Design of Vacuum Interrupter

The cross section of a vacuum interrupter is shown in figure 1.1. It consists of a fixed contact in which a copper electrode is hardened to an end plate while the moving contact is attached to the other end plate by a bellows. The cylindrical vacuum chamber is made of alumina ceramic. The ends of the chamber are metalized. A metal vapor condensation shield around the contacts prevents the surface of ceramic from being coated. The chamber is tightly sealed to maintain the vacuum.

Taking into considerations the current and voltage to be interrupted, to ensure minimum metal erosion and to minimize local heating there are three main designs for making contacts of the vacuum interrupter given below :

1. Butt contacts (for low current arc).
2. Spiral or transverse magnetic field(TMF) contacts (for high current arc).
3. Axial magnetic field(AMF) contacts (for high current arc).

The contacts materials are normally made of copper alloys such as Cr-Cu, Cu-Bi, Cu-Ag, etc. The pictorial representation of the different contact structures is shown in figure 1.2.

Applications of Vacuum Interrupters

Vacuum interrupters are primarily employed in th e medium voltage range(1. 5-38kV) switchgear. In recent years the researchers have been able to successfully implement 145kV vacuum circuit breaker is showing below. Switchgear employing vacuum interrupters can be employed in the following categories :

1. Circuit breakers.
2. Capacitance bank switching.
3. Auto-reclosers.
4. Contactors.
5. Load switching.
6. Inductive current switching.