Circuit breaker is one of the mechanical devices. You may not have heard of circuit breakers often. Therefore, in order to introduce circuit breakers to you, this article will explain the basic knowledge of circuit breakers and the working principle of circuit breakers.

What is a circuit breaker ?

First, let's take a look at the basic concept of circuit breakers.

A circuit breaker refers to a switching device that can close, carry and break the current under normal circuit conditions and can close, carry and break the current under abnormal circuit conditions within a specified time. Circuit breakers are divided into high-voltage circuit breakers and low-voltage circuit breakers according to their scope of use. The boundary between high and low voltage is relatively vague. Generally, those above 3kV are called high-voltage electrical appliances.

Circuit breakers can be used to distribute electrical energy, start asynchronous motors infrequently, protect power lines and motors, etc., and automatically cut off the circuit when they are seriously overloaded or short-circuited or undervoltage. Its function is equivalent to the combination of fuse switches and overheating relays. And after breaking the fault current, there is generally no need to change the components. At present, it has been widely used.

In the generation, transmission and use of electricity, power distribution is an extremely important link. The power distribution system includes transformers and various high and low voltage electrical equipment, and low-voltage circuit breakers are a kind of electrical appliances with a large number of uses.

Working principle of circuit breakers

Through the above introduction, I believe everyone has a basic understanding of circuit breakers. However, do you understand the working principle of circuit breakers? If you are not very familiar with the working principle of circuit breakers, you can find the answer in this part.

Circuit breakers are generally composed of contact systems, arc extinguishing systems, operating mechanisms, trippers, shells, etc.

When short-circuited, the magnetic field generated by the large current (generally 10 to 12 times) overcomes the reaction spring, the release pulls the operating mechanism to operate, and the switch trips instantly. When overloaded, the current becomes larger, the heat generation intensifies, and the bimetallic strip deforms to a certain extent to drive the mechanism to operate (the larger the current, the shorter the operation time).

There are electronic types, which use mutual inductors to collect the current size of each phase and compare it with the set value. When the current is abnormal, the microprocessor sends a signal to make the electronic release drive the operating mechanism to operate.

The function of the circuit breaker is to cut off and connect the load circuit, as well as to cut off the fault circuit, prevent the accident from expanding, and ensure safe operation. The high-voltage circuit breaker must break the arc of 1500V and the current of 1500-2000A. These arcs can be stretched to 2m and continue to burn without extinguishing. Therefore, arc extinguishing is a problem that must be solved for high-voltage circuit breakers.

The principle of arc blowing and arc extinguishing is mainly to cool the arc and weaken the thermal ionization. On the other hand, the arc is stretched by blowing to strengthen the recombination and diffusion of charged particles, and the charged particles in the arc gap are blown away at the same time, quickly restoring the dielectric strength of the medium.

Low-voltage circuit breakers are also called automatic air switches. They can be used to connect and disconnect load circuits, and can also be used to control motors that are not frequently started. Its function is equivalent to the sum of some or all functions of electrical appliances such as knife switches, overcurrent relays, undervoltage relays, thermal relays and leakage protectors. It is an important protective electrical appliance in low-voltage distribution networks.

Low-voltage circuit breakers have multiple 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. Structure and working principle Low-voltage circuit breakers are composed of operating mechanisms, contacts, protection devices (various trippers), arc extinguishing systems, etc.

The main contacts of low-voltage circuit breakers are closed manually or electrically. After the main contacts are closed, the free tripping mechanism locks the main contacts 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, and 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 tripping mechanism to operate and the main contacts to disconnect the main circuit. When the circuit is overloaded, the thermal element of the thermal release heats up and bends the bimetallic strip, pushing the free tripping mechanism to operate. When the circuit is undervoltage, the armature of the undervoltage release is released. The free tripping mechanism is also activated. The shunt release is used for remote control. During normal operation, its coil is de-energized. When distance control is required, press the start button to energize the coil.