Negative sequence quantities-based protection under inverter-based resources - challenges and impact of the German grid code

Abstract

Inverter-based Resources (IBRs), including Wind Turbine Generators (WTGs), exhibit different negative-sequence fault current characteristics compared to conventional synchronous generators (SGs). Depending on the type and control of IBR, their negative-sequence current contribution can be substantially lower in amplitude and different in phase. Therefore, large-scale integration of IBRs is expected to have a significant impact on negative sequence quantities-based protection elements including Instantaneous Negative Sequence Overcurrent (50Q), Negative Sequence Time Overcurrent (51Q), Directional Negative Sequence Overcurrent (67Q), and fault-identification FID scheme. This paper demonstrates misoperation of these functions in a practical multi wind park system. The misoperation problems are due to the wind parks with full scale converter (FSC) WTGs operating under traditional coupled sequence control (CSC). As illustrated in this paper, such misoperation problems can be eliminated effectively by utilizing a decoupled sequence control (DSC) scheme in FSC WTGs based on the recent VDE-AR-N 4120 Technical Connection Rules.