With increasingly stringent reliability and automation requirements in power systems, automation and intelligence demands have been placed on monitoring, control, and protection in power generation, transmission, distribution, and consumption. Circuit breakers, as the most crucial control element in power systems, form the foundation for the intelligence of electrical equipment. However, circuit breaker intelligence is not simply achieved by using computers. It requires maximizing the utilization of the electric arc's own energy to achieve self-diagnosis of operating status, controllable operation of the operating mechanism, and the integration of the latest sensor technology, microelectronics technology, and information transmission technology for a complete understanding of intelligence. Generally, in addition to fulfilling the original functions of conventional electrical equipment, intelligent electrical equipment primarily functions in the following ways: 1. It should possess the ability to sensitively and accurately acquire a large amount of surrounding information; 2. It should have the ability to process the acquired information; 3. It should have the ability to make judgments about the processed results, and the ability to implement and effectively operate the regenerated information from the processed results. Figure 1 illustrates the working principle of an intelligent circuit breaker that integrates a computer system and sensing devices. The main sensors can detect gas density and reflect the status of the operating mechanism by monitoring its movement and energy changes. The signals emitted by the gas density sensor enable continuous status monitoring, trend determination, and detection limits, and can also achieve conventional SF6 gas locking and alarm functions. Similarly, with the help of motion and energy sensors, the status of the operating mechanism can be monitored. Furthermore, the signals from these sensors can be used simultaneously for conventional position indication and motor control functions. Figure 1 shows the intelligent circuit breaker operating block diagram. If needed, additional sensors can be added to the basic system. Based on the test results of the ambient temperature, a more accurate assessment of status changes (and the reflected trend information) can be made. For systems without a serial interface to a higher level, time recording is very helpful in predicting changing trends. Additional current and voltage sensors form the basis for optimizing the circuit breaker's functionality. In summary, the operation process of an intelligent circuit breaker can be summarized as follows: The intelligent control unit continuously collects certain specific information from the power system to determine the current operating status of the circuit breaker, while simultaneously maintaining a ready-to-operate state. When the main control room of a substation issues a trip signal from the relay protection device due to a system fault, or issues an operation command to the circuit breaker during normal operation, the control unit calculates the predetermined optimal state of the operating mechanism corresponding to the circuit breaker's operating state according to a certain algorithm, and drives the actuator to adjust the operating mechanism to that state, thereby achieving optimal operation. Clearly, the intelligent control unit is the core component for realizing intelligent operation of the circuit breaker. 1. Intelligent Control Unit The intelligent control unit is the soul of an intelligent circuit breaker. It uses a microprocessor as its core component and comprehensively applies various modern technologies such as sensing technology, photoelectric conversion technology, digital control technology, microelectronics technology, and information technology to complete the intelligent operation of the circuit breaker and realize its intelligence. The basic functions of the intelligent control unit include: 1.1 Automatic identification of the circuit breaker's operating state. Accurate identification of the circuit breaker's operating state is a prerequisite for intelligent operation. For ultra-high voltage circuit breakers, their main tasks include breaking short-circuit current, load current, overload current, small capacitive current, and small inductive current. 1.2 Automatic adjustment of the circuit breaker's operating mechanism. This is the core function of the control unit. Therefore, the control unit must determine the corresponding adjustment amount of the operating mechanism based on the identification of the circuit breaker's operating status. 1.3 Record and display the circuit breaker's operating status. Since the circuit breaker does not operate for most of the operating time, the task of this unit is to continuously monitor the circuit breaker's operating status during this period. It also records each circuit breaker opening and closing event, including the magnitude of the breaking current, the breaking type, and whether any failure to open or close occurred. During a short circuit, the change in the short-circuit current should also be recorded to facilitate accident analysis and circuit breaker maintenance by the power department. Simultaneously, the cumulative breaking current of the circuit breaker can also be used to indicate the erosion of the circuit breaker contacts. 