A Modified PUTT Scheme for Transmission Lines Connecting DFIG-Based Wind Farm

With the large integration of wind turbine generators (WTGs) in the power grid, the protection of the transmission lines connecting to the WTGs has become a great concern. Doubly fed induction generators (DFIGs) are among the most widely installed WTGs, but the frequency deviation of the fault current measured at the wind farm side relays due to the short circuit behavior of DFIGs with the activation of the crowbar circuit has resulted in the failure of distance relays used for protection of transmission lines connecting DFIGs. This paper proposes a modified permissive underreaching transfer trip (PUTT) scheme that provides fast and reliable protection for the transmission lines connecting DFIG-based wind farms. By adding the frequency tracking elements to the conventional PUTT scheme, the modified scheme correctly blocks the maloperation of the distance elements during external faults, enables the trip of the relay during internal faults, and significantly improves the security of the relay at the wind farm side.