In October 2009, a grid failure occurred in Texas, USA, which caused a double fed wind farm to be connected to the grid through a line with 75% series capacitor, it causes a subsynchronous oscillation of about 20 Hz. The amplitude of system voltage oscillation exceeded 2.0 pu, resulting in the disconnection of wind turbines and the damage of crowbar circuit. Since 2011, subsynchronous oscillation problem of wind farms dominated by doubly fed induction generators (DFIGs) in North China has also happened many times when they are sent out through serial compensation lines. During the commissioning of a domestic demonstration project of flexible DC transmission, the subsynchronous oscillation with oscillation frequency of about 30Hz was recorded when the doubly fed wind farm was connected to the modular multilevel converter based flexible DC (MMC-HVDC) system, which led to the outage of the flexible DC system.

Santanghu area in Hami, Xinjiang is a typical weak AC system, where large-scale wind turbines are connected to the grid and sent out through long-distance AC. There are two 220kV wind power transfer stations in this area, with the names of Tiandianmahuanggou west wind power transfer station and Longyuanmahuanggou east wind power transfer station. The two 220kV wind power transfer stations share a 220kV transmission line, which is connected to 750kV Hami substation through Shanbei substation Power station.