Fuse Part 4

#channel2

[to read previous parts part1 part2 part3]
#Terms related to fuse

#Rated_Current : It is the maximum current which the fuse can carry without any heating or melting. It depends upon fuse element material,temperature rise and deterioration of the fuse by oxidation.
#Fusing_Current : It is the maximum current at which the fuse elements melts and disconnects the circuit. It is more than the rated current. If rated current is 5A, then 5A can easily flow through the fuse without heating but fusing current will be more than 5A.
if fusing current = I
k = constant depends upon metal of wire
d= diameter of fuse element
then, I = k.  d to the power (3/2)

#Fusing_factor: Ratio of fusing current to rated current.
for rewirable fuse it is 2 for copper.

#Prospective_Current: r.m.s value of the first loop of the fault current is called prospective current.

#Cut_off_Current: value of current reached before the fuse melts. Depends upon ¡) prospective current
¡¡) current rating of the fuse.

#pre_arcing_time: It is the time between time of fault occurs and instant of fuse melts.( 0.001 sec)

#arcing_time: it is the time taken from the instant of arc started to the instant of arc extinguished.

#BreakingCapacity_or_RupturingCapacity: It is the maximum current that can safely be interrupted by the fuse. This should be higher than the prospective current. Fuses for high voltage equipment, upto 115000 volts, are rated by the total apparent power(MVA) of the fault level in the circuit.

#Melting_ i square t
- is propotional to the total energy required to begin melting the fuse element.
#Clearing_ i square t
- is propotional to the total energy let through by the fuse when clearing a fault.
#Rated voltage- Rated voltage should be higher than the maximum voltage source. A fuse rated at 32 volts would not reliably interrupt current from a voltage source of 120 volts. If it is used, an arc is formed and plasma inside the glasstube(if it is glass tube fuse) may continue to conduct current.
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