To suppress the occurrence of electrical treeing, by using a cast thermosetting resin containing at least molten silica at a specific weight percent as part of a filler so as to improve the dielectric strength of the resin at a specific temperature.
Each parts composed of a central core 11, a secondary coil bobbin 21, a secondary coil 22, a primary coil bobbin 23, a primary coil 24, etc., are housed in a cylindrical coil case 13 and fixed in the case 13 with a cast resin 25 composed of an epoxy resin containing molten silica powder as part of a filler. The mixing ratio of the molten silica in the filler is adjusted to 20 to 85 wt.% so as to improve the dielectric strength of the resin 25 under a condition where the ambient temperature falls within the range of -40°C to 140°C. In addition, the filler of the resin 25 is prepared by mixing crystalline silica with the molten silica. Moreover, the spherical molten silica is used in the filler of the resin 25.
TAKEUCHI RYOZO
KOBAYASHI KAZUTOSHI
