Electrical treeing and breakdown of mechanically strained XLPE cable insulation

The authors describe experiments which have been designed to study the effect of mechanical strain on the short-term AC breakdown strength of cross-linked polyethylene (XLPE) cable insulation. Laboratory experiments were performed on mechanically stressed Rogowski-type test objects and on sharply bent samples of 12-kV XLPE cables. It was verified that introduction of strain significantly reduced the short-term AC breakdown strength of XLPE insulation. By application of 21% strain the breakdown field strength was reduced to 77% of that of nonstrained test objects. In testing 3-m-long cable samples bent to a maximum outer strain of 15%, the 63% breakdown voltage was reduced to 70% of that of an equal length of straight cable