Circuit breaker is a switching device which can close, load and break the current under normal circuit conditions, and can carry and break the current under abnormal circuit conditions (including short circuit conditions) within a specified time. China Circuit Breaker can be used to distribute electric energy, start asynchronous motors infrequently, protect power lines and motors, and automatically cut off circuits when they have serious overload or short-circuit or under-voltage faults. Their functions are equivalent to the combination of fuse switches and over-heated relays. And after breaking the fault current, there is no need to change parts. At present, it has been widely applied.

Circuit breakers are generally made up of contact system, arc extinguishing system, operation mechanism, release, shell and so on. China Circuit Breaker is divided into miniature circuit breakers, moulded case circuit breakers and frame type circuit breakers according to their structures.

Function of circuit breaker

Cut off and turn on the load circuit, and cut off the fault circuit to prevent accidents from expanding and ensure safe operation. The high-voltage circuit breaker to break 1500V, current 1500-2000A arcs, these arcs can be extended to 2m still burning non-extinguishing. Therefore, arc extinguishing is a problem that must be solved by high voltage circuit breaker.

Low-voltage circuit breakers, also known as automatic air switches, can be used to switch on and off the load circuit, but also can be used to control the motor starting infrequently. Its function is equivalent to the sum of some or all of the functions of the switch, overcurrent relay, Voltage-loss relay, thermal relay and leakage protector. LV circuit breaker is an important protective device in low-voltage distribution network.

LV circuit breaker has a variety of protection functions (overload, short circuit, under-voltage protection, etc.), adjustable operating value, high breaking capacity, easy operation, safety and other advantages, so it is widely used. The structure and working principle of low voltage circuit breaker are composed of operating mechanism, contacts, protective devices (various release devices), arc extinguishing system, etc.

Working principle of circuit breaker

When a short circuit occurs, the magnetic field generated by a large current (usually 10 to 12 times) overcomes the reaction spring, the release pulls the operating mechanism, and the switch instantaneously trips.

When the overload occurs, the electrorheological (ER) becomes larger, the calorific value increases, and the bimetal sheet deforms to a certain extent to promote the action of the mechanism (the greater the current, the shorter the action time).

The main contacts of LV circuit breaker are operated by manual operation or by electric switching. After the main contact is closed, the free tripping mechanism locks the main contact on the closing position. The coil of the overcurrent release and the thermal element of the thermal release are in series with the main circuit, and the coil and the power supply of the undervoltage release are in parallel. When the circuit is short-circuited or seriously overloaded, the armature of the over-current release closes and the free release mechanism acts, and the main contact disconnects the main circuit. When the circuit is overloaded, the heat element of the thermal release causes the bimetal sheet to bend and pushes the free release mechanism to move. When the circuit is under voltage, the armature of the undervoltage release is released. China Circuit Breaker also enables the free tripping mechanism to act. Split-excitation tripper is used for long-distance control. In normal operation, its coil is power-off. When distance control is needed, press the start button to make the coil energized and the armature drives the free tripping mechanism to disconnect the main contact.

Now there are electronic, using the transformer to collect the magnitude of each phase current, compared with the set value, when the current is abnormal, the microprocessor signals, so that the electronic release drive the operation mechanism.