Abstract
Much of oil filled (OF) cable has been used for a long time for 66 to 500kV extra high voltage cable. Sometimes we can see extremely degraded oil (several tens % of tanδ, for example) in joint box etc, but even with that sever situation, an event such as thermal breakdown has not taken place up to the present in actually operated transmission lines. The authors have reported the tanδ characteristics of oil impregnated paper with extremely high tanδ oil and the development of a simulation method of heat generation by dielectric loss in OF cable joint. In addition to that, the degradation characteristics of actual OF cable system have been investigated. The degraded oil distribution in actual cable system seems to be balance in nearly 27 yeas. The temperature rise of joint box is quite small even with the extremely degraded oil (tanδ=204%). With the experimental results, the OF cable system tanδ distribution is estimated and the possibility of unexpected heat generation in cable which has been installed in the conduit pipe section is proposed.
