The Working Principle of a Circuit Breaker

A circuit breaker typically consists of a contact system, an arc-extinguishing system, an operating mechanism, a trip unit, and an enclosure.

In the event of a short circuit, the magnetic field generated by the massive current (typically 10 to 12 times the rated value) overcomes the force of a counter-spring; the trip unit then actuates the operating mechanism, causing the switch to trip instantaneously. During an overload condition, the increased current intensifies thermal heating; a bimetallic strip deforms to a specific extent, thereby triggering the operating mechanism (the higher the current, the shorter the response time).

There are also electronic-type circuit breakers, which utilize current transformers to sample the current magnitude in each phase. By comparing these values ​​against a preset threshold, a microprocessor detects current anomalies and issues a signal, prompting the electronic trip unit to actuate the operating mechanism.

The primary functions of a circuit breaker are to connect and disconnect load circuits, as well as to interrupt fault circuits, thereby preventing the escalation of accidents and ensuring safe operation. High-voltage circuit breakers, in particular, are required to interrupt arcs involving voltages of 1500 V and currents ranging from 1500 to 2000 A-arcs that can stretch up to 2 meters in length yet continue to burn without extinguishing. Consequently, the effective extinguishing of such arcs constitutes a critical challenge that high-voltage circuit breakers must successfully address.