Structure of fast fuse:
Fuses are made up of six parts: magnetic shell, conductive plate, melt, quartz sand, arc extinguishing agent and indicator. The material of the melt is pure silver, with rectangular shape and [1] with a round hole and narrow neck.
The principle of arc extinguishing of fast fuse
The melt of the fast fuse is made of pure silver. Because the resistivity of the pure silver is low, the ductility is good, and the chemical stability is good, the melt of the fast fuse can be made into thin sheet and has a narrow neck structure. When a short-circuit fault occurs, the current density of the narrow neck is large, so the narrow neck is first fused and separated by quartz sand into many segments. In this way, the arc formed by melt fusing is divided into many segments by quartz sand. The arc current is small, and the space of distribution is small. It is easy to be absorbed by arc extinguishing agent. Because quartz sand is insulated, an insulator is formed immediately after the arc is extinguished, breaking the circuit
Characteristics of fast fuse
Anti - time current protection characteristics. The fuse has the characteristics of reverse time delay, that is, overload current, long fuse time and short fuse time when overload current is large. Therefore, the fuse will not fuse in a certain overload current and overload time range, and it can be used continuously. Fuses have different melting characteristic curves, which can be applied to different types of protected objects.
Current limiting characteristics
The melt of the fast fuse is a rectangular sheet with a series of round holes and narrow necks, and is filled with quartz sand arc extinguishing medium. In the narrow neck of the circular hole, the section area is small and the heat capacity is small. When the short circuit fault occurs, the fault current has not reached the expected short circuit current, that is, it is fused and the arc is separated into many small segments by quartz sand. In this way, the short-circuit current is increased and the quenching of the arc is accelerated.
Strong breaking ability
When a short-circuit fault occurs, the narrow neck of the round hole is first fused, and the arc is separated into many segments by quartz sand, and the arc is quickly extinguished. Because the quartz sand is insulated and the arc is extinguished, the fuse becomes an insulator immediately, breaking the circuit. As a result, the fast fuse has strong breaking capacity and can reach up to 50kA.
The impact energy of the load equipment is small
When a circuit has short circuit fault, the impact energy of the load device is W=I2Rt, I - short circuit current, R - circuit resistance, T - from short circuit fault to the time that the circuit is cut off. The fast fuse has short breaking time and good current limiting function, so the impact energy of the load equipment is small.