Investigations on the long-term behavior and switching function of fuse-elements for NH-fuse-links (gG) at higher thermal stress

In electrical power grids NH-fuse-links (gG) are widely used to protect electrical devices in case of overloads or shorts-circuit currents. New requirements of modern power grids, especially in the context of a growing share of renewable energies, implicate a much higher thermal stress level of the fuse-links. This can lead to an accelerated ageing of the fuse-elements, mainly due to the temperature-dependent ageing mechanisms of interdiffusion. The results are failures like unintended tripping or even a failed tripping of fuse-links. These failures reduce the security of supply, which is expected from the grid, and cause a major economic damage due to the high numbers of fuse-links used in the grid. Thereby the maximum temperature of the fuse-element is the most important criterion for a long-term stable use of fuse-links. Thus current research focuses on the investigation of the long-term behavior of such fuse-elements at higher thermal stress levels. Therefore the fuse-element's temperature distribution at normal operating conditions is investigated as well as extensive long-term experiments with several common used fuse-element types at different thermal stress levels are performed. The paper presents the considerations, on which the experiments are done, and the results of the long-term experiments. Further, a test stand for tripping tests of fuse-elements and first results of tripping tests with new fuse-elements are presented. With that, the impact of the ageing, due to the long-term thermal treatment, on the proper functioning of the fuse-elements should be evaluated and based on that results, conclusions for future limiting temperatures for fuse-elements should be drawn.