Analysis on and precautions against large-scale wind turbines off-grid

In the last few months, off-grid accidents of a large number of wind turbines in several large-scale wind power bases frequently occurred during the windy weather, severely threatening not only secure operation of wind farms but also secure the stable operation of power grid. This paper analyzes the cause of the “2.24” large scale wind turbines off-grid and other accidents, having found some common problems of the existing wind farms: firstly, almost none of wind turbines in operation has the low voltage ride through (LVRT) capability; secondly, dynamic reactive power compensation devices are functionally in-complete and chaotically managed; thirdly, poor construction techniques and equipment in-stallation are found in wind farms; fourthly, the main control system functions of wind turbines haven't been unveiled to users, and their coordinated control strategies do not meet the requirements, which demand wind turbines keep on-grid during grid voltage instantaneously drop; fifthly, all 35kV (10kV) systems in wind farms are not grounded, in which the single-phase grounding can quickly develop into phase to phase or three-phase fault to exaggerate the accident. Besides, the small current grounding line in 35kV systems is not reliable. In the current situation, this paper proposed countermeasures how to prevent large-scale wind turbine off-grid accidents, generally speaking, rectifying wind turbine LVRT capacity, refreshing wind turbine protection programs, opening reactive power regulation function of wind turbines, optimizing small current grounding line as well as improving the functions of dynamic reactive power compensation devices and strengthening the management of use, etc.