S-Transform Based Power Quality Indices for Transient Disturbances

Power quality indices characterize the nature of a power quality problem and serve as the basis for evaluating its negative impact. Due to the limitation of the traditional power quality indices in measuring transient disturbance signals, new power quality indices are developed in this paper based on S-transform. In the accurate time-frequency domain of S-transform, define four indices: instantaneous RMS (IRMS), instantaneous harmonic distortion ratio (IHDR), instantaneous waveform distortion ratio (IWDR) and instantaneous average frequency (IAF) and these indices can represent time-varying characteristics of transient disturbances. The accuracy of new power quality indices are verified using a set of disturbances, both represented mathematically with known parameters and simulated in PSCAD/EMTDC.