Distance Protection of Lines Connected to Induction Generator-Based Wind Farms During Balanced Faults

Wind farms (WFs) are increasingly integrated with high-voltage (HV) grids, for which distance relaying is normally the protection of choice. This paper reveals some serious defects of distance protection for the lines connected to induction generator (IG)-based WFs during balanced faults. 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 unfamiliar to the existing relaying practices. The detected failures can easily result in unnecessary WF tripping, thus jeopardizing the objectives pursued by the new grid codes that oblige WFs to remain connected to the grid during disturbances. 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 nondelayed protection of a distance relay over the entire line length is restored. A comprehensive performance evaluation confirms the findings of this paper and validates 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.

I. Introduction

Environmental concerns along with high energy costs have led to rapid growth of wind energy. The majority of wind energy facilities incorporate induction generators (IGs) [1]. The squirrel cage IG (SCIG) was the main technology deployed in early wind farms (WFs). Despite some drawbacks, SCIGs are cost-effective and continue to constitute a nonnegligible share of the currently installed wind capacity [2]. More importantly, doubly fed IGs (DFIGs) are widely employed in modern wind energy systems, particularly for the high power level, due to various advantages, such as variable-speed operation accompanied by reduced converter size [3].