Effect of Reactive Power Limit Modeling on Maximum System Loading and Active and Reactive Power Markets

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.