An accurate fault locator for underground distribution networks using modified apparent-impedance calculation

Underground distribution cables are usually characterized with different technical difficulties regarding detecting and locating their faults. Different factors participate into these difficulties including their remarkable charging currents, cable construction and variations of their equivalency resulted from the variety of bonding and grounding methodologies. In this paper, a new fault location algorithm is proposed for underground cables in particular. The algorithm is able to precisely calculate the fault distance depending on modifying the basic apparent impedance approach to cope with the aforementioned characteristics of cable segments. In order to evaluate the performance of the proposed algorithm, different investigation tests are performed depending on a typical 11 kV underground distribution feeder in the Egyptian distribution system. All applied test cases are prepared with MATLAB-Simulink using the SimPower toolbox with accurate representation of power system elements utilizing distributed parameter line models. Moreover, the performance of the proposed algorithm is compared with the original apparent impedance approach using the same simulation platform. The applied test results cover a wide variety of fault conditions including fault resistance and loading circumstances. The results corroborate the efficacy of the proposed algorithm for locating such faults in underground distribution systems.