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

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.