Analysis Based On Local Voltage Stability Index Of Power Systems And Its Margin Sensitivity

The voltage stability of power system has always been hotspot for many scholarsfor domestic and overseas. With the growing demand for electricity in China, and thecontinuous expansion of power grid, the operation of power grid has becomeincreasingly complex. Voltage collapse occurs frequently due to voltage instability.Therefore, to seek a reasonable voltage stability safety indicators, design effectivestrategies for voltage stability prevention and control, and provide new techniquetools and theoretical support for power line monitoring, prevention and correctioncontrol are of important significance for both theory and practice.At First，this paper introduces the background and significance of the topic aswell as the definition and classification of the power system voltage stability, thenintroduces the existing analysis methods of voltage stability in detail. Aiming at thelocality characteristic of system voltage stability, the local voltage stability index (Lindex) is analyzed in this paper, based on which the total differential equation isderived. Consequently the concept and physical meaning of the voltage stabilityindex-reactive sensitivity (L-Q sensitivity) are presented comprehensively.As L index failed to give more information associated with the node voltagestability, this paper represent the load node voltage stability margin sensitivitycalculation method based on the wide-area measurement information. In view of theinsufficiency of the system voltage stability margin, according to different operatingconditions, a variety of wide-area voltage stability margin sensitivity strategies areintroduced to improve system voltage stability.Aiming at the mixed node in power network where the generator and the loadcoexist, the combined impact of the generator and load in the mixed node for indexvalue is taken into account, and four schemes are proposed in order to improve theaccuracy of the local voltage stability index. Four schemes are as followed:1) themixed node is handled as generator internal potential node and load node where the voltage is controllable;2) the generator is connected to the mixed node via thestep-up transformer with zero-impedance;3) the load is connected to the mixed nodevia step-down transformer with zero-impedance;4) the generator is connected to themixed node via the step-up transformer and the load via step-down transformer. Theprocessing flow for on-line monitoring of the voltage stability based on the method ofthe paper are designed. Simulation results show that the method presented in thepaper is of certain reference for improving power system voltage stability on-linemonitoring of the accuracy.