| Circuit breakers are one of the most important terminal equipments in power supply and distribution systems to ensure the normal separation of circuit breakers.The gate action is an effective way to improve the power supply quality and power supply reliability of the power grid.The opening and closing action of the circuit breaker is completed by the operating mechanism.The dynamic characteristics of the operating mechanism will directly affect the stability and reliability of the opening and closing action of the circuit breaker.The object of this paper is the monostable permanent magnet mechanism.The dynamic characteristics of the permanent magnet mechanism include the speed of the moving iron core,the displacement of the moving iron core,the coil current and the capacitor voltage,etc.During the movement of the moving iron core,the driving coil is driven.The back EMF will hinder the change of current,and the current is one of the important electrical parameters that affect the opening and closing action of the circuit breaker.Therefore,it is important to study the variation law of the back EMF and calculate the back EMF.Firstly,the article introduces the working principle of monostable and bistable permanent magnet mechanism in detail,compares the characteristics of two permanent magnet mechanisms,and analyzes the magnetic circuit of the permanent magnet mechanism in the state of closing and closing.Then the mathematical calculation model of the monostable permanent magnet mechanism under static magnetic field is described.The mathematical model is used to calculate the electromagnetic attraction of the moving iron core in Ansoft Maxwell,and the dynamic model of the permanent magnet mechanism is built under the transient magnetic field.And the reaction force is calculated,the dynamic characteristic curve of the opening and closing process is simulated by the built single steady-state permanent magnet mechanism,and the curves of coil current,equivalent inductance and moving core speed are analyzed,and the electric parameters are changed.The way to study the influence of different electrical parameters on the dynamic characteristics of permanent magnet mechanism.Then,for the external excitation circuit,the coil is equivalent to the nonlinear inductance and the back EMF.The back EMF in the coil is part of the system’s full flux induced electromotive force.The back electromotive force is separated by calculating the induced electromotive force of the coil.Based on the back-EMF calculation method of the relationship between the whole flux linkage and the electrical parameters,the two methods are used to calculate the back-EMF curve of the circuit breaker opening and closing process,and the variation law of the back-EMF curve and the dynamic characteristics of the permanent magnet mechanism are analyzed.Finally,the back potential curves obtained by different methods are compared,the error of the results is quantitatively analyzed,and the causes of the errors are analyzed.The feasibility and effectiveness of the two methods of back calculation are verified. |
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