Modal Analysis of Power Systems Through Natural Excitation Technique

The analysis of electromechanical oscillatory modes offers essential information on the stability of power systems. This paper investigates the use of the natural excitation technique (NExT) in conjunction with the eigensystem realization algorithm (ERA) for the modal analysis of power systems. The NExT-ERA is a multivariate method utilizing data that are measured from several locations in the power grid. The method is capable of utilizing synchronously measured data from a wide area monitoring system (WAMS) as well as unsynchronized measurements, such as measurements of individual relays´ recorders. The performance of the NExT-ERA method is analyzed by applying it to data generated with test systems. The method is also applied to actual measurements received from the Nordic power system. The results indicate that the frequencies and damping ratios of electromechanical oscillatory modes can be analyzed by using the NExT-ERA method. Thus, the method is a promising identification technique for wide-area monitoring of electromechanical oscillations.