1.4 Function to communicate with a remote host computer. The control unit can transmit the circuit breaker's opening and closing records and other data to the host computer via the information transmission interface according to the host computer's requirements. The host computer then transmits operating commands, protection parameters, protection and reclosing methods, and other configuration requirements via the information transmission network. 2. Monitoring and Diagnosis of Circuit Breaker Operating Status Monitoring and diagnosis are crucial aspects of intelligent electrical equipment. It's difficult to imagine what would happen to intelligent electrical equipment without the technical support of monitoring and diagnosis. Advances in computer technology, sensor technology, and microelectronics technology have enabled the monitoring and diagnosis of intelligent circuit breakers. This requires the following functions: 2.1 Monitoring and Diagnosis of Arc-Extinguishing Chamber Electrical Life: Recording the number of closing and opening cycles, with alarms for exceeding limits; Weighted cumulative breaking current, i.e., statistically calculating the ΣIα (α=1.5～2) value, with alarms for exceeding limits. The electrical wear of contacts mainly depends on the magnitude of the arcing current and the duration of the arcing time. However, the arcing time is difficult to obtain for circuit breakers in actual use, and it can be disregarded from a statistical and cumulative perspective. Therefore, attention is often focused on the breaking current, leading to the development of cumulative breaking current recorders. However, the relationship between cumulative breaking current and contact wear is not a single-valued function. For the same cumulative breaking current, the wear is much less when the current in a single breaking operation is small compared to when the current in a single breaking operation is large. Therefore, the correct method is to convert the wear amount into the corresponding amount based on the magnitude of each breaking current. The total wear should be determined based on the circuit breaker's rated breaking current and rated number of breaking operations. The equivalent wear amount under different breaking currents should be determined by empirical curves obtained from experiments. For vacuum circuit breakers, in addition to electrical life, the vacuum level of the arc-extinguishing chamber is also monitored. Extensive research and practice have shown that some 12kV vacuum circuit breakers have achieved a short-circuit breaking operation of up to 50 times in type tests. After 50 breaking operations, the contact burn-off thickness is only about 0.6mm, indicating minimal burn-off. Furthermore, vacuum arc-extinguishing chamber products allow for a contact burn-off thickness of 3mm, demonstrating that vacuum circuit breakers have a large margin in terms of breaking capacity. Moreover, in actual operation, the number of short-circuit breaking operations is not very high. Correspondingly, the probability of a decrease in the vacuum level of the arc-extinguishing chamber of a vacuum circuit breaker is much higher. Statistics from 1999 show that of the 45 accidents involving vacuum circuit breakers nationwide, 9 were caused by a decrease in the vacuum level of the arc-extinguishing chamber. This demonstrates the crucial importance of monitoring the vacuum level of the arc-extinguishing chamber for vacuum circuit breakers. 2.2 Monitoring and Diagnosis of Circuit Breaker Mechanical Faults Extensive statistical data over many years indicates that 70%–80% of accidents occur in the operating mechanism and control circuit of high-voltage circuit breakers. The mechanical parts of circuit breakers are relatively complex and do not operate for a long time, making them more difficult to monitor than the relatively mature rotating machinery monitoring technology. Multiple technologies are often required for comprehensive judgment, including: (1) Monitoring the current waveform of the closing and opening coils, with abnormal alarms; (2) Monitoring the open circuit of the closing and opening coils, with open circuit alarms; (3) Monitoring the travel distance, with over-limit alarms; (4) Monitoring the closing and opening speed, with over-limit alarms; (5) Mechanical vibration, with abnormal alarms; (6) The number of pressurizations, pressurization time, and pressure of the hydraulic mechanism; (7) The spring compression state of the spring mechanism, the working state of the transmission mechanism and the locking part, and the working time of the motor; (8) The permanent magnet mechanism: coil condition, magnetic stability, and spring compression state, etc.; (9) Mechanical vibration signals of key parts. The mechanical vibration waveform of the closing and opening operation of a high-voltage circuit breaker is very complex, usually containing multiple sub-waves. The seemingly chaotic waveform is actually a superposition of multiple sub-waves, each representing a vibration event. By analyzing the vibration waveform and separating each wavelet, the number of events, the time of occurrence of each event, and the intensity of the event can be obtained, and multiple pieces of information about the mechanical parts of the circuit breaker operation process can be obtained. There are many methods for waveform analysis, such as wavelet analysis, shape comparison, statistical process processing, etc. The acceleration sensor used for measurement should be