Adaptive algorithm in distance relay compatible with smart grid requirements during Sub Synchronous Resonance in transmission line

Abstract

Smart grid includes utility system and Distributed renewable. It provides bidirectional power flow and communication among utility, Distributed Generations (DG) and consumers. Sub Synchronous Resonance (SSR) is mostly concern in transmission line. In addition, swing characteristic of impedance during SSR causes activation of Out of Step Blocking (OSB) element of distance relay. During SSR, the magnitude of voltage and current is increased. It also increases probable occurrence of ferroresonance. In this paper, impact of SSR in utility system is analyzed on DFIG (DoublyFed Induction Generator) and distance relay with OSB element in wind farm by PSCAD/EMTDC software. As smart grid requires a self-healing protection, an intelligent algorithm based on sub harmonic measurement and ferroresonance analysis is proposed for distance relay. It distinguishes ferroresonance from other nonlinearities in smart grid based on wavelet transform and neural network and applies time domain analysis to determine ferroresonance of different types. The algorithm is able to comply with smart grid protection strategies. It receives the commands based on protection strategy to make a suitable decision in such conditions to increase reliability and availability in smart grid. Finally, the algorithm is examined in SSR condition to certify the correct operation.