電気絶縁紙の低水分域での高温超低周波誘電分散とOFケーブル乾燥終点判別への応用

抄録

In recent years the oil filled(OF) cables have been confined to the extra high voltage of 275_??_500kV. In these circumstances, much longer drying time due to thicker insulation is required in order to remove moisture from insulating paper during OF cable manufacturing. Therefore it is important to decide the appropriate drying time to avoid the thermal degradation caused by excessive thermal drying. Additionally, in the cable insulation of semi-synthetic paper such as polypropylene laminated paper, the prolonged drying time because of gas barrier of plastic layer is inevitable in the same manner. By the basic and applicable investigation for the drying judgment of OF cable insulation, the following conclusions have been proved.
(1) Dielectric loss in very low frequency region (approx. 10^-2Hz) can be gotten in the insulating paper during vacuum thermal drying by the measurement of absorption current. This dielectric loss, which is considered to be attributable to the ionic conduction(proton migration), become lower with the decrease of water content and higher due to thermal degradation during thermal drying.
(2)In order to clarify drying limitation of insulating paper, tan δ of oil impregnated paper was precisely examined in low water content range(less than 0.1wt.%). Consequently, unlike the most results in past reports, the influence of water content on tan δ appeared more dominantly in low temperature (room temperature), rather than in high temperature (100°C).
(3) Using the absorption current value, which corresponds to the dielectric dispersion in approx. 10-2Hz, as an indicator during OF cable drying process, it has been proved that required drying time can be decided appropriately according to the difference depending on each cable structure.