Circuit breaker refers to the switch device that can close, carry and open the current under the normal circuit condition and under the abnormal circuit condition within the specified time.
The circuit breaker can be divided into high-voltage circuit breaker and low-voltage circuit breaker according to its scope of use. Generally if more than 3KV it is called high-voltage electrical appliances. The function of the circuit breaker is to cut off and connect the load circuit and the fault circuit, so as to prevent the accident from expanding and ensure the safe operation.
The simplest circuit protector is a fuse. The purpose of fuse design is to disintegrate when it is heated to a certain degree or above. It can only work once. When every time it is burnt, it must be replaced with a new one. A circuit breaker and a fuse do the same thing. When the current goes up to an unsafe level, it breaks the circuit. But it can be used repeatedly.
The circuit breaker is generally composed of contact system, arc extinguishing system, operating mechanism, release, shell, etc. The basic circuit breaker consists of a simple switch connected to a bimetal or electromagnet.
Electricity magnetizes the electromagnet (See how it works and find out why). Increasing the current will enhance the magnetic force of the electromagnet, and decreasing the current will reduce the magnetic force. When the current jumps to an unsafe level, the electromagnet is strong enough to pull down the metal rod connected to the switch link. The entire linkage moves so that the moving contact deviates from the fixed contact, thus disconnecting the circuit.
In case of short circuit, the magnetic field generated by high current (generally 10-12 times) overcomes the reaction spring. The release pulls the operating mechanism to act, and the switch trips instantaneously. When the overload occurs, the current becomes larger, the heat generation is intensified, and the bimetallic sheet deforms to a certain extent to push the mechanism action (If the greater the current is, the shorter the action time is).
If there is electronic type, use mutual inductor to collect the current of each phase, and compare with the set value. When the current is abnormal, the microprocessor will send a signal to make the electronic release drive the operation mechanism.
The high-voltage circuit breaker shall open 1500V arc with current of 1500-2000A, which can be stretched to 2M and still burn continuously. Therefore, arc extinguishing is a problem that must be solved for high voltage circuit breakers.
Low voltage circuit breakers, also known as automatic air switches, can be used to turn on and off load circuits, or to control infrequent starting motors. Its function is equivalent to closing switch, which is an important protective device in low-voltage distribution network. Low voltage circuit breaker is widely used because of its multiple protection functions, convenient operation and safety etc. The main contact of LV circuit breaker is closed by manual operation or electric operation. When the circuit is short circuited or seriously overloaded, the armature of the over-current release is engaged to make the free release mechanism act and the main contact disconnects the main circuit.