Computation of sheath transient response in a single-point bonded cable section

The procedure that was adopted for the computation of traveling-wave phenomena in a slngle-point bonded buried cable section is described. Also included is the method of representing the non-linear cable covering protection units (CCPU´s) and the results of computation are presented so as to illustrate the transient performance of the CCPU´s when a typical three-phase single-point bonded cable section is faulted. The system model accounts for frequency-dependent parameters such as conductor, sheath and earth path skin-effects. The system is first defined in terms of its basic wave propagation characteristics, i.e., its unit step response functions in the time domain. For this purpose the modified Fourier transform method is applied and the transient solution to include specific system boundary conditions is completed in the time domain using convolution and Bergeron´s method of characteristics. In this way the non-linear voltage-current relationships of the CCPU´s can be taken into account much more readily and with comparatively greater efficiency than would be the case using the modified Fourier transform method throughout.