The working principle of a circuit breaker is to automatically cut off the current when an overload or short circuit occurs, thereby protecting the line and equipment. This is achieved through internal thermal and magnetic tripping mechanisms.
Overload Protection (Thermal Trip): When the current exceeds the rated value for an extended period, the bimetallic strip heats up and bends, pushing the tripping mechanism to trip the switch. The action time is inversely proportional to the current magnitude (the larger the current, the faster the action).
Short Circuit Protection (Magnetic Trip): When a short circuit occurs, the current surges instantaneously. The electromagnetic coil generates a strong magnetic field, rapidly attracting the armature and impacting the tripping mechanism to achieve millisecond-level tripping.
Arc Extinguishing System: When a circuit breaker interrupts a large current, an electric arc is generated. The arc-extinguishing grid elongates, cools, and extinguishes the arc, preventing contact burnout.
Leakage Current Protection (e.g., with RCD function): Based on Kirchhoff's current law, it detects whether the current in the live wire and neutral wire is balanced. If a leakage current occurs (such as from an electric shock), and the residual current exceeds a threshold (typically 30mA), the trip unit will be triggered to quickly cut off the power.
Modern circuit breakers may also integrate an electronic control unit for more precise protection and remote monitoring functions.
