Introduction about Vacuum Contactor

The Vacem VCKG AC high-voltage vacuum contactor series is suitable for power systems with rated AC 50Hz, working voltage of 6kV~10kV, and working current of 160A~630A. High voltage vacuum contactor is a high-voltage control electrical appliance, it provides remote control and frequent operation of electrical equipment such as high-voltage motors, power transformers, capacitors, etc, in the power system. Contactors are widely used because they have a series of advantages such as long service life, frequent operation, small size, light weight, no explosion, no pollution, low price, convenient maintenance, and good breaking performance. The structure of the contactor is simple and clear, there is an incoming copper plate on the upper side and an outgoing copper plate on the lower side, ensuring installation, maintenance, and reliability.

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     The main structure of vacuum contactors:

     1. Vacuum Interrupter:

The vacuum interrupter is made of ceramic tubes made of 95 ceramic insulation material. It has advantages such as long service life, high mechanical strength, heat resistance, and impact resistance. The contact material is made of Cu-WC with anti friction and low chopping current, this material can reduce over-voltage and improve the electrical life of vacuum interrupters.

      2. Solenoid

The contactor adopts a DC double coil operating system, has the ability to save power while maintaining a closed state during operation. The contactor is equipped with a rectifier device, which facilitates user communication and operation.

      3. Drive unit

The driving unit generally adopts an electric holding mechanism. Its working principle is to make the closing coil close by energizing the electromagnetic coil, while the holding coil completes the holding. Switching principle is to let the holding coil in the electromagnetic coil power off, and then use the spring to realize switching action.

4. Auxiliary contact (normally open/normally closed)

The working principle is that after the contactor is closed, the action coil is powered off and held in action by mechanical locking. Then, release the contactor. The tripping coil voltage can reliably release the contactor within the range of 85% Us to 110% Us.

5. Power module

Rectifying alternating current into direct current and filtering auxiliary opening contact arc.

       Precautions for using vacuum contactors:

       When using vacuum contactors, attention should also be paid to adjusting the mechanical characteristics of the contacts.

（1）The opening distance of the high-voltage vacuum contactor contact is mainly determined by the insulation coordination parameters, breaking parameters, contact material, and the design of the vacuum interrupter. In application, it is not the larger the contact opening, the better, but as far as possible to adjust the contact opening to the lower limit, in order to reduce the operating power consumption and improve the life.

（2）The determination of contact overtravel is related to factors such as contact material performance, breaking and making current, electrical life parameters, contact pressure, and dynamic thermal stability parameters. In practical applications, it is not advisable to choose too large contact overtravel. Generally, it should be 15% to 40% of the contact opening distance, usually around 2mm.

（3）The determination of contact pressure for high-voltage vacuum contactors is related to the structure of the contacts, material properties, contact conditions, breaking and making currents, electrical life parameters, dynamic and thermal stability parameters, and mechanical performance requirements. In order to ensure that under the action of electric repulsion between the contacts, the contacts do not open and do not undergo welding, the pressure of the contacts should be adjusted to be greater than the electric repulsion between the contacts, as well as the impact of electric repulsion caused by other reasons in the electrical circuit.

Vacuum contactors have strong arc extinguishing ability, good voltage resistance, high operating frequency, long service life, no arc spraying, small size, light weight, and long maintenance cycle. The manufacturing process of its vacuum interrupter requires high requirements, and if the process is poor, the vacuum of the arc extinguishing chamber is prone to decrease.

If the material of the vacuum contactor contact is not good, there will be a phenomenon of "cut-off overvoltage" when breaking the current. When breaking the current, due to the strong arc extinguishing ability of the vacuum interrupter , the arc current is not naturally cut off when crossing zero, but suddenly drops from a certain value of the current to zero, resulting in high overvoltage. The cutoff voltage can endanger the safe operation of electrical equipment.

Vacuum contactors typically consist of an insulating insulation frame, metal bases, transmission arms, electromagnetic systems, auxiliary switches, and vacuum switch tubes. When the electromagnetic coil controls the voltage, the armature drives the crank arm to rotate, causing the main contact inside the vacuum switch tube to be connected. After the electromagnetic coil is powered off, due to the action of the opening spring, the main contact is disconnected.

The vacuum switch tube of the high-voltage vacuum contactor is composed of an upper cover, a lower cover, a metal corrugated tube, and a ceramic tube, the vacuum switch tube is made of corrugated porcelain tube made of 95 porcelain insulation material. It has the characteristics of large creepage distance, high mechanical strength, heat resistance, and impact resistance. A pair of dynamic and static contacts are encapsulated inside the switch tube, and the contact material is made of wear-resistant and low cutoff value Cu-W-Wc. This reduces overvoltage caused by current interception during the breaking process and improves the electrical life of the vacuum switch tube while meeting the breaking performance requirements. When the metal corrugated pipe moves axially, it drives the moving contact to perform opening and closing actions.

Applications and maintenance of vacuum contactor:

Keep the contactor clean during use. Check and adjust the clearance regularly, and check whether the nut under the arc extinguishing chamber (vacuum interrupter) is loose.

For the contactor in use, the vacuum arc extinguishing chamber (vacuum interrupter) needs to be checked regularly (to make the power frequency withstand voltage method). The 12kV vacuum tube can withstand greater than 38kV.

The contactor should be fully inspected and adjusted under one of the following conditions.

1. Annual routine inspection and cleaning;

2. After 100,000 operations;

3. When the vacuum arc extinguishing chamber (vacuum interrupter) is damaged;

4. Check the connection of the auxiliary device. Poor contact of the contactor should be repaired or replaced.