A new definition of voltage sag duration considering the voltage tolerance curve

This paper presents a new definition of voltage sag duration which takes into consideration of the voltage tolerance characteristics of individual electrical equipment. The magnitude and the duration of voltage sag are important parameters which characterize the voltage sag event. The conventional voltage sag characterizing method can overestimate the voltage sag in case of non-rectangular sag. Furthermore, it does not take the voltage tolerance characteristics of each equipment into account. Therefore the proposed method in this paper utilizes the minimum voltage (V_min) of voltage tolerance curve of each equipment. The voltage sag profile is approximated with the k^th radical root function and the effective duration is newly defined considering the voltage tolerance characteristics. The new voltage sag duration is applied to the non-rectangular sag originated from induction motor starting and compared to the maximum time(t_max) to determine whether the voltage sag event can affect the equipment or not.