Wide range algorithm for directional earth-fault protection without voltage inputs

In this study, algorithm for a directional earth-fault relay is modified to work properly without voltage inputs. The presented modification of the algorithm implies that only current inputs are required, and the algorithm is used in isolated neutral networks. The main modification of this algorithm is that only one phase current is used as a reference quantity instead of the zero sequence voltage or three phase currents. The algorithm is further upgraded by using the phase current of the supply feeder as a reference signal for all relays of outgoing feeders. This way the reference quantity becomes more stable and the number of measurements per feeder is reduced to only one. The introduction of simple communication between relays on feeders, a wide operation range is achieved. With this algorithm detection of earth-fault is ensured regardless of the network load: purely capacitive, predominantly resistive or purely inductive. The algorithm successfully detects the faulted line and phase containing a phase-to-earth fault. The aim of this study is to design low-cost directional relays with no voltage inputs, a small number of current measurements and a wide range of possible network loads.