A modified sag characterization using voltage tolerance curve for power quality diagnosis

This paper newly defines a voltage sag duration considering the voltage tolerance characteristics of individual electrical device for power quality (PQ) diagnosis. The conventional sag characterizing method has the possibility to overestimate voltage sag in case of nonrectangular sag. Furthermore, it cannot take the voltage tolerance characteristics of individual device into account. The proposed method utilizes the monitored parameters (V_sag,V_avg,d) at PQ monitor and the minimum voltage (V_min) of voltage tolerance curve. The voltage sag profile is approximated using k^th order radical root function and finally the sag duration is modified from this function. The proposed method is applied to the nonrectangular sag due to induction motor reacceleration. It effectively evaluates the actual effects of voltage sag on the customer equipments whether the sag is rectangular or not.