A simple method to electrically determine the limits of conductive/non conductive parts of a stator bar

The insulation of high voltage stator bars is covered with layers of tape or varnish that have different conductivity to prevent slot discharge or to spread the voltage along the end winding. The limit between these layers is visible when there's a change in the color or texture. The electrical limit is not always easy to spot, for example if an insulated tape covers the limit of the conductive layer. It can be useful to control the real location of the tape/varnish limits. This paper presents a simple way to determine the limits between conductive and nonconductive parts of a stator bar, based on a special field sensor. The method can be applied on a single bar as well as a full generator. A location precision of plusmn1 mm can be obtained with the method without destructive action. The paper presents in detail the method, both from the theoretical and practical point of view, and shows some examples