Application Study Of Wide-Area Measurement System In Power Systems

Wide-Area Measurement System (WAMS) is an organic assembly which includes the Phasor Measurement Units (PMUs), high speed digital communication equipments and grid dynamic analytic equipments. A new technology being developed in recent years is recognized as one of the three front subjects in power systems. WAMS can obtain the real time steady and dynamic information of each bus at the same referenced time, which provides the conditions for steady and dynamic system supervision and control, also makes sure the safety of the system.This thesis will study and analyze the WAMS and the PMU unit firstly. Then use the synchronous system data measured by the PMU to study the application on the system supervision. The main work is as follows: 1) On the base of researching the inspecting theory, expound the observability concept from algebraic and topological view points. Build a mathematic model for the PMU optimal placement of power grid observability. And study the two typical DFS (Deep First Search) and SA (Simulate Anneal) algorithms, and propose a new optimal algorithm: MST (Minimal Spanning Tree) algorithm. This algorithm is based on the graph theory and innovatively proposes the searching rules: search the buses to furthest overlay the grid. And this method can improve the quality of the solutions and the computing speed; also achieve the solutions'variety. The results of the example simulation show: MST overcomes the disadvantages of DFS and SA, but keeps the advantages of them; it can acquire an excellent balance between the astringency of the solution and the calculation speed. In the PMU optimal palcement for New England 39-bus grid, from the MST algorithm, using 9 (23% of the buses'total number) PMU can realize the grid observability, which is easy to apply in the real grid.2) The traditional methods of fault localization use the perfect line parameters. These methods have difficulties in further improving the precision because of the unstable line parameters. To solve this problem, this thesis proposes using PMU to calculate the dynamic line parameters: use the synchronous node voltage and line current phasor data and the long line equations to calculate the real time line parameters. This method can avoid the fault locating error caused by the parameters unstable. Then build a precise model for the transmission lines, which considers the distributed line capacitor. The new proposed fault localization algorithm is based on the PMU two ends data, not subjected to the operation modes, environment, distributed capacitor, fault resistance and fault location and achieves 99.95% precision. The simulation results illustrate the correctness and accuracy of this new method.3) An inspecting index of the online voltage stability based on the PMU real time measurement data is researched. To solve the voltage unstable problem caused by the loss of reactive power, propose an inspecting index of the online voltage stability which considers the distributed capacitor. Calculate and give the equation of this index. Because the line model of this index is more accurate, the indication effect is better than other indexes. And its independence to the inactive power direction makes its algorithm simple and easy to realize on the computer. The results of the IEEE example show: using this index, the online voltage inspection can be realized only according to the PMU real time data. Also the inactive power margin of the nodes can be reflected, providing the more accurate information for the voltage stability control (or unstable protection), which make sure the safety of power systems.