What is a vacuum contactor? What are its structural components?

A vacuum contactor is an electrical device used to control and interrupt current in a circuit. It achieves its function by establishing an electrical break in a vacuum environment and features high interruption capability, rapid disconnection, and long lifespan.

1. Core Definition and Function

A vacuum contactor is a control device that uses a vacuum interrupter (also called a vacuum interrupter tube) as the arc-extinguishing and insulating medium to frequently connect and disconnect the main circuit under normal current conditions.

Core Function: Similar to a more powerful "switch" controlled by an electromagnetic system.

Main Features: Frequent operation (up to thousands of times per hour), long lifespan, strong arc-extinguishing capability, and high safety.

Difference from a Vacuum Circuit Breaker: This is the key point. Both use vacuum interrupters, but their design goals differ:

Vacuum Contactor: Designed for frequent switching, it can withstand extremely high numbers of operations (mechanical life up to millions of times, electrical life hundreds of thousands of times), but its short-circuit breaking capacity is weaker. It usually needs to be used in conjunction with a fuse or an upstream circuit breaker, which provides short-circuit protection.

Vacuum Circuit Breaker: Designed for protection, it has a strong short-circuit current breaking capacity, but its operating life is much shorter than that of a contactor (typically tens of thousands of times), making it unsuitable for frequent operation.

2. Main Structural Components

Vacuum Interruptor (Core Component):

A sealed glass or ceramic shell, internally maintained under a high vacuum (pressure below 10^-4 Pa).

Inside are a pair of disc-shaped contacts (stationary and moving contacts), typically made of copper-chromium alloy, possessing characteristics of arc resistance, weld resistance, and low gas content.

The moving contact is connected to an external operating mechanism via a metal bellows, which allows contact movement while maintaining the vacuum seal of the interrupter.

Electromagnetic Operating System:

Includes coil, iron core, armature, etc.

When the coil is energized, it generates electromagnetic force, driving the armature and its connected moving contact to close.

When the coil is de-energized, the contacts quickly open thanks to a tripping spring (sometimes in conjunction with its own weight).

Insulating Frame and Transmission Mechanism:

Supports and secures all components, providing phase-to-phase and phase-to-ground insulation.

Precisely transmits the actions of the electromagnetic system to the moving contact of the vacuum interrupter.

Auxiliary contacts (auxiliary switches):

Miniature switches linked to the main contacts, used for indicating the status of the control circuit (such as on/off signals) and interlocking.when the coil is enetgized,it generates electromagnetic force,driving the armature and its 

3. Working Principle

Connection Process: The control circuit energizes the electromagnetic coil → the iron core is magnetized, attracting the armature → the transmission mechanism overcomes the spring force, pushing the moving contact of the vacuum interrupter forward → it contacts the stationary contact and maintains a certain pressure, thus completing the main circuit.

Disconnection Process: The control circuit cuts off the coil power supply → the electromagnetic force disappears → under the action of the opening spring, the armature is released, and the transmission mechanism quickly pulls the moving contact back → the contacts separate. At the moment of separation, a vacuum arc is generated between the contacts (maintained by the ionization of metal vapor). Due to the extremely high insulation strength and extremely fast dielectric recovery speed of the vacuum environment, when the alternating current crosses zero, the metal vapor rapidly diffuses and condenses, the arc cannot be maintained and extinguishes, and the circuit is reliably disconnected.

4. Key Advantages

High Lifespan and High Frequency: Minimal contact wear in the vacuum medium results in a mechanical and electrical lifespan far exceeding that of air contactors.

Safe and Environmentally Friendly: The arc-extinguishing and insulating medium is a vacuum, free of oil and gas, eliminating the risk of fire or explosion. The arc is sealed within the arc-extinguishing chamber, eliminating the risk of arc ejection and ensuring operator safety.

Simple Maintenance: The vacuum arc-extinguishing chamber is a maintenance-free sealed element, requiring no medium inspection or replacement as needed for oil-immersed or SF6-based equipment. Only simple mechanical checks are required daily.

Small Size and Light Weight: Thanks to the high insulation performance of the vacuum, its size is significantly smaller than that of air contactors at the same voltage level.

High Breaking Capacity: Reliably breaks rated operating current and a certain overload current with a short arc time.

Adaptable to Harsh Environments: Good dustproof, moisture-proof, and explosion-proof performance, suitable for harsh environments such as mines and chemical plants.

5. Typical Application Areas

Due to their reliability and long lifespan, vacuum contactors are widely used in applications requiring frequent start-stop or forward/reverse rotation:

Motor Control: Starting, stopping, and reversing control of high-voltage (typically 3.6kV - 12kV) high-power motors, such as water pumps, fans, compressors, and ball mills.

Power Capacitor Bank Switching: Used for reactive power compensation, requiring extremely high operating frequencies.

Electric Furnace Transformer Control: Electric arc furnaces and ladle refining furnaces in the metallurgical industry.

Mining and Port Equipment: Hoists, conveyor belts, cranes, etc.

Power Systems: Used for voltage transformer switching in substations, etc.

Summary

Vacuum contactors are key actuators in high-voltage, frequent control applications in modern industry. They perfectly combine vacuum technology with electromagnetic operating mechanisms, providing a safe, reliable, long-life, and virtually maintenance-free circuit switching solution. When selecting a vacuum contactor, it is essential to clearly define its "frequent operation" requirement and to use it in conjunction with protective devices capable of short-circuit breaking (such as fuses) to form a complete motor control and protection system (i.e., the "F-C circuit": fuse-contactor circuit).

Shaanxi Huadian vacuum contactors, with their ultra-long lifespan, extremely high reliability, and near-zero maintenance costs, help you improve equipment uptime and reduce total lifespan costs. Please contact us if interested.

Email:pannie@hdswitchgear.com.

Whatsapp/Wechat:+8618789455087