What is the function of the fuse?
A fuse is an electrical protection component installed in a circuit to ensure the safe operation of the circuit. It is widely used in power distribution systems and control systems, mainly for short-circuit protection or overload protection. It is an electrical appliance that uses a metal conductor as a fuse to disconnect the circuit and connect in series in the circuit. When a circuit fails or is abnormal, the current continues to increase, and the increased current may damage some important or valuable components in the circuit, burn the circuit, or even cause a fire.
If the fuse is correctly placed in the circuit, then when an overload or short-circuit current passes through the fuse, the fuse will melt itself and cut off the current when the current abnormally rises to a certain height and at a certain time, thereby protecting the power system, various electrical equipment and household appliances in the event of an overload or short circuit.
Its principle is mainly to use the thermal effect of current (Q=I²Rt), where Q is the heat generated in joules (J), I is the current passing through the resistor in amperes (A), R is the resistance value of the resistor in ohms (Ω), and t is the time the current passes through the resistor in seconds (s). This formula shows that when current I passes through resistor R, the heat Q generated in time t can be calculated by multiplying the square of the current by the resistance value and the time. This heat can cause the fuse to melt and disconnect the circuit, controlling the harmful effects of overcurrent to an acceptable level.
Structure of the fuse
Generally, fuses are composed of four parts.
The first is the fuse element, which is the core of the fuse.
The fuse element is equivalent to a special wire connected in series in the circuit. When the circuit is short-circuited or overloaded, the current is too large, and the fuse melts due to overheating, thereby cutting off the circuit. Therefore, for the material of high-voltage fuse, the requirement is that it has a low melting point, stable characteristics, easy to melt and easy to extinguish the arc.
The materials used to make high-voltage fuses include copper, silver, zinc, lead, lead-tin alloy, etc. The melting points of these materials are also different, so different currents require different materials, and their melting temperatures correspond to 1080℃, 960℃, 420℃, 327℃, and 200℃ respectively. The instructions for the use of these different materials are as follows:
① The melting point of metals such as zinc, lead, and lead-tin alloy is relatively low, but the resistivity is relatively high. Therefore, the cross-sectional area of the fuse element to be used is relatively large, and more metal vapor is generated when it is melted, which is not conducive to arc extinguishing. It is mainly used in circuits below 1kV.
② Copper and silver have high melting points, but low resistivity, good electrical and thermal conductivity. Therefore, the cross-sectional area of the fuse element to be used is small, and the metal vapor generated when melting is small, which is easy to extinguish the arc and can be used in high-voltage and high-current circuits. However, if the current passing through is too large and the temperature is too high for a long time, it is easy to cause damage to other components in the fuse.
To make the fuse element melt quickly, a large current must flow through it, otherwise it will prolong the melting time, which is not good for the protection of the equipment. In order to eliminate this shortcoming, a small ball of tin or lead is often welded on the copper or silver melt to reduce the melting temperature of the melt and improve the protective performance of the melt.
For fuses of the same type and specification, the material should be the same, the geometric dimensions should be the same, the resistance value should be as small as possible and consistent, and most importantly, the fusing characteristics should be consistent.
The second is the contact part, which usually has two.
It is an important component connecting the melt and the circuit. It must have good conductivity and should not produce obvious installation contact resistance.
The third is the fuse shell.
The fuse element is generally thin and soft. The function of the shell is to fix the fuse element and make the three parts a rigid whole for easy installation and use. It must have good mechanical strength, insulation, heat resistance and flame retardancy, and should not break, deform, burn or short-circuit during use. Only in this way can it resist arc temperature and mechanical force impact and maintain the overall integrity of the fuse.
The tube body is generally made of ceramic or melamine tube. Different types of fuses use different materials.
For example, British Standard fuses are mainly used for equipment produced in Commonwealth countries. The shell is made of ceramic material. The product has the characteristics of small size and high cost performance and is especially favored by UPS manufacturers below 240V.
North American fuses are the most widely used, covering most power electronic products. The North American standard fuse shell is made of melamine mesh cloth and ceramic lamination process, with strong impact resistance, small Joule integral value, low power loss, and excellent DC performance. It is widely used in substations, electric vehicles and other occasions.
The European standard square body fuse is made of ceramic material. This product has the characteristics of low operating temperature, low power loss, and small Joule integral value. It is suitable for applications requiring compact structure, superior performance, and high power, especially in electric vehicles, EV charging, energy storage and other fields.
The fourth is the fuse base (support), which usually serves to fix or protect the fuse.
Fuses used in power circuits and high-power equipment not only have the four parts of a general fuse, but also have an arc extinguishing device. Because the circuits protected by this type of fuse not only have a large working current, but also have a high voltage across the two ends when the fuse is blown, it often happens that the fuse has melted (blown) or even vaporized, but the current is not cut off.
