Impedance based directional relaying for smart power networks integrating with converter interfaced photovoltaic plants

Non-linear behavior of converter interfaced power plant during fault condition imposes problems on power system grids. The control structure and dynamic nature of converters associated with these power electronics -based renewable plants inherently affect the output voltage and current. The varying fault characteristics introduced by PV plants deteriorate the secure operation of the conventional directional relay used for trans-mission lines. In the present work, a directional relaying algorithm based on impedance for the transmission line connected with PV plant is offered. The proposed method does not involve any phasor estimation process to compute the impedance utilizing the superimposed components of relaying signal and the magnitude of the computed impedance is used to discriminate the exact fault direction. The feasibility of the proposed technique has been realized by simulating the Modified WSCC 9-bus and IEEE 39-bus system using EMTDC/PSCAD under different adverse power system conditions. The performance of various existing angle based directional relaying methods has been analysed in presence of a PV plant in the Modified WSCC 9-bus/IEEE 39-bus system. Comparative assessment with the previously proposed conventional directional protection algorithm reveals the accuracy and applicability of the proposed method.