Functional Requirements for Ultrafast Thomson Coil Actuator in Arc Commutation Hybrid DC Circuit Breaker

Hybrid DC circuit breakers featuring an ultrafast Thomson coil actuator are a key technology for enabling envisioned medium voltage DC grids. Particularly, the design of the actuator is considered challenging and has therefore been addressed in research for more than 20 years. These investigations have focused on actuators in conjunction with current injection type DC circuit breakers. However, these results cannot be transferred to arc commutation hybrid DC circuit breakers. For this breaker topology, the interaction between actuator parameters and breaker performance is not well understood, yet it is essential in order to define functional requirements for the actuator. This paper provides the first investigation of this interaction, by integrating an analysis of the commutation process into the design consideration. New insights regarding the contact separation time of the actuator and its implications to the overall circuit breaker performance are presented. Resulting feasible operating regions of the actuator are established—combining requirements to contact separation time and average velocity—and it is discussed how these are influenced by different fault current scenarios, grid voltages and relay times. Through a demonstration case, we exemplify that an optimal actuator design features a trade-off between velocity and contact separation time.