Characterization and testing of epoxy powder insulated conductors

A significant recent development in conductor insulation is the electrostatic powder coating of copper and aluminum rectangular cross section wire for use in liquid filled transformers. DuraBIL∗ turn insulation is a single layer of epoxy povrier deposited electrostatically on conductors, then baked and cured, linking polymers to form a continuous coating. Bonded tightly to the conductor, the coating is of uniform thickness, flexible, abrasion resistant, rigid, and chemically stable. All these characteristics add to unit reliability and service life. This paper will review the testing methods used to evaluate epoxy powders to be applied to aluminum or copper conductors. Analytical techniques used to evaluate critical powder properties will be discussed. Data from particle size analysis, gel time, moisture content, and other properties will be presented. Methods of interpreting the data obtained will also be described. Also, to be presented will be the various functional or performance tests including the evaluation of physical, thermal, and electrical properties of DuraBIL∗ epoxy powder coated conductors. Data obtained through thermal analysis will be used to differentiate between cured and incompletely cured insulated conductors. This paper will also cover the functional testing used to verify the polymerized coating for use in liquid filled transformers.