A fuse is also called a current fuse, and the IEC127 standard defines it as a "fuse-link". It is mainly used for overload protection. If the fuse is properly placed in the circuit, the fuse will fuse and cut off the current when the current rises to a certain height and heat abnormally, which protects the safe operation of the circuit.
The fuse invented by Edison more than a hundred years ago was used to protect the expensive incandescent lamps at that time. With the development of the times, the fuse protects electrical equipment from overcurrent and overheating, and avoids serious damage to electronic equipment caused by internal faults.
When a circuit breaks down or is abnormal, the current will continue to rise, and the rising current may damage some important components in the circuit, or it may burn the circuit or even cause a fire. If the fuse is correctly installed in the circuit, the fuse will fuse and cut off the current when the current abnormally rises to a certain height and heat, thereby protecting the safe operation of the circuit.
The fuse invented by Edison more than a hundred years ago was used to protect the expensive incandescent lamp at that time. With the development of the times, the fuse protects electronic/electric equipment from overcurrent/overheating and avoids serious damage caused by internal failure of electronic equipment.
When the current flows through the conductor, the conductor will generate heat because of the resistance of 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 for the current to flow through the conductor; according to this formula we 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 the temperature coefficient of resistance is not considered). When current flows through it, it will heat up, and its heat will increase with the increase of time. The current and resistance determine the speed of heat generation. The structure of the fuse and its installation status determines the speed of heat dissipation. If the rate of heat generation is less than the rate 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, then more and more heat will be generated. And because it has a certain specific heat and quality, the increase in heat is manifested in the increase in temperature. When the temperature rises above the melting point of the fuse, the fuse blows. This is how the fuse works. We should know from this principle that you must carefully study the physical properties of the materials you choose when designing and manufacturing fuses, and ensure that they have consistent geometric dimensions. Because these factors play a vital role in the normal operation of the fuse. Similarly, when you use it, you must install it correctly.
Generally, a fuse is composed of three parts: one is the melted part, which is the core of the fuse, which cuts off the current when it is blown. The melt of the same type and specification of the fuse must have the same material, the same geometric size, and the resistance value. It should be as small as possible and consistent. The most important thing is to have the same fusing characteristics. Household fuses are usually made of lead-antimony alloy. The second is the electrode part, usually two. It is an important part of the connection between the melt and the circuit. It must have good electrical conductivity, no obvious installation contact resistance should be produced; the third is the bracket part, the melt of the fuse is generally slender and soft, and the function of the bracket is to fix the melt and make the three parts a rigid whole for easy installation and use, It must have good mechanical strength, insulation, heat resistance, and flame resistance, and should not be broken, deformed, burned, or short-circuited during use.
When the current between the conventional non-fusing current and the rated breaking capacity (current) specified by the relevant standards is applied to the fuse, the fuse should operate satisfactorily without endangering the surrounding environment. The expected fault current of the circuit where the fuse is placed must be less than the rated breaking capacity current specified by the standard. Otherwise, when the fuse is blown in the fault, there will be continuous arcing, ignition, blown fuse, melted together with the contact, and the fuse mark cannot be recognized, etc. phenomenon. Of course, the breaking capacity of inferior fuses does not meet the requirements of the standard, and the above-mentioned hazards will also occur during use.
1. Normal operating current runs at 25°C, and the current rating of the fuse is usually reduced by 25% to avoid harmful fusing. Most traditional fuses use materials that have a lower melting temperature. Therefore, this type of fuse is more sensitive to changes in ambient temperature. For example, a fuse with a current rating of 10A is generally not recommended to operate at a current greater than 7.5A at an ambient temperature of 25°C.
2. Voltage rating The voltage rating of the fuse must be equal to or greater than the effective circuit voltage. The general standard voltage rating series are 32V, 125V, 250V, 600V.
3. The resistance of the resistance fuse is not important in the entire circuit. Since the resistance of a fuse with an amperage less than 1 is only a few ohms, this issue should be considered when using a fuse in a low-voltage circuit. Most fuses are made of materials with a positive temperature coefficient. Therefore, there are cold resistance and thermal resistance.
4. The current carrying capacity of the environmental temperature fuse, the experiment is carried out under the environmental temperature of 25 ℃, this kind of experiment is affected by the change of the environmental temperature. The higher the ambient temperature, the higher the operating temperature of the fuse and the shorter its life. On the contrary, operating at a lower temperature will extend the life of the fuse.
5. Fuse rated capacity is also called breaking capacity. The rated capacity of the fuse is the maximum allowable current that the fuse can actually blow under the rated voltage. When short-circuited, the fuse will pass through the instantaneous overload current that is larger than the normal operating current many times. Safe operation requires that the fuse remain intact (no burst or break) and eliminate short circuits.
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