Analysis of the working principle of drop-out fuse
High voltage Cut-out fuse is an overcurrent protection device widely used in power distribution network. It is economical, easy to operate and has strong adaptability to outdoor environment.
The drop-out fuse breaks the circuit by melting the fuse, thereby isolating the fault area and ensuring the safety of power equipment.
Wenzhou Shuguang Fuse Co., Ltd. will introduce the working principle, function and use environment of the cut-out fuse.
1. Structural composition and basic principles
The cut-out fuse is mainly composed of a fuse tube, a fuse, an arc extinguishing device, upper and lower contacts and a mounting bracket.
The fuse tube is generally made of epoxy resin material with gas-generating properties, with a fuse fixed inside and filled with quartz sand as an arc extinguishing medium.
When the system current exceeds the rated voltage, the fuse is heated and melted, and the gas-producing 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 cool quickly and extinguish in the quartz sand gap.
In normal working state, the fuse tube is closely connected with the upper static contact by spring tension, thus building a conductive path. After the fuse is melted, the fuse tube loses the support of mechanical tension. Under the action of gravity, the fuse tube flips down and falls, forming a clearly identifiable 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 action characteristics of the fuse depend on the material characteristics and geometric structure of the fuse. The fuse is generally made of silver-copper alloy, which has low resistivity and stable melting point. By accurately designing the cross-sectional area and length of the fuse, the time-current characteristics can be customized. When a short-circuit fault occurs in the system, the short-circuit current vaporizes the fuse within 1-10 milliseconds. At this time, the gas-producing material quickly decomposes to produce insulating gases such as hydrogen and carbon dioxide. Combined with the adsorption effect of quartz sand, the arc extinguishing process can be completed within half a power frequency cycle.
When overload current occurs, the fuse delays melting by virtue of the heat accumulation effect. This hierarchical protection feature can not only avoid false operation caused by instantaneous load fluctuations, but also effectively prevent equipment damage 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
Breaking capacity and selectivity: Through the coordination of fuse characteristics and superior protection devices, accurate isolation of the fault section can be achieved. In radial distribution networks, the fuse time of lower-level fuses is usually more than 20% faster than that of upper-level fuses, ensuring the selectivity of protection actions.
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 of -40℃ to +80℃, and the arc extinguishing medium can maintain stable performance in areas below 2000 meters above sea level.
4. Typical application scenarios
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 winding turn-to-turn short circuits.
Protection of parallel capacitor banks: Taking into account the harmonic amplification effect of capacitor banks, fuses with inverse time characteristics are used to prevent insulation breakdown of capacitors due to overvoltage.
As a manufacturer with more than 30 years of experience in fuse manufacturing, we can provide you with comprehensive and fast quotations. Welcome to inquire.
