Study On Fault Analysis Method Of Power System Based On Phase Components Method

At present, the symmetrical components method proposed by Fortescue in 1918 still take the leading position in the field of power system fault analysis. The method makes the fault three-phase network decoupled in sequence coordinates under the premise of that all components are symmetrical. Then the single-phase representation is extended into an asymmetric operation system which makes the fault calculation very convenient. However, there are more and more un-transposed or incompletely transposed transmission lines, power electronic devices and other asymmetric components in modern power system. If the symmetrical components method is used for fault analysis of that system, large errors would be brought out. They will have serious impact on the rational choice of the electrical wiring diagram, the optional of the electrical equipments and current-carrying conductors with enough thermal stability and mechanical strength, the decision of measures for limiting short-circuit current and the advisable configuration and setting of relay protection and automatic devices in power system.In recent years, the phase components method is usually used in power system fault analysis which including asymmetric components. But complex calculation steps and large amount of computations become the bottleneck. Furthermore, some existing component models in phase coordinates are transformed from the models in symmetrical components method and power electronic devices are seldom considered.On the basis of summing up and drawing on the experience of the related research work at home and abroad, this paper proposed a general fault analysis method by improving the phase component models of some common components in power systems, setting up TCSC phase component model and optimizing the traditional phase components method by matrix similarity transformation. The effectiveness and accuracy of that method are verified by simulation. And by applying it into fault calculation of double-circuit lines with different topologies, a general fault calculation method is proposed which is suitable for various faults of the double-circuit lines. Specific research work is shown as following:(1) Some urgent problems are found by detailed analysis of the component model, network model and fault calculation of the fault analysis method in phase coordinates.(2) The conventional fault analysis method in practice based on symmetrical components usually overlooks some factors. The transformer leakage reactance model and equivalent model of incompletely transposed transmission lines are typical examples. This paper studies the problem and error brought out by the two models by simulation and improves the existing fault analysis models of some components, such as, generator and double-circuit transmission lines.(3) The traditional phase components methods usually make a three-phase network with n nodes equivalent to a single-phase network with 3n nodes which would make the algorithm more complex. As most components in power systems are symmetrical now, this paper looks the three-phase node as the basic node and improved the traditional phase components method by matrix similarity transformation utilizing the symmetries of three phases on some nodes and branches to make the traditional phase components more efficient.(4) There is no general computer calculation model for all kinds of faults in inherently unbalanced power system until now. To alleviate these problems, this paper presents a new algorithm which is suitable for the analysis of various complex faults in inherently unbalanced power systems. An equation is developed on the basis of transformed phase components method and multi-port theory. Then, another equation of the general fault boundary condition is developed on the basis of general form of faults. Finally, a common mathematical model for computer is developed with the aforesaid two equations that can be used to analyze all kinds of simple faults and complicated faults, including faults with various fault impedances. EMTP simulation results show its accuracy.(5) This paper studies the general phase components model for double-circuit lines with different topologies. And a new algorithm is proposed which is suitable for the analysis of any single fault in ac double-circuit lines with different topologies on the basis of aforesaid improved phase components method. This paper analyzes the system model of the power system including double-circuit lines which have different topologies specifically. The effectiveness and efficiency of the new method has been verified by theoretical analysis and simulation.(6) This paper analyzes the TCSC working principle and operating characteristics in case of fault, derives the fundamental impedance expression of single-phase TCSC and proposes its phase components model. The feasible pattern changes of TCSC in case of fault are studied. The aforesaid improved phase components method is used in power system fault analysis which including TCSC. Simulation results show that the improved phase components method is effective and accurate for fault calculation of power system with TCSC.The improved phase components method proposed in this paper is perfect for any single fault and simultaneous fault calculation in power system with TCSC. This paper also proposes a general method for analyzing any fault in ac double-circuit lines with different topologies on the basis of aforesaid improved phase components method. The methods are especially suitable to the fault calculation of power system with asymmetric parameters. They are simple, flexible and easy to understand. It would have great significance for the power grid planning, relay protection setting and electrical equipment choosing.