reasonably selected according to the different targets being monitored (electromagnetic vibration, component vibration, operational vibration, particle jumping, etc.). The installation position of the vibration sensor should also be carefully arranged; (10) Detection of the current and voltage waveforms of the closing and opening coils. The coil current waveform contains a lot of operating system information, such as whether the coil is connected, whether the iron core is stuck, whether there is an obstacle to tripping, etc.; (11) Mechanical characteristics of closing and opening: speed, overshoot, bounce, impact, etc., which can also be reflected in the vibration waveform; (12) Monitoring of the on/off status of the control circuit. This has a good monitoring effect on the failure to open or close caused by the auxiliary switch not being in place or poor contact; (13) Energy storage status of the operating mechanism. A fundamental starting point for judging whether the monitored signals are normal is to compare them with the situation under normal conditions. Normal conditions are within a certain range and can only be determined through experimentation and statistical processing under specific conditions. Typically, several waves from a single operation are compared horizontally in the time domain, frequency domain, and amplitude, and vertically with previous operations to arrive at a diagnostic conclusion. 2.3 Monitoring of Insulation Status: Gas circuit breaker gas pressure, exceeding limit alarms, and interlocking. Monitoring partial discharge to predict insulation accidents. Intelligent technology evolves the acquisition, processing, and reasoning of information from simple algebraic numerical calculations to simulating the human brain's ability to identify, think about, predict, optimize, and make decisions regarding uncertainties. Introducing intelligent technology into an insulation diagnostic system based on online monitoring data, the diagnostic mechanism is divided into four levels: online data preprocessing, symptom set extraction, fault type determination, and decision-making, as shown in Figure 2. Figure 2: Hierarchical Structure of Power Equipment Fault Diagnosis. Research shows that due to the large amount of data and complex influencing factors in online monitoring, intelligent technology is particularly suitable for online insulation diagnosis. In the preprocessing stage of online data, relevant methods are used to remove false points, and the influence of the environment on the measurement data is weakened by analyzing the correlation between online data and environmental factors and using cubic fitting curves. In the symptom set extraction stage, considering the dynamic characteristics of the data and the influence of random errors, the residual between the data to be tested and the model is used as one of the symptoms of the fault, and a time-series analysis method based on relative comparison is adopted. Studies have proven that these methods are effective. For the latter two levels of insulation diagnosis, namely the fault type and decision level, more online monitoring data needs to be accumulated, and in-depth research is needed on the online data characteristics of fault types, patterns, and severity. The accumulation of expert knowledge and the improvement of diagnostic methods will also be a long-term process. 2.4 Monitoring of the temperature of current-carrying conductors and contact points The contact of current-carrying conductors and busbar connections, joints, and other contact points are affected by vibration torque, which changes the contact resistance and the temperature of the contact points. Therefore, it is necessary to monitor the temperature of these points. This typically involves using the intensity of infrared radiation or mounting a temperature-sensing element on a conductor to convert it into a signal, transmit it to a low potential, and then reconstruct it as a temperature signal. The challenge lies in obtaining a low-voltage operating power supply on the high-potential conductor. Another method utilizes a heated emitting device to transmit abnormal overheating information to a low-potential receiving device. Recently, a non-contact method has emerged where infrared light is directly shone onto a current-carrying conductor at a low potential to obtain the temperature of the measured object from the emitting side. There is also a passive measurement method using a photosensitive thin-film silicon temperature sensor, as shown in Figure 3. Figure 3 shows a temperature probe developed using a temperature-sensitive Fabry-perot groove. The device consists of a thin silicon wafer with rectangular grooves etched into its top and bottom sections. A layer of glass with a different coefficient of thermal expansion than the silicon wafer is then bonded to the top of the wafer. When the temperature changes at this point, internal stress is generated due to the different coefficients of thermal expansion of the two materials, altering the depth of the groove. Multicolor light is fed into a Fabry-perot slot using optical fiber, and the reflected modulated light is also sent out through the optical fiber. The modulated output signal is measured using optical interferometry. Fiber optic sensing systems composed of Fabry-perot slots have corrosion-resistant, compact components with high measurement sensitivity and are unaffected by electromagnetic interference, making them suitable for online temperature monitoring of intelligent high-voltage electrical appliances. 