Introduction: Discussion on online detection of vacuum circuit breakers: 1. Development trend and existing problems of vacuum circuit breakers; 2. Solution to online detection method of vacuum circuit breakers; 3. Implementation of specific methods. Keywords: mechanical and electrical faults 1 Development trend and existing problems of vacuum circuit breakers The advantages of vacuum circuit breakers are not only that they are oil-free equipment, but also that they have long electrical life, mechanical life, large breaking insulation capacity, strong continuous breaking capacity, small size, light weight, can be frequently operated, fire-free, less operation and maintenance, and low failure rate. They are ideal electrical equipment for unattended substations. At present, they are being developed and used extensively at home and abroad, and have the trend of completely replacing oil arc extinguishing medium. At present, most substations have adopted multi-functional microcomputer (electronic) protection devices, and the degree of comprehensive automation has also increased. The requirement of unattended operation has been basically met. Therefore, the main electrical equipment is required to have a certain online detection (self-test) function, and vacuum circuit breakers should be no exception. The common faults of vacuum circuit breakers are mainly manifested in two parts: (1) Mechanical faults. Since the probability of this type of failure is smaller compared with that of electrical failure, the implementation of online detection still requires relevant departments to further unify the scheme in terms of structure, size and combination. (2) Electrical failure. This type of failure is the main problem that directly threatens the safe and stable operation of the power grid, and its probability cannot be ignored. Compared with mechanical failure, primary electrical failure of vacuum circuit breaker is not only serious in nature, but also has greater concealment, suddenness, randomness and difficulty in timely prediction. Therefore, it is common to see manufacturers reminding users to observe the arc breaking physical phenomenon of vacuum interrupter in the factory report. Therefore, this type of failure not only threatens the safety of the power grid, but is also a major problem that is very likely to cause personal and national economic losses. 2 Solving the online detection method of vacuum circuit breaker At present, there are many online detection methods for vacuum circuit breakers, the common ones are as follows: ① Capacitive induction method; ② Artificial neutral point method; ③ High voltage electric field induction method; ④ RC voltage divider method; ⑤ Photoelectric remote sensing method. In addition, there is also an online measurement method for vacuum circuit breakers based on the Penning discharge principle (electromagnetic wind). In summary, each has its own characteristics. While these methods can also detect a decrease in the breaking capacity of a vacuum circuit breaker due to leakage in the vacuum interrupter under specific conditions, and achieve alarm and interlocking purposes through electrochemical processing, there are still many issues to discuss before widespread adoption. [align=center]Figure 1 Schematic diagram of the artificial neutral point method[/align] Regarding the artificial neutral point method (see Figure 1), C and R in the figure are formed using high-voltage capacitors or high-value resistors to create an artificial neutral point. Although the overall circuit resistance (resistance) is very large (the capacitive reactance is very large when using high-voltage capacitors), it does not have much impact on the entire system under normal operating conditions. Using high-voltage potential and N (grounding) point reference to detect the integrity of vacuum circuit breakers has certain rationale and characteristics. If this method is widely used, and some vacuum circuit breakers are under maintenance or malfunctioning, it is obvious that they form a virtual grounding point between the main system and ground. Therefore, this cannot be ignored in safe operation, relay protection setting calculations, and distribution network organization schemes. Other solutions also suffer from drawbacks such as large size, complex structure, poor anti-interference, low seismic resistance, difficulty in transmitting data over long distances, and effectiveness only on vacuum circuit breakers with glass enclosures or those easily observable. Therefore, the practical impact and feasibility of these methods must be carefully considered before widespread adoption. In fact, online monitoring of vacuum circuit breakers can be achieved using other methods, and they are not particularly complex. This research focuses on measuring the negative pressure changes in the vacuum interrupter. The key is that the online monitoring device itself must not only have good electrical insulation, a small size, and reliable operation, but also be as safe, standardized, easy to use, require minimal maintenance, and have stable operation. Furthermore, it must have both remote data transmission and local notification functions, and its communication capabilities must conform to standard transmission characteristics, unlike relay protection where each method is unique. To effectively perform online monitoring of vacuum circuit breaker interrupters, it is essential to comply with the current power grid's operating mechanism and feedback requirements; otherwise, wishful thinking will only solve a localized problem and introduce unnecessary duplication of work or burdens. 3. Implementation of the Specific Method The basic method is to use mechanical sensors to change the refraction angle and conductivity of the optical signal transmitted by the optical fiber, thereby changing the transmission amount of the optical fiber at the receiving end. Then, the subsequent processing circuit performs discrimination, processing, and transmission, thereby achieving the purpose of online detection. The advantages of using this method are: (1) It can effectively solve the insulation problem of high-voltage electrical appliances to the ground. (2) The detection sensitivity is not only practical but also relatively high. (3) It has strong resistance to photoelectric, magnetic field, radiation, vibration and environmental pollution. (4) The structure is simple and it is integrated with the vacuum interrupter. (5) It is very convenient to use and basically requires no maintenance. (6) It has the basic conditions for realizing local and remote monitoring. (7) It has a long service life, basically the same as the vacuum interrupter. (8) It is inexpensive. There is a pressure detection component—a sensor (corrugated tube, elastic film or other elastic element)—on the top or bottom cover of the vacuum interrupter. An auxiliary tension element is set inside it to enhance the fatigue resistance of the detection device. An adjustment device and an information transmission element are also provided on the top of the detection device to form an information sensor. Under normal circumstances, the pressure detection component (under a high vacuum state inside the vacuum interrupter) is in a highly compressed state under the action of the external atmospheric pressure. When there is a leak in the vacuum interrupter (the outside atmosphere enters), it will change the internal vacuum pressure of the vacuum interrupter, thereby forcing the pressure detection component to change its compressed state, activating the information sensor, changing the light source transmission junction of the transmitting and receiving optical fibers, and changing the amount of irradiation received by optical fiber B from optical fiber A. The photoelectric converter G1 of the subsequent processing circuit (see Figure 2) changes the output parameters of IC1 (operational amplifier) ​​as the transmission amount of optical fiber B changes. Then, the subsequent processing circuit processes these parameters again to finally achieve the purpose of alarm and lockout. [align=center] Figure 2 Schematic diagram of the basic method of online detection[/align] The feasibility of this method not only has the advantages of convenient material selection, reasonable overall design structure, and high electrical insulation capability, but also simple implementation method and no additional impact on the power grid due to the presence of the detection device even in the event of a serious circuit breaker accident. The reasons why this method is feasible are: (1) The detection device made of special materials has good free recovery stiffness and the measurement capability can reach 10⁻⁷. (2) Organic optical fiber has good light guiding performance (short distance) and its own conversion characteristics have a certain linearity. (3) Organic optical fiber has good electrical insulation capability, which can reach more than kV/cm on average. (4) Organic optical fiber does not require special photoelectric conversion to transmit signals over short distances. (5) Organic optical fiber has good flexibility, corrosion resistance and flame retardancy, making it suitable for this project.