Research on Main Transformer Protection of Doubly-Fed Wind Farm Based on Fault Current Frequency Difference

There are differences in the electromagnetic transient characteristics between the wind power access system and the traditional power grid during the fault, resulting in the problem of adaptability deterioration of the relay protection equipment in the wind power access system. In the PSCAD simulation platform, the adaptability of the traditional transformer protection in the wind field is further analyzed. When the fault occurs in the transformer zone, the differential protection cannot be quickly and stably operated, the transition impedance causes the protection to be rejected, and the traditional transformer protection does not adapt to the wind power access system. Based on the analysis of the characteristics of the doubly-fed wind farm and the system fault transient current frequency, the transformer protection based on the difference of current frequency is proposed, and the action criterion is constructed by using the difference of instantaneous frequency. The simulation results show that the protection method can reliably and sensitively identify various types of short-circuit faults inside and outside the transformer, adapt to different wind speeds, and withstand the ability of transition resistance.