Thermal degradation characteristics of oil-filled cable joint with extremely degraded tan Delta d oil

Much of oil-filled (OF) cable has been used for a long time as 66- to 500-kV extrahigh-voltage cable. Sometimes we can see extremely degraded tan Delta *d oil (several tens of percent of tan Delta *d, for example) in joint boxes, etc. The values of tan Delta *d calculated by a simple combination model of paper/oil show that the oil-impregnated paper with such a high tan Delta *d oil likewise has an extremely high tan Delta *d, which must result in thermal breakdown. However, such an event has not taken place up to the present in actually operated transmission lines. This fact suggests that some mechanism for the suppression of tan Delta *d has acted in the paper insulation impregnated with degraded tan Delta *d oil. Therefore, we investigated in detail the tan Delta *d characteristics of paper impregnated with extremely high tan Delta *d oil. In addition, based on the investigation results, we developed a method for simulation of heat generation by dielectric loss in an OF cable joint (which has degraded tan Delta *d oil). ? 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 178(1): 1-10, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21184