CHARACTERIZATION OF VOLTAGE SAGS IN INDUSTRIAL DISTRIBUTION-SYSTEMS

This paper describes the various characteristics of voltage sags exper ienced by customers within industrial distribution systems; Special em phasis is paid to the influence of the induction motor load on the cha racterization of voltage sags. During a fault, an induction motor oper ates as a generator for a short period of time and causes an increase in sag magnitude. Its reacceleration after the fault clearance results in an extended post-fault voltage sag. The influence of the induction motor on the imbalanced sags caused by single line-to-ground faults ( SLGF's) and line-to-line faults (LLF's) has been analyzed in detail. F or an imbalanced fault, the induction motor current contains only posi tive- and negative-sequence components, Induction motors create a low impedance path for the negative-sequence voltage due to an imbalanced fault. This causes a small sustained nonzero voltage with large phase- angle jump in the faulted phase and a voltage drop in the nonfaulted p hases with a small phase-angle jump. The symmetrical components of the induction motor during the imbalanced sags have been studied. The res ults show that induction motor behavior is determined by positive- and negative-sequence voltages during the imbalanced sag.