Fuse arc extinguishing refers to the ability of a fuse to safely and quickly extinguish the arc generated during the process of melting (the melt melts due to overcurrent). This is the core function of fuses to reliably cut off fault currents and protect circuits.
Here is a detailed explanation:
Generation of electric arc:
When a short circuit or severe overload occurs in the circuit, the current flowing through the fuse increases sharply.
The melt inside the fuse (usually a special alloy wire or sheet) rapidly heats up due to Joule heating and eventually melts.
At the moment when the melt melts, the current does not immediately drop to zero. Molten metal forms high-temperature, highly conductive metal vapor at the fracture site.
This metal vapor will be ionized under the high voltage difference (power supply voltage) at both ends of the fracture, forming a conductive plasma channel, which is called an arc.
The hazards of electric arcs:
Continuous conductivity: The arc itself is conductive, and if the arc continues to exist, current can still flow through it, making it impossible to truly cut off the faulty circuit and losing its protective function.
High temperature: The center temperature of the arc is extremely high (up to thousands of degrees Celsius), which can burn out the fuse housing, surrounding components, and even cause a fire.
Energy release: Electric arcs can release enormous amounts of energy, which may lead to dangers such as explosions and splashing of molten metal.
Damaged equipment: Continuous short-circuit current can cause further damage to power sources, circuits, and other equipment.
The process and principle of arc extinguishing:
One of the core goals of fuse design is to quickly and reliably extinguish the arc generated during melting. Common methods include:
Fill quartz sand:
This is the most commonly used and effective method (especially in high breaking capacity fuses).
The fuse tube shell is tightly filled with high-purity quartz sand with strictly controlled particle size.
When the melt melts and generates an arc, the arc is surrounded by quartz sand.
Quartz sand has extremely high specific heat capacity and thermal conductivity, which can quickly absorb the huge heat of the arc and rapidly cool the arc area.
Molten metal vapor splashes onto quartz sand particles, rapidly solidifying and increasing the resistance of the arc path.
Quartz sand particles may partially melt under the high temperature of the arc, forming glassy substances that further block the arc channel.
Under the multiple effects of cooling, segmentation, and elongation of quartz sand, the resistance of the arc rapidly increases and the current sharply decreases, ultimately reliably extinguishing at zero current crossing.
Narrow slit arc extinguishing (ceramic tube/fiber tube structure):
Some fuses (especially fast melting type) use ceramic tubes or high-strength fiber tubes as the outer shell.
Melts are usually designed to be placed in multiple segments or specific shapes inside the tube.
When the fuse is blown, an electric arc is generated in the narrow lumen space.
High temperature arc causes the gasification and decomposition of pipe wall materials (such as ceramics or fibers), producing a large amount of high-pressure gas.
These high-pressure gases rapidly expand within narrow pipelines, forming a strong longitudinal airflow that fiercely blows the arc towards the pipe wall.
The material of the pipe wall can absorb heat, elongate and divide the arc, cool it down and eventually extinguish it.
Melt design:
The shape of the melt (such as variable cross-section design, M-shaped design) can induce the arc to occur simultaneously at multiple points, dispersing the arc energy.
Some molten materials, such as silver, can produce steam with good arc extinguishing properties during gasification.
The importance of arc extinguishing capability:
Safe circuit disconnection: This is the fundamental manifestation of fuse protection function. Fuses that cannot effectively extinguish arcs are dangerous.
Limiting fault energy: Rapid arc extinguishing can minimize the total energy (I ² t) released by short-circuit current, protecting downstream equipment from excessive electric force and thermal stress damage.
Improve breaking capacity: The excellent arc extinguishing design enables the fuse to safely break extremely high short-circuit currents (high breaking capacity).
Preventing fires and explosions: Effectively extinguishing high-temperature arcs is the key to preventing electrical fires.
Limiting arc voltage: Good arc extinguishing design can also control the overvoltage that may occur during melting within a safe range.
Summary:
Fuse arc extinguishing is the process of using its internal structure (such as quartz sand filling, special tube shell, melt design) to forcibly cool, divide, and elongate the arc when the fuse melts due to overcurrent, and completely extinguish it when the current crosses zero. This is one of the most critical mechanisms by which fuses can reliably and safely cut off fault currents, protecting circuits and personal and property safety. The arc extinguishing ability directly determines the breaking ability, safety, and reliability of the fuse.