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What is a circuit breaker

qianjia | 13/07/2021

Everyone should be familiar with the circuit breaker. It plays a great role in the safety of a family. There are many types of circuit breakers, the different installation locations, and the function of installation all involve the choice of circuit breakers.

Meaning of circuit breaker

Circuit breaker refers to a switching device that can close, carry and break current under normal circuit conditions and can close, carry and break 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 division of high and low voltage is relatively fuzzy. Generally, those above 3kV are called high-voltage electrical appliances.

Circuit breakers can be used to distribute electrical energy, start asynchronous motors infrequently, and protect power lines and motors. They can automatically cut off the circuit when they experience serious overload, short circuit, and undervoltage faults. Its function is equivalent to a fuse switch Combination with overheating and underheating relays, etc. Moreover, it is generally not necessary to change parts after breaking the fault current. 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 widely used electrical appliances.

Basic principle of circuit breaker

When the power strip is short-circuited, the short-circuit current flows through the faulty power strip, through the cable wires, and of course also the switching appliances, and cause electrical fires. In an emergency, we certainly expect a certain circuit of switching equipment (circuit breaker) to perform protection tripping. After a short period of time, a main switch circuit breaker performs trip protection.

But after the circuit breaker completes the protection, can we close it and continue to supply power to us? What's the knowledge in this?

When the normal operating current flows through the circuit breaker, as time goes by, the protection and control device in the circuit breaker detects little heat generation. If the heat generation threshold limit value is not exceeded, the circuit breaker will of course not perform a trip operation; When an abnormally large current flows through the circuit breaker, the protection and monitoring device in the circuit breaker detects a large amount of heat generation. If the heat generation threshold is exceeded, the circuit breaker performs a trip operation.

The threshold here refers to the protection setting value of the circuit breaker.

We call the abnormal large current flowing in the circuit breaker an overcurrent. Overcurrent includes overload current and short-circuit current.

In other words, the greater the overcurrent, the shorter the circuit breaker action time, and the faster it performs line protection. This feature has a proper term, called the inverse time protection feature of the circuit breaker.

Now, let's take a bit of mathematics and see what is called inverse time characteristic.

Let’s look at the two power functions Y=K/X and Y=K/X2. Here, let K=1,

We can immediately think: if the ordinate Y is the action time t of the circuit breaker, and the abscissa X is the multiplier nIe of the rated current of the circuit breaker (n is the multiplier, Ie is the rated current of the circuit breaker), we can open the circuit The device performs line protection operation according to the protection mode that the larger the current, the faster the action time.

In fact, the protection operation of the circuit breaker is carried out according to this principle. The corresponding curve is called the inverse time protection characteristic curve of the circuit breaker.

This is the circuit protection characteristic curve of the circuit breaker. We see that the overload protection characteristics t=f(I) and Y=f(1/X) are so similar, in fact, they are the same kind of functional relationship.

Circuit breaker installation method

Wiring mode behind the board: The biggest feature of the wiring behind the board is that the circuit breaker can be replaced or repaired without rewiring, just disconnect the front-level power supply. Due to the special structure, the product has been equipped with special mounting plates and mounting screws and wiring screws according to the design requirements when leaving the factory. Special attention should be paid to the fact that the reliability of the large-capacity circuit breaker will directly affect the normal use of the circuit breaker, so during installation It must be taken seriously and installed strictly according to the requirements of the manufacturer.

Plug-in wiring: On the installation board of the complete set, install a circuit breaker mounting seat first, with 6 plugs on the mounting seat, and 6 sockets on the circuit breaker connection board. There are connecting plates on the surface of the mounting base or bolts behind the mounting base, and the mounting base is pre-connected with power cords and load lines. When in use, insert the circuit breaker directly into the mounting base. If the circuit breaker is broken, just pull out the broken one and replace it with a good one. Its replacement time is shorter than the front and back wiring of the board, and it is convenient. A certain amount of manpower is required for plugging and unplugging. Therefore, for China's plug-in products, the frame current is limited to a maximum of 400A. This saves maintenance and replacement time. When installing the plug-in circuit breaker, check whether the plug of the circuit breaker is tightly pressed, and securely fasten the circuit breaker to reduce contact resistance and improve reliability.

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