Currently, oil and gas-insulated circuit breakers are being replaced with vacuum circuit breakers. This type of switching equipment is designed to protect power circuits from short circuit currents and overload at various voltage levels from 10 kV to 220 kV. The reasons for replacing equipment are not only due to operational wear and tear and obsolescence. Oil circuit breakers have a rather short tripping life, 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, SF6 circuit breakers contribute to the development of the greenhouse effect, they are difficult to manufacture and maintain. Breakers of this type are quite expensive, require control over the use of SF6 gas, and also place high demands on the quality of the injected gas.
The advantages of vacuum circuit breakers are as follows:
1. Ecological safety.
2. A large number of commutations.
3. Low cost foroperation.
4. Simplicity of design.
5. High reliability.
6. Small sizes.
7. Explosion and fire safety.
8. No noise pollution.
Disadvantages of vacuum circuit breakers include:
1. Relatively low rated and breaking currents.
2. Probability of switching surges.
Vacuum switching devices are developed by a number of countries, such as Japan, China, Russia, etc.
The vacuum circuit breaker can be presented in tank and column versions. In the first case, the role of insulation is played by dry air, which is pumped under pressure. This design makes it possible to make the vacuum switch 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 electrical circuit will be interrupted in several places in order to extinguish the resulting electric arc more effectively.
The pressure of dry air is 5 atmospheres, since at high values the arc chute, which is installed in the vacuum circuit breaker, can lose its stability and become irreparably deformed. However, it is believed that the tank vacuum circuit breaker has become more widespread thancolumn switch.
The process of extinguishing an electric arc in a vacuum circuit breaker occurs as follows: in a vacuum arc chamber, a longitudinal magnetic field is superimposed on the passing arc. This creates the effect of the so-called longitudinal magnetic blow, due to which the arc length increases. As you know, the longer the arc length, the easier it is to extinguish. In this regard, the voltage of the electric arc has a great influence on the dimensions of the circuit breaker, since the higher the voltage, the larger the dimensions of the arc chute and, therefore, the larger the overall installation must be.
Opening of the electrodes is carried out by a spring drive, the spring cocking of which is carried out using an electromagnet.
