High voltage fuse is a fuse with an AC voltage greater than 1000V. It is an essential safety mechanism in high voltage systems to prevent electrical overloads and short circuits. It can be used in instrument transformers and small power transformers, as well as power systems.

Principle of operation of HV fuses

High Voltage Fuse consists of a fusible body which is a thin wire made of a metallic material. When the current exceeds the rated capacity of the fuse, the heat generated melts the fuse, thus breaking the circuit and preventing further damage. The fuse body is usually encapsulated in a non-conductive housing to prevent accidental contact with energized parts.

Types of High Voltage Fuses

There are several types of high-voltage fuses: cartridge fuses, liquid-type fuses, and dropout Fuses.

Cartridge HV Fuses are suitable for systems up to 33 kV and have a breaking capacity of approximately 8700 A at that voltage.Fuses rated at 200 A (6.6 kV) and 50 A (33 kV) are also available for various high voltage applications.These fuses are cylindrical in shape and are available in different lengths and diameters. The fuse body in the cartridge fuse is completely enclosed and is usually housed in a ceramic case. In some high-voltage fuse configurations dual fuse elements are operated in parallel, one with low resistance (silver) and the other with high resistance (tungsten). Under normal load conditions, the low resistance element handles standard current. However, when a fault occurs, the low resistance fuse element burns out and the high resistance element steps in. The high-resistance element reduces the short-circuit current and eventually breaks the circuit.

Liquid type fuse can be used in circuits rated up to about 400 A for systems with voltages of 132 kV or higher and has a breaking capacity of about 6100 A. It is widely used in high voltage systems. It is filled with carbon tetrachloride.

Dropout Fuses（Expulsion Fuses） designed for 11kV applications with breaking capacity up to 250 MVA.They open automatically when the current limit is exceeded. They are commonly used in overhead feeders and transformers. Due to their cost-effectiveness, they are widely used in the protection of feeders and transformers.

Proper selection of fuses is critical to maintaining the safety and reliability of high voltage systems. Improper selection can result in inadequate protection, premature fuse operation, or failure to operate when needed. Therefore, the specific requirements and characteristics of the system must be considered when selecting high voltage fuses.