In the present work, a new test facility of combined triple stresses aging for stator bars insulation of generator was introduced. The facility can efficiently stimulated the three stresses, which are imposed to stator bar insulation of generator in operation, and conduct single factor, combined double factors and/or triple factors aging test at random. In order to satisfy the different requirements put forward to specimens in different measurement and consider the fact that mechanical stresses are applied differently at the local bar, test bars are divided into several specimen pieces and treated in different way. The results of PD detection performed on different specimens subjected to electrical, combined electro-thermal or combined three factors aging, respectively, have given sufficiently information on the synergistic effect of electrical and thermal, mechanical stresses on stator bar insulation with micdepoxy aging. It is proved that the *
Different portions of stator insulation are subjected to multistresses with different strength during the operation of large generators. In order to study the aging extent of stator insulation in different portions, diagnostic tests are performed on the specimens from stator bars of a large turbogenerator, which has operated for 16 years. The tests include, polarization index test, dielectric loss measurement at various voltages and temperatures, ac current measurement, partial discharge test and acoustic detection. The test results are discussed and it is shown that the aging extent of stator insulation of endwindings is more serious than that of the insulation in the slots. Results also indicate that endwindings were subjected to stronger stresses than the slot portions of coils were. Finally, the suggestion could be made that during predictive maintenance testing of large turbogenerators, more attention should be drawn to the insulation of endwindings.
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