Interaction of Varnish with Magnet Wire Enamel

The interaction of varnish with magnet wire enamel can lead to a reduction in the thermal life rating of the insulation system (ASTM D2307-64T). The recognition of this reduction in life rating is encountered first by varnished twisted pairs of enameled wire. An attempt is made to determine the mechanism of this interaction by studying the system microscopically, by differential thermal analysis and by infrared analysis. The microscopic analysis defines the nature of the bond between magnet wires and the type of coverage that the varnish gives to the magnet wire. It also reveals some information on the type of attack on the enamel and varnish system. Thermal analysis and infrared analysis are used to determine, if possible, whether the thermal decomposition of the magnet wire enamel is accelerated by the presence of the varnish and to reveal some background information as to the nature of this accelerated decomposition. This can then act as guide for the selection of varnishes with enamels that will minimize interactions that reduce the thermal life of insulation.