Chinese name: current fuse mbth: fuse alias: fuse is also called: fuse material: development history, function, basic function, working principle, structure, classification, parameters and terms, melting calorific value, rated voltage, development history 65438+1980s, Edison applied for the first fuse patent equivalent to the safety valve in the circuit, which opened the history of fuse development. Fuses are widely used, leading to numerous designs. Different industries have different requirements for fuses, resulting in different varieties (traditional tubular fuses, miniature fuses, patch fuses, automotive fuses, industrial fuses, etc.). ).？ The differences in industry development and environmental conditions in different countries in the world also lead to many differences in fuse use in different regions. These differences are reflected in the tubular electronic small fuse products, and gradually formed two major systems in North America and Europe. C60127-4The universal modular safety wire test diagram combined the two systems and took the first step. The fuse industry in China began in the1950s, when it began to copy from the Soviet Union, with few varieties/outdated structure/backward testing methods. At the end of 1970s, the localization of color TV sets promoted the development of small fuse industry, and the delay fuses supporting color TV sets began to approach international standards. GB9364。 China's first national standard for miniature fuses -88 adopted the corresponding parts of IEC60 127, while GB9364.4 formulated by revising GB9364-97 and 201adopted the corresponding parts of IEC60 127, but the fifth, ninth, and first/. The fuse invented by Edison 100 years ago was used to protect the expensive incandescent lamp at that time. With the development of the times, fuses protect electronic/power equipment from current/overheating and avoid serious damage caused by internal faults of electronic equipment. Basic function Electrical performance: Fuses are connected in series in electronic circuits, which generally require low resistance (low power consumption). When the circuit works normally, it is only equivalent to a wire, which can conduct the circuit stably for a long time. When the current fluctuates due to power supply or external interference, it should also be able to withstand a certain range of overload; Only when there is a large overload current (fault or short circuit) in the circuit, the fuse will act and protect the safety of the circuit by disconnecting the current. Safety: in the process of fusing fuse circuit, due to the existence of circuit voltage, arc will occur in the melt breaking gap, and high-quality fuse should avoid this arc as much as possible; After the fuse is disconnected, it should be able to withstand the circuit voltage applied at both ends. Working principle When current flows through a conductor, the conductor will heat up because of a certain resistance. The calorific value follows this formula: q = 0.24 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. When the fuse is energized, the temperature of the melt will rise due to the heat converted by the current. When the normal working current is loaded or the overload current is allowed, the heat generated by the current can gradually reach a balance with the heat radiated/convected by the melt, the shell and the surrounding environment. If the heat dissipation rate can't keep up with the heat generation rate, heat will gradually accumulate on the melt, so the temperature of the melt will rise. Once the temperature reaches and exceeds the melting point of the molten substance, it will liquefy or vaporize, thus cutting off the current and playing a role in safety protection for circuits and people. A general fuse consists of three parts: one is the fuse part, which is the core of the fuse and plays the role of cutting off the current when it is blown. Melts of the same kind and specification should have the same material, the same geometric size, the smallest resistance value and, most importantly, the same fusing characteristics. The second is the electrode part, usually two, which is an important part of the connection between the melt and the circuit. Must have good conductivity, should not produce obvious installation contact resistance; Third, the support part, the fuse melt is generally slender and soft. The function of the bracket is to fix the melt and make the three parts become a rigid whole, which is convenient for installation and use. It must have good mechanical strength, insulation, heat resistance and flame retardancy, and there should be no phenomena such as fracture, deformation, combustion and short circuit during use. Fuses used in power circuits and high-power equipment not only have three parts of general fuses, but also have arc extinguishing devices, because the circuit protected by this fuse not only has a large working current, but also has a high voltage at both ends when the melt melts, and often the melt has melted (melted) or even vaporized, but the current has not been cut off. The reason is that at the moment of melting, under the action of voltage and current, an arc is generated between the two electrodes of the fuse. This arc extinguishing device must have strong insulation, good thermal conductivity and electronegativity. Quartz sand is a commonly used arc extinguishing material. In addition, some fuses have fuse indicating devices, which are used to change their appearance to a certain extent when the fuse is operated (fused), and are easy to be found by maintenance personnel, such as: emitting light, changing color, popping up solid indicators, etc. According to the protection form, it can be divided into overcurrent protection and overheating protection. Fuses used for over-current protection are usually called fuses (also called current-limiting fuses). Fuses used for overheating protection are generally called "temperature fuses". Temperature fuses are divided into low melting point alloy