New Algorithm for Rotor Ground Wall Condition Assessment of Large Salient-Pole Generators

Deterioration of ground-wall insulation is one of large salient poles generators failure modes. A failure in this insulation can seriously compromise the machine's operation, causing stray current circulation between poles, leading to vibrations, and resulting to costly unplan maintenance. Therefore, it is crucial to act before a failure occurs by planning an appropriate corrective maintenance. Monitoring the insulation to ground resistance by measurements is one important way to do so. Unfortunately, there are some challenges interpreting the results, such as the lake of references, insulation materials with different dielectric properties, the influence of the environment, making the assessment of the rotor insulation health a complex puzzle. Based on analysis of thousands of insulation resistance tests results from a large fleet of salient pole generators ranging from few to hundreds of MVA, a new algorithm is proposed to help assist decision makers. It will be shown that the interpretation of results could be standardized with algorithms leading to a comprehensive health index with a certain degree of confidence. This allows non-experts to have a clearer view of the rotor ground wall insulation condition and quick comparison of assets together. Moreover, it is proposed that these assessments can be conducted with the generator in service. Combining on-line and off-line tests could be a precious tool to quickly alert if a degradation occurs and reduce unit downtime.