Experience with Micadur® synthetic-resin insulation for stator windings of high voltage rotating machines

The firm with which the author is associated has been using shellac-bonded micafolium for insulating the stator windings of high-voltage rotating machines since 1910, and also, from 1930 onwards, asphalt-bonded micafolium, though largely for higher-voltage machines. Both systems follow European practice in that the required number of layers is wrapped around the slot portion of bar in broad sheets, and then hot pressed. Both have proved themselves very well in practice, and therefore continue to be used today. Difficulties due to creeping, which have been associated with other insulation systems using narrow mica tapes wound in several stages and impregnated with asphalt under vacuum, have not arisen with these two systems.