G. Yalcinkaya et al., CHARACTERIZATION OF VOLTAGE SAGS IN INDUSTRIAL DISTRIBUTION-SYSTEMS, IEEE transactions on industry applications, 34(4), 1998, pp. 682-688
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.