S-transform-based Expert System for Classification of Voltage Dips
Dan Chen · Proceedings of the CSEE · 2007
Based on the time-frequency representation, known as S-transform, an expert system for classification of voltage dips (sags) is proposed. Different voltage dips, induced by faults, self-extinguishing faults, transformer energizing and motor induction, are analyzed and distinguished according to their distinct characteristics in three-phase magnitude, harmonics, step changes and phase angle shift. Applying S-transform, these characteristics are extracted and quantified using magnitude factor, increments of harmonics, numbers of step changes, and increments of maximum phase angle shift. Then the illation algorithm and rules of expert system are constructed, and a binary-decimal conversion classification approach is introduced for well and truly outputting the classification results. Moreover, a simple method for analysis of multistage voltage dips is presented. The results of simulation and actual examples show this expert system is effective for classifying voltage dips.