Comparative evaluation of glass conducting armour materials for form-wound stator coils

Semiconducting armour tape with a particulate-loaded binder is typically used for maintaining the ground potential plane within the slot section of a vacuum-pressure impregnated (ATI) stator coil. This paper compares the measured resistances as a function of distance from the ground plane for three commercially available semiconducting glass armour tapes. Results are presented from room temperature resistance tests performed before and after VPI processing, and from an elevated temperature cycle resistance test on the fully processed bars. Similar previous resistance tests and the relative merits of using woven glass and polyester fleece are discussed. The paper also describes results from voltage endurance (VE) tests on different conducting armour and groundwall configurations, and observations of surface deterioration under the ground plane.