Impact of LVRT capability of wind turbines on distance protection of AC grids

When a transmission line close to a wind farm (WF) with doubly fed induction generators (DFIGs) experiences a short circuit (SC) fault, the resulting voltage dip on the WF terminal bus may trigger actions from the crowbar circuits of DFIGs. These actions prevent high rotor currents that can be damaging to power electronic converters. Under this condition, DFIGs have to absorb reactive power from the external power grid to provide generator excitation. As a result, it will further depress the voltage at the WF terminal bus and affect the protective relay operation of transmission lines in severe situations. This paper is concerned with the performance of distance relays on a power grid with WFs that are equipped with crowbar circuits. Numerical simulations are conducted on IEEE 39 bus system with WF connections. It is found that the fault on the terminal line of a WF is likely to induce mis-coordination of distance relays, leading to system security problems.