Failure Mode Assessment of the Generator Stress Grading System

In this paper different kinds of electrical driven failure modes in the end-winding region, are discussed and classified. Failure types related to the stress grading system are analyzed via numerical simulation models and root causes are given for the different defects based on the calculation results. Typical pictures of various findings are presented and explained. In a last step possible diagnostic measurements to identify issues related to the stress grading are discussed and some PD-pattern are presented exemplarily. The aim of this work is to give the basis to correlate findings in the end-winding and especially the highly stressed stress grading area with their most likely cause of defect.