Optimized low voltage power fuses for current requirements in low voltage power grids

Low voltage power fuses with soldered silver fuse elements are widely used in electrical power systems because of their simple cost-effective work principle and high breaking capacity. An altered load profile caused e.g. by distributed energy generation may have a significant impact on the long-term behavior of conventional protection devices. With changing requirements in the low voltage power grids, the respective current profiles become more volatile leading to more strict normative switching requirements e.g. for fuses applied in photovoltaic systems (PV). Further, peak currents above the rated current can occur to a certain extend and age the fuse elements due to higher thermal stresses. Consequently, additional aging mechanisms have to be taken into account for electric fuses in DC-applications. A good long-term reliability of the fuses is needed to minimize the operational costs. Therefore, long-term investigations at high thermal stress inside an oven, at constant- and cyclic DC-load at fuse-elements were conducted. With these long-term tests, the influence of growing intermetallic compounds, electromigration and oxidation on the electric resistance and the fusing behavior were analyzed. Optimized fuse elements with a good long-term behavior were determined. A reliable fusing behavior after aging was confirmed for the optimized fuse geometry even under full switching capacity.