Instability of Low-Frequency Oscillation in Longitudinal Power System due to Autoparametric Resonance

Abstract

In this paper, autoparametric resonance in longitudinal power systems is investigated. The resonance occurs in narrow area of parameters, and even if it occurs, it is swiftly suppressed by generator dampings in the previously studied power systems. This paper shows that the autoparametric resonance occurs very naturally in longitudinal power systems. First, it is shown through simulations that a low-frequency oscillation con-spicuouly changes its magnitude, which gets larger with fault-period, and finally causes a system-separation. Next, the above phenomenon is reproduced by strictly solving the mode equations, and it is clarified that the resonance occurs between two modes with the lowest and the second lowest frequencies. Furthermore, it is shown with the Mathieu diagram that the resonance gets stronger with system size, and accordingly it becomes an important factor to determine the system size. The stable system size gets larger with effects of generator dampings and AVR, but gets smaller with generator capacity, which means that the resonance gets stronger with system capacity, too. Lastly, the resonance potentially exists in a real-size system, but it is not actualized owing to AVR and generator dampings.