Analysis of Electrical Field in a 6 kv Form-Wound Coil with Flat Shape Voids

Abstract

During the manufacturing process of form-wound coils small voids in the insulation groundwall may appear. These voids are usually caused by the presence of impurities, dirtiness,unsuitable pressure or temperature during pressing and curing processes, etc. The electrical stress into these voids may produce air ionization and thus partial dischargeactivity inside the insulation system. This phenomenon is one of main causes of the time life reduction in this type of winding. This paper presents a study of the electrical field distribution into a flat shape void placed at different positions of the insulation groudwall of a form wound coil. Several finite element models were developed in order to obtain the electric field distribution in the void when placed at different positions and orientation with respect to the electrical field direction. Results presented in this paper are preliminary and belong to a wider study focused on thecharacterisation of the partial discharge pattern of the insulating system of form-wound coils after their manufacturing process.