Detection of very high resistance faults - A new function of transmission line current differential relays

In the paper a new method of high resistance fault detection meant for current differential protections of two-terminal transmission lines is presented. The method is based upon calculation of line differential admittance in pre-fault and in faulty conditions. As the ground fault current during high resistance faults is comparable and, sometimes for long transmission lines, even lower than the line capacitive current, the use of differential admittance determined in pre-fault conditions enables significant enhancement of the fault detection sensitivity. The method proposed is tolerant to communication channel delay and asynchronous sampling and offers very simple detection algorithm that can easily be implemented. The paper also presents high resistance fault detection results on data obtained from intensive simulation fault tests carried out in EMTP model of a transmission line for great number of simulation cases, including the ones with broken conductor with one or both ends grounded.