Voltage dips and swells detection by sliding fast Fourier transform: Possibilities for application in modern distribution networks

Abstract This paper deals with applying the sliding Fast Fourier Transform analysis to detect voltage dips and swells in modern distribution networks. Significant odd and even voltage harmonics appear during voltage dips and swells, and they can be used to detect these events. Since the voltage waveshape during the dips and swells have the same harmonic content, the separation of these events can be done by calculating the angles of the voltage harmonics at the moment of the event. In the case of voltage swells phase angles of the 1 st and the higher order harmonics have the same polarity, while in the case of voltage dips phase angles of the 1 st and of the higher order harmonics have the opposite polarity. The presented approach is verified by analyzing mathematical signals and signals measured in real distribution networks with renewable sources. The limitation of the analyzed method is that the amplitude of voltage variation during the dip or swell in a real distribution network cannot be reliably associated with the calculated values of voltage harmonics. This limitation can be overcome by considering the value of 1 st voltage harmonic, or RMS voltage value calculated for one cycle or half cycle of the voltage wave.