2.5 Overall Block Diagram of the Monitoring and Diagnostic System The overall block diagram of an intelligent circuit breaker device or its intelligent monitoring and diagnostic system is roughly shown in Figure 4. For signal transmission, if the cable is flat, the distance is very short, and parallel data signals are mostly used; if the distance is long, serial signals are mostly used, requiring only two cables, and there can be multiple signal acquisition units, each additional unit adding only one address code. Due to the difficulty in diagnosing the degree of abnormality and the location of the fault, computer decision-making is sometimes challenging. Many devices still rely on human analysis of information to make a final decision. The computer only issues alarm signals for those confirmed out-of-limit values. Figure 4. Overall Block Diagram of the Diagnostic System. The signals acquired by the sensors are not limited to those described above. A highly intelligent circuit breaker, in addition to self-monitoring the deterioration or variation in electrical, mechanical, and insulation aspects, should also have corresponding self-checking measures for aspects such as gas sealing status, vacuum degree of the vacuum interrupter, hydraulic pressure of the hydraulic mechanism, and characteristic deterioration of surge arresters in the combined electrical system. 3. Intelligent Operation of Circuit Breakers Intelligent operation of circuit breakers is the most typical application of intelligent circuit breakers. It introduces intelligent technology into the electrical performance of circuit breakers, enabling them to better complete breaking tasks and improve breaking reliability, thereby enhancing the overall technical performance of the circuit breaker. This has a very important role and value in both production operation and research and manufacturing. Currently, it is believed that it should include at least the following two aspects: First, the operating performance of the circuit breaker should be able to automatically select and adjust the reasonable predetermined working conditions of the operating mechanism or the interrupter according to different operating conditions issued by the power grid. For example, in the breaking operation of self-controlled circuit breakers, the contacts break at a lower speed under small loads, ensuring the required arc-extinguishing energy while reducing mechanical losses. Upon receiving a short-circuit signal, they break at full speed to achieve optimal electrical and mechanical breaking performance. Currently, the development of such expert systems is underway. Variable-speed operation breaks the traditional concept of a single-function circuit breaker, effectively representing the intelligentization of the aforementioned execution functions. This is a highly beneficial attempt to modify the operating mechanism of high-voltage circuit breakers. Furthermore, the circuit breaker is required to close at zero voltage and break at zero current, which is completely consistent with the synchronous breaking and phase-selective closing conditions of circuit breakers. Synchronous breaking can greatly improve the circuit breaker's analytical capabilities; a low-cost, small-capacity switch can break currents more than 10 times its capacity. Phase-selective closing can avoid system instability and overcome inrush current and overvoltage in capacitive loads. In the field of power electronics, a soft-switching technology has become popular in recent years, enabling semiconductor switching devices to close at zero voltage and break at zero current. Electronic operation can be considered the key to realizing soft-switching technology in circuit breakers. Currently, the most pressing applications are: operating parallel reactors, operating capacitor banks, operating transformers, and operating transmission lines. Each application places certain demands on the performance of circuit breakers and control devices, fundamentally solving overvoltage problems. This is of great significance for promoting reactive power compensation and stabilizing power systems. Vacuum-triggered switches and general electromagnetic mechanism vacuum switches have already achieved the switching of parallel capacitor banks with phase-selective closing. Further work will use intelligent circuit breakers with permanent magnet mechanisms to directly achieve phase-selective closing. The permanent magnet operating mechanism greatly improves the controllability of the mechanism, progressing from millisecond-level mechanism control time dispersion to microsecond-level electrical signal control, and from mechanical energy storage and mechanical tripping to electrical energy storage and direct electrical signal triggering (electronic tripping). The new operating theory of vacuum circuit breakers should include two parts: control accuracy analysis and reliability design, design of high-reliability control circuits, and analysis and optimization of mechanism motion characteristics. The realization of synchronous breaking and phase-selective closing of circuit breakers: Modern sensor technology makes the acquisition of AC zero-point signals very reliable and convenient. Similarly, we can easily obtain the zero-point signal (corresponding to the peak value of a sinusoidal signal) of the rate