Norwegian Experience with Electrical Insulation for Large Rotating Machinery

This paper deals with the stator winding insulation primarily of water-wheel generators and experience in Norway with this important part of rotating machines. Until 1962, first shellac, and later asphalt bonded micafolium were used as ground insulation of high-voltage machines. In 1962, a new insulation system based on a mica-splitting tape with modified polyester resin as impregnant was introduced. The advantages of this new system include high mechanical strength at elevated temperatures and superior thermal endurance characteristics. The system also has proved to be practically noninflammable, which could justify omission of the automatic fire-extinguishing equipment normally used nowadays to protect generators against fire. In spite of higher material costs, the overall price of the new system compares favorably with the old systems. The reason for this is that the new system has only a few different materials, the materials are easy to handle, and the production process is simple and easy to control. The new insulation system is being used today in Norway for all machine ratings above 500 kVA and all voltages above 3 kV.