Voltage-sag magnitude and phase jump due to short circuits in distribution systems with variable fault resistance

Voltage sags mainly caused by line faults in transmission and distribution systems have become one of the most important power quality problems facing industrial and commercial customers, as well as utilities. Voltage sags are normally described by characteristics of both magnitude and duration. Phase-angle changes that greatly affect several electronic equipment should be taken into account in identifying and characterizing the sag phenomenon. In this article, voltage sags due to line faults, such as three phase-to-ground, single line-to-ground, and line-to-line faults, for fault impedance (resistance) variation are firstly characterized by using symmetrical component analysis. Different line fault types, fault resistance magnitudes, and their effect on voltage sag magnitude variations together with phase-angle jumps are examined. In order to verify the analyzed results, simulations based on power circuit models are presented. The described methodology is useful in short-circuit studies by giving a quick qualitative assessment of the voltage sag magnitude and phase jump when fault resistance is changed between its extreme values.