Pages: 10-23

Abstract

Transformers are crucial equipment in a power system, which require reliable solutions for their protection to ensure smooth operation. Identification between internal fault current and inrush current is a challenging problem in the design of transformer protection relay. Current transformer saturation and large inrush currents are the most reported cause of the discrimination algorithms mal-operation. In order to eliminate the impact of the current transformer (CT) saturation on the performance of the proposed technique, the currents are compensated by a CT saturation compensation algorithm in the first step. This paper presents a novel algorithm for power transformer differential protection which differentiates internal faults from magnetizing inrush currents using wavelet packet transform (WPT). The technique is based on pattern recognition of the instantaneous differential currents using wavelet transform. The high-frequency components generated during the disturbance are extracted using a wavelet-based processor stage. In this method, an appropriate criterion at a suitable frequency range is developed. The proposed algorithm is evaluated using various simulated inrush and internal fault current cases on a power transformer that has been modeled using Electromagnetic Transients Program software (EMTP). The results obtained from the proposed technique show good accuracy for discriminating faults in the considered system. In addition, the proposed algorithm uses data of the differential current with a time of quarter cycle under the analysis.