What Is a Fuse Cutout?

What Is a Fuse Cutout?

A fuse cutout is an electrical protection device used in overhead line systems to prevent distribution transformers from being damaged by surges. The working principle of these devices is to connect the fuse to the series of the transformer feeder cable. The connection is through a hinged tubular fuse, in this way the fuse is fixed in position on the cut body. If the link melts and separates under over-current conditions, the fuse holder will drop freely under its own weight, rotate to the hinge, and hang vertically, making its state clearly visible. Most fuse cutout is designed with a metal ring on the fuse holder. When maintenance and repair personnel need to work on the transformer, the fuse can be manually disconnected.

The distribution transformer installed on the tower is an integral part of the overhead power grid and transmits the power drawn directly from the line to the user point on the ground. These transformers are particularly susceptible to overcurrent damage caused by frequent surges on overhead power lines, just like the user points they feed. A fuse cutout is a commonly used protection device on overhead line transformers. It can not only prevent the destruction of electrical spikes but also can be used as a switch to isolate the transformer and the distribution network. The function of the fuse can also give a clear and intuitive indication of the fault situation from a considerable distance so that the fault can be found easily and quickly.

Although there are many different variations of the basic fuse cutout concept, the core operating principles have always remained the same. Such devices usually consist of a pair of contacts separated by heavy porcelain insulators. The lower contact is designed to accept the hinged end of a non-conductive tubular fuse, which allows the fuse to rotate freely on the contact assembly. The length of the fuse holder allows it to contact the upper contact assembly, effectively forming a bridge between the two. The fuse connection is fixed on the upper contact through the fuse holder and connected to the upper contact and the lower contact assembly.

With this structure, the fuse can be connected between the upper and lower contact assemblies to form a conductive channel, and the fuse holder can be fixed between the upper and lower contact assemblies at the same time. The input power from the overhead line is connected to the upper contact, and the output power of the transformer is connected to the lower contact. In this way, power is fed to the upper contact, connected to the lower contact via a fuse, and then to the transformer. If a power surge occurs on an overhead line, the fuse link will melt, effectively cutting off the power supply to the transformer, and allowing the fuse holder to rotate on its hinge and descend from the upper contact. Most fuse cutout assemblies are installed horizontally or inclined to facilitate the brown fuse to fall off.

The separated fuse holder will become a clearly visible indicator, indicating that the fuse has blown, and maintenance personnel can react quickly. Most fuse cutout designs also include a brass ring mounted on the upper part of the fuse, the non-hinge end. This allows maintenance personnel to manually disconnect the fuse and isolate the transformer when needed.