What Are The Working Principles Of Circuit Breakers?

Circuit breakers are generally composed of contact systems, arc extinguishing systems, operating mechanisms, releases, casings, etc.
When there is a short circuit, the magnetic field generated by the high current (usually 10 to 12 times) overcomes the counter force spring, and the release device pulls the operating mechanism, causing the switch to trip instantaneously. When overloaded, the current increases, the heat generation intensifies, and the bimetallic sheet deforms to a certain extent, pushing the mechanism to operate (the larger the current, the shorter the action time).

There is an electronic type, which uses a transformer to collect the current magnitude of each phase, compares it with the set value, and when the current is abnormal, the microprocessor sends a signal, causing the electronic release to drive the operating mechanism to act.
The function of a circuit breaker is to cut off and connect the load circuit, as well as cut off the faulty circuit, to prevent accidents from expanding and ensure safe operation. The high-voltage circuit breaker needs to break the 1500V arc with a current of 1500-2000A, which can be extended to 2m and 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 ionization. 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 electrical appliances such as knife switches, overcurrent relays, voltage loss relays, thermal relays, and leakage protectors. It is an important protective device in low-voltage distribution networks.

Low voltage circuit breakers have various protection functions (overload, short circuit, undervoltage protection, etc.), adjustable operating 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), and an arc extinguishing system.

The main contact of a low-voltage circuit breaker is 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 is attracted, causing the free release mechanism to operate and the main contact to disconnect the main circuit. When the circuit is overloaded, the thermal element of the thermal release heats up, causing the bimetallic sheet to bend and pushing the free release mechanism to operate. When the circuit is under voltage, the armature of the undervoltage release is released. It also enables 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 required, press the start button to turn on the coil.