Research On Characteristics Of The Out-of-step System Based On Wide Area Measurements

With the grid size larger and the structure more complex, inter-regional focal line structure tends to blur. The traditional offline determined splitting sections are no longer meeting the growing interconnected grid. Only making a full awareness of the out-of-step interconnected power system's running state, can propose the splitting measure adapted to out-of-step multi-machines system. Therefore, the study of large grid's out-of-step feature is the premise of all work. WAMS can provide simultaneous, accurate, small electrical delay measurement information of the whole network, and its construction and development provides new opportunities to solve the step splitting problem. To a new stage for the current large-scale interconnected power grid development, and the using of real-time dates of WAMS, researching characteristics of out-of-step large interconnected power systems provides an important basis for further study of the whole network step splitting control, and has important practical significance.The outward manifestation of the out-of-step power system is mainly about dramatic changes for electrical quantities. Under the guidance of idea, that "research-based simulation, analysis-supplemented theory", this paper carried out simulation observation of out-of-step examples for the New-England 39-units system and IEEE 118-units system. To make full use of WAMS information provided, this paper chose the typical two-terminal electrical quantities,which fully reflected the out-of-step oscillation nature, to make depth analysis. In this paper, carried out theoretical derivation about the phase angle of the voltage across the two ends, the variation of reactive power flow across the two ends and the frequency of voltage across the two ends where the oscillation center line and given the simulation results. This paper also carried out a qualitative analysis of multi-machine system about the distortion of out-of-step electrical characteristics and some special phenomena.The nature of the out-of-step power system is generator, because the generator groups are unable to run in accordance with the same angular velocity, leaving the relative power angle widening. To fully understand the out-of-step characteristics of multi-machine systems, it is necessary to study how the formation of unstable modes. That is, after the disturbance to instability, at which stage, how the oscillation mode of the system evolution into unstable modes. In the study of this aspect, trajectory section eigenvalues method was introduced. This paper proposed an idea on researching instability modes, namely "vertical comparison and transverse track", to research the evolution of the power system's instability modes. And for the synchronous oscillation, pendulum swing instability and multiple swing instability examples were carried out research and analysis, respectively. Finally, combined with the out-of-step characteristics of electrical quantities, presents a method to study the systematic unstable modes, and verify the accuracy of the simulation method.In summary, the out-of-step characteristics of the power system are analyzed in two ways. One is carried out theoretical analysis and simulation verification about variation of each electrical quantities and their special phenomenon after the grid out of step. Another is the use of trajectory section eigenvalues method to analyze the nature of the system instability, studied the process of formation and evolution of unstable modes and proposed an algorithm to research the grid instability mode.