Study On Multi-frequency Oscillation Identification Based On Wide Area Measurements

The possibility of power system oscillations caused by disturbance is increasing in the complex grid operating environment in China.The types of complex power system oscillations are diverse and the modes are variable,showing new oscillation characteristics.Thus bringing new challenges to the reliability of the power swing blocking and out-of-step splitting devices.With the application of wide-area measurement device and the improvements of communication,favorable condition is provided for oscillation identification using wide area information.This paper focuses on the out-of-center tracking and oscillation identification principle using the advantage of wide-area information in multi-frequency cases.The main contribution of the paper is as follows:1)The variation characteristics of electrical quantities and oscillation characteristics under the multi-frequency oscillations are studied.Firstly,embarking from the model of multi-frequency oscillations,the expression of voltage and current under multi-frequency oscillation is deduced and their regularities of distribution are analyzed.Then,based on the definition of oscillation center,the oscillation center location function is constructed to realize the quantitative description of oscillation center location.On this basis,the distribution rule of oscillation center location and out-of-step center location are introduced.Finally,an out-of-step center location method based on voltage phasors is proposed.2)A new oscillation center identification method based on the frequency variation trend of each side is proposed.Firstly,based on the expression of voltage and current at any point in the system,the frequency expressions of voltage and current are deduced.Then,the variation trend and distribution rule of voltage and current frequency in multi-frequency oscillation system are analyzed.The relationship between the frequency distribution of the system and the oscillation center as well as the out-of-step center is studied.Finally,an oscillation center tracking scheme based on the trend of system bus frequency is proposed.The proposed scheme can effectively track the oscillation center of the multi-terminal oscillating system.3)The scheme of blocking and re-opening distance protection under multifrequency oscillation is proposed.Firstly,the expression of the measured impedance under the multi-frequency oscillation is deduced,and the variation characteristics of the measured impedance as well as its influence on the operating characteristics of the impedance relay are analyzed.Then,based on the relationship between the out-of-step center location and the measured impedance,the out-of-step center position factor is defined,and a protection blocking criterion based on out-of-step center position factor is constructed.Finally,the protection re-opening criterion based on the out-of-step center factor amplitude variable is proposed,using the saltation characteristics of the amplitude and phase at the out-of-step center when fault occurs.This scheme can effectively block the protection during the oscillation,and can re-open the protection quickly even when fault and the out-of-step center occurs at the same time.