Effects of Voltage Impulses on Solid Dielectric Cable Life

Underground power cables on electric utility systems are frequently subjected to lightning impulses during normal service. They can also be subjected to impulses from fault locating equipment (thumpers). The effects of these impulses on the power cable´s life is not well defined. Various cable designs were aged in the laboratory using an accelerated water treeing test. Some samples were subjected to lightning impulses, some to thumping impulses and some were aged without impulses applied. The impulse effects were evaluated using time to failure data, ac breakdown data and impulse breakdown data. The results show that lightning or thumping impulses do not affect cable ac or impulse breakdown strength. There is also no visual difference between wafers taken from impulsed and control samples. However, there is a strong indication that lightning impulses can reduce cable life. Interestingly, almost all the aging failures occurred while the cable were warm. No failures occurred during the impulse application. Also, increased cable wall thickness extended cable life for one insulation but not for another. ..