Hello, everyone. Today I'd like to share with you about the fuse in power circuit protection. What's your understanding of fuse?

Basic introduction of fuse:

Fuse is also called current fuse, which is defined as "fuse link" in iec127 standard. It mainly plays the role of overload protection. If the fuse is correctly placed in the circuit, the fuse will fuse itself and cut off the current when the current abnormally rises to a certain height and heat, so as to protect the safe operation of the circuit.

The fuse invented by Edison more than 100 years ago was used to protect the expensive incandescent lamp at that time. With the development of the times, the fuse protects the power equipment from the injury of current overheating and avoids the serious injury caused by the internal failure of electronic equipment.

Definition of fuse

When the circuit breaks down or is abnormal, the current increases continuously, and the increased current may damage some important devices in the circuit, burn the circuit or even cause fire. If the fuse is correctly placed in the circuit, the fuse will fuse itself and cut off the current when the current abnormally rises to a certain height and heat, so as to protect the safe operation of the circuit.

Appearance of fuse

1. Filamentous. The fuse of the early primitive type is directly locked with screws, which is used for old switches and sockets of various sizes.

2. Sheet (bare sheet). It is more convenient to use than the old silk.

3. Glass tube. There are several different sizes, which are common in electronic products.

6.3 x 32 mm (diameter x length)

5 x 20 mm

4. Ceramic tube. There are several different shapes and sizes to avoid glass bursting.

5. Plastic sheet with metal sheet pin: Automobile fuse.

6. Surface mount element (SMD) type.

7. Cylindrical, plug-in type: directly welded to the circuit board, used inside the product.

Function and working principle

effect

The fuse invented by Edison more than 100 years ago is used to protect the expensive incandescent lamp at that time. With the development of the times, the fuse protects the electronic / power equipment from current / overheating injury and avoids serious injury caused by internal failure of electronic equipment.

working principle

When the current flows through the conductor, the conductor will heat up because there is a certain resistance in the conductor. And the calorific value follows this formula: q = i2rt; Where q is the calorific value, 0.24 is a constant, I is the current flowing through the conductor, R is the resistance of the conductor, and t is the time when the current flows through the conductor; According to this formula, it is not difficult to see the simple working principle of the fuse. When the material and shape of the fuse are determined, its resistance R is relatively determined (if its resistance temperature coefficient is not considered). When the current flows through it, it will generate heat, and its calorific value is increasing with the increase of time. The size of current and resistance determines the speed of heat generation, and the structure and installation condition of fuse determine the speed of heat dissipation. If the speed of heat generation is less than the speed of heat dissipation, the fuse will not blow. If the rate of heat generation is equal to the rate of heat dissipation, it will not fuse for a long time. If the rate of heat generation is greater than the rate of heat dissipation, more and more heat will be generated. Because it has a certain specific heat and mass, the increase of heat is reflected in the increase of temperature. When the temperature rises above the melting point of the fuse, the fuse will blow. This is how the fuse works. We should know from this principle that when designing and manufacturing fuses, you must carefully study the physical properties of your selected materials and ensure that they have consistent geometric dimensions. Because these factors play a vital role in whether the fuse can work normally. Similarly, when you use it, you must install it correctly.

Basic composition

The general fuse consists of three parts: one is the melt part, which is the core of the fuse. When fusing, it plays the role of cutting off the current. The melts of the same type and specification should have the same material, the same geometric size, the resistance value as small and consistent as possible. The most important thing is that the fusing characteristics should be consistent. Household fuses are usually made of lead antimony alloy; The second is the electrode part, which usually has two parts. It is an important part connecting the melt and the circuit. It must have good conductivity and should not produce obvious installation contact resistance; The third is the support part. The fuse melt is generally thin and soft. The function of the support is to fix the melt and make the three parts into a rigid whole, which is convenient for installation and use. It must have good mechanical strength, insulation, heat resistance and flame retardancy, and there shall be no fracture, deformation, combustion and short circuit in use.

Arc extinguishing device

The fuses used in power circuits and high-power equipment not only have three parts of general fuses, but also arc extinguishing devices, because the circuit protected by such fuses not only has a large working current, but also has a high voltage at both ends when the melt melts. It often appears that the melt has melted (fused) or even vaporized, but the current has not been cut off, The reason is that at the moment of fusing, under the action of voltage and current, arcing occurs between the two electrodes of the fuse. The arc extinguishing device must have strong insulation, good thermal conductivity and negative electricity. Quartz sand is a commonly used arc extinguishing material.

Fuse device

In addition, some fuses have fusing indication devices, which are used to make certain appearance changes after the fuse acts (fusing), which are easy to be found by maintenance personnel, such as lighting, discoloration, pop-up solid indicator, etc.

To sum up, the fuse is an indispensable part of the power circuit and plays a key role. If you have any questions, please feel free to leave a message. If you want to know more, please pay attention to us. I'll see you next time.