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A Review of Results From Thermal Cycling Tests of Hydrogenerator Stator Windings

A Review of Results From Thermal Cycling Tests of Hydrogenerator Stator Windings,10.1109/TEC.2011.2127479,IEEE Transactions on Energy Conversion,Maren

A Review of Results From Thermal Cycling Tests of Hydrogenerator Stator Windings  
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Thermal cycling of generators, occurring during in- termittent operation of power stations, increases the thermome- chanical stress on the stator groundwall insulation and can, there- fore, contribute to failure of the generator. Thermal cycling stresses can, to some extent, be replicated and accelerated in laboratory tests. Such tests are performed to ascertain whether a new stator winding insulation system can handle intermittent operation, to evaluate the relative difference between different types of insula- tions or to investigate degradation processes and failure mecha- nisms. Results from thermal cycling tests of hydrogenerator stator windings are reviewed. Only stator windings of air-cooled hydro- generators with thermoset groundwall insulation of mica-epoxy or mica-polyester are considered. The published literature of labora- tory experiments performed in order to study effects of thermal cycling on groundwall insulation through different types of diag- nostic measurements is described and discussed. Partial discharge (PD) and tanδ measurements gave, in some cases, an indication of a trend in the condition during thermal cycling, while in other cases it was difficult to interpret the test results. Many agree that measurement of breakdown voltage of stator windings can give an indication of the aging and remaining lifetime of the insulation. The ability of other measurements such as tanδ, PD, and voltage endurance to assess the remaining lifetime of the stator winding is less convincing since the results vary greatly.
Journal: IEEE Transactions on Energy Conversion - IEEE TRANS ENERGY CONVERS , vol. 26, no. 3, pp. 890-903, 2011
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