| The accurate measurement of transmission line parameters plays an extremely important role in the safe and stable operation of power grid.With the development of power systems,the transmission corridors are becoming narrower,and it is very common for multiple parallel transmission lines to share a part of the corridor.The coupling situation of these non full line parallel transmission lines is complex,and there is no corresponding measurement methods of zero sequence distribution parameters of transmission lines at present.In this paper,the research in the field of transmission line parameter measurement is divided into three aspects: measurement theory,measurement method and anti-interference measurement method.The existing parameter measurement theory and methods are classified,and the gaps and difficulties in the current research on line parameter measurement are analyzed.According to the common forms of the transmission lines,this paper establishes the physical model of multi-circuit non full line parallel transmission lines.Considering that the electromagnetic environment of the coupled part and the uncoupled part of the lines is quite different,the distributed parameters of the multi-circuit non-full-line parallel line are discussed in two parts.With the Laplace transform method,the transmission matrix of each part of the lines is solved,and then the network characteristic equations of multi-circuit non full line parallel transmission lines are derived by eliminating the data of un-measurable points.As the most basic and core part,the derivation process of double-circuit non full line parallel line parameters provides a solution idea for multi-circuit non full line parallel line parameter measurement.The order of the transmission matrix of three-circuit and four-circuit non full line parallel transmission lines is relatively high.Considering the symmetry of the parameters,the order of the transmission matrix is reduced by introducing linear transformation to obtain the classical second-order matrix form which is easy to solve.Although this paper only establishes the common physical models of three-circuit and four-circuit non full line parallel lines,the solution idea is also applicable to other wiring forms of three-circuit and four-circuit non full line parallel lines.According to the situation that the actual line parameter measurement may be disturbed by the nearby lines under operation,this paper analyzes three common anti-interference measurement methods.The measurement principle of each anti-interference method is analyzed by the lumped parameter model,and then extended to the distributed parameter model.The core idea is to eliminate or avoid the influence of interference through specific operations.Due to the theoretical differences in anti-interference measurement,the selection of incremental method,harmonic method and non-power frequency method should be determined according to the actual measurement environment of the lines and the needs of the parameters to be measured.Based on PSCAD and MATLAB simulation software,this paper verifies and analyzes three kinds of zero-sequence distribution parameter measurement methods of non-full-line parallel transmission lines and zero-sequence distributed parameter anti-interference measurement methods of the transmission lines under strong electromagnetic environment.With the synchronous timing function of GPS,the voltage and current at both ends of the multiple-circuit lines are measured synchronously under four independent measurement methods.All zero sequence parameters can be accurately solved by substituting the measured data to the calculation formula given in this paper.This method does not simplify any solving steps in deriving the formula of the zero sequence distributed parameters,and the measurement accuracy of the parameters is not affected by the change of the transmission line length and the theoretical initial values of the parameters.Compared with the simulation results of the traditional methods and the existing methods,this proposed method has smaller parameter measurement error,and can reduce the wiring modes required for parameter measurement,which is easy to be applied in engineering practice. |
