非均質線路における雷サージ伝搬特性

This paper describes lightning surge propagation characteristics on a nonuniform line, of which dimension and con-figuration are dependent on location. We can find some nonuniform lines in electric power systems such as incomingline from first transmission-line tower to substation entrance, telecommunication line and transmission line associatedwith induced voltage, tapered line and tower. It is important to make the propagation characteristics on the nonuniformline clear for rational insulation design of transmission and distribution lines. The line constants of the nonuniform lineare expressed as a function of the location. As a result, the surge impedance varies along the line. The wave propagationcharacteristics of the nonunform line are different from those of the uniform one. Wave deformation of the lightningsurge on the nonuniform line is caused by multiple reflections on the nonuniform line due to discontinuity of the surgeimpedance of the line. It is impossible to derive analytical formula to represent the surge characteristics of the nonuniformline in time domain with no assumption nor approximation. A formula to estimate the propagation characteristicsis desired to explain experimental and calculated results of voltages and currents in an electric power system includingthe nonuniform line. This paper proposes a method to obtain an approximate formula to represent the lightning surgesalong the nonuniform line using a lattice diagram method. The formula of the lightning surge as a function of time is derivedfrom a series expression as a limit of elementary length. The proposed formula is very simple and useful to studythe propagation characteristics. The paper also concerns a long grounding conductor, which is frequently used to obtainlow grounding resistance. The grounding conductor is a uniform line, but no formula to estimate voltages on thegrounding conductor is proposed because of existence of shunt conductance. The method proposed in this paper to dealwith the nonuniform line is applicable to the long grounding conductor. The paper shows an approximate formula of thevoltage on the long grounding conductor. The accuracy of the proposed formula is estimated by comparing calculatedresults by an exact solution using a numerical Laplace transform. This paper describes that sending-end voltage on thenonuniform line is varied with logarithmic function, and that on the long grounding conductor with exponential function.