A new method of voltage stability margin estimation based on local measurements

The paper presents a method of monitoring the local voltage stability of the power system at the receiving node. To estimate the voltage stability margin a simplified equivalent circuit - called the Thevenin´s equivalent is used. Publication concerns three main issues: creation and updating of the Thevenin´s circuit model, determination of voltage stability margin and verification of proposed methods. Two methods of Thevenin´s model parameters calculation are presented: analytical and based on local phasors measurements. To define the Thevenin´s parameters by using analytical method there is a need to know current configuration of power system. The second method uses only available locally measurements. During the changes of load admittance, actual value of bus voltage, apparent power and derivatives of apparent load power against the node voltage dS/dV are determined. This allows to update continuously parameters of Thevenin´s circuit and to follow the ongoing changes in the power system. These changes may be caused by normal switching operations or unexpected faults. Thevenin´s model parameters are used to calculate local voltage stability margin. The paper presents also the performance and accuracy tests of the algorithm used in calculation of Thevenin´s model parameters and algorithm for determining voltage stability margin.