566 / 2017-05-14 19:18:18

Research on Integrated Design of Vacuum Switch Based on Permanent Magnetic Actuator for Hybrid DC Contactor

hybrid DC contactor,railway traction system,Permanent Magnetic actuator,vacuum switch,FEA and multibody dynamics analysis,integrated design

The hybrid DC contactor is essential in the railway traction system because of its advantages including arcless interruption and low line loss, which is able to enhance the reliability and safety of the whole system. This paper focused on the fast mechanical switch applied in hybrid DC switch to conduct steady-state operating current. An integrated design of vacuum switch based on Permanent Magnetic (PM) actuator is proposed. In this design, the stainless steel bellows within conventional vacuum switch, which connected vacuum chamber to moving terminal, is removed to avoid vacuum failure caused by air leakage and eliminate restriction of bellows’ fatigue life. Besides, both monostable structure and springs’ position can contribute to achieve smaller size. Thus, a mechanical switch with strong compactness, high reliability and low maintenance is obtained. The mechanical switch also is demanded to be as fast as possible to reduce the total interruption time of the hybrid DC switch. In this paper, firstly, a 2kV hybrid DC switch topology based on current commutation is briefly introduced. It consists of mechanical switch, solid-state switch, passive RCD circuits for snubber and MOV for energy absorption, as shown in Fig. 1. Secondly, designed schematic and operation principle of integrated switch is discussed. Proposed vacuum switch is given in Fig. 2, including a monostable PM actuator. Permanent magnets are imbedded in a yoke. Single coil controlled by external circuit with 110V DC source for closing or opening operation is located above permanent magnets. And opening spring is designed to provide holding force at the opening position while contact spring is set inside to ensure sufficient contact and reduce the possibility of rebouncing. The movable contact is directly driven by an armature through a pole contained an insulator and two springs. The maximum contact distance is 3mm and over-traveling distance is 1mm. Then, an enclosure vacuumized inside covers the entire actuator including contact parts. The size of this mechanical switch is 7 cm in diameter and 10 cm in height. Thirdly, FEA and multibody dynamics analysis methods are applied to analyze static and dynamic characteristics of the PM actuator. The magnetic flux line distribution of PM actuator and the movable contact displacement curve during an opening operation have been obtained by simulation, which indicates that the average velocity of movable contact meets requirements of 2kV vacuum interrupter theoretically. Finally, prototype is developed according to the calculated results and experiments are carried out to verify the simulation results in the full-text. As for contactor with frequent operation, the tests of mechanical life and electrical life can be conducted respectively. All experimental results prove that proposed mechanical switch is able to provide fast protection and satisfy requirement of hybrid DC contactor.