What are the preventive measures for common failures of drop-out fuses?
1. Reasonable selection of drop-out fuses
The 10kV drop-out fuse is suitable for outdoor places where the ambient air is free of conductive dust, corrosive gases, flammable, explosive and other dangerous environments, and the annual temperature difference ratio is within ±40°C. The selection is based on two parameters: rated voltage and rated current, that is, the rated voltage of the fuse must match the rated voltage of the protected equipment (line). The rated current of the fuse should be greater than or equal to the rated current of the melt. The rated current of the melt can be selected as 1.5 to 2 times the rated load current. In addition, the selected fuse should be checked according to the three-phase short-circuit capacity of the protected system. Ensure that the three-phase short-circuit capacity of the protected system is less than the upper limit of the rated breaking capacity of the fuse, but must be greater than the lower limit of the rated breaking capacity. If the rated breaking capacity of the fuse (generally refers to its upper limit) is too large, it is likely that the three-phase short-circuit capacity of the protected system will be less than the lower limit of the rated breaking capacity of the fuse, making it difficult to extinguish the arc when the melt melts, eventually causing accidents such as fuse burnout and explosion.
2. Correctly install drop-out fuses
(1) The 10kV drop-out fuse is installed outdoors, and the distance between phases should be greater than 70cm. And it should be installed firmly and reliably on the cross arm (frame) with a vertical distance of not less than 4m from the ground. The European-style cable joint should not have any shaking or shaking. If installed above a distribution transformer, a horizontal distance of more than 0.5m should be maintained from the outermost contour boundary of the distribution transformer to prevent other accidents caused by the falling fuse tube.
(2) The melt should be tightened during installation, otherwise it will easily cause the contact to heat up. The melt used must be a standard product from a regular manufacturer and have a certain mechanical strength.
(3) The fuse pipe should have an inclination angle of 25° (±2°) downward, and the length of the fuse pipe should be adjusted appropriately. It is required that the duckbill tongue can hold more than two-thirds of the contact length after closing to avoid malfunction of falling on its own during operation. The fuse pipe should not push the duckbill to prevent the fuse pipe from falling in time after the melt melts.
3. Operate drop-out fuses normally and reasonably
In rural power grid 10kV distribution line branch lines and distribution transformers with a rated capacity less than 200kVA are allowed to operate with load according to the following requirements:
(1) The operation is carried out by two people (one person supervises and one person operates), but they must wear tested insulating gloves, insulating boots, and goggles, and use qualified insulating rods matching the voltage level for operation. Operation is prohibited in weather with lightning or heavy rain.
(2) When operating the gate, it is generally stipulated that the middle phase should be pulled off first, then the leeward side phase should be pulled off, and finally the windward side phase should be pulled off. This is because the distribution transformer has been changed from three-phase operation to two-phase operation, and the arc sparks generated when the middle phase is broken are minimal and will not cause a short circuit between phases. The second step is to pull off the leeward side phase. Because the middle phase has been pulled apart, the distance between the leeward side phase and the windward side phase has doubled. Even if overvoltage occurs, the possibility of causing a short circuit between phases is very small. When the windward phase is finally disconnected, there is only capacitive current to the ground, and the spark generated is already very slight.
(3) When closing the gate, the operation sequence is the opposite when closing the gate. First close the windward phase, then close the leeward phase, and finally close the middle phase.
(4) Operating the fused pipe is a frequent project. If you don't pay attention, it will cause burns on the contacts, resulting in poor contact, overheating of the contacts, annealing of the springs, and worse contact contact, forming a vicious cycle. European-style cable joints, therefore, use moderate force when pulling and closing the fused pipe. After closing, carefully check that the duckbill tongue can tightly hold more than two-thirds of the tongue length. You can hook the upper duckbill with the opening lever and press down a few times, and then gently try to pull it to check whether it is closed properly. When closing, it is not in place or securely, and the static contact pressure on the fuse is insufficient, which can easily cause contact burns or the fuse tube to fall on its own.
4. Strengthen the operation and maintenance of drop-out fuses
In order to make the fuse operate more reliably and safely, in addition to strictly selecting qualified products and accessories (including fuses, etc.) produced by regular manufacturers in accordance with regulatory requirements
Special attention should be paid to the following matters during operation and maintenance management:
(1) Whether the rated current of the fuse matches the melt and load current values appropriately. If the match is inappropriate, it must be adjusted.
(2) Each operation of the fuse must be done carefully and not carelessly. Especially during the closing operation, the moving and static contacts must be in good contact. Check whether the rotating part of the fuse is flexible, whether there is any abnormality such as corrosion or poor rotation, whether the parts are damaged, and whether the spring is corroded.
(3) Standard melt must be used in the fusion tube. It is forbidden to use copper wire and aluminum wire to replace the melt, and it is not allowed to use copper wire, aluminum wire and iron wire to tie the contacts.
(4) For newly installed or replaced fuses, the acceptance process must be strict and must meet the regulatory quality requirements. The installation angle of the fuse pipe must reach a tilt angle of about 25°.
(5) After the melt is blown, it should be replaced with a new melt of the same specification. Do not connect the melt after melting and then put it into the melt tube for continued use.
(6) The fuse should be inspected regularly, no less than once a month at night, to check for discharge sparks and poor contact. If there is discharge, it will be accompanied by a hissing sound, and treatment should be arranged as soon as possible.
Yichang Hengyuan Technology Co., Ltd. specializes in the production of European-style cable joints, plug-and-pull heads, cable branch boxes, American-style elbow joints, high-voltage vacuum circuit breakers, high-voltage load switches, arresters, zinc oxide arresters, tank arresters, over-voltage protectors, counters, monitors, heat-shrinkable cable accessories, Manufacturer of cold shrink cable accessories, T-heads, wall bushings, European cable accessories, American cable joints, transformer neutral point protection devices, fuses, isolating switches, PT cable heads, elbow cable joints, 10kV outdoor terminals, switch cabinets, cable intermediate joints, cable accessories and other products
