Estimation of transient sheath overvoltages in power-cable transmission systems

In a previous paper, the theory of natural modes was applied to power-cable transmission systems to analyse steady-state and transient effects which were of significance to power-system engineers. In the present paper, using this theory as a basis, computer results are given for transient sheath overvoltages resulting from the application of a unit step of voltage between the conductor and the sheath of one of the cables of an underground power-transmission system. The results are derived from a mathematical model which includes for the effects of the frequency dependence of the cable parameters, as well as the multiconductor aspect of the travelling-wave problem. The results obtained lead to an explanation of the generation of transient sheath overvoltages in terms of well defined modes of propagation. This forms the basis of a qualitative method for predicting transient sheath voltages up to, and slightly beyond, the first peak value. The method becomes quantitative once the `universal' curve defined in the text is known.