The Working Principle of the Vacuum Contactor

Figure 1: Nonreversing vacuum contactor.

The vacuum contactor uses the vacuum interrupter to extinguish the arc to frequently connect and cut off the normal working current. It is usually used in 6kV, 380V (660V, 1140V) AC motors with long-distance on and off, low-voltage frequent start and stop.
Low-voltage vacuum AC contactors are widely used in various industries such as coal mines, electric power, metallurgy, textiles, high-rise buildings and so on.
The vacuum contactor has strong arc extinguishing ability, good pressure resistance performance, high operating frequency, long life, no arc spraying, small size, light weight and long maintenance period.

How do Vacuum Contactors Work?

The vacuum contactor is usually composed of insulating frame, metal base, transmission arm, electromagnetic system, auxiliary switch and vacuum switch tube and other components. When the electromagnetic coil passes the control voltage, the armature drives the arm to rotate, so that the main contact in the vacuum switch tube is connected. After the electromagnetic coil is powered off, the main contact is broken due to the action of the opening spring.

Figure 2: CV series compact vacuum contactor.

The vacuum switch tube is composed of the upper cover, the lower cover, the metal bellows and the ceramic tube, etc. It has the characteristics of large creepage distance, high mechanical strength, heat resistance and impact resistance. A pair of moving and fixed contacts are encapsulated in the vacuum switch tube, and the contact materials are Cu-W-Wc with wear-resistant and low cut-off value.
In this way, under the condition that the breaking performance is satisfied, the overvoltage caused by the cut-off during the breaking process can be reduced, and the service life of the vacuum switch tube can be improved. When the metal bellows moves axially, it drives the moving contact to do the opening and closing action.

In the electromagnetic system, the actual suction characteristics and the reaction force characteristics are well matched, and the advantages of low noise and power saving during the operation of the contactor are brought into play. The stranded double coil is composed of starting and maintaining two windings, which are switched by an auxiliary switch. In order to facilitate the user to operate the AC power supply, the contactor has a bridge rectifier device.

Mechanical lock: When the closing coil is energized, the contactor is pulled in and the mechanical lock is locked; when the trip coil is energized, the mechanical lock is tripped and the contactor is released. When the trip coil is in the hot state, its voltage is within the range of Us85%-110%, so that the contactor can be released reliably.

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