An analysis of overvoltages in large MV-cable installations

In MT installations with very long cables, important overvoltages can occur during faults, sudden load changes or simple switching operations. A careful analysis of these phenomena can be of fundamental importance to implement correct measures needed to reduce stress on installation components and therefore avoid dangerous insulation failures. For a proper evaluation of the phenomenon, reference is made to a real electrical system concerning an underground installation, namely the LNGS laboratory of the Italian National Institute of Nuclear Physics (INFN), the largest laboratory of its kind in the world for civil applications. The results of the study, however, are general and can therefore be applied to any MT-cable installations of considerable extension. In this paper some criteria for investigating the phenomena are suggested, along with possible solutions to reduce the entity of overvoltages potentially harmful to electrical installations.