1. Technical Problems in the Application of Vacuum Circuit Breakers ** Operating Overvoltage:** Vacuum circuit breakers often generate high current-cutting overvoltages and arc-reignition overvoltages during operation. In operation and management, it is necessary to prevent and suppress these overvoltages technically, such as appropriately increasing the contact gap to suppress arc-reignition overvoltages, and installing high-performance metal oxide surge arresters or RC protection devices for prevention. **Vacuum Interruptor Leakage:** As the service life of the vacuum interruptor increases and the number of interruptions rises, as well as due to external factors, its vacuum level gradually decreases, affecting its breaking capacity and withstand voltage level. Currently, the longitudinal magnetic field arc-extinguishing principle and copper-chromium contact materials are commonly used to reduce contact burn-out and improve electrical life. However, improper adjustment of the conductor rod concentricity will affect the sealing strength of the vacuum interruptor, leading to leakage. Ensuring proper concentricity adjustment and selecting appropriate usage and storage environments are important measures to solve the vacuum interruptor leakage problem. **Closing Bounce:** The time from the moment the contacts first make contact to the instant the contacts stabilize during circuit breaker closing is called the closing bounce time. Both practical and theoretical analysis show that it is a crucial factor affecting the electrical life of the arc-extinguishing chamber. However, since it is much shorter than the arc burning time during closing, the most significant hazard of bounce within a certain range is accelerated contact wear, leading to a shortened electrical life of the arc-extinguishing chamber. Closing bounce is caused by the inelastic collision of the moving and stationary contacts. The bounce value is related to many factors, such as the contact spring force, closing speed, opening distance, contact material, installation and commissioning quality, and the machining accuracy of components. Temperature rise. The circuit resistance of the vacuum circuit breaker is the main heat source for temperature rise, and the circuit resistance of the arc-extinguishing chamber typically accounts for more than 50% of the total circuit resistance. The vacuum between the contacts and the casing creates thermal insulation, so the generated heat can only be dissipated to the outside through the moving and stationary conductive rods. The stationary end of the vacuum arc-extinguishing chamber is directly connected to the stationary support, while the moving end is connected to the moving support through conductive clamps and flexible connections. Because of the numerous connecting links on the moving end and the long heat conduction path, the highest temperature rise is concentrated at the junction of the moving conductive rod and the conductive clamp. In practical applications, considering the poor overload capacity, the load current should be strictly controlled to keep it below the rated current. 2. Maintenance of Vacuum Circuit Breakers Pay attention to the adjustment of mechanical parameters. The operating mechanism is the most complex and precision-required part of the vacuum circuit breaker's mechanical structure. The proper configuration of mechanical parameters directly affects the technical performance and mechanical life of the vacuum circuit breaker. Therefore, it is essential to carefully perform the adjustment of mechanical parameters, strictly adhere to the mechanical parameter requirements, and standardize the management and storage of spare parts to ensure the consistency, versatility, and reliability of the technical performance indicators and quality of spare parts. Strictly control the closing and opening speeds of the vacuum circuit breaker, adjusting them according to the product manual. If the closing speed is too low, the pre-breakdown time will be prolonged, increasing contact wear. Furthermore, because vacuum interrupters generally use copper welding and undergo high-temperature degassing treatment, their mechanical strength is low and their vibration resistance is poor. Excessive closing speed can cause significant vibration, impacting the bellows and reducing its lifespan. A specific vacuum circuit breaker has an optimal closing speed. Vacuum circuit breakers have short arcing times during circuit breaking, with a maximum arcing time not exceeding 1.5 half-waves of the power frequency. Sufficient insulation strength of the arc-extinguishing chamber is required when the current first crosses zero. Ideally, the contact travel should reach 50%–80% of its full travel within the power frequency half-wave during breaking. Therefore, strict control of the switch opening speed is necessary. The opening and closing buffers of the vacuum circuit breaker must have good characteristics to minimize impact and protect the lifespan of the vacuum arc-extinguishing chamber. Strict control