Analysis On The Working Principle And Technical Characteristics Of Drop-out Type Fuse
High Voltage Fuse is an overcurrent protection device widely used in power distribution networks. Its core function is to disconnect the circuit by melting the fuse, thereby isolating the fault area and ensuring the safety of power equipment. This article will analyze the structural principle, action mechanism, technical characteristics and typical application scenarios.
The drop-out fuse consists of a melting tube, a fuse, an arc extinguishing device, upper and lower contacts and a mounting bracket. The melting tube is usually made of epoxy resin material with gas-generating properties, with a fixed fuse inside and filled with quartz sand as an arc extinguishing medium. When the system current exceeds the set threshold, the fuse is heated and melted, and the gas-generating material in the fuse tube decomposes under the high temperature of the arc to produce high-pressure gas, forming a longitudinal arc blowing effect, forcing the arc to quickly cool and extinguish in the quartz sand gap.
Under normal working conditions, the fuse tube maintains close contact with the upper static contact through spring tension to form a conductive path. After the fuse is melted, the fuse tube loses mechanical tension support and flips down under the action of gravity, forming a clearly visible disconnection point. This mechanical drop feature not only provides an intuitive fault indication, but also ensures that the operator can quickly locate the fault location.
2. Action characteristics and arc extinguishing mechanism
The operating characteristics of the fuse depend on the material properties and geometric structure of the fuse. The fuse is usually made of silver-copper alloy, which has low resistivity and stable melting point. The time-current characteristics can be customized by accurately designing the cross-sectional area and length of the fuse. When a short circuit occurs in the system, the short circuit current vaporizes the fuse within 1-10 milliseconds. At this time, the gas-generating material decomposes rapidly to produce insulating gases such as hydrogen and carbon dioxide. With the adsorption effect of quartz sand, the arc extinguishing process can be completed within half of the power frequency cycle.
For overload current, the fuse achieves delayed melting through the heat accumulation effect. This hierarchical protection feature can not only avoid false operation caused by instantaneous load fluctuations, but also effectively prevent equipment from being damaged due to long-term overload. The rated breaking capacity of the fuse can reach 12.5kA-20kA, which can meet the protection requirements of 10kV and below distribution systems.
3. Key technical features
... Economical and easy to maintain: Compared with circuit breakers, drop-out fuses do not require operating power, and maintenance costs are reduced by more than 60%. The fuse replacement operation can be completed on the ground through an insulating pull rod, which significantly improves operation and maintenance efficiency.
Environmental adaptability: The specially designed rainproof fuse can withstand ambient temperatures from -40°C to +80°C, and the arc extinguishing medium can maintain stable performance in areas below 2,000 meters above sea level.
... Distribution line protection: Installed at the 10kV overhead line branch node as a line segment protection device. When a phase-to-phase short circuit is caused by lightning strikes, tree barriers, etc., the fuse can cut off the fault current within 0.1 seconds.
Distribution transformer protection: As the primary side overcurrent protection of transformers below 35kV, its rated current is selected as 1.5-2 times the rated current of the transformer, which can effectively prevent internal faults such as short circuit between winding turns.
Parallel capacitor bank protection: In view of the harmonic amplification effect of the capacitor bank, a fuse with inverse time characteristics is used to prevent the insulation breakdown of the capacitor due to overvoltage.
5. Key points for installation and operation and maintenance
... VI. Summary
As an important protection element of the power distribution system, the NBM drop-out fuse has been widely used in the power network due to its reliable action characteristics and economic advantages. With the application of new nano-composite arc-extinguishing materials, its breaking capacity and service life continue to improve, providing a basic guarantee for the construction of smart distribution networks. In the future, the self-recovery characteristics of fuse materials need to be further studied to adapt to the complex working conditions brought about by the access of new energy.
