Abstract: A sandwich type insulation for electrical machinery comprising a laminate of a polymeric material such as polyimide which contains particles of an inorganic corona resistant material, said polymeric material being bonded to mica paper consisting of mica, wherein said mica paper may be impregnated with polymeric resin containing particles of inorganic corona resistant material. The resultant insulation may be used as a tape or wrapper.

Abstract: A circuit for monitoring the temperature of the contacts of an electrical switching device (such as a circuit breaker), comprises an electrical analogue circuit of the thermal characteristics of the switching device. The analogue circuit comprises electrical resistance and capacitance, interconnected so as to form an electrical model of the heat flow paths and capacitances respectively, in the switching device. The preferred embodiment also provides a temperature sensing device to introduce to the analogue circuit a voltage signal the magnitude of which is proportional to the exterior temperature of the switching device. The analogue circuit is connected in a series circuit relationship with a current controller. The current controller controls the amount of current flowing through the analogue circuit. The current controller is in turn controlled by a voltage control signal proportional to the amount of current being carried by the switching device.