of contact travel and overtravel is crucial. Adjustments must be made strictly according to the product installation instructions. Testing must be performed after major overhauls, and the results compared to factory records. It is a misconception to believe that a larger opening distance is beneficial for arc extinguishing, leading to arbitrarily increased contact travel. Otherwise, excessive stress on the bellows during closing can damage the bellows, compromise the arc-extinguishing chamber seal, and cause leakage. The reduction in overtravel corresponds to the wear of the contacts. Therefore, each adjustment beyond the travel limit must be recorded. When the cumulative wear of the contacts exceeds 4 mm, the arc-extinguishing chamber should be replaced. When contact wear causes poor contact between the moving and stationary contacts, the problem can also be detected by testing the circuit resistance. The contact springs should be carefully inspected for deformation or damage. The vacuum level of the arc-extinguishing chamber should be checked regularly. A power frequency withstand voltage test (42 kV) should be performed regularly. Based on the "Preventive Testing Regulations for Power Equipment" and the actual situation of the unit, the power frequency withstand voltage test cycle for the vacuum circuit breaker should be established. Experience shows that the phenomenon of arc-extinguishing chambers exceeding the natural leakage rate due to process deficiencies generally occurs in the first 1-2 years of use. Therefore, in the first two years of operation, close monitoring should be conducted according to the specific conditions of the substation. Ideally, a power frequency withstand voltage test should be performed every 0.5, 1, 1.5, and 2 years after the vacuum circuit breaker is put into operation. After 2 years, the frequency test frequency should be adjusted based on the operating conditions to determine whether it should be performed once or twice a year. Currently, due to the lack of sophisticated instruments for on-site vacuum testing without disassembly, power frequency withstand voltage testing remains a relatively effective method for detecting vacuum levels. When possible, a field vacuum tester can be used to test the vacuum level of the vacuum interrupter without disassembling it. Vacuum level testing can be performed concurrently with the power frequency withstand voltage test as an auxiliary method. Several different models of field vacuum testers are available on the market. The maintenance cycle of vacuum circuit breakers should be rationally scheduled. The vacuum level of the vacuum interrupter's break point should be verified using the power frequency withstand voltage method in conjunction with seasonal (annual) preventative tests. After 2000 normal operation cycles (closing and opening load current) and 10 interruptions of rated current, all bolts should be checked for looseness. The inspection methods and requirements should follow the maintenance and inspection requirements for vacuum circuit breakers. If the specified technical parameters are met, continued use is permitted. Care should be taken during installation and maintenance. The permissible storage period for vacuum interrupters is 15-20 years; therefore, spare parts should not be excessive, and the storage and operating environment should be free of corrosive chemical gases. When adjusting the contact gap, the compression of the bellows should be controlled to prevent plastic deformation. The rebound of the trip buffer should not be excessive, as this will affect the lifespan of the bellows. If poor thread fit is found during installation and adjustment, the cause should be identified before handling. Do not use excessive force to tighten the vacuum interrupter to prevent damage to the bellows. The wiring of the secondary circuit and the contacts of the auxiliary switches should be intact to avoid affecting the reliability of the circuit breaker operation. Check and measure the resistance value of each phase of the main conductive circuit. The contact resistance of the contacts is related to the pressure between the contacts. Within a certain range, the higher the pressure, the lower and more stable the contact resistance. Generally, the contact resistance of each phase of a vacuum circuit breaker should not exceed 80 mW. Check the lubrication of the transmission parts and whether the fastening bolts are loose. Keep them clean and perform all operations according to the machine manual. Take care to protect the vacuum interrupter from any external impact. Strictly conduct handover acceptance. After installation or major repair, relevant parameters must be tested and verified. The main parameters to be retested include: closing bounce, opening synchronization, opening distance, compression stroke, closing and opening speed, closing and opening time, DC contact resistance, break insulation level, and transmission acceptance test, all of which should meet the requirements of vacuum circuit breakers.