Direct-Current Breakdown Test Method Based on Electrode-Embedded Fully Extruded Molding Crosslinked Polyethylene Sample

In the traditional direct-current (dc) breakdown test method, a large uncertainty is associated with using the breakdown strength of 1-mm-thick samples as the basis to determine the insulation thickness in cable design because of flashover. An electrode-embedded fully extruded molding sample is proposed in this work. Finite-element methods are used to verify the no surface flashover characteristic. The dc breakdown tests on crosslinked polyethylene (XLPE)-A and XLPE-B extruded samples with an insulation thickness of hundreds of microns to several millimeters are conducted at different temperatures, and the test results are compared with traditional dc breakdown tests. The breakdown strength of sheet and extruded XLPE samples decreases with an increase in thickness. The breakdown strength of extruded samples is higher than that of sheet samples at the same thickness. The oil gap discharge near the electrode in the traditional breakdown test method reduces the breakdown strength of the sheet XLPE sample. The increase in the temperature reduces the thickness effect of the breakdown strength. The extruded sample can make up for the thickness limitation of the traditional breakdown test method and can reflect the intrinsic insulation characteristics of the insulating material more accurately.