of change of AC voltage or current. The remaining question is when to issue the control signal before or after the zero point of the voltage or current rate of change. Currently, the development of synchronous circuit breakers still requires further reliability verification and design. Its related significance is the complete controllability of the circuit breaker, and its development may become the most typical new concept switching device. In the 1990s, ABB launched CAT (Curcuit Breaker with Artificial Interiligence Technology): CAT was developed and tested specifically for ELF type SF6 circuit breakers (open type) and ELK type enclosed switchgear (GIS), as shown in Figure 5. Figure 5 CAT wiring diagram. CAT is a modular electronic device composed of three independent phase modules, which allows the circuit breaker to operate independently of each phase at the optimal switching time. Its effects are: reducing instantaneous overvoltage during switching; reducing the stress of current on the equipment. For high-voltage circuit breakers that frequently use opening and closing resistors, CAT (Cyclic Array Control) is a reliable alternative. Installed in the circuit breaker's control circuit, CAT processes information from voltage or current transformer inputs and issues circuit breaker operating pulses at optimal operating conditions. For example, depending on grid parameters, CAT can effectively reduce the inrush current when capacitor banks are switched on to 30% of its original value. For automatic reclosing with parallel compensation lines, even for long lines, the operating overvoltage value can be kept below twice the per-unit value. When disconnecting parallel reactors, CAT can eliminate harmful arc reignition within the circuit breaker, thus preventing reactor insulation degradation. It can be seen that CAT achieves controlled operation of the circuit breaker to a certain extent, exhibiting some characteristics of intelligent operation. In fact, phase-controlled high-voltage circuit breaker technology has been widely applied abroad for over a decade. The table below briefly illustrates the role of phase-controlled high-voltage circuit breakers. 4. Discussion on Issues Related to Intelligent High Voltage Electrical Appliances Intelligent circuit breaker technology is not only a conceptual shift and theoretical development, but also a technological breakthrough in many fields. Its realization will inevitably involve the application of new technologies, new materials, and new processes to continuously improve the quality and technological content of products. However, the core issue in this process is the sampling, transmission, and control system of information. In these fields, some technologies are relatively mature, while others are still in the development, research, and trial operation stages, requiring a stage of continuous summarization, improvement, and refinement. Specifically, the following aspects are addressed: 4.1 Key Technologies (1) Sensing Technology. Partial discharge, high-voltage conductor temperature measurement, high-voltage side current and voltage measurement technologies, especially the photocurrent and voltage sensing technologies currently under development, which are quite challenging; (2) Microcomputer Technology. Developing successful intelligent software is the key to microcomputer technology. In the software system, the main program is the core program. The main program first completes the initialization of the microcontroller and peripheral interface chips; then, the main program continuously detects and displays the working status of the circuit breaker, ready to communicate with the host computer at any time to transmit relevant control and status information. (3) Research on electromagnetic interference technology shows that the normal noise in the system is the power frequency 50Hz and its higher harmonics. Any form of transient process (such as various overvoltages and various short-circuit faults) and carrier communication signals that occur in the primary circuit will be coupled to the secondary system through different paths. In addition, the corona and flashover caused by the high electric field will also generate electromagnetic radiation. The surge noise of the switching power supply of the secondary control circuit will also cause disturbance to the power transmission. When the high-power electromagnet operates, it will cause changes in the spatial magnetic field and induce current in the nearby conductive circuit, which will test the control circuit in the operating mechanism. To solve the electromagnetic compatibility problem, strict shielding, isolation and grounding measures should be taken for each interference source. The digital transmission of signals can greatly reduce the degree of interference. The introduction of photoelectric conversion can not only perform electrical isolation, but also ensure that the signal transmission process is not affected by electromagnetic fields. Since the signal transmission and control system of intelligent circuit breakers have low operating voltage and signal transmission level and low withstand voltage level, external electromagnetic field interference can easily cause it to fail or be damaged. However, this situation has little impact on the traditional electrical system. Therefore, electromagnetic compatibility is a new issue for the intelligentization of circuit breakers. (4) Signal processing technology. For some technologies, obtaining monitoring signals is only the first step; fault diagnosis is necessary to make judgments and decisions. For example, complex signals obtained from partial discharge monitoring require fault diagnosis to achieve fault classification, fault location, and expected lifespan estimation. Monitoring the mechanical state of circuit breakers using mechanical vibration methods also requires signal processing for accurate identification. Current research on the arc state of circuit breakers also starts with arc voltage, using software processing to diagnose the arc state. 