This paper presents a comparative investigation of
various representations of reactive power limits in maximum
loadability and active and reactive power market studies. Previously
proposed optimal power flow (OPF) models for these types
of analyses are first reviewed and briefly discussed. Different
models for representing reactive power limits in these optimization
problems are then presented, concentrating in particular
on the proper modeling of the generators’ capability curves
as terminal voltages change, which has been identified as a
shortcoming of previous studies. Comparative numerical analyses
of the effect of various reactive power limit models in maximum
loading and active and reactive power dispatch and pricing levels
are presented and discussed, to thus quantify the effect these
various limit representations have on the corresponding results.
Two test systems, namely, the CIGRE-32 benchmark system and
a 1211-bus dispatch model of a European network, are used
for numerical studies. The presented results show that in most
OPF applications, the improvement on the reactive power limits
representation lead to subtle differences at the cost of increased
computational complexity, which in some cases may be difficult
to justify in practice.