This paper provides an in-depth overview of the working principle, main structure, and key characteristics of vacuum circuit breakers. By analyzing their practical application in substation environments, the advantages, disadvantages, common faults, and corresponding troubleshooting methods are identified. This analysis serves as a reference for the operation and maintenance of vacuum circuit breakers, helping to ensure safe and efficient power system performance.
Keywords: vacuum circuit breaker, principle, structural characteristics, fault, treatment method
1. Introduction
In power systems, it is essential to connect or disconnect components such as transformers and lines in a substation due to faults, inspections, or changes in operating modes. These operations include reliably switching circuits under normal conditions, performing flexible switching during mode changes, quickly isolating fault currents to limit damage, and ensuring the safety of personnel during maintenance by isolating live parts. To accomplish these tasks, various switching devices must be installed in the substation, with circuit breakers playing a central role. Among them, the circuit breaker is the most critical component, with a complex structure, especially for high-voltage applications.
A high-voltage circuit breaker is a device designed to open and close circuits under normal conditions and automatically interrupt fault currents quickly. Its primary requirements include sufficient breaking capacity, fast operation time, and high reliability. The most important function of a circuit breaker is arc extinction, which leads to different arc extinguishing mechanisms depending on the type of circuit breaker. Common types include oil, air, SF6, vacuum, self-generated gas, and magnetic circuit breakers. Vacuum circuit breakers, which use vacuum as both the insulating and arc-quenching medium, have gained popularity in recent years, particularly in 10kV substation equipment. This paper explores the design, functionality, and practical use of vacuum circuit breakers.
2. Working Principle, Main Structure, and Characteristics of Vacuum Circuit Breakers
2.1 Working Principle
When the moving and fixed contacts of a vacuum circuit breaker are separated by the operating mechanism, an electric arc forms between them. Under high temperatures, the contact surfaces vaporize, and when a magnetic field is present, the arc moves rapidly along the contact surface. Part of the metal vapor condenses on the shield, and the arc is extinguished at the natural zero-crossing point, allowing the dielectric strength between the contacts to recover quickly.
2.2 Main Components
A vacuum circuit breaker consists of three main parts: the vacuum interrupter, the operating mechanism, and the insulating base.
2.2.1 Vacuum Interrupter
The vacuum interrupter includes the outer casing, conductive system, and shielding system. It is typically made of ceramic, glass, or glass-ceramic materials. The conductive system comprises fixed and moving contacts, while the shielding system prevents arc products from damaging the insulation and improves electric field distribution.
2.2.2 Operating Mechanism
Common operating mechanisms include spring-operated, electromagnetic, and energy-stored types. Each has its own advantages and is suitable for different applications.
2.2.3 Additional Components
Other elements such as the base, insulators, and support structures contribute to the overall stability and insulation of the circuit breaker.
2.3 Key Features
Vacuum circuit breakers offer several benefits, including a small contact gap (around 10mm for 10kV models), short arcing time (less than half a cycle), fast dielectric recovery, long electrical life, compact size, and suitability for capacitive loads. These features make them ideal for use in modern power systems. Popular models include ZN12-10, VS1, and ZN30.
3. Common Faults and Troubleshooting
Despite their advantages, vacuum circuit breakers can still experience issues, mainly related to the operating mechanism, contacts, and vacuum integrity. Common faults include reduced vacuum levels, electrical wear of contacts, and mechanical failures.
3.1 Reduced Vacuum
If the vacuum level drops below 6.6×10â»Â² Pa, the interrupter is considered faulty. This can result from leaks in the seal or gas release from internal materials. Testing methods include spark meter checks, observing arc color, power frequency withstand voltage tests, and using a vacuum degree tester.
3.2 Electrical Wear of Contacts
Repeated current interruption causes contact wear, increasing resistance and reducing performance. Regular inspection of contact thickness and resistance helps identify wear. If the wear exceeds manufacturer specifications, the vacuum tube must be replaced.
3.3 Refusal to Trip or Close
Issues like low DC voltage, poor contact in the trip circuit, or mechanical misalignment can prevent proper operation. Diagnosing these problems involves checking both electrical and mechanical components.
4. Conclusion
Vacuum circuit breakers are widely used in power systems due to their high breaking capacity, strong arc-extinguishing ability, long service life, and ease of maintenance. They play a vital role in 10kV applications, offering significant advantages over other types. However, they are not immune to faults, and maintenance personnel must be familiar with troubleshooting techniques to ensure reliable and safe power supply.
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