Magnetic Circuit Analysis and Calculation of Permanent Magnetic Actuator of Vacuum Circuit Breaker
Since the first vacuum circuit breaker was successfully developed by U.S. GE in 1961, the technical level of vacuum circuit breakers has rapidly increased. Vacuum circuit breakers are increasingly used in power systems as a switching element for controlling and distributing electrical energy. The pressure field maintains its leading position. Vacuum circuit breaker technology has been improved in terms of capacity, voltage, intelligence, and miniaturization. The secondary technology of vacuum circuit breakers has shifted from traditional technology to modern integrated technologies featuring microelectronics, new materials, computer control, servo drives and precision machinery. The rapid development of vacuum circuit breakers lies in its excellent vacuum arc extinguishing performance. Its mechanical life span has increased from the traditional 2,000 times to several tens of thousands. Therefore, the mechanical life and reliability of the operating mechanism matched with it become The more prominent problem is that the use of traditional circuit breaker operating mechanisms to drive vacuum circuit breakers is obviously difficult to demonstrate its advantages of high lifetime and reliability. Therefore, a highly simplified, energy-saving, and highly reliable mechanism is required to satisfy the vacuum circuit breakers. Drive requirements. In recent years, the magnetic properties of rare earth permanent magnetic materials have developed rapidly. China is a big producer of NdFeB. Increasing the added value of permanent magnetic materials is the common wish of the majority of permanent magnet technology workers. In this paper, some theoretical and computational problems of permanent magnetic materials applied to vacuum circuit breakers are analyzed and discussed. Through the magnetic conductance calculation and magnetic network analysis methods, the equivalent magnetic circuit of the permanent magnet operating mechanism of vacuum circuit breakers is analyzed. A corresponding mathematical model was constructed to provide an engineering solution for the further development of designing a vacuum circuit breaker permanent magnet actuator. 2 Working principle The working principle of the permanent magnet operating mechanism of the vacuum circuit breaker is as shown. It has a permanent magnet (2), an opening (1), and a closing control coil (5). This kind of permanent magnet mechanism is based on the advantages of the spring mechanism and the traditional electromagnetic mechanism, and overcomes its shortcomings. It replaces the traditional locking device with the magnet (2), so that the vacuum circuit breaker is closed and the position is maintained by the permanent magnet (2 ) to achieve, without the use of electromagnetic coils to provide retention. The role of the electromagnetic coil is only used for the switching of the switch. After the closing control coil (5) is energized, it moves the moving core (4) downward and the magnetic force generated by the magnet is kept in the closing position; when the opening control coil (1) is energized, the moving core (4) is in the opposite direction. Movement, also by the magnetic force generated by the magnet to keep it in another working position, that is, the opening position, that is, when the control coil does not pass current, its moving core has two stable working states, closing and opening, also known as double Steady-state electromagnetic mechanism. 3 Based on the analysis of the equivalent magnetic circuit, the magnetic circuit of the permanent magnet operating mechanism is analyzed. The 3* magnets; 4* iron cores; 5-closed coils are symmetrical about the magnetic circuit to obtain the equivalent magnetic circuit on the left side of the mechanism, as shown. In this magnetic circuit, the magnetomotive force Fm of the permanent magnets separates a transient magnetic potential of the gate coil/transient current at a certain moment. Like the circuit, the magnetic circuit can also use the loop method to solve the magnetic circuit equation, so the magnetic circuit equation is: the left equivalent magnetic circuit of the permanent magnet operating mechanism Gfl*- is the core magnetic flux of the upper and lower two; G middle magnetic Road magnetic conductance; å¦ Left upper magnetic circuit flux: Nine lower left magnetic flux; *- Middle magnetic flux; Fu upper magnetic flux: F, lower magnetic flux. If the magnetic path and magnetic motive force of the magnetic circuit are known, then by substituting, the moving iron core (breaking position) and the upper end yoke constitute a magnetic circuit with a small magnetic resistance against the magnetic field of the permanent magnet, and vice versa. The air gap at the lower end of the core is high and the magnetic resistance is high. Therefore, the magnetic flux passes almost entirely through the upper end of the moving iron core. In this part, the magnetic flux density is concentrated, the magnetic field suction reaches the maximum, and a large holding force is formed. At this time, the holding force can reliably ensure that the iron core is in a stable open state. When the position of the iron core is at -6.5 mm (the extreme limit position at the lower end), the magnetic field of the permanent magnet constitutes a magnetic circuit with a small magnetic resistance, and the iron core is in a stable closing state. . Because the electromagnetic attraction test of the moving core during the movement is more complicated, we have shown that the above-mentioned calculation results are basically consistent with the measured values ​​through the electromagnetic suction tests of the two extreme positions, so as to verify that the calculation method described in this paper can be directly applied in engineering. . 6 Conclusion In conclusion, the magnetic network model algorithm of the permanent magnet operating mechanism is a method between numerical calculation (finite element) and classical analysis. All three methods have their own characteristics. The magnetic network model method can be used as an engineering algorithm. It is characterized by a small amount of calculation, fast iteration and convergence, and this method can be used as a primary selection tool when selecting a solution. This paper uses the magnetic network model method to analyze the equivalent magnetic circuit of the permanent magnet operating mechanism of the vacuum circuit breaker as a basic analysis model of the engineering magnetic circuit design of the permanent magnet mechanism. Using the corresponding analysis results, the bistable permanent magnet is programmed. The equivalent static magnetic circuit calculation software of the operating mechanism calculates (or checks) the static magnetic attraction force and holding force at the static state. The calculated result is consistent with the test result. It is the design of the vacuum circuit breaker permanent-magnet operating mechanism designer when selecting the optimal solution. , provides a solution. The permanent magnet mechanism can generally use the finite element method for accurate calculation. However, due to the above characteristics, the magnetic network model analysis method is suitable for engineering and technical personnel as a tool for design selection and verification. The engineering design of the permanent magnet mechanism still needs in-depth work: in combination with the structure of the vacuum circuit breaker, the quality of the moving parts and the role of the external force, further application of the analysis results of this paper and the established mathematical model as a magnetic circuit for the vacuum interrupter The basis for the calculation of the road parameters, thus completing the engineering task of designing the vacuum circuit breaker permanent magnet operating mechanism. The magnetic network model algorithm used in this paper achieves the purpose of improving the development efficiency and saving the design cost in the actual use of the enterprise. 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