Research On Several Key Techniques Of Wide Area Security Monitoring System For Power Grid

With the implementation of 1000 kV EHV AC strategy, a wide area power system covering thousands of kilometers with installed capacity of 8×10~5 MW will be formed soon in China. Although the construction of national interconnected power grid benefits a great deal, it challenges the security, stability and economy of this power grid unprecedentedly. The present studies of large-scale blackout mechanism indicate that the vulnerability of power grids in blackouts has tight relationship with the load level and the network topology. As a result, there is a great practical significance and engineering value in the construction of reliable and effective wide area security monitoring system. Deficiency in robustness of the security monitoring systems played an important role in triggering and spreading the blackouts in history. Under such engineering background, this thesis conducts research on the robustness of wide area security monitoring system and obtains some innovative research results.Firstly, the monitoring system robustness is defined and the crucial impact of monitoring system robustness on power grid security is analyzed with the case study on multiple blackouts in the past. The characteristics and limitations of SCADA/EMS are presented and the WAMS is considered to be the future development highlight of power grid monitoring system. Problems in robustness which exist in the monitoring system based on the hybrid WAMS/SCADA measurement in the future are also analyzed.Secondly, a novel method is proposed to overcome the problems of numerical instability and divergence encountered in the traditional parameter identification methods. At first, the relative residual is employed to judge the existence of parameter error. Then the voltage and current phasors gathered by PMUs are used to establish the direct relationship among the variables on both ends of the branch. By this direct relationship, those branches with parameter errors can be identified and their parameters can be estimated by optimization method. Under this condition, all the parameters of transmission lines and transformers in the power grid can be estimated when only half of the buses are equipped with PMUs.Thirdly, an algorithm of PMU placement considering high risk cascading failures is proposed. Owing to the cascading failure, lines trip one by one, which makes the WAMS ultimately lose its observability. This method employs Risk Theory and Hidden Failure model to identify the high risk cascading failures and then optimally place the PMUs with modified simulating annealing method so as to ensure the full observability of WAMS when certain high risk cascading failure happens. The comparison simulations are carried out on IEEE 39 test system and the results justify that this new method can keep the balance between economy and robustness very well.Fourthly, an algorithm of optimal PMU placement considering multiple constraints is proposed. The minimal PMU placement set can be found when not only the installed PMUs are taken into consideration, but also the key infrastructures with certain problems, such as voltage stability, power angle stability, small signal stability and electromagnetic loop network are directly monitored. The practical application of this new method in Zhejiang power grid is also presented in this chapter.Fifthly, a novel fault location algorithm for transmission lines using synchronized voltage phasor is presented. On the basis of symmetrical component method and linear superposition principle, the additional positive sequence network is established and the matching index on fault point is proposed. Then with this index the fault can be located by traversing searching method. By only using synchronized voltage phasor, the fault location accuracy of this method is not affected by the saturation of current transformer. The simulations carried out on IEEE 9 test system have shown that the proposed technique locates the fault point accurately and adaptively, excluding influence from factors such as fault resistance, fault type and so on.Sixthly, a WAMS/SCADA based mixed dynamic voltage phasor tracing algorithm is proposed to estimate the voltage phasor of unobservable buses due to topology change or PMU malfunction in power system. Modeling load characteristic with historic data from SCADA, this method uses Gauss-Seidel iteration method to solve the nonlinear equations and estimates the voltage phasor of unobservable buses with high accuracy voltage phasor of neighboring buses measured by PMU.At last, an architecture of high robustness wide area security monitoring system is presented by integrating the robustness enhancement methods proposed from chapter 2 to chapter 6 into the WAMS/SCADA/EMS system that may be equipped by Zhejiang electric power corporation in the coming years. This architecture integrates the advantages of WAMS, SCADA and FMS and employs the hybrid measurement technology to overcome the limitation of the single measurement system. Moreover, the optimal PMU placement method that meets the requirement of high robustness wide area security motoring system is studied.