4.2 Lifespan Issues Generally, the lifespan of electronic equipment is far shorter than that of high-voltage electrical equipment, which is a contradiction. Solutions include: improving the reliability of electronic equipment, which can be addressed through design, manufacturing, and appropriate improvement of operating conditions; having self-testing functions; adopting comprehensive judgment; and using modular design for components with the same function to reduce costs and increase backup capacity, thereby improving the overall reliability of electronic equipment. 4.3 Economic Issues Currently, with the continuous price reduction of equipment such as computers, the price of monitoring equipment is also decreasing. This trend will continue. However, considerable funding is still required. For example, the GIS monitoring equipment displayed by Mitsubishi Electric Corporation of Japan at the '97 International Power Equipment and Technology Exhibition included a device with approximately 10 functions, such as partial discharge monitoring, and its price was less than 1/10 of the GIS itself. This is significantly cheaper than the 1/3 price mentioned a few years ago. Using domestically produced equipment would be even cheaper. Foreign countries are also very concerned about the economic aspects of monitoring technology and have conducted numerous economic analyses. The following formula can be used as a condition for adopting monitoring equipment: C 5. Current Status of Intelligent Circuit Breakers In recent years, many intelligent circuit breakers have entered the market. Typical examples in the high-voltage field include Toshiba's C-GIS and ABB's EXK intelligent GIS. Both utilize advanced sensor technology and microcomputer processing technology, enabling online monitoring of the entire combined electrical appliance and its secondary system on a single computer control platform. In the medium-voltage field, typical examples include Fuji's intelligent vacuum circuit breaker from the early 1990s and ABB's VM1 vacuum circuit breaker introduced in recent years. The former includes three functions: automatic protection, early maintenance, and information transmission. The protection function allows the circuit breaker itself to detect and judge overcurrent and short-circuit faults and issue commands to reliably trip the circuit breaker. The early maintenance function refers to the circuit breaker issuing alarms when vacuum levels decrease, electrical contact temperatures rise abnormally, or the trip coil breaks, prompting operators to take the circuit breaker out of service for maintenance. The information transmission function refers to the output of circuit breaker status signals in addition to normal control signals. The VM1 vacuum switch is ABB's latest product. Besides its novel integrated insulation structure, its most significant features include contactless secondary control and the use of new sensors, in addition to the permanent magnet operating mechanism. The switch's position sensor and auxiliary contacts are both contactless proximity switches or optical switches. The new model's current sensor signals can be directly converted into digital signals, replacing traditional electromagnetic voltage and current transformers. Currently, advanced industrial countries worldwide are optimistic about the development prospects and potential benefits of intelligent high-voltage electrical appliances in the high-voltage field of power systems, and have increased their research and development efforts. Typical examples include ABB's CAT circuit breaker, which incorporates artificial intelligence technology and, as discussed earlier, achieves a certain degree of controlled operation of the circuit breaker. ABB's photoelectric current and voltage sensors have replaced traditional electromagnetic current and voltage transformers in the high-voltage field, solving the sensing technology challenges in intelligent high-voltage electrical equipment. Currently, the widespread application of digital signal transmission technology has greatly mitigated the impact of interference during signal propagation. The application of these advanced technologies has created favorable conditions for the development of intelligent circuit breaker technology. The intelligentization of circuit breakers is a transformative undertaking, involving technological advancements and innovations across numerous fields, such as sensing technology, microelectronics, computer technology, information technology, and the circuit breaker itself and its operating mechanisms. It requires significant investment and development. However, it is foreseeable that as the challenges of intelligentization are overcome one by one, high-performance intelligent circuit breakers will soon become commonplace and widely appreciated.