Detection and Characterization of the Instantaneous Point-on-wave of Voltage Sags in terms of Point of Inception and Point of Recovery

This paper proposes an analytical algorithm to detect and characterize voltage sags in terms of voltage sag inception and recovery angles which are commonly known as point-on-wave (POW). A preliminary study has identified that only three possible recovery angles can take place in each phase for all possible voltage sag inception angles. Based on these three voltage sag recovery points, voltage sag signals can be clustered into three groups each separated by 180 degree. This analysis shows that for a fault induced voltage sag the actual points of inception POI) and points of recovery (POR) depend on a few parameters such as PAJ (Phase Angle Jump), Y/Δ connection of transformer and load, and fault clearing time of protective devices. The proposed method is validated using voltage sag waveforms of different types of symmetrical and asymmetrical faults obtained from two different radial distribution networks. From the simulation results it is observed that for some particular starting angles the actual voltage sag duration may increase significantly which can be harmful for some sensitive equipment even if the sag is shallow in magnitude. This analysis also shows that the magnitude of the current transient also depends on voltage sag starting angle. A large current transient can cause disruption of some sensitive equipment.