Which of the following fuse is very fast in operation?
Right Answer is:
The semiconductor fuse is very fast-acting and is commonly referred to as an I2T fuse. Besides the voltage and current ratings of the fuse, the I2T rating plays an important role. For the proper protection of the SCR coordination of the SCR’s and fuse’s I2T ratings are critical. The I2T of the fuse must be smaller than the SCR’s in order to protect the SCR.
The semiconductor fuse operates at a high temperature (over 100°C) in order to make it fast-acting. As with all fuses, steady-state operation of the fuse should be at approximately 80% of its current rating.
Fig. shows the internal structure of the semiconductor fuse. The fusing element is made of silver with one or more notches. The cross-section of the fuse at the notch is less. When heavy current flows through the fuse, there is a high current density at the notch. Because of high current density, the temperature rises at the notch, and arc is developed. This arc reduces the current flow. Therefore high voltage is formed across the notch. This further increases the temperature. Therefore the fuse element is vaporized and arc length is increased. Due to increased arc length, the current further reduces.
At some stage, the current is zero and the fuse becomes open. There is no arc and the complete voltage appears across the fuse. Note that the fuse has to withstand the voltage in open conditions. The fusing element is embedded in quartz sand. This helps to conduct heat and serves as a quenching medium for the arc at the time of fusing.
KitKat fuse is a low voltage fuse.
Cartridge fuse is a high voltage fuse.