Introduction of current-limiting fuse

The current-limiting fuse is a closed fuse that can limit short-circuit current and can quickly cut off the fault current. Its structure is characterized by placing the melt in a closed porcelain tube filled with quartz sand. There are also additional current-limiting resistors in series to limit the short-circuit current and reduce the overvoltage caused when the current is cut off. So, let us take a look at the introduction of the current-limiting fuse. Here are some answers.

Here is the content list:

•  The structure of the current-limiting fuse.

•  The characteristics of the current-limiting fuse.

•  The design points of the current-limiting fuse.

  
  

The structure of the current-limiting fuse.

The fuse of the current-limiting fuse is installed in a porcelain tube filled with quartz sand. When the fuse is blown by overcurrent, an arc is generated in the porcelain tube. The arc is quickly extinguished due to the cooling and de-ionization effect of the quartz sand on the arc. The current-limiting fuse has a strong arc extinguishing ability, which can extinguish the arc before the short-circuit current reaches the maximum value. It can limit the short-circuit current value and reduce the dynamic and thermal stability requirements of the electrical equipment in the circuit. When the current-limiting fuse breaks the circuit, no free gas is discharged, so it is widely used in indoor power distribution devices.

The characteristics of the current-limiting fuse.

The main structure of the current-limiting fuse is composed of a melted tube, current-limiting fuse melt according to the rated current, contact seat, wiring board, supporting insulator, and bottom plate. One or more fuse wires are wound on the ribbed porcelain core, or wound into a spiral shape and installed directly in the tube. The tube is filled with quartz sand and has copper end caps at both ends. After installation, it is welded firmly with the top cover to keep the seal. When the short-circuit current or the overload current passes, the melt immediately melts, and the generated arc is in close contact with the quartz sand to strengthen the de-ionization and cooling effect so that the arc is quickly extinguished and the indicator pops up. In addition, the current-limiting fuse has a strong ability to extinguish the arc and has a current limiting effect, which can extinguish the arc before the short-circuit current reaches the maximum peak value. This is of great significance for limiting short-circuit current, reducing electrical equipment movement and thermal stability. This kind of fuse does not discharge free gas when breaking the circuit, so it is widely used in indoor devices.

The design points of the current-limiting fuse.

First, the expanded length of the fuse must ensure that the arc is extinguished when a thin metal wire is used as the expanded length of the fuse. Second, the particle size of quartz sand has a great influence on the arc extinguishing performance of the current-limiting fuse. The test shows that it is more appropriate when the particle diameter is 0.2~0.3mm. Third, measures to limit over-voltage. When the current-limiting fuse breaks the circuit, the arc current is forced to cross zero, which is prone to over-voltage. To limit the overvoltage below 2.5 times, variable cross-section melts are often used. For example, in the RN1 type fuse, three sections of copper wires with different cross-sections are connected. Fourth, the measure to reduce the temperature rise of the fuse tube is to use red copper as the fuse material for the current-limiting fuse, which has a higher melting point, and when an overcurrent passes, the temperature rise is very high. Soldering a tin ball or enameling a layer of tin at the change of the melt section can lower the melting point so that the temperature rise of the fuse tube can be reduced. Fifth, the structure of the fuse tube to make the quartz sand in the fuse tube effectively extinguish the arc, the melt often adopts multiple parallel connections. Appropriate distance should be kept between each melt and between the melt and the tube wall to avoid the arc burnt out of the porcelain tube and the arc connection.

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