LOAD MODELING IN OPTIMAL POWER FLOW RECOGNIZING VOLTAGE LIMITS

Abstract

ABSTRACT Effects of load modeling in OPF studies under certain conditions are analyzed for the IEEE/AEP 5, 14, 30, 57 and 118 bus systems. Eight 8 test situations are created by changing the loads of three of the systems. In contrast with earlier work, generator voltages are allowed to vary within specified limits. Reactive generation constraints are considered as before and transformer taps not optimized in this study. The fuel cost is selected as the objective and exponential load models with identical exponents used at all buses for the modeled cases. All loads are assumed to vary with the respective bus voltages and to have specified values at nominal voltage. The optimization is carried out with an optimization package which uses the Projected Augmented Lagrangian Technique of nonlinear programming. It is concluded that: incorporating load models for the active powers in OPF studies gives entirely different operating conditions than those obtained using a standard OPF. Incorporating reactive power load models when the active powers are considered as specified constants does not produce such a big difference in the operating conditions. However incorporating both active and reactive power load models produce the most significant changes’ in the operating conditions. The new operating conditions obtained when both active and reactive loads are modeled as functions of voltage, give a reduced total fuel cost, by lowering the total active power demand which may not be desirable. An alternate approach is suggested where the total active power demand is constrained to a pre-specified value.