Components and Features of Vacuum Circuit Breaker

The vacuum circuit breaker, a medium and high voltage switching device employing a high-vacuum environment for arc extinction and insulation, has become a pivotal technology in modern power systems. Introduced in the 1960s, its outstanding performance characteristics have driven its adoption across medium and high voltage distribution networks (3.6kV to 40.5kV), gradually replacing conventional oil and minimum oil circuit breakers.

These vacuum circuit breakers are mainly composed of key elements like the vacuum interrupter, operating mechanism, and insulating supports, boasting benefits such as compact size, light weight, suitability for frequent switching duties, and maintenance-free arc quenching. Their principle of operation hinges on the high dielectric strength and rapid recovery of vacuum to quickly extinguish electrical arcs at the point where current crosses zero.

Compared with SF6 circuit breaker, vacuum circuit breaker is more environmentally sound and cost-effective, while offering superior breaking capacity and a smaller footprint than air circuit breakers. Consequently, they are widely used in substations, industrial and mining power networks, railway power supply, and renewable energy generation.

Main Components of Vacuum Circuit Breaker

Vacuum circuit breakers, with their intricate electrical switching design emphasizing balanced electrical performance, mechanical robustness, and operational ease, rely on their specific vacuum circuit breaker components. The complete assembly functions through the synchronized action of several functional modules, each carefully designed and subjected to stringent testing to ensure dependable operation in various service conditions. A detailed overview of its key components and their functional attributes follows:

Vacuum Interrupter

The vacuum interrupter stands as the most critical component of a vacuum circuit breaker, its performance directly dictating the entire device’s breaking capacity and service life. This component features a fully sealed structure, maintaining a high vacuum environment of 10⁻⁴ to 10⁻⁶ Pa internally, providing ideal conditions for rapid arc extinction.

Insulating Envelope Assembly

The insulating envelope assembly is constructed from high-performance ceramic or microcrystalline glass materials, possessing excellent dielectric properties and mechanical strength. Connected to the end covers through a specialized metallization and sealing process, it ensures the long-term hermeticity of the vacuum interrupter, providing a stable vacuum environment for arc quenching.

Contact System

The contact system, with its moving and fixed contacts as core components, works collaboratively to complete the current making and breaking function. The circuit breaker contacts are made from special materials such as copper-chromium alloys, precision-machined to form a specific contact structure. Innovative spiral groove or cup-shaped designs utilize electromagnetic forces to control arc movement, achieving rapid arc extinction while maintaining insulation strength.

Shielding System

A multi-layered shielding system, composed of a main shield and end shields, effectively absorbs metal vapor and ensures uniform electric field distribution. This design not only protects the insulating envelope but also significantly enhances the device’s voltage withstand capability.

Bellows Assembly

The bellows, manufactured from special stainless steel materials and subjected to precise heat treatment processes, feature a unique structural design capable of withstanding frequent mechanical movement while maintaining excellent vacuum sealing performance.

Auxiliary Components

These include guide devices ensuring coaxiality, getter materials maintaining the vacuum, and grading rings optimizing the electric field. These precisely designed auxiliary components collectively guarantee the reliable operation of the vacuum interrupter.

Manufacturing Process

Strict process control, including ultra-high vacuum evacuation and high-temperature baking, is employed, along with advanced testing methods such as helium mass spectrometry leak detection. Each product must pass multiple tests, including power frequency withstand voltage and lightning impulse tests, to ensure compliance with stringent operating requirements.

Technical Features of Vacuum Circuit Breakers

Vacuum circuit breakers, leveraging their unique design principles and material technology, exhibit multifaceted vacuum circuit breaker advantages within power systems. The following provides a detailed analysis from the perspectives of electrical performance, mechanical characteristics, and operation & maintenance:

Electrical Performance Advantages

Vacuum circuit breakers possess significant features in terms of electrical performance:

Superior Arc-Extinguishing Capability: Utilizing a vacuum medium (10⁻⁴ to 10⁻⁶ Pa) allows the arc to extinguish rapidly at the current zero crossing. The dielectric recovery speed can reach 10kV/μs, significantly faster than other types of circuit breakers.

High Insulation Strength: The dielectric strength of vacuum is more than 10 times that of air (breakdown field strength >30kV/mm), enabling a more compact equipment design.

