Abstract: This paper introduces the basic structure and working principle of vacuum circuit breakers. Based on the modern concept of condition-based maintenance, various sensor technologies are used to collect data on the online working status of vacuum circuit breakers, and the data is processed and judged to realize online real-time status monitoring of vacuum circuit breakers. A set of online monitoring systems for vacuum circuit breakers is also designed. Keywords: Vacuum circuit breaker; Online monitoring; Data acquisition 1 Structure and Principle of Vacuum Circuit Breakers Vacuum circuit breakers are widely used in power control systems. Under vacuum conditions (generally 10⁻⁴ to 10⁻⁷ Torr), the insulation strength of the vacuum gap is very high, and the arc is easily extinguished. Therefore, vacuum circuit breakers have strong arc-extinguishing capabilities, high dielectric strength, and fast dielectric recovery speed after interruption. The idea of ​​using vacuum conditions to extinguish arcs was proposed as early as the late 19th century, but it could not be put into practical use at that time due to limitations in vacuum technology, materials, and metallurgy. After the 1950s, with the development of many new technologies in the electronics industry, many problems in the manufacture of vacuum interrupters were solved, and vacuum switches gradually reached the practical level. In the 1970s, vacuum circuit breakers with breaking capacities of 60-80kA and voltage levels of 10-35kV were manufactured, making vacuum switches the leading type of circuit breaker in power distribution voltage levels. The main arc-extinguishing mechanism of a vacuum circuit breaker is the vacuum arc-extinguishing chamber, as shown in Figure 1: [align=center] Figure 1 Structure of vacuum arc extinguishing chamber[/align] As shown in Figure 1, the structure of the vacuum arc-extinguishing chamber resembles a large vacuum tube. The outer shell has both glass and ceramic constructions. The moving contact is sealed by a metal bellows, which expands and contracts within the allowable elastic deformation range, resulting in a sufficiently high mechanical life. A floating potential metal shield is installed around the moving and stationary contacts, serving to condense and absorb metal vapor, distribute the electric field uniformly, and protect the surface insulation of the outer shell. The arc-extinguishing principle of a vacuum circuit breaker differs from that of other types of circuit breakers. Other circuit breakers mainly utilize the arc-extinguishing medium to extinguish the arc. Vacuum circuit breakers use vacuum to prevent arc reignition, thus achieving arc extinguishing. Therefore, whether the arc can reignite after the current crosses zero depends on the recovery of the arc gap dielectric strength. If it recovers, it can effectively prevent the arc from reigniting; otherwise, the arc will continue to burn until the next zero-crossing point, at which point it may be extinguished. Therefore, a fully functional online condition monitoring system for vacuum circuit breakers is an important guarantee for ensuring the safe and reliable operation of power control equipment. 2. Online Condition Monitoring Process of Vacuum Circuit Breakers Condition monitoring refers to understanding and mastering the operating status of equipment. This includes using various detection, measurement, monitoring, analysis, and judgment methods, combined with the system's history and current status, considering environmental factors, to assess the operating status of the switchgear, determine whether it is in a normal or abnormal state, display and record the status, and issue alarms for abnormal situations so that operators can handle them promptly. It also provides information and basic data for fault analysis, performance evaluation, rational use, and safe operation of the switchgear. Generally, the status of switchgear can be divided into normal state, abnormal state, and fault state. A normal state refers to a situation where the equipment as a whole or in part is free of defects, or where defects exist but its performance is still within permissible limits. Abnormal state refers to the fact that the defect has expanded to a certain extent, causing the status signal of the switchgear to change to a certain extent, and the performance of the switchgear has deteriorated, but it can still maintain operation. At this time, attention should be paid to the development trend of equipment performance, that is, the switchgear should be operated under supervision. Fault state refers to the fact that the performance indicators of the equipment have dropped significantly, and the equipment can no longer maintain normal operation. The fault state of switchgear is also divided into severity, including early faults where faults have already emerged and have a further development trend; general functional faults where the degree is not serious and the switchgear can still barely operate "with the disease"; serious faults that have developed to the point that the switchgear cannot operate and must be shut down; destructive faults that have led to disaster accidents; and sudden emergency faults that occur instantly due to some reason. The steps of status monitoring are mainly divided into the following three steps: (1) Signal acquisition During the operation of switchgear, there will inevitably be changes in various quantities such as force, heat, vibration and energy, which will generate various different information. According to different diagnostic needs, different signals that can characterize the working state of the equipment are selected. (2) Signal processing This is to classify and process the acquired signals to obtain the process that can characterize the machine characteristics, also known as the feature extraction process. (3) Status identification compares the characteristic parameters of the switching equipment obtained after signal processing with the specified allowable parameters to determine the status of the equipment and whether there is a fault. As shown in Figure 2: [align=center] Figure 2 Monitoring process on device[/align] 3 Online status monitoring principle of vacuum circuit breaker Since the 1990s, microcomputer multifunctional online monitoring systems based on digital waveform acquisition and processing technology have emerged. This system utilizes advanced sensor technology, computer technology, and digital waveform acquisition and processing technologies to achieve