Testing of a wavelet packet transform-based differential protection for resistance-grounded three-phase transformers

This paper presents an extension of real-time tests of a wavelet packet transform (WPT)-based technique for three-phase power transformers differential protection. The proposed technique is implemented using a DS1102 digital signal processor (DSP) board and tested on two different three phase power transformers with neutral resistance-ground. Different magnetizing inrush and internal fault currents are investigated with CT saturation for different loading conditions, including capacitive loads. The results show a complete independence from transformer parameters, load types, grounding method or CT saturation. Furthermore, the proposed technique has high speed, good accuracy, small required memory and reliable responses with reduced computational burden. In all cases of the investigated internal faults, the proposed algorithm is capable of identifying the fault and generating a trip signal in less than a quarter cycle based on 60 Hz system.