Fault Studies and Distance Protection of Transmission Lines Connected to DFIG-Based Wind Farms
Smart Grid Key Laboratory of Ministry of Education, Tianjin University, Tianjin 300072, China
Maintenance Company of Tianjin Electric Power Company, Tianjin 300250, China
Electric Power Dispatching Control Center of Guizhou Power Grid Company, Guiyang 550002, China
Author to whom correspondence should be addressed.
Appl. Sci. 2018, 8(4), 562; https://doi.org/10.3390/app8040562
Received: 12 February 2018 / Revised: 30 March 2018 / Accepted: 31 March 2018 / Published: 5 April 2018
(This article belongs to the Special Issue Large Grid-Connected Wind Turbines)
Doubly fed induction generator (DFIG) based wind farms are being increasingly integrated into power grids with transmission lines, and distance protection is usually used as either the main or the backup protection for the transmission line. This paper analyzes the composition of a DFIG short circuit current and indicates the existence of a rotor speed frequency component. By analyzing several real fault cases of the DFIG-based wind farms connected to transmission lines, the weak power supply system and current frequency deviation of the wind farm side are illustrated. When a fault occurs on the transmission line, the short circuit current on the wind farm side is small and its frequency may no longer be nominal due to the existence of rotor speed frequency component, whereas the voltage frequency remains nominal frequency because of the grid support. As a result, the conventional distance protection cannot accurately measure the impedance, which can result in unnecessary circuit breaker tripping. Therefore, a time-domain distance protection method combined with the least-squares algorithm is proposed to address the problem. The efficacy of the proposed method is validated with real fault cases and simulation.