The reason is that at the moment of blowing, an arc occurs between the two electrodes of the fuse under the action of voltage and current. This arc extinguishing device must have strong insulation and good thermal conductivity, and be negatively charged. Quartz sand is a commonly used arc extinguishing material.
It can absorb the conductor and buffer the arc temperature and mechanical impact, split and cool the arc, and generate a large amount of gas pressure, which has a deionizing effect on the arc and extinguishes the arc quickly, thereby cutting off the circuit or isolating the faulty equipment from the power grid, ensuring the safe operation of other areas or other equipment on the power grid.
In addition, some fuses have a blown indicator device, which is a parallel conductor line. When the main fuse element blows, it blows together. The high temperature triggers the gunpowder or the stored elastic force, giving a visible displacement or indicating the switch action. Its function is that when the fuse is actuated (blown), its appearance changes to a certain extent, which is easy for maintenance personnel to find, such as: glowing, changing color, popping out a solid indicator, etc.
Fuse production process
Raw material selection
the manufacture of fuses requires the use of materials with good electrical conductivity and flame retardancy, such as metal materials such as copper, silver, aluminum, tungsten, and non-metal materials such as ceramics and glass fiber. When selecting one of these materials, it is necessary to select according to the characteristics and requirements of the actual circuit, and ensure that the rated current and breaking capacity of the fuse can be met.
Manufacturing components
the components of the fuse mainly include the fuse element, contacts, tube shell, fuse holder and other parts. These components need to go through mold manufacturing, injection molding, cooling, demoulding and other processes to ensure the accuracy of their appearance and size. Among them, the manufacturing of fuses usually adopts stamping, molding, punching and other processes to prepare the fuse element. It is necessary to accurately control its material viscosity, diameter and length and other parameters to ensure the rated current and circuit-breaking capacity of the fuse.
Assembly
assembly is a very important part of fuse production. It is necessary to assemble each component according to the design requirements and ensure the normal operation of the components. Quality inspection is also required during the assembly process. All parameters must meet the quality requirements before proceeding to the next step.
Testing
it is a critical link in the fuse manufacturing process, mainly including electrical performance testing and mechanical performance testing. In the electrical performance test, it is necessary to detect whether the fuse’s rated current and circuit breaking capacity and other parameters meet the standards, and whether there is leakage and other problems. In the mechanical performance test, it is necessary to detect whether the mechanical strength of the fuse meets the use requirements.
Packaging and shipment
Finally, after the production of the fuse is completed, it needs to be packaged and shipped to ensure its safety during transportation and use. Special attention should be paid to not using rough materials that may damage the fuse.
Fuse Technology Development Direction
With the development of emerging technologies such as new energy and renewable energy, new requirements are constantly being put forward for fuses. Fuse manufacturers need to continuously improve the level of materials and manufacturing processes to better meet circuit safety and equipment protection, which is mainly reflected in the following aspects.
1. Higher performance requirements
With the diversification and modernization of electronic products, people have also put forward many new protection requirements for circuits. As a result, many new types of fuses with novel protection functions will appear one after another, such as faster fusing action, strong pulse resistance, small rated current or larger rated current, and smaller size, etc.
2. Development towards intelligence and miniaturization
New protection types: electrostatic protection, lightning protection, electromagnetic interference protection, etc. The development of fuses may be towards miniaturization, surface mounting, multi-function or multi-circuit integration, becoming a new product with overcurrent protection characteristics and other circuit protection characteristics, and even with reusable functions.
3. Developing towards a more environmentally friendly direction
Today’s fuses usually contain lead, cadmium and other heavy metals, which pollute the environment and cause harm to the human body. With the advancement of technology, especially the development of new materials, fuses will become more and more environmentally friendly, and gradually bid farewell to these heavy metals that pollute the environment.
4. Safety performance will be further improved.
When breaking current, current fuses may explode, spray arcs, etc. due to harmonic resonant overcurrent, thus causing harm to the environment. We believe that with the development of technology, these problems will be solved.
5. Digital Trends
Digitalization of the design process in manufacturing: that is, simulating the manufacturing process and using the powerful computing function of computers to test the trial of parts, so as to accurately rationalize the design and improvement of parts and processes, saving design and testing time.
Realization of the digital production process: using computers to achieve complete automation of the production process, combining the entire production system and logistics transportation system to complete the entire production process of manufacturing.
6. Refinement
With the continuous improvement of manufacturing methods, precision is constantly improving. For example, in the 20th century, the so-called ultra-precision manufacturing error was reduced to 10μm, then to 1μm, and then to 0.1μm. At the end of the century, it reached 0.01μm, and now it has reached 1nm. With the continuous improvement of nanotechnology in the future, the manufacturing process will also fully enter the nano era.
7. Integration and automation development trend
The development of integration is the product of high automation, that is, the entire manufacturing process is transformed from the original decentralized to complete integrated and continuous manufacturing. The future integration will be the integrated manufacturing of the entire finished product, which will enable the entire process of design, production, assembly, finished product inspection, and delivery to be completed in an automated system.
