Study on a C-class solvent-free silicone impregnating varnish

In this paper, a new class of C-grade solvent-free silicone impregnating varnish was prepared by synthesizing polysilicone oligomers bearing methyl and phenyl groups. These oligomers also contained vinyl and hydrogen siloxane components which, under the influence of heat and platinum catalysis, induced crosslinking of the impregnating varnish. The varnish without any solvents kept liquid and flowed easily at room temperature (RT) and was heated to cure to a rigid membrane at high temperature up to 473 K. The properties of the varnish before and after curing were depicted in details, and the mechanism for synthesis of the solvent-free silicone impregnating varnish was introduced. The solvent-free silicone impregnating varnish was used on the winding as dielectric shield for a motor or electric device by vacuum pressure impregnation (VPI) which is the most conventional method for impregnation of the winding for a motor. The silicone varnish, which contained no decomposable and physiologically problematic components, was of very low volatility suitable for VPI. The application technology and processing conditions of the silicone impregnating varnish were discussed in details and a simulant procedure and a practical sketch about the four steps involved in the VPI process employing the silicone impregnating varnish were illustrated.