TESTING ELECTRIC CABLES AND THEIR JOINTS

摘要

A method of testing a jointed high-voltage cable involves establishing a condition in which at least one joint interrupts the metallic return conductor of the cable without interrupting the dielectric screen (3). Test voltage is applied between the cable conductor and return conductor (4), and an instrument (8) sensitive to frequencies above 2MHz is used to observe whether partial discharges are occurring. The method succeeds because the semiconducting dielectric screen is virtually insulating at these frequencies, and avoids the need to strip bands of the dielectric screen (and subsequently reinstate them without facility for testing quality of reinstatement). A joint in the jointed cable is tested by applying a metallic electrode around the joint area (but spaced sufficiently from the metallic return conductor of the adjacent cable length(s)) and connecting the RF test instrument between that electrode (7) and earth.