Instantaneous Overcurrent Protection Of Drop-out Fuses

In power distribution network operation, the drop out fuse unit device plays the role of a line "guardian." Its core value lies in its instantaneous response to faults. When a line suffers an overload or short-circuit impact, and the current exceeds the rated safe current of the drop out type fuse device, a precisely designed physical action program is immediately activated. This process involves not only the melting of the fusible element but also the coordinated action of the mechanical structure and the arc-extinguishing material.

Fuse Triggering and Energy Conversion

The fault current flows through the fusible element (usually a silver-copper alloy), generating a thermal effect. The current density rapidly rises to a critical value, and the local temperature of the fusible element reaches its melting point within milliseconds. The fuse thus vaporizes and melts, triggering the first step of circuit disconnection. At this instant, the tension force of the fuse on the moving joint of the fuse tube completely disappears, and the locking mechanism is released, preparing for a mechanical drop.

Arc Suppression and Mechanical Drop

At the moment the fusible element breaks, an arc is generated in the contact gap. The high temperature of the arc acts on the arc-extinguishing tube (gas-generating material) on the inner wall of the fuse tube, causing the material to decompose and produce a large amount of high-pressure gas. This airflow is ejected at high speed longitudinally along the fusible tube, strongly blowing away the electric arc. The airflow passes through the arc region, carrying away ionized particles, extinguishing the arc when the current crosses zero.

The connection between arc extinguishing and isolation: After the arc is extinguished, the moving contact on the fusible tube loses the tension constraint of the fuse wire. Under its own weight and the elastic force of the contact area, the fusible tube rotates around its lower axis and falls. This action creates a clearly visible disconnection gap, confirming the isolation status of the faulty circuit from both electrical and visual perspectives.