The Development History, Function, Working Principle, Structure, Classification and Parameter Terminology of Current Fuse
Fuse is also called current fuse or fuse. IEC127 defines it as "fuse-link". The key part (fuse) is made of silver-copper alloy with high resistivity and low melting point. When the current of the fuse rises abnormally to a certain height and a certain degree of heat, the fuse will cut off the current itself, thus playing the role of protecting the safe operation of the circuit.
History of Development
In the 1980s, Edison applied for the first patented fuse equivalent to a safety valve in the circuit, which opened the history of fuse development. The fuse has been used more and more widely, and many designs have been produced. There are different requirements for fuse in all walks of life, resulting in shape/size/installation form/material/structure/specifications/characteristics/applications. Various varieties (traditional tubular fuse, miniature fuse, patch fuse, automobile fuse, industrial fuse) are available.
The differences of industry development and environmental conditions in the world have resulted in many differences in fuses used in different areas. These differences reflected in the tubular electronic small fuses gradually formed two major systems in North America and Europe. IEC60127-4 universal die fuses attempted to integrate the two systems, taking the first step.
The Fuse Industry in China started in 1950s and began to copy all the fuses of the Soviet Union at that time. There were few varieties/old structures/backward test methods. In the late 1970s, the localization of color TV promoted the development of small fuse industry, and the delay fuse matched with color TV began to approach the international standard.
The first national standard for small fuses in China, GB9364. -88, is equivalent to the corresponding part of IEC60127. The revised GB9364-97 and the revised GB9364.4 formulated in 2011 are equivalent to the corresponding part of IEC60127, but the fifth, ninth and tenth parts of the standard have not yet been formulated.
More than one hundred years ago, Edison invented the fuse to protect the expensive incandescent lamp. With the development of the times, the fuse protects the electronic/power equipment from over-current/over-heat and avoids serious damage caused by internal faults of electronic equipment.
Electrical performance: Fuses are connected in series in electronic circuits, generally requiring small resistance (low power consumption). When the circuit is working normally, it is only equivalent to a conductor, which can be stable for a long time. When current fluctuation occurs due to power supply or external interference, it should also be able to withstand a certain range of overload. When a large overload current (fault or short circuit) occurs in the circuit, the fuse will operate, and the safety of the circuit will be protected by disconnecting the current.
Safety: In the process of fuse breaking circuit, due to the existence of circuit voltage, arc will occur in the gap between melt breaking. High-quality fuses should avoid this kind of arc as much as possible; after the fuse breaking circuit, they should be able to withstand the circuit voltage added at both ends.
When current flows through a conductor, the conductor will heat up because of the resistance of the conductor. And the calorific value follows this formula: Q = 0.24I2RT, 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, T is the time when the current flowing through the conductor.
When fuse is electrified, the temperature of melt will rise because of the heat converted by current. When normal working current or allowable overload current is loaded, the heat generated by current and the heat radiated through melt, shell and surrounding environment will gradually reach balance; if the heat dissipation rate can not keep up with the heating rate When the temperature reaches or exceeds the melting point of the melt material, it will liquefy or vaporize, thus disconnecting the current and playing a role in protecting the circuit and the body.
The general fuse consists of three parts: one is the melt part, which is the core of the fuse, and plays the role of cutting off the current when fusing. The fuses of the same kind and specification should be of the same material, geometric size, resistance value as small as possible and consistent, and the most important thing is to have the same fuse characteristics; the other is to have the same fuse characteristics. There are usually two electrodes, which are important parts of the connection between melt and circuit. They must have good conductivity and should not produce obvious installation contact resistance. Thirdly, the fuse melt is generally thin and soft in the support part. The function of the support is to fix the melt and make the three parts rigid and convenient. In installation and use, it must have good mechanical strength, insulation, heat resistance and flame retardancy, and should not produce fracture, deformation, combustion and short circuit in use.
The fuses used in power circuits and high-power equipment not only have three parts of the general fuse, but also have 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 is fused, which often leads to melting (fusing) or even fusing. It has been vaporized, but the current has not been cut off. The reason is that the arc phenomenon occurs between the two electrodes of the fuse at the instant of the fuse under the action of voltage and current. This arc extinguishing device must have strong insulation, good thermal conductivity and negative electricity. Quartz sand is a common arc extinguishing material.
In addition, there are some fuses with fuse indicator device. Its function is that when the fuse moves (fuses), it changes its appearance, which is easy to be found by maintenance personnel, such as: luminous, discoloration, pop-up solid indicator, etc.
According to the form of protection, it can be divided into: