Study of reactive power/voltage sensitivities in interconnected power system networks

Abstract

The strong coupling between bus voltages and reactive power injections has been widely used in steady state power flow algorithms. In the Newton-Raphson formulation the Jacobian matrix represents small-signal sensitivities relating real and reactive power injections to bus phase angles and voltage magnitudes respectively [1]. Decoupled approaches neglect real power-voltage and reactive power-phase angle relationships. While running the power flow analysis, the generator busses, where the real power injection and voltage magnitude are specified a priori, are changed to load busses with the voltage specification dropped if reactive power limits are violated. The papers describing optimal reactive power scheduling methods follow a similar procedure for evaluating appropriate generator reactive power levels [2]. Direct relationships between bus voltage and reactive power injection limits leading to useful sensitivities are derived in this paper using a line-voltage-drop model. Additional relationships between bus injection and line reactive flows become available in this approach. The paper presents detailed derivation of the new relationships, and applies the procedure to a typical power system network. The results illustrate the practical usefulness of the new approach in determining the limits on reactive power injection for a given bus voltage in generator busses. The conclusions outline future application of the approach for developing new reactive power optimization algorithms.