Type detection of voltage sags through voltage unbalance factor

This paper presents a new method to characterize and detect the type of voltage sag through complex voltage unbalance factor (CVUF). Different types of voltage dip due to unbalance faults in power system are evaluated in term of CVUF and an attempt is made to characterize and detect the types of dip through this factor. Phase angle jump and zero sequence voltage have been considered for the real and accurate characterization of voltage sag. A new term VUF gradient (VUFG) has been defined to show that how fast dip severity reduces with the propagation of dips. Analysis result in, VUFG is more in case of dip associated with line to line (LL) or double line to ground (LLG) faults where as it is small for dip is associated with single line to ground (SLG) fault. Further it has been revealed that the CVUF plane has the ability to characterize, detect, show the effect of dip propagation through transformer and determine dip severity simultaneously and hence characterization of dips through this plane is very informative, logical and real.