There were many accidents of large-scale wind turbines disconnecting from power grid in2011.As single- phase-to-ground fault cannot be correctly detected，single-phase-to-ground fault evolved to phase-to-phase fault. Phase-to-phase fault was isolated slowly，thus leading to low voltage.And wind turbines without enough low voltage ride-through capacity had to be disconnected from the grid.After some wind turbines being disconnected from the grid，overvoltage caused by reactive power surplus made more wind turbines disconnect from the grid. Based on the accident analysis，this paper presents solutions to above problems，including travelling waves based single-phase-to-ground protection，adaptive low voltage protection，integrated protection and control，and high impedance fault detection.The solutions lay foundations in theory and technology to prevent large-scale wind turbines disconnecting from the operating power grid.