In the era of modern industrial civilization, circuit breakers have become one of the most essential electrical protection devices, playing a crucial role in both industrial and household applications. When the current flowing through the wiring exceeds safe limits, this simple yet effective device automatically cuts off the power supply until the fault is resolved. Without circuit breakers, electrical faults and equipment malfunctions could easily lead to dangerous situations such as electrical fires, making daily electricity usage not only inconvenient but also risky. This article aims to provide you with a comprehensive overview of circuit breakers, starting with their fundamental working principles.
Circuit breakers function primarily by either electrically or manually closing the main contacts. To better understand how they operate, let’s explore the working principle based on different operational states of the circuit breaker.
Under normal operating conditions, the circuit is connected, meaning the main contacts are closed, and the free-tripping mechanism locks them in place. At this stage, the overcurrent release coil and the thermal element of the thermal release are connected in series with the main circuit, while the under-voltage release coil is connected in parallel with the power supply.
When a short circuit or severe overload occurs, the armature of the overcurrent release is activated, triggering the free-tripping mechanism to open the main contacts and disconnect the circuit. In the case of an overload, the thermal element heats up, causing the bimetallic strip to bend and push the free-tripping mechanism into action, thereby breaking the circuit.
During a low-voltage condition, the armature of the under-voltage release is released, which also activates the free-tripping mechanism. For long-distance control operations, a shunt release is typically used. Under normal conditions, the release coil remains de-energized. However, when remote control is initiated, pressing the start button energizes the coil, allowing the armature to move and trigger the free-tripping mechanism, thus opening the main contacts and cutting off the power supply.
[Image: A schematic diagram illustrating the internal components of a circuit breaker.]
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