Time-frequency and time-scale domain analysis of voltage disturbances

This paper discusses the analysis of voltage disturbance recordings in the time-frequency domain and in the time-scale domain. The discrete short-time Fourier transform (STFT) is used for the time-frequency domain; dyadic and binary-tree wavelet filters for the time-scale domain. The theory is explained with special emphases on the analysis of voltage disturbance data. Dyadic wavelet filters are not suitable for the harmonic analysis of disturbance data. Filter center frequencies and bandwidths are inflexible, and the results do not give easy insight in the time behavior of the harmonics. On the other hand, band-pass filter outputs from discrete STFT are well associated with harmonics and are thus more useful for power system analysis. With a properly chosen window size, the discrete STFT is also able to detect and analyze transients in a voltage disturbance. Overall, the STFT is more suitable than wavelet filters for the analysis of power system voltage disturbance data.