Travelling Wave-Based Fault Location Scheme for Aged Underground Cable Combined with Overhead Line

This paper presents a novel wavelet-based travelling wave fault location algorithm for aged underground cables in transmission systems. Such transmission systems consist of overhead lines combined with underground power cables. Applying the singularity detection feature of wavelets as a powerful signal processing tool, the first and second initial arrival of the voltage travelling waves at the first end of the overhead as well as at the terminal end of the aged cable line can be identified reliably without the need for detection the sign of these waves. In this paper modal signals, rather than the phase signals, are the inputs to the relay.The proposed algorithm is capable of eliminating the effect of the change in the propagation velocity of the travelling waves over the age of the cable. It can be used on-line following the operation of digital relays or off-line using the data stored in the digital transient recording apparatus. Extensive simulation studies carried out using ATP/EMTP show that the proposed algorithm provides an accepted degree of accuracy in fault location under different fault conditions.