Advanced voltage sag characterisation. Part I: Phase shift

The authors discuss an important, but often neglected voltage sag characteristic: the phase shift. Firstly, a critical review of existing methodologies and approaches is presented. Then, theoretical and experimental results on the ranges and relationships of phase shift values are reviewed. A numerical example and several recorded ‘non-conventional’ voltage sag waveforms are used to highlight some of the problems encountered in calculating a phase shift. Equipment and procedures to test single-phase and three-phase equipment sensitivity to voltage sags are also discussed from a phase shift point of view.