online monitoring of more parameters. This monitoring system can continuously monitor each measured quantity in real time. Therefore, the monitoring content is rich, the information volume is large, the processing speed is fast, and the monitoring results can be displayed, stored, printed, and alarmed, realizing full automation of status monitoring. The development of online monitoring technology has gradually replaced offline monitoring and made up for the defects of offline monitoring. The online status monitoring system realizes various functions such as data acquisition, data processing, status identification, and database. Its basic principle is that when electrical equipment is in operation, various measuring tools are used to measure its operating current, voltage, and other characteristic parameters. Appropriate sensors are used to extract the measured signal (electrical and non-electrical), convert it into a standard form of signal that the monitoring device can detect, input it into a digital signal acquisition device, perform A/D conversion, and then conduct corresponding data analysis and feature extraction. Its principle block diagram is shown in Figure 3: [align=center] Figure 3 Principle diagram of on-line monitoring system[/align] The sensor is the entry point device of the online monitoring system. Its sensitivity and performance directly affect the measurement accuracy, thus causing significant errors in data processing. The prerequisite for the correct operation of the monitoring system is to have good, reliable, and highly sensitive sensors. Therefore, the sensor must be sensitive, reliable, and have good linearity, capable of converting the measured signal without distortion. Different measured signals require different sensor types. The data acquisition device converts the measured signal into a digital quantity or digital waveform for data processing. The entire acquisition device operates under the program control of a computer. To meet measurement accuracy, the acquisition device is required to have a certain sampling speed and A/D conversion accuracy, as well as an appropriate number of channels. In order to acquire high-frequency signals, the acquisition device is also required to have a fairly high sampling frequency. The core component of the data processing system is an industrial computer. The main functions of the system are as follows: (1) Control the data acquisition device to acquire the measured signal at an appropriate frequency, and be able to read the acquired data from the data acquisition device; (2) Process the acquired data, analyze the processed data, and judge the status of the detected equipment; (3) Establish a database, and be able to extract historical data at any time. And be able to realize display and printing functions. The database is the key difference between the monitoring system and the instrument system. The database is used to store and process various information about the operation of the equipment, and has management and retrieval functions. The database includes static data such as the structural parameters, characteristic parameters, and working parameters of the equipment, dynamic parameters such as monitoring and operation data, and also records various types of historical data, such as typical fault data and normal data. The historical data recorded by the system has a great guiding role in operation and maintenance, and can form trend charts to judge the health status and development trend of the equipment. The database should be able to record all detailed data over a period of time. 4. Implementation of the Vacuum Circuit Breaker Online Condition Monitoring System Based on the aforementioned analysis, the implementation structure of the vacuum circuit breaker condition monitoring system is shown in Figure 4: [align=center] Figure 4 Structure diagram of state monitoring system of vacuum breaker[/align] As shown in Figure 4, the vacuum circuit breaker condition monitoring system is structurally divided into two main parts: a data acquisition system and a data processing system. The software used is Matlab and C language. The acquisition system selects suitable data acquisition devices and sensors, and utilizes the fast execution speed of C language to develop a data acquisition program, ensuring that the system can acquire data quickly, accurately, and in real time. The data processing system utilizes Matlab's interactive interface and convenient visualization functions to develop a data processing program. This includes the creation of the main interface of the monitoring system and data processing. Overall, this monitoring system is implemented using Matlab as the development platform. Data acquisition and data processing operate independently. The data acquisition program, written in C, controls the hardware to collect data, while the data processing program, also written in Matlab, handles data reading, processing, display, alarm functions, printing, and database access. Remote communication is also implemented using C. 5. Conclusion This system utilizes minimal hardware, with most tasks performed by an industrial control computer, minimizing system costs and reducing the likelihood of data distortion due to hardware failures. It ensures the safe and reliable operation of the vacuum circuit breaker and guides daily maintenance, allowing for the creation of optimal maintenance plans, reducing maintenance costs, and improving economic efficiency. The author's innovation lies in designing an online condition monitoring system for vacuum circuit breakers. Through comprehensive measurement methods, the system accurately grasps the equipment status, analyzes data to assess the circuit breaker's condition, predicts its lifespan, prevents malfunctions and even accidents, and provides rational decisions for appropriate maintenance and repair. Vacuum switch condition monitoring meets the needs of vacuum switch technology development and maintenance. It is an advanced monitoring method and represents the future direction of power equipment maintenance. References [1] Zhang Mingguang. Computer control system for boiler feedwater and hydrazine addition [J]. Microcomputer Information, 2002, 7-12: 26-27 [2] Yuan Shun. Condition monitoring and diagnosis technology of high voltage switchgear [M]. Machinery Industry Press, 2001 [3] Chen Huagang, Wu Yuehua, Pan Jinluan. Fault diagnosis and treatment of high and low voltage switchgear [M]. 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