The Structural Characteristics And Working Principle Of Drop-out Fuse Links.

The drop out fuse consists of six parts: a magnetic shell, a conductive plate, a fuse element, quartz sand, an arc extinguishing agent, and an indicator. The fuse element is made of pure silver, is rectangular in shape, and has a narrow neck with a circular hole. The fuse element of the drop-out fuse is made of pure silver. Due to the low resistivity, good ductility, and good chemical stability of pure silver, the fuse element of the drop-out fuse can be made into a thin sheet with a narrow neck and a circular hole structure. When a short-circuit fault occurs, the current density is high at the narrow neck, so the narrow neck melts first and is separated into many small segments by the quartz sand. In this way, the arc formed by the melting of the fuse element is divided into many small segments by the quartz sand, resulting in a smaller arc current and a smaller distribution space, which is easily absorbed by the arc extinguishing agent. Since the quartz sand is insulating, an insulator is immediately formed after the arc is extinguished, disconnecting the circuit.

Inverse time-current protection characteristics: The fuse has inverse time-delay characteristics, meaning that the fusing time is long when the overload current is small, and the fusing time is short when the overload current is large. Therefore, within a certain range of overload current and overload time, the fuse will not blow and can be used continuously. Fuses have various different fusing characteristic curves, which can be applied to the needs of different types of protected objects.
Current limiting characteristics:
Because the fuse element of the drop-out fuse is a rectangular thin sheet with a series of narrow necks and circular holes, and is filled with quartz sand as an arc extinguishing medium [1]. The cross-sectional area at the narrow neck is small, and the heat capacity is small. When a short-circuit fault occurs, the fault current is interrupted before it reaches the expected short-circuit current, and the arc is separated into many small segments by the quartz sand. This both limits the increase in short-circuit current and accelerates the extinction of the arc.
High breaking capacity:
When a short-circuit fault occurs, the narrow neck is the first to melt, and the arc is separated into many small segments by the quartz sand, and the arc is quickly extinguished. Since the quartz sand is insulating, after the arc is extinguished, the fuse immediately becomes an insulator, disconnecting the circuit. Therefore, the drop-out fuse has a high breaking capacity, up to 50kA. The impact energy borne by the load equipment is small.
When a short-circuit fault occurs in the circuit, the impact energy borne by the load equipment is:
W = I²Rt
Where I is the short-circuit current; R is the resistance of the circuit; and t is the time from the occurrence of the short-circuit fault to the circuit being disconnected. Drop-out fuses have a short breaking time and excellent current-limiting capabilities.