Vacuum contactors and their specifications

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:

1. The VI must coordinate with the solenoid operation.
2. The contact must be designed for the expected electrical life and yet must not be too costly.
3. The VI must maintain its voltage-withstand capability during its whole life.
4. 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.
5. 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.
6. 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

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