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Working principle of circuit breaker


Circuit breakers are generally composed of contact systems, arc extinguishing systems, operating mechanisms, releases, enclosures, etc.

When there is a short circuit, the magnetic field generated by the large current (usually 10 to 12 times) overcomes the reaction spring, the release pulls the operating mechanism, and the switch trips instantaneously. When the overload occurs, the current becomes larger, the heat generation intensifies, and the Bimetal deforms to a certain extent to push the mechanism to act (the greater the current, the shorter the action time).

There is an electronic type, which uses a transformer to collect the current of each phase and compare it with the set value. When the current is abnormal, the microprocessor sends a signal, causing the electronic release to drive the operating mechanism to operate.

The function of a circuit breaker is to cut off and connect load circuits, as well as cut off faulty circuits, to prevent accidents from expanding and ensure safe operation. The high-voltage circuit breaker needs to break 1500V, with an arc current of 1500-2000A, which can be stretched to 2m and still continue to burn without extinguishing. Therefore, arc extinguishing is a problem that high-voltage circuit breakers must solve.

The principle of arc blowing and extinguishing is mainly to cool the arc and reduce thermal dissociation. On the other hand, by blowing and elongating the arc, the recombination and diffusion of charged particles are strengthened. At the same time, the charged particles in the arc gap are blown away, quickly restoring the insulation strength of the medium.

Low voltage circuit breakers, also known as automatic air switches, can be used to connect and disconnect load circuits, as well as to control infrequently started motors. Its function is equivalent to the sum of some or all functions of knife switch, overcurrent relay, voltage loss relay, thermal relay, Residual-current device and other electrical appliances. It is an important protective appliance in low-voltage distribution network.

Low voltage circuit breakers have various protection functions (overload, short circuit, undervoltage protection, etc.), adjustable action values, high breaking capacity, convenient operation, safety, and other advantages, so they are widely used. The structure and working principle of a low-voltage circuit breaker are composed of an operating mechanism, contacts, protective devices (various releases), arc extinguishing systems, etc.

The main contacts of low-voltage circuit breakers are manually operated or electrically closed. After the main contact is closed, the free release mechanism locks the main contact in the closed position. The coil of the overcurrent release and the thermal element of the thermal release are connected in series with the main circuit, while the coil of the undervoltage release is connected in parallel with the power supply. When a short circuit or severe overload occurs in the circuit, the armature of the overcurrent release engages, causing the free release mechanism to operate and the main contact to disconnect the main circuit. When the circuit is overloaded, the heating of the thermal element of the thermal release makes the Bimetal bend upward and pushes the free release mechanism to act. When the circuit is under voltage, the armature of the undervoltage release is released. It also causes the free release mechanism to operate. The shunt release is used for remote control. During normal operation, its coil is powered off. When distance control is needed, press the start button to turn on the coil.

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