Study On Oscillation Identification Based On Wide Area Measurements

Low frequency oscillation often occurs in the situation of grid interconnection in China and may cause distance protection mal-operation, which threatens the safe and stable operation of power system. Meanwhile, grid complication increase the possibility of multi-frequency oscillation greatly and brings challenges on traditional oscillation identification method based on local information. With the application of wide-area measurement device and the improvements of communication, favorable condition is provided for oscillation identification using wide area information.The paper focuses on the power swing blocking and rapid open of fault in swing, especially on discrimination of a three-phase fault from a power swing. The contribution of the paper is as follows:1) An oscillation identification scheme based on sine impedance measurement is proposed. Define the ratio of the voltage sine component and the amplitude of current as sine impedance measurement, its simple calculation method was deduced; Then summing the sine impedance of both line sides. The sum is equal to the line impedance in oscillation and is bigger than the line impedance on the contrary. Finally, oscillation identification scheme is constructed based on the difference of the sum of sine component of impedance. Simulation results show that the proposed scheme can discriminate three-phase fault from a power swing with system impedance unknown.2) An oscillation center tracking and distance protection blocking scheme based on wide area measurement is proposed in this paper. Firstly, the voltage sine component on two sides of the line is calculated. Then, the oscillation center location function and the electric distance ratio can be calculated to realize real-time tracking of oscillation center. Finally, the swing blocking and re-open scheme is constructed through the difference of electric distance ratio between oscillation and fault. Simulation results show that the proposed scheme can realize fast-track of power system oscillations central location and improve the performance of distance protection swing blocking and re-open effectively.3) An oscillation identification scheme under multi-frequency oscillation situation is studied in the paper. Based on the three-machine equivalent model of power system multi-frequency oscillation, the variation characteristics of measured impedance and effects on operating characteristics of impedance relay is analyzed under multi-frequency oscillation situation. Then, the corresponding swing blocking scheme distance protection is constructed using the action information of wide area protection. And the re-open scheme of symmetry fault in oscillation based on dynamic phasor fitting error of measured current during swing blocking constructed. Finally, simulation results of a three-machine system and a real regional power grid in PSCAD verify the correctness and feasibility of the proposed scheme.