Research on Operating Mechanism for Ultra-Fast 40.5-kV Vacuum Switches

The continuous development of the voltage-source-converter-based multiterminal high-voltage direct-current transmission system has led to a great need for dc circuit breakers to isolate short-circuit faults in the dc side. The operating time of dc breakers is mainly dependent on the mechanical contacts separation time. In this paper, three key units of the ultra-fast operating mechanism, including drive unit, buffer unit, and holding unit were investigated. A prototype of the 40.5-kV ultra-fast vacuum switch has been developed where the Thomson-coil actuator (TCA) is used to fulfill the function of the drive unit and the buffer unit, and a bistable spring mechanism is used as the holding unit. The state equations of the bidirectional TCA used as the drive unit and buffer unit in the operating process are completed based on the equivalent circuit method and finite-element method. The experimental and simulation results of the prototype are compared and they are in good agreement as expected. Therefore, the mathematical model is verified. The factors that influence the drive unit and the buffer unit performances are discussed. The achieved operating time of the prototype is about 2.3 ms.