Design And Optimization Analysis Of10kV High-speed Circuit Breakers

In recent years, power quality is increasingly demanded with the rapid development of Chinese power industry. Circuit breakers are the most important control and protection devices in power system, and the operating time and reliability of circuit breakers have become more stringent. Among them, high speed mechanical switch is gradually becoming a research hotspot in power systems, for its fast switching speed, large conduction flow, etc.Repulsion mechanism has the advantage of short excitation time and high starting speed. But the duration of repulsion force is short, and the output power decreases obviously with the stroke between the contacts increases. While, permanent magnetic actuator (PMA) has good holding characteristics at the opening and closing position of the actuator, but the moving reaction is much slower. Based on their advantages and disadvantages, this paper put forward a novel high speed actuator, in which repulsion mechanism is in charge of driving the rapid opening, while PMA is used for closing and holding force.In previous researches, the optimal design of high speed mechanism switches focused on the coil plate and the discharging circuit, including the size of the coil, the distance between coil plates, voltage of the discharging capacitor, capacitance, etc. In this paper, a two-dimensional static and dynamic finite element model of10kV mechanical switch is established in ANSOFT. The material and structure of coil frame and the enclosure of repulsion mechanism are found to have a great impact on the efficiency of repulsion mechanism. In the optimization analysis of repulsion mechanism, a more efficient coil-to-coil repulsion structure is proposed, instead of the traditional coil-to-copper structure. A hybrid structure of coil frame is designed in the form of iron and epoxy coil skeleton. These designs can effectively improve the efficiency of repulsion mechanism, which helps opening the switch rapidly. In the optimization analysis of PMA, the holding force of the actuator is found to be significant for moving bounces. The closing speed of the actuator can be increased by reducing the excitation time of coil, rather than sacrificing the holding force of PMA, which means reducing the turns and diameter to increase the closing speed.Based on finite element analysis and simulation of the actuator, the prototype10kV vacuum circuit breaker was manufactured, and the simulation results were verified by experiments. Moreover, due to the pulse characteristics of repulsion mechanism, two assistant opening methods are used to ensure the reliability of opening process, which are opening spring and opening coil in PMA. These two methods are compared on10kV prototype. The results show that the switch is more reliable and much simpler by using assistant opening spring. The opening bounces of the actuator can be reduced by adding mechanical buffer devices or decreasing the voltage of discharging capacitor. This paper has provided a better guidance for the development of high-speed repulsion mechanism in10kV circuit breakers.