Protection of Renewable Energy Systems
The recent progress in renewable energy (RE) technologies has led to the erection of RE power plants (REPPs) up to the order of several hundred megawatts. Unlike their predecessors, which generally appeared in the form of dispersed generation (DG) coupled mainly with distribution systems, such large REPPs are naturally part of high-voltage transmission networks and hold non-negligible proportions of the generation. On the other hand, RE-based DGs are becoming pervasive in modern distribution systems. As a result, the fault ride-through (FRT) requirement has become an essential part of modern grid codes.
This seminar investigates the challenges brought about by the FRT requirement now affecting protective relaying for systems with which REPPs are integrated. Some serious defects of distance protection for the lines connected to induction generator (IG)-based wind farms (WFs) during balanced faults are revealed. It is shown that for the squirrel cage IG (SCIG) WFs, distance protection becomes insecure, while for the doubly-fed IG (DFIG) WFs, the relay performance is utterly unreliable, due to operating scenarios that are unique to such WFs, and are not addressed by the existing relaying practices. The detected failures can easily result in unnecessary WF tripping, thus jeopardizing the objectives pursued by the FRT requirement. Moreover, a novel modified permissive overreach transfer trip (POTT) scheme along with a fault current classification technique is proposed to address these problems for both types of IG-based WFs, and the accurate non-delayed protection of a distance relay over the entire line length is restored. The results of a comprehensive performance evaluation are presented to confirm the findings of this study and validate the efficacy of the proposed solution for all operating conditions. Results are particularly promising for the DFIG-based WFs with nonzero crowbar resistance, which is the most likely situation confronted by distance relays.