Low Current Chopping: Employing special contact materials (such as CuCr50) keeps the current chopping value below 5A, effectively suppressing switching overvoltages.

Wide Frequency Band Breaking Capability: They can reliably interrupt both 50/60Hz power frequency currents and high-frequency (hundreds of Hz) fault currents.

Mechanical Performance Characteristics

The mechanical system of vacuum circuit breakers is specially designed for:

Ultra-Long Mechanical Life: Featuring a precision guiding structure and high-quality bellows, the mechanical lifespan can reach up to 30,000 operations (IEC standard requires ≥10,000 operations).

Low Operating Energy Requirement: Compared to SF6 circuit breakers of the same capacity, the operating energy is reduced by 30-50% (approximately 150J for a 12kV/31.5kA product).

Fast Breaking Speed: The opening time is typically controlled within 20-40ms, ensuring rapid clearing of faults.
Modular Design: The vacuum interrupter and operating mechanism adopt standardized interfaces, facilitating vacuum circuit breaker maintenance and replacement.

Environmental Adaptability

Vacuum circuit breakers demonstrate excellent performance across various environmental conditions:

Temperature Adaptability: They can reliably operate within a wide temperature range of -30℃ to +60℃.

Pollution Resistance: Compared to SF6 circuit breakers, the completely sealed vacuum interrupter is unaffected by external contamination.

Seismic Performance: Optimized structural design allows them to meet seismic acceleration requirements of 0.3g.

Altitude Compensation: Special design models are available for reliable operation in high-altitude areas up to 4000m.

Operation and Maintenance Advantages

Vacuum circuit breakers offer unique benefits in terms of operation and maintenance:

Long Maintenance-Free Period: The sealing life of the vacuum interrupter exceeds 20 years, requiring no vacuum level testing during this period.

Status Visualization: Newer products are equipped with intelligent devices such as contact wear indicators and mechanical characteristic monitoring.

Environmental Friendliness and Safety: They do not contain SF₆ gas, and their Global Warming Potential (GWP) is 0.

Good Economic Efficiency: The total life cycle cost is 30-40% lower than traditional circuit breakers.

Performance in Special Applications

Vacuum circuit breakers exhibit unique advantages in specific operating conditions:

Capacitor Bank Switching: They can withstand inrush current surges up to 200 times the rated current.

Transformer Magnetizing Current Interruption: They can effectively suppress current chopping overvoltages.

Frequent Operation Applications: They are suitable for high operating frequencies (dozens of times per day), such as in electric arc furnace power supply.

DC Interruption: With specific topologies, their application can be extended to DC fields.

Technical Development Trends

Current major technical development directions include:

Voltage Level Enhancement: Breakthroughs are being made in the development of products with voltage ratings of 72.5kV and above.

Intelligent Integration: Incorporating intelligent functions such as mechanical characteristic monitoring and arc diagnostics.

Application of New Materials: Exploring novel materials like graphene-enhanced contacts and nano-insulation materials.

Environmental Process Improvement: Implementing green manufacturing technologies such as lead-free soldering and recyclable designs.

Application and Future of Vacuum Circuit Breakers

As a core device in medium voltage switchgear of modern power distribution systems, vacuum circuit breakers have gained widespread application in industrial and commercial sectors due to their compact structure and high reliability.

In industrial power distribution, vacuum circuit breakers are particularly suitable for harsh environments such as metallurgy and chemical industries, where their fully sealed structure effectively resists dust and corrosive gas intrusion.

Within commercial building power distribution systems, their modular design makes them the preferred equipment for electrical rooms in office buildings, shopping malls, and other commercial spaces.

Liyond, as one of the most professional electrical switchgear manufacturers, designs its products with full consideration of the practical needs of various application scenarios. Their indoor vacuum circuit breaker features an optimized structural design that ensures performance while also prioritizing ease of installation and maintenance. Additionally, Liyond provides outdoor circuit breaker solutions tailored to different environmental requirements.

Regarding technical innovation, Liyond continuously monitors industry development trends and consistently optimizes product performance. By improving the materials and structural design of key components, they enhance product reliability and service life. Looking ahead, Liyond will continue to deepen its expertise in the field of vacuum circuit breakers, committed to providing customers with even higher quality power distribution solutions.