Comparison among different diagnostic systems for medium voltage cable lines

Power quality is becoming more and more important for electrical utilities. One of the drivers for its improvement is the reduction of the number and duration of outages due to faults on the power distribution cable lines by means of effective condition assessment techniques. Several systems have been made available on the market for this purpose. A wide investigation was carried out in collaboration between Enel Distribuzione and CESI in order to evaluate, through laboratory and on-site tests, the performances of four different medium voltage cable diagnostic systems. The aim of the program was to compare the diagnostic information given by each of the systems under investigation in terms of partial discharge inception voltages, location of PD spots and PD pulse amplitudes. Laboratory tests were carried out on different cables having artificial defects either in joints and in the cables themselves. Tests on site were performed on selected lines of the Italian national network. The paper reports the main results obtained and discusses the criteria for the selection of the most appropriate condition assessment methods for the different types of configurations foreseen in the system.