Ultrafast Hybrid Electromagnetic Actuator for Air Circuit Breaker in DC Traction System

Air circuit breakers (ACBs) are widely used in the dc traction power supply system to interrupt fault current. To trip ACB rapidly, over-current tripping device (OCTD) and Thomson-coil actuator (TCA) are configured in ACB. However, the response time of OCTD is strongly affected by the fault current and it might be too long for remote or high-resistant faults. To cover the shortcoming of OCTD under these faults, TCA is configured additionally, resulting in extra mechanical devices and increased risks of mechanical failure. To solve the problems of OCTD and TCA, a novel ultrafast hybrid electromagnetic actuator (UHEA) is proposed in this article. The proposed UHEA is to add an auxiliary winding (AW) wrapped on the conventional OCTD, with AW connected to a precharged capacitor through thyristors. By using multiple thyristors to control the discharge of capacitor through AW, fast tripping of ACB can be obtained under random faults. Advantages of the proposed UHEA are: its response time is only −2 ms, faster than existing tripping devices by at least 36%, and is hardly affected by fault current, showing low dispersion of response time; it can replace OCTD and TCA inside ACB, simplifying actuators and reducing risks of mechanical failure.