Dynamic residual phasor method for diagnosis of voltage unbalance in a noisy power system

This paper presents a unique fault diagnostic to detect voltage unbalance in a three phase noisy power system. This has been achieved by continuously adding the three phase voltages resulting in a residual voltage. This voltage has been transferred to the frequency domain using DFT algorithm through which the fundamental residual voltage phasor is obtained. Training data have been generated through computer simulation which reveals that (i) presence of harmonics in the voltage waveforms does not affect the fundamental component of the residual phasor in the frequency domain and (ii) unbalance in the voltages affect the fundamental component of the residual phasor in phase and magnitude thus making the residual phasor a dynamic one and hence the name. From the results of computer simulation some rules have been generated such that the amplitude and phase angle of the dynamic residual voltage phasor can be used as a diagnostic to detect the unbalance in a power system in a noisy environment. An algorithm is developed using the rules which has been validated through unknown signals in laboratory.