Improved Maintenance Approach for Large Generator Armature Windings Subject to Insulation Migration

Forced outages due to failures of asphalt-mica insulated armature windings have been investigated. Based on information obtained from the public utilities, it is shown how the grounding and maintenance methods affect the possible core damage on older large turbine-generators. The probability of an outage can be greatly reduced by planned inspection, maintenance tests, and by replacement of those faulty bars which are most likely to fail.