Analysis of the Blowout Mechanism of Current-Limiting Fuses and Non-Contact Sensing Evaluation Methods

Online condition assessment of current-limiting fuses for medium-voltage motors without power interruption or disassembly remains challenging. This paper proposes an online degradation identification method for current-limiting fuses based on non-contact current-rate sensing with temperature compensation. A fuse current stress test platform was established, and high-current impact tests simulating actual operating conditions were conducted using a 7.2 kV/160 A fuse as the research subject. Experimental results reveal that under prolonged current impact, the cold resistance of the fuse exhibits multiple irreversible step-like increases. Further analysis indicates that the magnitude of these cold resistance steps aligns closely with the resistance model of the fuse's multi-branch internal structure, suggesting that the preferential melting of individual fuse elements is the primary mechanism causing discrete degradation transitions. Based on this mechanism, an online monitoring device for fuses was developed with a non-contact measurement link. A step-judgment method was proposed, using the relative increase in equivalent internal resistance as a physical threshold and integrating statistical significance testing. During the 351st current impulse test, the monitoring device successfully identified a step-like decrease in the current-rate feature, which corresponded to an irreversible increase in cold-state resistance, enabling online early warning of a single fuse-element melting event.