Impedance Derivation and Wave Propagation Characteristics of Pipe-Enclosed and Tunnel-Installed Cables

This paper has proposed an impedance formula of pipe enclosed and tunnel-installed cables of which the thickness of the pipe and tunnel wall is finite. Thus, it is composed of a two-layered conductor (i.e., the first medium is the finite thickness pipe or the finite thickness tunnel wall, and the second medium is the outer conductor to infinite). The impedance by the formula developed in the paper shows a quite different characteristic from that calculated by an existing impedance formula which was derived from the assumption of an infinitely thick pipe.Wave propagation and transient voltage characteristics are investigated using the proposed formula, and a difference from those by the existing formula is made clear. The proposed impedance formula has made it possible a detailed and more accurate analysis of wave propagation and transient overvoltage characteristics on pipe-enclosed and tunnel-installed cables.