A breaker which used vacuum as an arc extinction medium is called a vacuum circuit breaker. In this circuit breaker, the fixed and moving contact is enclosed in a permanently sealed vacuum interrupter. The arc is extinct as the contacts are separated in high vacuum. It is mainly used for medium voltage ranging from 11 KV to 33 KV.

Vacuum circuit breaker has a high insulating medium for arc extinction as compared to the other circuit breaker. The pressure inside the vacuum interrupter is approximately 10^-4 torrent and at this pressure, very few molecules are present in the interrupter. The vacuum circuit breaker has mainly two phenomenal properties.

1. High insulating strength: In comparison to various other insulating media used in circuit breaker vacuum is a superior dielectric medium. It is better than all other media except air and SF₆, which are employed at high pressure.
2. When an arc is opened by moving apart the contacts in a vacuum, an interruption occurs at the first current zero. With the arc interruption, their dielectric strength increases up to a rate of thousands time as compared to other breakers.

Zinc-sprayed solid insulated ring main unit is optimized and improved on the basis of the original insulation structure In the solid insulated ring main unit, its insulation structure is to cover all the conductive elements with solid insulating materials, and the solid insulating materials are perfectly bonded with the conductors, and the heat emitted by the conductors can be quickly conducted outward through the solid insulation layer, which greatly reduces the temperature rise during the normal operation of electrical appliances. If the outer surface of the insulating structure is sprayed with a layer of metal zinc, it can not only increase the heat dissipation area, but also play the role of shielding the electric field and preventing radio signal interference, effectively reducing the resistance to the ground, and the voltage along the surface is less than 30V, realizing touchable and full shielding to improve safety. At the same time, it also reduces the interference of external radio signals. The acquisition of remote signals is stronger and the error is smaller. All built-in conductive parts are connected flexibly, which increases the radius of the fillet and increases the level of partial discharge.