Piezoelectric Actuation in MCBs
A novel contact opening mechanism has been developed using a piezoelectric actuator to open the contacts in a low contact opening velocity circuit breaker. The arc control on the contacts is critical for a successful current interruption 10,000-100,000 A. in low voltage 250 Volts devices. Previous work has shown how arc root commutation from the contact region into the arc chamber is affected by arc chamber materials, contact materials and the gasp behind the moving contact for contact velocity between 1 meter per second to 10 meters per second. This work in extended using a commercially available piezoelectric actuator to open the contacts. Contact opening speeds are assessed and the arc root mobility is characterized under this operating regime. a flexible test apparatus and solid state high speed arc imaging system are used to gather data on the arc root during the opening of the contacts. New experimental results are presented on the anode and cathode root velocity and arc root motion in an arc chamber with piezoelectric actuated contact opening. These results can be used to improve the design of high current low voltage circuit breakers suitable for piezoelectric actuation.
In a circuit breaker, the actuator would be coupled to a mechanism and this will play a large part in the dynamics of the system. To design the mechanism and predict its performance, the actuator can be built into a complete system model as a mass spring system. The piezoelectric actuator described here has sufficient movement to open directly a set of contacts. However, the contact velocity is below that normally required for effective current limitation. However, recent research has shown that it may be possible to improve arc control to an extent that it may be possible to obtain effective arc control with contact velocities of the order of 1 ms . This could permit direct actuation using a piezoelectric actuator. The stroke of the actuator studied here is in the right order of magnitude for a contact system, but marginal for a short circuit device. The force from the actuator would also be insufficient for direct contact action. Force and displacement can be improved preferably by improving the performance of the actuator but also by using the actuator as an intermediate stage in the mechanism. The discrepancy between the actuator performance and the requirements of the contact system needs to be minimized to provide the simplest mechanical system.