Fault detection and discharging characteristics of an underground of an underground power cable

Abstract

The traditional way to transmit power over long distances is to use EHV-AC overhead line system. However, geographical barriers, hostile terrains and atmospheric conditions seriously impair overhead systems. Also, space is a prominent issue in densely populated cities. Hence in many developed countries, underground cable system has been prevalent over decades. There are two main industrial issues that should take care for handling the power cables are testing for the untouched power cable and secondly to detect the location of any short circuited faults. Work in this thesis is mainly split into two parts, firstly locating the short circuited faults which are very obvious to occur for an aged power cable and secondly the different factors that affect the discharging characteristics of the cable Most of the power cables are being decades old and are in a verge of having faults while some are having continuous faults. One of the most strenuous task is to locate the position of fault in power cables. Any hindrance in the supply will have a great impact on business as well as economic part. Therefore getting an accurate detection and location of the fault has become very important to control the damage and to restore the service as fast as possible There are many techniques which are available to locate faults, but each one have its own advantages and disadvantages. Contrary to the conventional reflectometry based methods, this work explores a technique based on Sweep frequency response analysis (SFRA) in which reflection of the wave are not required. Sweep frequency response analysis (SFRA) are mostly used in transformer for checking the healthiness of its winding and to locate different faults and defects in it. In the present work, using the same concept of SFRA in transformer, detection and location of fault in a cable has been investigated using PSpice simulation. HVDC power transmission, power cables are taking the place of overhead lines at a rapid rate. Before laying a power cable, the cable undergoes some testing. While testing HVDC power cables, manufacturers often encounter difficulty of handling, as a prior knowledge of the time at which the power cable would discharge completely is not known. The present work explores the discharging time of cables of different lengths and also analyzes the factors which affect the discharging phenomenon, and tries to give a proper time after which a tested cable can be handled safely. The complexity arises because of the fact that a cable behaves as a distributed parameter transmission line. The discharging phenomenon has been simulated using PSPICE software and also the results are verified analytically.