Study on New After Laying Test Methods for XLPE Cable Lines

Abstract

An after laying test is required to demonstrate the soundness of XLPE underground cable lines with joints. AC voltage application is desirable for the test, however, the equipment for AC application must be very large because it must supply large capacitive current for cables. DC voltage is normally applied, which can be supplied with a small equipment, however, the effectiveness of the DC application is questioned because the electrical stress distribution is quite different from that with AC application and, moreover, DC application could damage insulation properties of cables.
The authors targeted Oscillating Wave (OSW) method and Very Low Frequency (VLF) method as alternative after laying tests. They first developed modeling methods of various defects on underground cable lines and applied OSW and VLF to these defect models. They found OSW and VLF methods have higher fault detection capability than DC voltage application. They also demonstrated that the defects which can be easily detected with OSW method is difficult to be detected with VLF method and vice versa. They showed that serial application of the both methods highly improve the fault detection ability for XLPE underground cable lines.