Control of electrical-insulating varnishes

Varnish treatment of electrical equipment is an important step in its manufacture. Varnish coatings protect apparatus from moisture and dirt and maintain the high electrical-insulating level required for insulation. The quality of the varnish film deposited depends upon the condition of the varnish in the processing tanks. Thickness of deposited varnish films varies with viscosity and body. Heavy films interfere with armature-coil sizes and make problems of heat transfer in field coils and magnet coils more difficult. Thin films give inadequate protection from moisture and dirt. Conducting contaminating materials are introduced into the tanks from rehabilitated apparatus and manufacturing atmosphere. These indicate that close control of tank varnish is necessary for consistently high quality of apparatus treated. Methods of control are discussed which include both laboratory tests of the varnish and physical tests which can be concluded at the tank. A system of daily inspection of tanks for proper quality and daily adjustments before use is described. Dielectric properties of the varnish film and the liquid varnish and periodic chemical analysis of samples from each tank reveal the condition of the varnish. A system of portable cold pressure filtering for removing much of the contamination present is described. It should be recognized by the electrical industry that insulating varnishes are complex chemical mixtures, and care should be maintained in their use. It is important that they be under the control and supervision of persons with the proper training and experience. Constant quality control is necessary for satisfactory results.