A new method for discrimination of internal fault from other transient states in power transformer using Clarke’s transform and modified hyperbolic S-transform

Abstract

In this paper, a new method is proposed for discriminating internal faults from other abnormal conditions in power transformers such as inrush currents, external faults, over-excitation, and ultra-saturation. Since the differential current signals are non-stationary, a powerful tool such as S-transform is needed for their time-frequency analysis. In this study, some important characteristics are extracted using the Clark’s transform and modified hyperbolic S-transform according to which different conditions are distinguished and classified. These features include energy contour of first level, variance index, standard deviation of second harmonic component, and a special criterion. In this paper, all possible transient conditions and the effects of the saturation of current transformers are considered. Various simulations for different operating conditions of transformer are performed via PSCAD/EMTDC software. Also, the entire process of modified hyperbolic S-transform and the proposed algorithm are done in MATLAB software. Simulation results show that the proposed algorithm can be reliably used for the identification and classification of different faults in transformers.