Fuses protect overhead line systems from power surges by placing a fuse in series with transformer power wires. When a surge occurs, the fuse link melts, cutting power to the transformer and allowing the fuse holder to swing and fall off, indicating a blown fuse. Fuse cutout designs also include a brass ring for manual disconnection.
A fuse is an electrical protective device used on overhead line systems to prevent distribution transformers from being damaged by power surges. These devices work by placing a fuse in series with the transformer power wires. The connection passes through a tubular fuse holder which is hinged so as to secure the fuse holder in position on the cut body. If the link melts and separates under an overcurrent condition, the fuse holder will fall freely under its own weight, pivot downward on its hinge and hang vertically, giving a clear visual indication of its status. Most fuse cutout designs also incorporate a metal ring on the fuse holder, which allows maintenance and repair personnel to manually disconnect the fuse should it be necessary to work on the transformer.
Mast-mounted distribution transformers are an integral part of overhead power networks, feeding power drawn directly from the lines to points of consumption on the ground. These transformers are especially susceptible, as are the utilities they supply, to overcurrent damage caused by the frequent surges that occur on overhead power lines. The fuse switch is a protective device commonly installed on overhead line transformers, which not only prevents damage from power surges, but also can be used as a circuit breaker to isolate the transformer and its distribution network. The way fuses work also provides a clear visual indication of a fault condition from considerable distances, facilitating quick troubleshooting.
Although there are many different variations of the basic fuse blow concept, the basic operating principles remain the same throughout. The devices typically consist of a pair of contacts separated by a heavy porcelain insulator. The bottom contact is designed to accept the hinged end of a non-conductive tubular fuse holder, which allows the holder to rotate freely on the contact set. The length of the fuse holder allows it to make contact with the upper contact group, effectively forming a bridge between the two. The holder is secured to the upper contact by a fuse, which passes through the fuse holder and is secured to both the upper and lower contact sets.
This arrangement sees the fuse form a conductive path between the upper and lower contact assemblies while holding the fuse holder in place between the two. The incoming power from the overhead line is connected to the top contact and the outgoing power to the transformer to the bottom contact. This way power is supplied to the top contact, through the fuse to the bottom contact and then to the transformer. If a surge occurs on overhead lines, the fuse link will melt, effectively cutting power to the transformer and allowing the fuse holder to swing on its hinge and fall off the top contact. Most fuse assemblies are mounted horizontally or at an inclined angle to facilitate free fall of the blown fuse.
The separate fuse holder then becomes a clearly visible indicator that the fuse is blown, enabling rapid response by repair crews. Most fuse cutout designs also include a brass ring mounted on the upper, non-hinged end of the fuse holder. This allows repair crews to manually disconnect the fuse and isolate the transformer should the need arise.
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