Low voltage (LV) Fuse
This type of fuses are applicable for low voltage ( such as 230 Volt) and current ratings, like the domestic applications. It is of two types based on the type of enclosure. They are semi enclosed type or rewireable type and totally enclosed or cartridge type. Semi enclosed fuses are seen at supply terminals from where the line is taken and fed to the consumer house, most commonly the meterbox unit.
Semi enclosed Rewireable fuse
This is the most commonly used fuse in house wiring. It is also known as kit-kat type fuse. The fuse consists of a porcelain base which carries the fixed contacts. Incoming or outgoing live or phase wires are connected to this base. Another part of the fuse consists of porcelain fuse carrier ( or fuse holder) which holds the fuse element. If fuse holder or carrier gets damaged during use it can be replaced without replacing the entire fuse unit. The fuse wire may be lead, copper, aluminium. Let us see how this fuse works?
When fault occurs in the system, the fuse element blows off and the circuit is interrupted. We take out the fuse carrier and then replace the blown fuse element by new one. Supply is restored by re inserting the fuse carrier in the porcelain base. The fusing current in this type of fuse is twice the rated current. Re wireable fuse have IS specifications and the standard ratings are 6,16, 32, 63 and 100 A. Fuse wire used should have current rating less than the fuse rating. Semi enclosed fuses are made up to 500 A rated current with breaking capacity of 4000 A in 400 V service. This fuse is mainly used for domestic and lightning loads. Semi enclosed fuse type have two advantages – low replacement cost and it can be replaced without the user coming in contact with the live wire. There are some drawbacks such as low rupturing capacity, slow operating speed, no current limiting feature, unreliable operation, chance of fire or flame.
Totally enclosed or cartridge type fuse
Here the fuse element is enclosed totally as the name suggests. A container is there which encloses the fuse element and metal contacts are provided on either side of the container. Cartridge type fuses overcomes the shortcomings of the semi enclosed type fuse. These fuses are further classified as D-type and link type cartridge fuse. Link type fuses are again of two types- knife blade and bolted. Let us discuss about the D -type and link type fuses.
D type cartridge fuse: It comprises of fuse base, adapter ring, cartridge and a fuse cap. The cartridge is pushed into fuse cap and cap is screwed on the base. The standard ratings are 6, 16, 32 and 63 amperes. The breaking or rupturing capacity is 4 kA for 2-4 amp fuses and 16kA for fuses 6-63 A. Operation of this type of fuse is reliable.
Link type cartridge or high rupturing capacity (H.R.C) fuse: This type of fuse have high rupturing or interrupting capacity. Breaking capacity of this of fuse is also high. Modern power system uses this type of fuse. HRC fuse is another common name of this kind of fuse. Manufacturers have upgraded its operation and structure since its invention. The different components are fuse element, cartridge, outer element, filling powder, fuse link and end plates of brass. Fusing factor for link type fuses is 1.45. IS 2208-1962 defines the specifications of HRC link fuses.
High voltage (HV) fuses
We have discussed low voltage fuses so far. But the current rating and breaking capacity of such fuses prevents it from using in modern high voltage power system. Engineers have made high voltage fuses which can be used in wider prospect. There are a few kinds of HV fuse namely – cartridge type, liquid type and metal clad fuses. High voltage fuses have breaking capacity of 8700A at 33kV voltage level. Other ratings are also available with this kind of fuse.