Vacuum Circuit Breaker Electrical Life & Reliability Guide

1. Rational Selection of Electrical Life for High-Voltage Vacuum Circuit Breakers

The electrical life of a high-voltage vacuum circuit breaker refers to the number of full-load interruption operations specified in technical standards and verified through type tests. However, since the contacts of vacuum circuit breakers cannot be repaired or replaced in actual service, it is essential that these breakers possess sufficiently high electrical life.

New-generation vacuum interrupters employ longitudinal magnetic field contacts and copper-chromium contact materials. The longitudinal magnetic field electrodes dramatically reduce arc voltage under short-circuit and interruption currents. Copper-chromium materials help distribute the arc more evenly across the contact surface, significantly reducing contact erosion per unit of arc energy. This combination has led to a breakthrough improvement in the electrical life of high-voltage vacuum circuit breakers. Currently, the interrupting and closing performance of high-voltage vacuum circuit breakers in China is both high and stable.

In early Chinese models, the electrical life was only around 30 operations. Some units have been in service for over 20 years, and to date, no vacuum circuit breakers have been retired due to electrical life exhaustion from short-circuit interruptions, nor have any incidents been caused by insufficient electrical life. This clearly indicates that existing high-voltage vacuum circuit breakers generally meet the electrical life requirements of power systems. Therefore, the electrical life for short-circuit interruption does not need to be excessively high.

2. Temperature Rise in High-Voltage Vacuum Circuit Breakers

The loop resistance of a high-voltage vacuum circuit breaker is the primary source of heat causing temperature rise, and the interrupter’s loop resistance typically accounts for more than 50% of the total. Contact resistance at the contact gap is the main component of the interrupter’s resistance. Since the contact system is sealed within the vacuum chamber, heat can only be dissipated through the moving and stationary conductive rods.

The stationary end of the vacuum interrupter is directly connected to the fixed support, while the moving end connects via a contact clamp and flexible connector to the moving support. Although upward motion of the moving end aids heat dissipation, the longer thermal path and multiple connection points result in the highest temperature rise typically occurring at the junction between the moving conductive rod and the contact clamp.

In practice, effectively utilizing the stationary end—which has better heat dissipation—for heat transfer, thereby diverting heat away from the moving end, is an effective method to control excessive temperature rise.

3. Leakage Issues in Vacuum Interrupters

The bellows in most vacuum interrupters are made of 0.15mm-thick stainless steel by stamping. Inappropriate selection of service environment—such as pollution level, humidity, salt fog—or exposure to harmful gases and condensation can cause pitting corrosion on the bellows, leading to leaks at the bellows, cover plate, and sealed interfaces.

Ensuring proper alignment during installation, and selecting suitable operating and storage environments, are key measures to prevent leakage in vacuum interrupters.

4. Importance of Mechanical Parameter Adjustment in High-Voltage Vacuum Circuit Breakers

The mechanical life of high-voltage vacuum circuit breakers in China is typically 10,000 to 20,000 operations, with ongoing research aiming to extend this to 30,000–40,000. Electromagnetic operating mechanisms are widely used due to their simple structure, high reliability, ease of adjustment and maintenance, and operator familiarity. However, spring-operated mechanisms are also commonly used in some regions. The operating mechanism is the most complex and precision-critical part of the breaker’s mechanical structure, and many manufacturers lack the production capabilities to meet the required machining precision.

To ensure reliability, China has adopted a modular design, separating the operating mechanism from the breaker body. Specialized factories with better production conditions manufacture the mechanisms, which are then integrated with the breaker via the output shaft. Proper configuration of mechanical parameters is directly related to technical performance and mechanical life. Therefore, optimal mechanical parameter adjustment is crucial. An ideal buffer characteristic should exert minimal counterforce when the moving part first contacts the buffer, then rapidly increase in stiffness with travel to maximize absorption of kinetic energy, effectively limiting contact bounce and travel during opening.

5. Improving Operational Reliability of High-Voltage Vacuum Circuit Breakers

• Understand the basic structure of vacuum circuit breakers, be familiar with their technical specifications, select appropriate operating conditions, maintain close communication with manufacturers, and correctly utilize advanced features;

• Carefully perform mechanical parameter commissioning and ensure compliance with specified mechanical requirements to guarantee fundamental functionality;

• Standardize the management and storage of spare parts to ensure consistency, interchangeability, and reliability of their technical performance and quality;

• Maintain detailed operation records and conduct accident analysis. Summarize experience, collaborate closely with manufacturers, and continuously improve the advancement, reliability, and cost-effectiveness of vacuum circuit breakers.