Analysis Of The Operation Process And Technical Points Of Drop-out Fuse
1. Overview
High Voltage Fuse is a key device in the power system. For 10kV distribution lines and distribution transformers, it plays an important role in short-circuit protection and overload protection. It has a simple structure, low cost and easy maintenance. It is widely used in branch lines of overhead distribution lines, incoming line side of distribution transformers and other scenarios. The particularity of this device is that after it is melted, it can be visibly disconnected by its own gravity, forming an obvious disconnection point, and it also has the function of an isolating switch.
2. Structure and work Working principle
1. Core components
It consists of a melting tube, a fuse, an upper static contact, a lower moving contact, a mounting bracket, and an arc extinguishing device. The melting tube is made of gas-generating materials (such as steel paper tubes), filled with quartz sand as an arc extinguishing medium, and the fuse is a low-melting-point alloy material. The three constitute a composite structure.
2. Action Mechanism
When the system current exceeds the set value, the fuse is heated and melted, and an arc is generated. Under the high temperature of the arc, the gas-generating material on the inner wall of the melting tube decomposes, generating high-pressure gas to blow the arc longitudinally, and coupled with the adsorption effect of quartz sand, the arc is extinguished quickly. When the fuse breaks, the mechanical balance of the fuse tube is immediately broken, and it automatically falls, forming a significant disconnection point.
Workflow
1. Power outage preparation stage
(1) Check the line double number and equipment nameplate parameters
(2) Use a tester to test each phase to confirm that there is no voltage
(3) When installing a temporary grounding wire, it must be operated in order from near to far.
2. Fuse operation
② Disconnect the middle phase (B phase) first, then disconnect the leeward side phase (C phase), and finally disconnect the windward side phase (A phase)
③ Hook the pull ring on the upper end of the fuse with the operating lever and pull it downward at a constant speed of 45°
Closing operation:
① Check the burning condition of the fuse and whether the fuse is intact.
② Aim at the duckbill contact and hold the lower end of the melting tube with the operating rod
③ First close the windward side phase (phase A), then the leeward side phase (phase C), and finally the middle phase (phase B)
3. Post-operation inspection
(1) Confirm that the drop angle of the melting tube meets the 90°±5° standard
(2) The contact length of the contact should be greater than 85% of the diameter of the melting tube
(3) The angle between the axis of the melting tube and the vertical line shall not exceed 30 degrees.
In terms of insulation coordination, a safety distance of not less than 0.7 meters must be maintained during operation, and the effective insulation length of the operating rod should be not less than 1.5 meters.
In terms of arc extinguishing capability, the rated breaking current should reach 1.2 times or more of the maximum expected short-circuit current at the installation point.
Mechanical life: Normal operation cycle number is not less than 2000 times, contact pressure is maintained in the range of 50-70N
Environmental adaptation: Altitude does not exceed 2000m, ambient temperature -40℃~+40℃, ice thickness ≤10mm
V. Operation and maintenance precautions
... Fuse selection: select based on 1.5 times the rated current of the transformer, and the error must be controlled within ±3%.
During abnormal handling, if a single-phase fuse is found, be sure to cut off the load first, and never replace the fuse tube under load.
Anti-misoperation: The installation angle must be maintained at an inclination of 15° - 30° to ensure that the fuse tube can fall reliably.
VI. Technological development trends
The new generation of intelligent fuses integrates temperature sensors and communication modules, which can monitor the temperature rise of contacts and fuse status in real time. The application of nano-composite arc-extinguishing materials has increased the breaking capacity by more than 30%. In addition, some products already have fault location and remote status monitoring functions.
