Fast operating moving coil actuator for a vacuum interrupter

Vacuum circuit breakers are the dominant technology in medium voltage distribution networks since they are environmentally friendly and maintenance free. It is a challenge to design an actuator for a vacuum circuit breaker, which achieves a high operating speed whilst maintaining high efficiency. A fast operating moving coil actuator for a vacuum interrupter (VI) has been developed. An analytical model of the actuator was initially developed and then simulated using a three-dimensional finite element (FE) model. The model showed that the opening force was higher than the closing force due to asymmetry in the structure of the actuator, which resulted in a reluctance force component. The complete operating actuator prototype was built to avoid known problems such as contact popping, bounce, rebound and welding. The magnetic field distribution and the static electromagnetic force on the moving coil were measured and provided a good correlation with the FE model simulation predications. The opening operation of the actuator prototype was compared for different capacitor supply voltages. A maximum velocity of 2.3 m/s was achieved when the capacitor was charged to 150 V. The actuator demonstrated successful operation at atmospheric pressure and also in a vacuum chamber. The opening time of the actuator in the vacuum was approximately 5 ms, compared to 5.5 ms at atmospheric pressure. We designed and built this actuator to illustrate that the moving coil actuator is capable to operate the vacuum circuit breaker quickly with high efficiency. Tests showed that further design optimizations for improving the operating speed and efficiency of the moving coil actuator are essential and the options have also been suggested.