Abstract This paper analyzes the spring operating mechanism of a vacuum circuit breaker that has repeatedly failed to operate. Through field experiments, suggestions for improving the structural characteristics and certain parameters of the mechanism are proposed, along with measures to prevent failure to operate. Keywords Vacuum circuit breaker, operating mechanism, tripping device, parameters Mechanical failure is the main cause of vacuum circuit breaker failures, and the operating mechanism is a frequent site of mechanical failures. According to statistics on high-voltage switch accidents of the North China Power Group Corporation in 1997 (see "Summary of High-Voltage Switches in the Directly Subordinate Power Grid of North China Power Group Corporation in 1997"), in 1997, mechanism failure to trip accounted for 33% of the accidents in the high-voltage switches of the directly subordinate power grid of the entire group company, all of which were 10 kV switches. During transmission and commissioning, circuit breakers of other voltage levels also exhibited failure to trip and failure to close; the three failure-to-trip faults that occurred in 1997 were all in 10 kV switch mechanisms. It is evident that failure to trip accidents (faults) of high-voltage switch operating mechanisms account for a large proportion of all high-voltage switch accidents (faults). Strengthening the maintenance and management of 10 kV switch mechanisms, especially the tripping device of the operating mechanism, is a very important task. In recent years, especially in the last two years, our company's 10 kV switches have experienced several cascading trips caused by the operating mechanism's failure to trip, and multiple instances of vacuum circuit breaker operating mechanisms malfunctioning. Therefore, we conducted on-site disassembly and testing of the relevant vacuum circuit breaker operating mechanisms. Based on the test results and mechanical structure analysis, we proposed improvement schemes for the maintenance and structure of the vacuum circuit breaker operating mechanisms. 1. Experimental Process We conducted mechanical characteristic and mechanism disassembly inspections on vacuum circuit breakers that had experienced accidents during operation and exhibited malfunctions during transmission and testing. The selected switch is a ZN□-10 Q/1250-25 type indoor high-voltage vacuum circuit breaker (equipped with a dedicated spring energy storage operating mechanism), manufactured in June 1996 and put into operation in March 1997. Some of its technical parameters are as follows: Closing time: ≤75 ms; Opening time: ≤65 ms; Rated voltage/current of opening and closing coils: DC 220 V/1 A; Overcurrent trip: 5 A; Overtravel: 4±1 mm; Contact distance: 11±1 mm; Average closing speed (last 6 mm): 0.9±0.3 m/s; Average opening speed (last 6 mm): 1.1±0.2 m/s; The opening and closing coils use DC solenoid coils. During the opening time test, 80%–100% of the rated voltage was applied. The trip unit failed to operate or operated with a delay, occurring approximately 10% of the total number of tests. The circuit breaker's delayed action waveform is shown in Figure 1. 2. Experimental Analysis and Countermeasures t′＝t1－t2＝4.193－1＝3.193 (s) t0＝0.065 s Δt＝t′－t0＝3.128 (s) Where t′——actual circuit breaker opening time; t0——normal maximum circuit breaker opening time; Δt——circuit breaker delayed action time. When the mechanism issues a tripping signal, from the tripping pressure plate issuing the tripping signal to the current flow time at the circuit breaker contact (I-DL), combined with the DL dry contact action time analysis, the circuit breaker operates with a delay of approximately 3.1 s compared to normal tripping. Through disassembly test analysis of the mechanism, it was found that although the moving iron core of the tripping coil operates, it cannot immediately break the tripping element for a "crisp trip." Instead, the moving iron core is attracted for a period of time before releasing the tripping lever to trip, or even fails to trip at all. Visual inspection revealed no abnormalities in the mechanism itself. However, structural analysis indicated that the entire opening process, from the action of the opening spring on the main shaft to the transmission to the switch conductive rod, requires the rotation of five pivot pins (as shown in Figure 2). The rotational friction consumes a significant amount of opening work, resulting in reduced transmission efficiency. Additionally, on-site observation showed that some opening coils were too close to the opening lever, resulting in a small core idle stroke. Insufficient acceleration force could also cause the tripping element to fail to release. Furthermore, the lack of static force measurements on relevant components, coupled with improper adjustment of the transmission device and significant geometric errors, is also a major factor contributing to low transmission efficiency and mechanism failure to open. Through experimental analysis, in response to the above-mentioned factors that may cause failure, we have taken the following measures for the operating mechanism of the vacuum circuit breaker: (1) Considering the disadvantage of the small starting suction force of the DC electromagnet, in order to improve the spring opening power, the impact force of the opening core is increased; at the same time, in order to match the selection of the secondary circuit anti-pumping relay and to consider the fluctuation of the power supply voltage, in order to prevent the voltage drop on the opening coil from being too low and causing failure to open, the opening coil (parameters: DC 220 V, resistance less than 175 Ω, current less than 1.5 A) is replaced with a solenoid DC coil with DC 220 V, resistance 88 Ω, and current 2.5 A. (2) The low voltage operation test of opening and closing is carried out again. (3) The spring opening and closing mechanism is disassembled and inspected, the gaps of each part and the depth of the latch are checked, the screws of each part are tightened, and lubricating oil is added to each rotating part. 3 Conclusion Vacuum circuit breakers and their operating mechanisms are favored by users due to their simple mechanism, easy maintenance, and suitability for frequent operation. In vacuum switch operating mechanisms using tripping springs, although the work done by the operating mechanism during tripping is not significant, with the main energy consumed in the tripping mechanism, it is still suitable for the reliable operation requirements of the circuit breaker. Considering the current state of domestically produced spring mechanisms, the tripping mechanism of the circuit breaker should have sufficient margin while meeting design requirements. Alternatively, two tripping devices can be installed to ensure reliable tripping. In terms of use and maintenance, it is not advisable to implement the long-cycle, high-frequency maintenance or even maintenance-free promises advocated by some manufacturers. Instead, daily maintenance and periodic inspections should be carried out in a timely manner to prevent the circuit breaker from refusing to operate due to jamming of the mechanism or improper adjustment.