shapes, temperature-sensitive trigger shapes and memory alloy shapes. (Temperature fuses are used to protect heating equipment or easily heated equipment from overheating. It echoes the temperature rise of electrical appliances and has nothing to do with the working current of the circuit. Its working principle is different from that of "current limiting fuse". According to the scope of use, it can be divided into: power fuse, machine tool fuse, electrical instrument fuse (electronic fuse) and automobile fuse. According to the volume, it can be divided into: large, medium, small and micro. According to the rated voltage, it can be divided into high-voltage fuses, low-voltage fuses and safe voltage fuses. According to breaking capacity, it can be divided into high breaking capacity fuse and low breaking capacity fuse. According to the shape, it can be divided into: flat-headed tubular fuse (which can also be divided into internal welding fuse and external welding fuse), pointed tubular fuse, straw cutter fuse, spiral fuse, plug-in fuse, flat fuse, wrapped fuse and patch fuse. According to the material, it can be divided into: glass fuse tube and ceramic fuse tube. According to the fusing speed, it can be divided into: ultra-slow fuse (generally represented by TT), slow fuse (generally represented by T), medium-speed fuse (generally represented by M), fast fuse (generally represented by F) and ultra-fast fuse (generally represented by FF). According to the standard, it can be divided into: European fuse (VDE), American fuse (UL) and Japanese fuse (PSE). According to the types, it can be divided into current fuses (patch fuses, miniature fuses, plug-in fuses and tubular fuses), temperature fuses (RH (bulk fuses), RP (resistance fuses) and RY (metal case fuses)) and self-recovery fuses (plug-in fuses, laminated fuses and patch fuses). According to the sizes, it can be divided into patch fuses 0603, 0805 and 6544. Non-patch type φ 2.4× 7, φ 3× 7, φ 3.6× 10, φ 4.5× 15, φ 5.0× 20, φ 5. 16× 20, φ 6× 25, φ 6× 30, φ. Parameters and terminology: Rated current: also known as rated working current of fuse, code-named in. The rated current of the fuse is determined by the manufacturing department under laboratory conditions. The rated current values are generally 100mA, 200mA, 3 15mA, 400mA, 500mA, 630mA, 800mA, 1.6A, 2A, 2.5A and 3./kloc. Voltage drop: Apply rated current to the fuse. When the fuse reaches thermal balance, that is, the temperature is stable, measure the voltage at both ends of the fuse, code-named Ud. Because the voltage drop at both ends of the fuse will have a certain impact on the circuit, the voltage drop is clearly defined in the European Code. Fuse resistance: usually divided into cold resistance and thermal resistance. Cold resistance is the resistance measured with a test current less than rated current 10% when the fuse is at 25℃. The thermal resistance is converted from the voltage drop measured by taking the full rated current as the test current, and its calculation formula is r heat =Ud/In. Usually, the thermal resistance is greater than the cold resistance. At the same time, Jabisen fuse resistor has two functions: patch resistance and fuse. In general, the JEPSUN fuse resistor acts as a resistor, but when the fuse needs to work, it can be blown and act as a fuse. Overload current: Overload current means that the current flowing through the circuit is higher than that during normal operation. If the overload current cannot be cut off in time, it may cause damage to other devices in the circuit. Short-circuit current refers to the current generated by partial or total short-circuit in the circuit, which is usually very large and greater than overload current. Fuse characteristics: namely time/current characteristics (also called ampere-second characteristics). There are usually two expressions, namely I-T diagram and test report. I-T diagram is a curve formed by connecting the coordinate points of the average fusing time of fuses under different current loads in a coordinate system composed of load current as X coordinate and fusing time as Y coordinate. Each type of fuse has a corresponding curve, which can represent its fusing characteristics. This curve can be used as a reference for selecting fuses. The test report is a record of the test data of the test according to the test items required by the standard. Our I-T chart and test report are based on the data measured under experimental conditions, and their graphs or test reports are different under actual use conditions, so the test report and I-T chart provided by our company are for reference only. Breaking capacity: also known as rated short-circuit capacity, that is, the maximum current that the fuse can safely break at rated voltage (AC is the effective value). It is an important safety index of fuze. The code name of the broken ability is Ir. Temperature rise: Temperature rise refers to the difference between the temperature of the fuse when it is stable and the temperature before it is energized when the specified current value (UL is 100%, and Japanese code is 1 15%) passes. The melting heat energy value is the energy value required for fuse melting, and its code name is I t, which is pronounced A2Sec. It is the product of the square of the corresponding current and the fusing time when the fuse is disconnected in 8 milliseconds or less. The time limit is less than 8ms, which means that all the heat generated by the fuse is used for fusing, and it is too late to dissipate heat. For each different fuse component, it is a constant, and it is a parameter of the fuse itself, which is determined by the design of the fuse. The nominal working voltage of rated voltage fuses is Un, and the standard rated voltages of general fuses are 32V, 60V, 125V, 250V, 300V, 500V and 600V. The fuse can be used at a voltage not greater than its rated voltage, but it is generally not allowed to be used in a circuit with a circuit voltage greater than the rated voltage of the fuse.