| Transmission lines are one important part of power system, the accurate measurement of its parameter is fundamental in relay protection setting calculation of power system and of great importance in system security.This paper introduces the current research status and commonly used measurement methods of the transmission line parameters. Given that in practical engineering, such situation that new overhead wires are been erectly built on running ones is commonly existed, a new mixed-measurement method of power frequency parameters of multi-coupled transmission lines is proposed.First of all, this paper adopts the “Π-shaped”circuit model of multi-coupled transmission lines considering the capacitance parameters. The model is been simplified by alternating transposition to a balanced level. Using symmetrical component method, the positive sequence circuit model and zero sequence circuit model considering capacitance parameters are obtained.Secondly, this paper gives the mixed-measurement method for parameter calculation of transmission lines in practical engineering. Thorough researches of parameter calculation of multi-coupled lines consisted of erectly distributed running wires and newly built wires are analyzed, in condition that the parameters of the formerly existed lines are known and unknown. First of all, specific measurement solutions for different line combinations are proposed, measurement equations are written based on the data obtained, and corresponding parameters are resolved. For resolution with more than one newly built wires, the least square parameter estimation theory is used.Thirdly, simulation models of the multi-coupled transmission lines have been built and run in computer. The simulation results verify the accuracy of the algorithm.Lastly, considering the zero-sequence signal generation method mentioned in the paper that one phase of the running lines needs short-time disconnection, the possible harm to the grid and simulation analysis of its feasibility is done. |
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