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 (Qave) 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.