Detecting delaminated stator winding insulation using the ramped high-voltage DC test method

High-voltage DC tests have traditionally been used to detect cracks and fissures, surface contamination, and moisture in rotating machine insulation systems. Not generally recognized, however, is the ability of DC testing to diagnose delaminated groundwall insulation. This impaired insulation condition is generally evaluated using AC tests, such as dissipation factor tip up and partial discharge measurements. In this paper, the ramped high voltage DC test method is described, and its ability to detect and monitor delaminated stator winding insulation is demonstrated. Supporting field data are presented and analyzed.