Assessing the condition of hydrogenerator stator winding insulation using the ramped high direct-voltage test method

Ramped high direct-voltage tests have proven to be an effective and nondestructive means for reducing in-service stator winding failures. The measured current versus applied voltage response obtained during these off-line tests can be used to detect cracks and fissures, moisture absorption, tape separations, conductive surface contamination, lack of epoxy cure, and internal delamination. Ramped voltage test results have been used to determine when corrective actions are needed and what the appropriate actions are. When done properly, the test can identify stator windings that are approaching failure without accelerating the deterioration process.