1. Excessive Resistance

Electromigration occurs in the metal of high-voltage fuse elements under high temperatures, triggering localized material loss and void formation, which directly raises the fuse resistance.

High heat may melt soldering joints, weakening the connection between the fuse element and electrodes and further boosting overall resistance. Volatilization of solder or flux onto local sections of the fuse element creates micro-defects and elevates resistance. Evaporation of the fuse base metal also contributes to higher resistance. For silver-based fuse elements, silver electromigration is an additional factor driving resistance rise.

2. Blown Fuse Elements

A high-voltage fuse is deemed faulty once it loses its inherent protective performance. Aging of the fuse element often causes it to blow at the rated current or even under lower load currents, so fuse blowing is classified as a typical failure mode in this article.

Blowing of high-voltage fuses falls into three categories: intentional normal blowing, abnormal blowing induced by aging, and abnormal blowing stemming from manufacturing defects. Normal blowing is generally caused by circuit or load malfunctions, whereas unplanned abnormal blowing may in turn damage connected circuits and loads. This paper focuses primarily on aging-triggered abnormal blowing.

3. Poor Electrode Contact

In high-temperature and high-humidity operating environments, electrode metals are prone to oxidation, which increases contact resistance and leads to electrode overheating, and eventually severe contact failure. Mechanical vibration can loosen electrode connections and also result in poor contact.

Conclusion

High-voltage fuses suffer performance degradation and aging during long-term service. Nuclear power plants shall conduct regular inspections on high-voltage fuses, monitor their aging progression, and formulate targeted preventive maintenance strategies to avoid severe system losses arising from the failure of high-voltage current-limiting fuses.

As core protective components, high-voltage fuses require root-cause analysis whenever a blowing incident occurs to identify whether aging is the culprit. If aging is ruled out, inspect all identical fuses installed in the system to check for latent aging issues. If no aging signs are found, troubleshoot and rectify faulty associated components to prevent recurrent blowing failures.

High-voltage fuses age via multiple mechanisms, dominated by electromigration and metal evaporation of fuse elements, followed by chemical corrosion. Some aged fuses display visible exterior defects detectable by visual inspection, while others show no obvious surface abnormalities. Non-destructive assessment relies on precision testing technologies such as high-precision resistance measurement and infrared thermal temperature detection. Under microscopic observation, aged fuse elements exhibit distinctive micro-defects including localized material depletion, surface bulges, and solidified burrs formed after high-temperature cooling.