Modal analysis of reflection of TDR in overhead distribution lines

Abstract

Detection of a fault point in an overhead distribution system is necessary for accident restoration in power grid. Applying a pulse wave to the overhead distribution line and measurement of reflection wave, which is called TDR measurement with utility-pole-interval resolution, can detect distance to the fault point. In this report, an overhead distribution line is treated as a three-conductor transmission line with earth ground. Eigen modes in the transmission line are derived by inductances and capacitance matrices calculated by electrostatic or magnetostatic simulator. In addition, a fundamental matrix of an equivalent circuit model of a fault point is expressed by impedances and admittances. The fundamental matrix is converted to a modal S parameter. Reflection coefficient with mode conversion of disconnection fault case is calculated using derived S parameter. The calculated reflection coefficients are in good agreement with calculation results using a circuit simulator. As a results, considering mode conversion in the TDR method can detect type of fault in the overhead distribution lines.