What is vacuum switch?
Vacuum switch is a special device that is used to extinguish an electric arc in vacuum. Appliance is designed to monitor and control the rated currents and prevent the effects of short circuits.
Principle of operation and design
Gas under vacuum has minimal electrical conductivity, in contrast to the its normal state. This physical property is used in the system`s operations.
In such type of devices in the closed space of the chamber a vacuum is created at the moment of disconnection of contacts. Such conditions allow to successfully extinguish the electric arc.
To create such an environment type, complete impermeability is required. Therefore, the walls of the chambers are made of special alloys or ceramics. Careful material selection will allow them to maintain its operability for several decades.
When the contacts are disconnected, the current line is not immediately interrupted. This phenomenon occurs in a period of 45 milliseconds, which is almost imperceptible by human eye.
This is facilitated by plasma, which is formed by ionized metal`s evaporation. It is able to conduct current for some more time. After the separation of contacts, the arc is still able to pass between them, but when it reaches zero point it disappears.
During the extinguish process, metal vapors which formed a plasma begin to settle on the surface of contacts. As a result, the electrical strength of the vacuum gap is strengthened.
Vacuum Switch Classification
Thanks to a simple and reliable design, such systems are very popular. They can perform work in networks with voltage up to 35kV. Such equipment even operates in power lines where they complete tasks with voltage up to 220kV.
Due to the large variation, the devices are divided into several series, in accordance with the allowable voltage level:
- Up to 1000V ;
- Up to 35kV ;
- Over 35kV.
There is also one more separate category of appliances. They function as load switches.
Advantages and disadvantages
The represented system has both advantages and disadvantages. The simplicity of design can be attributed to the positive factors. It also greatly simplifies the repair process and saves time.
Chamber in which the arc extinguish process takes place has a block structure. This solution allows to make a quick replacement of the whole module.
Thanks to special wall materials, high reliability and safety of the device is provided. Such switches also have several advantages:
- Long term switching durability.
- Minimum outgoing noise level.
- High degree of fire safety.
- Good explosion protection.
- Small compact size.
- Ability to work in any position.
- No environment pollution.
In addition to advantages, the design has some disadvantages. Device has low rated and tripping currents. In addition, equipment has a small resource for extinguishing the arc in a short circuit.
In general, despite some drawbacks, vacuum switches are a simple and at the same time reliable devices. Such system has been successfully operating in electrical networks for a long period of time.