Analysis For Fluctuation Mechanism Of Tie-Line Active Power Of Interconnected Power System And Its Relative Appications

Power system low frequency oscillation is an important stability issue of the large-scale interconnected power system. Along with the increasing use of the wide-area measurement system(WAMS) in grid monitoring and controlling, new methods for the monitoring of low frequency oscillation and the location of disturbance sourses come forward. The daily statistics of valid disturbances recorded in the historical data of WAMS can reflect the stability level of a power grid. As the change of damping ratio is usually taken as an important figure to indicate the change of the stability level of a power grid, so the thearetical study of the relationship of oscillation times and the damping ratio is of great significance to analysis and assess the grid stability. For a large system, the disturbance exerted on different nodes causes different variation and waveform of tie-line active power, which means the node sensitivity varies with different node. How to use the node sensitivity to accelarate the process of the location of disturbance and to guide grid planning is worth studing.In this paper, the formulas of the small signal analysis including power disturbance on the grid is given firstly, then the time domain expression is deducted and the relationship between damping ratio and response of the oscillation magnitude of the tie-line active power is analyzed. Based on that, two ways of applications are put forward in terms of assessing the damping level of the power grid based on the daily oscillations number recored by WAMS and pre-location of disturbance sourses based on node sensitivity. Finally, cases study based on the 10-machine 39-bus power system and models of certain areas of hubei grid verified the validity of the proposed methods.The theoretical method can give a dedail description of how the disturbance is allocatied through both the network equation and dynamic equation, which proves to be a quick and relatively precise way to analysis the characteristics of the tie-line active power occilation, as an alternative of the time domain simulation of the system. Its first application way can evaluate the system damping level by the observation of daily oscillations number recored by WAMS, while its second application way can provide pre-knowledge of possible disturbance sources to accelarate the process of the location of disturbance when accident happens and can regulate resonable load layout in the grid planning phases by adding more monitoring and precaution on nodes with high sensitivity based on the indicator of sensitivity.