A circuit breaker is a device used to protect circuits from damage caused by overcurrent, overload, and short circuits. The electromechanical circuit breaker (EMB), recognized as a standard component in the industry, consists of two independent triggering devices: one is a bimetallic strip, which has a slower response speed and triggers the trip upon overcurrent; the other is an electromagnetic device, which has a faster response speed and initiates the trip upon a short circuit. EMB has a preset trip current (usually a fixed value) and possesses two characteristics: instantaneous trip (electromagnetic triggering) and delayed trip (thermal triggering/bimetallic strip triggering), which can safely and reliably handle short circuits and overload situations.
Although the EMB structure is simple and the effect is reliable, it still has some drawbacks. The first one is the speed issue. The action time of the EMB is at the millisecond level, during which the fault current may still cause equipment damage and even harm to personnel. The second one is the arc problem. When the contacts separate, an arc will be generated, and it is necessary to safely dissipate the arc energy. However, this process will bring thermal stress and mechanical stress to the circuit breaker.
Replacing mechanical contacts with semiconductor switches can completely eliminate arcs, as the current interruption is accomplished electronically before the physical contacts separate. Semiconductor switches can be turned off within microseconds, significantly reducing the peak current of short circuits. Moreover, unlike mechanical components, semiconductor switches are specifically designed for high-frequency operation and do not age over time. Devices using semiconductor switches are called solid-state circuit breakers (SSCB) and are typically used to protect DC circuits and AC circuits.
