Impact and Challenges of Conventional Protection Solutions in Wind Farm Connected Grids

Session Title: Protection and impact of converter dominated networks and low inertia systems*
Chair: Campbell Booth

With the high penetration of variable renewable sources in the power system today, it is obvious that the merging of conventional power systems and converter-based systems such as wind farms or other types of non-conventional systems has become unavoidable. The result of this merge is a hybrid system consisting of linear and non-linear dynamics. Therefore, the conventional protection functions, such as line distance protection and line differential protection functions, have met new challenges, since conventional protection systems are mainly based on phasor-domain calculations and symmetrical sequence component principles with the assumption that the power systems are linear systems.  

This paper performs an analysis of different fault signature characteristics under wind farm connected grid conditions based on typical type-III (Doubly Fed Induction Generator (DFIG)) and type-IV (Permanent  magnetic synchronous generator (PMSG)) wind farm generators used in existing power grids. This analysis includes the evaluation of symmetrical components within different types of faults and frequency variations during the fault period. The impact on conventional protection functions are described following the basic analysis of fault signals. Furthermore, the paper elaborates on the impact on distance protection, phase selection functions, directional detection, zero sequence current based directional earth fault protection and line differential protection functions. In this study the electromagnetic transient simulation program PSCAD/EMTDC has been used to model the dynamics of type-III and type-IV wind farms. Based on the preceding analysis, possible challenges and recommended improvements for power system protection are discussed.  

Finally, the paper concludes the above analysis with important lessons-learned for the protection systems in wind farm connected power grids. Lastly, future possible directions of research are provided.