Research On Fault For Common-Tower Double-Circuit Lines And Its Fault Location

With the development of the power system, the double-circuit transmission lines on same tower without parallel operation is used increasingly, which helps to improve the transmission capacity of lines and the utilization rate of the transmission corridor, and has important the economic and social value. However, the distance between the lines of the transmission line is small, so the coupling between the lines must be taken into account. The line can be run at the same voltage level and can run at different voltage level, and the parameters of the circuit may be asymmetric. What is more, the lines fault wide variety and complexity. Because these factors the double-circuit transmission lines on same tower without parallel operation is facing huge challenges on fault analysis and fault location. Aiming at the above problems, the paper the fault analysis and fault location of the line are studied and discussed in this paper, with the different situations of operation on complete-journey or on incomplete-journey of the line.According to the characteristics of double-circuit transmission lines on same tower without parallel operation, in this paper the line models are given when the transmission lines are operation on complete-journey or on incomplete-journey. Then the paper analyzes the two kinds of model using phase sequence transform decoupling. By this way, the type line is completely decoupled positive sequence components, negative sequence component and the presence of coupling zero-sequence component. In order to facilitate study, this paper presents a general fault model of the line, and introduces the theory of the loosely coupled transformer. The paper analyzes the relationship of voltage and current of the loosely coupled transformer secondary side under different load conditions to get its input impedance and equivalent admittance circuit.On the analysis of single line fault of the lines, the zero sequence decoupling model of loosely coupled transformer is proposed, which is used to decouple the zero sequence network. Based on it, the method to establish the zero sequence equivalent circuit is proposed. After the zero sequence network decoupled, the expression of zero sequence impedance equivalent is deduced in the paper. Then using symmetrical component method calculates and analyzes the line faults, thereby completing the failure analysis and calculation problem of double-circuit transmission lines on same tower without parallel operation, when fault occurred in single line. For non-operation of the whole line with the rod, based on the use of zero-sequence fault analysis method described decoupling model, complete with rod segment and its unusual rod segment single circuit lines of research and analysis. Then using the method completed the fault study of incomplete-journey double-circuit lines, based on the zero sequence decoupling model of loosely coupled transformer, when the single line fault occurred on complete-journey or on incomplete-journey of the lines. The method in this paper is proved by the result of PSCAD/EMTDC, and the method has better calculation accuracy.To analyze and calculate the complex inter-line fault in the double-circuit transmission lines on same tower without parallel operation, the paper proposed a method to established the zero sequence network equivalent circuit, based on the zero sequence decoupling model of loosely coupled transformer. Then using the method and combined with the composite sequence network diagram and fault boundary conditions complete the analysis and calculation of inter-line fault in the double-circuit. The paper summarizes 6 kinds of typical failure forms under inter-line grounding faults or inter-line phase faults, based on analyzing composition in the form of inter-line fault. According to analyzing failure, the paper presents the general boundary conditions and the way of composite sequence network diagram connection of the lines inter-line faults, thereby the fault boundary conditions and the composite sequence network diagram of any inter-line faults are obtained easily, and the inter-line faults calculation is completed. Then the paper uses the given boundary conditions and the connecting way of the composite sequence network to analyze general boundary conditions and composite sequence network of six kinds of typical faults, then calculate the faults. The method can be used to analyze inter-line faults of different parameters of two lines and the incomplete-journey double-circuit lines. PSCAD/EMTDC simulation shows that using the method to calculate inter-line faults has better accuracy. And the method has a definite physical meanings as well as good practicability.When single line fault occurred on the double-circuit transmission lines on same tower without parallel operation, the method of fault location is unable to carry on the accurate fault location. Aiming at this problem, a method of fault location that need single-ended electric parameters is proposed. The method only needs to know the fault line single-ended voltage and current, and uses the zero sequence decoupling model of loosely coupled transformer to eliminate fault line contralateral current and the influence of adjacent line coupling. What is more, the method has high accuracy of fault location. Then the simulation calculation results verify the accuracy of the method. However, the fault location based on single-ended data is vulnerable to the influence of system impedance. So taking the contralateral electric parameters impedance into account, the fault location method that uses double-ended information of fault lines is proposed. And the method uses double-ended information of fault lines, combined with the fault sequence network and boundary conditions, to construct the corresponding fault location function. To complete decoupling the zero sequence network, the method needs the current of double-ended fault line and voltage at one end of fault line, combined with its own characteristics of this type line. According to the different fault boundary conditions, the method can construct the fault location equation that is adapt to the fault, thus the fault location of double-circuit transmission lines on same tower without parallel operation is completed. In principle, the fault location method can avoid the influence of resistance and system impedance. The simulation results show that this method has high precision and meet the requirements of high voltage grade line fault location. What is more, these methods that are proposed in the paper are suitable for the fault location study of incomplete-journey the double-circuit transmission lines on same tower.