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失步振荡过程中应采用瞬时频率来表征失步过程中的电网特性.该文搭建基于瞬时频率的两机振荡模型,分析失步振荡过程系统频率特性.失步振荡中心处电压瞬时频率等于两侧机组频率和的均值,失步振荡中心两侧母线瞬时频率变化趋势相反,没有交集,在系统功角摆开至 180°时,达到其极值.当振荡中心落在系统内部,电流瞬时频率介于机组频率之间,且仅当两侧机组电压幅值相等时,线路上电流瞬时频率等于失步振荡中心电压瞬时频率.理论分析基于瞬时频率信息的振荡中心定位方法:装设在线路一侧的振荡解列装置,只需引入线路对侧变电站母线电压瞬时频率信息即可判断振荡中心是否落在本线路上,并能定位振荡中心的位置.仿真验证了所提振荡中心定位方法的正确性.“,”Instantaneous frequency should be used to reflect power system characterization in the process of out-of-step oscillation. A two-machine oscillator model based on instantaneous frequency was set up to study voltage and current frequency response in the process of out-of-step oscillation. Voltage instantaneous frequency of out-of-step oscillation center is equal to the unit frequency combined. The bus voltage instantaneous frequency move in opposite direction and have no intersection in two sides of the out of step oscillation center. Voltage instantaneous frequency reaches its extreme value when power system angle is 180°. The current instantaneous frequency between the two unit frequency if the oscillation center falls within the system, and only when both units have the same voltage amplitude , the instantaneous frequency is equal to the instantaneous voltage of out of step oscillation center. A method to pinpoint oscillation center based on instantaneous frequency was put forward. Oscillation splitting device installed in substation can not only judge that whether the oscillation center is on line but also can accurately pinpoint the oscillation center position, by simply introducing voltage instantaneous frequency information of the other substation. Simulation results verify the correctness of oscillation center location method.