The present invention relates to an insulation system for winding of electric rotating machines and a process for the production of such an insulated winding for electric rotating machines. More particularly, the invention pertains to an insulated winding for electric rotating machines having thermal resistance of class H or more obtained by impregnating and curing a novel thermosetting resin and a process for the production of such an insulated winding for electric rotating machines.
An improvement in the thermal resistance of a winding insulation is a conclusive factor for increasing the capacity of electric rotating machines and miniaturizing and weight saving of the machines. A tape or sheet of a polyimide, polyamideimide, aromatic polyamide or the like resin has heretofore been used as an insulating material having thermal resistance of class H (180.degree. C.) for winding for such electric rotating machines. On the one hand, a polyimide resin varnish or a polyamideimide resin varnish is known as an insulating varnish of class H for impregnating insulating material but they are difficult to be a solventless varnish since they are condensation resin varnishes. Therefore, they are not suitable for winding for electric rotating machines in which the formation of voids is undesirable.
As a solventless varnish for impregnating insulating materials, an epoxy resin varnish has been widely used, but the epoxy resin has thermal resistance of class F (155.degree. C.). When the resin is heated at a temperature of 180.degree. C. or more, therefore, delamination occurs owing to heat deterioration between the insulating layers of the winding and particularly between the conductor and the insulating layer. Thereby thermal conduction is reduced and the temperature of the winding further increases. Also, corona starting voltage is reduced and dielectric breakdown is brought about.
Particularly, mechanical vibration is large in electric rotating machines. Therefore, said insulating layer is easy to peel from the conductor if the adhesive property of the varnish forming the insulating layer is poor. Since the machines are not immersed in an oil like a transformer, a corona is generated and dielectric breakdown occurs.
A silicone resin varnish is known as another varnish having excellent thermal resistance, but it is inferior in adhesiveness and is not suitable for such electric rotating machines.