The vacuum contactor is a special type of LBS that has been developed to primarily switch 3 phase electric motors. The switching elements are VI , which are mounted on a frame. They are closed by energizing an electric solenoid and are opened by a spring when the current to the solenoid is switched off.
The special needs of the VI for use in a vacuum contactor:
- The VI must coordinate with the solenoid operation.
- The contact must be designed for the expected electrical life and yet must not be too costly.
- The VI must maintain its voltage-withstand capability during its whole life.
- A contact material has to be chosen that ensures the expected the electrical life, maintains its mechanical integrity, maintains a low contact resistance, maintains its HV withstand capability, is resistant to contact welding, and is a low surge material; that is, it resists voltage escalation.
- The internal design of the shielding has to effectively prevent the deposit of too much metal vapor on to the internal ceramic walls for the life of the VI.
- The bellows must be capable of maintaining its performance for the mechanical and electrical life of the VI.
Pic show a side view from a SIEMENS vacuum contactor