Implementation of a transient energy method for directional detection in numerical distance relays

Changes in the operating conditions in today's dynamic power systems environment imposes greater demands on the protective relays for transmission and bulk lines. Heavy load currents, series compensated lines, reduced fault clearing time requirements and adaptation to rapidly changing system conditions are just some of the challenges that modern transmission line protective relays have to resolve. Conventional operating principles for directional detection, based on negative or zero sequence voltages or currents polarization in some cases do not satisfy the requirements for improved sensitivity and fast operation under varying system conditions. A method for directional detection based on the transient energy phenomena is presented in the paper. The method uses superimposed components derived from pre-fault and fault current and voltage samples. Three phase power is then calculated on a per sample basis and then integrated for several consecutive samples to determine the transient energy and its sign.