Dropout Fuse Units: A Key Part in Overhead Power Systems
A Dropout Fuse Unit (DFU), often called an expulsion fuse cutout, is a basic protection device. It is widely used in medium-voltage overhead power networks—usually up to 38 kV. It has two main jobs. It keeps transformers, feeders and other equipment safe from too much current. It also acts as a clear, safe switch for repair work.
The unit has three main parts. There is an insulator made of molded epoxy resin or porcelain. A metal base, which connects to the power line, is another part. The third is a removable fuse holder. This holder holds the fuse link—the part that melts when things go wrong. It is also made to swing easily.
Under normal conditions, the holder stays firmly closed. Two things keep it that way: the pull from the fuse link itself and a spring-loaded lock. The “dropout” feature is what makes this unit work. When there is too much current for too long, or a short circuit happens, the fuse link inside the holder melts. This creates an electric arc.
Gas builds up inside the fuse tube because of this. That gas helps put out the arc. Most importantly, the melted link no longer pulls the holder. This triggers the release mechanism. Gravity then makes the fuse holder swing down and open up. This action creates a clear gap in the circuit—you can see it right away.
This one move does two vital things. It stops the current to fix the fault. It also gives repair workers a clear, physical point to work with. That makes their jobs much safer when they need to fix or replace parts.
Dropout fuse units have big advantages. They are simple to use. They do not cost a lot. And they show clearly when something is wrong. A fallen holder tells workers exactly which part of the system has a problem. This lets them find and isolate the fault fast, cutting down the time spent figuring out why the power is out.
The visible gap also matters for safety. It makes sure workers follow the rules—locking and tagging equipment before they start repairs. All in all, abimat dropout fuse units are still a must-have in overhead power systems.
They combine two important jobs well: protecting against too much current and working as a safe switch. For power companies, this means a strong, cheap solution. It is also easy to maintain, keeping both the power equipment and the workers safe.
