there is a possibility of an explosion during the shutdown process.
In turn, gas-insulated switches contribute to the development of the greenhouse effect, they are difficult to produce and maintain. Switches of this type are quite expensive, require control over the use of SF6 gas, and also impose high demands on the quality of the injected gas.
The advantages that vacuum circuit breakers have are as follows:
1. Environmental safety.
2. A large number of switching.
3. Low operating costs.
4. Simplicity of design.
5. High reliability.
6. Small size.
7. Explosion and fire safety.
8. No noise pollution.
The disadvantages of vacuum circuit breakers include:
1. Relatively small rated currents and tripping currents.
2. The probability of switching overvoltages.
A number of countries are developing vacuum switching devices , such as Japan, China, Russia, etc.
The vacuum circuit breaker can be presented in a tank and column design. In the first case, the role of insulation is played by dry air, which is pumped under pressure. This design makes the vacuum circuit breaker absolutely safe for the environment. The most important feature of the tank design is that during dismantling there is no need to collect the gas of the insulating medium.
A vacuum circuit breaker may have one or more breaks per pole. This means that the electric circuit will be interrupted in several places in order to extinguish the arising electric arc more efficiently.
The dry air pressure is 5 atmospheres, since at large values the arcing chamber, which is installed in the vacuum circuit breaker, can lose its stability and irreparably deform. Nevertheless, it is believed that the tank vacuum circuit breaker is more widely used than the column design circuit breaker.
The process of extinguishing an electric arc in a vacuum circuit breaker is as follows: in a vacuum arcing chamber, a longitudinal magnetic field is superimposed on the passing arc. This creates the effect of the so-called longitudinal magnetic blast, due to which there is an increase in the length of the arc. As you know, the longer the arc, the easier it is to extinguish. In this regard, the voltage of the electric arc has a great influence on the size of the circuit breaker, since the higher the voltage, the larger the dimensions of the arcing chamber and, therefore, the larger the overall installation should have.
The opening of the electrodes is carried out by a spring drive, the cocking of the spring of which is carried out using an electromagnet.