Principle of Fault Direction Identification for the Outlet near the Main Transformer of Doubly-fed Wind Power Station

Among the many new forms of energy, wind power generation has become one of the most potential forms of renewable power supply for commercial development due to its mature technology and large-scale development conditions. The compound voltage direction overcurrent protection of transformer is the backup protection of interphase short circuit of transformer and adjacent equipment. However, the traditional principle of direction identification based on power frequency phasor has adaptability problems in doubly-fed wind power access system. In this paper, the fault characteristics of the main transformer of a double-fed wind power station are analyzed. The calculated voltage and measured voltage are exactly the same when the forward direction fault occurs at the main transformer outlet, and the change trend is approximately opposite when the negative direction fault occurs. Based on the change trend of voltage waveform, the principle of fault direction identification at the outlet of main transformer in doubly-fed wind power station is proposed. The simulation analysis shows that the principle can identify the fault direction accurately.