The Use of Partial Discharges as an Online Monitoring System for Underground Cable Joints

With their vast amount of joints, underground cable systems are expensive to maintain; therefore, measurement equipment must be cost-effective. This study proposes the long-term placement of partial-discharge (PD) monitoring units at cable joints. The unit consists of a peak detect circuit and a digital signal processor for acquiring and converting the sensors´ PD signals into discharge sequence data, whose data are then provided to a remote computer for analysis and display of the condition of the cable joint. Finally, a cable joint with artificial defects was tested by accelerated aging tests to verify the performance of the equipment. Two characteristics, namely, the average discharge quantity (Q_ave) and the discharge phase region, are proposed and plotted against each other to render an evolution locus, which reveals a shape of an upside-down letter N. The locus allows a judgment to be made on the state of the insulation in the cable joint. These results further justify work to further develop the method as an online cable monitoring system.