Research On On-line Monitoring Of Voltage Stability Based On Phasor Measurement Unit Information

In recent years, blackouts of the grid resulting from voltage collapse,which is caused by the voltage instability,have sometimes occurred worldwide,resulting in great economic losses and social impacts.Therefore seeking for reasonable voltage stability indicators to provide technical means to monitor the grid voltage online has important theoretical and practical significance for the stable operation of the whole grid system.The traditional method,offline analysis of voltage stability based on flow equations, not only has intensive calculation but also have difficulty in real-time tracking changes in the actual system operation modes.With the development of the simultaneous measurement technology,PMU (Phasor Measurement Unit) has been widely used in the power grid, providing a wealth of accurate, reliable, high-speed data for the real time monitoring of the power grid dynamic process, making the online real-time analysis and monitoring system security status possible, and providing a new solution idea for voltage stabilization online monitoring of the large load center.Voltage stability usually appears as a local phenomenon, Voltage instability often began to cause from the weakest node of voltage stability in the system and gradually spread to the surrounding relatively weak nodes (regional), and eventually cause the system voltage collapse.Firstly,the paper introduces the background and purpose or significance of the subject, as well as the definition and classification of power system voltage stability and a comparative detailed review of the existing voltage stability analysis methods. Secondly, basing on the Chongqing power grid model and the basic database,this paper carries out simulation and calculation of the various types of contingencies.which can assess static security and stability of Chongqing power grid and find out the cricial contingency of the Chongqing power grid.Then the factors of instability are simulated and analyzed.By means of combined PV curve with sensitivity index method and eigenvalue analysis method in the modal analysis technology to identify voltage weak nodes and the major influence factors. The maximum transmission power and the PV curve of the system can be calculated by the continuous power flow method.And the system sensitivity index and the full mode method are analyzed and calculated in the steady-state operating point and limit operating point of the grid in this paper. By comparing and synthesizing the results to identify the voltage weak node and.the transition of the weak node along with the change of system operation mode more accurately. And based on this result to configure the measurement points of PMU online monitoring.On the base of above-mentioned, The voltage stability index which based on the existence of the real solution of the branch voltage equationis is derived in this paper. And based on this index, the new index of the branch condition of the two running sections is defined. Finally The validity and feasibility of the proposed indicators are simulated and verified,which based on electrical information of the key nodes and branches measured by PMU in the EPRI36 node system.