Monitoring of interarea oscillation mode by synchronized phasor measurement

There is a low-frequency interarea oscillation mode in middle and western 60-Hz areas of Japan. Its stability determines available transfer capacity of a tie-line. We propose a method of monitoring its stability by phasor measurements synchronized using the global positioning system. The phase angle between two places deviates randomly. However, its Fourier spectrum shows a clear peak corresponding to the interarea mode. We estimate its frequency and damping from the spectrum. The estimation results agree well with those obtained by curve fitting for large disturbances. It is also possible to estimate the eigenvector. We examine how the eigenvalue varies with the total generation and power flow in the areas.