Directional ground relay failure caused by line-to-ground with load-side broken conductor fault

Classic power system fault analysis considers canonic situations, such as three-phase, line-to-line, double line-to-ground and line-to-ground faults. However, in practice, other faults occur that may be undetected by the protection systems. For example, a fault happens when a line conductor breaks and falls to the ground at the load side in a radial distribution network. This particular fault is called the “line-to-ground with broken conductor fault”. The aim of this work is a deep analysis of this particular contingency. In the first part, the proposed theory based on symmetrical components transformation is presented. Subsequently, the study of a MV radial distribution test network is considered in order to show the protection trip failure conditions.