Derivation of a semiconducting layer impedance and its effect on wave propagation characteristics on a cable

An impedance formula of a semiconducting layer at the core and sheath surfaces of a cable has been developed. The formula becomes identical to that derived by Schelkunoff when the semiconducting layer is neglected. A transient current waveform calculated by using the formula agrees well with that calculated by a numerical electromagnetic analysis method FDTD. The inner, outer and mutual impedances of a two-layered conductor show quite different characteristics from those of a single conductor neglecting the semiconducting layer. The characteristic results in the total cable impedance being oscillatory as a function of the semiconducting layer resistivity. A similar characteristic is observed in the cable admittance considering the semiconducting layer. Thus, transient voltage wave deformation is significantly different from that of a cable neglecting the semiconducting layer and is quite dependent on the resistivity. The difference is dominated by the semiconducting layer admittance and the impedance causes a minor effect, considering the fact that the thickness is less than 10 mm and the resistivity greater than 0.1 Ω m in an actual cable.