Types of Fuses
Since the invention of first fuse by Edision, several improvements have been made and now-a-days, a variety of fuses are available at surrounding of us. Additionally, some fuses feature a mechanism for putting out the arc that forms when the fuse element melts.
In order to allow for the safe replacement or rewiring of fuses, it is common practice to have an isolating switch in series with them. If such means of isolation are not available, When inserting or removing the fuse carrier, the fuse must be shielded to prevent accidental user contact with a live metal part.
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| Fig: Typical fuses |
Fuses may be classified into two terms:
1. Low voltage fusesLow voltage fuses:
From the name "low voltage fuses" it is clear to us regarding this types of fuses. No need to give any more definitions. However, the low voltage fuses can be sub-divided into two classes.
A. Semi-enclosed rewireable fuse.
Rewireable fuse is also known as kit-kat fuse which is used where low value of fault current are to be interrupted. A base and a fuse carrier make up the device. Fuse elements blow out and the circuit is cut off when a fault occurs.
To replace the blown out fuse element we have to taken out the fuse carrier. Then the fuse carrier is reinserted in the base to restore the power supply.
This type of fuse has two advantages.
1.The detachable fuse carrier permits the replacement of fuse element without any danger of coming in contact with live metal parts.
2.The cost of fuse element replacement is very negligible.
B. High Rupturing capacity(H.R.C.) cartridge fuse.
H.R.C. cartridge fuse resolves the main issue of low and unsure breaking capacity of semi-enclosed rewireable fuse. It is composed of a heat-resistant ceramic body with a metal end cap to which a silver current-carrying element is soldered.
The body's empty space is completely filled with powder that surrounds the fuse element. The filling powder material may be chalk, plaster of paris, quartz or marble dust and it acts as an arc quenching and cooling medium.
C. H.R.C. Fuse with tripping device.
Sometime, H.R.C. cartridge fuse is equipped with a tripping device. When the fuse element blows out under fault conditions, the tripping device causes the circuit breaker to operate.
High voltage fuses:
The low voltage fuses have low current rating and breaking capacity. Therefore, they can not be used successfully on modern high voltage circuits. Intensive research has led to the development of high voltage fuses.
Cartridge type fuse:
With a few added special features, it has a similar structure to the low voltage cartridge type fuse. Some designs employ fuse elements wound in the form of a helix which helps to avoid corona effects at higher voltages.
Up to 33 kV, high voltage cartridge fuses are employed, and at that high voltage, they have a breaking capacity of around 8700 A.
Liquid type fuse:
These fuses, which are filled with carbon tetrachloride, can be used in a wide variety of high voltage systems. They can be utilized for circuits with rated currents up to about 100A and system voltages up to 132kV. They may have breaking capacity of the order of 6100A.
Metal clad fuse:
An alternative to the oil circuit breaker has been developed in the form of metal-clad oil-immersed fuses. Such fuses can be used for very high voltage circuits and operate most satisfactorily under short-circuit conditions.
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