A fast mechanical switch for medium voltage hybrid DC and AC circuit breakers

The paper presents the design and experimental results of a Thomson coil based fast mechanical switch for hybrid AC and DC circuit breakers rated at 30 kV voltage and 630 A current. The compact design with optimized circuit parameters and geometric dimensions of components targets 2 mm travel within 1 ms when driven by a 2 mF capacitor bank pre-charged to 500 V. The use and design of a disc spring as the damping and holding mechanism is presented. Structural design of a complete switch assembly rather than just the actuator is given. Experimental results show that the switch can travel 1.3 mm in the first 1 ms, and 3.1 mm in the first 2 ms when driven by a 360 V 2 mF capacitor bank. Such fast mechanical switches facilitate hybrid circuit breaker interruptions within 2 or 3 milliseconds for ultra fast and highly efficient protections in 5–35 kV medium voltage DC as well as AC systems.