Insulation endurance under combined thermal and electrical stresses in wind turbine generator

The stator insulation of wind turbine generator (WTG) in wind farms would be subject to the high repetitive impulse, due to the inverter unit application, thermal and environmental stresses. In order to study the resistances of insulation system of WTG stator to this operation environment, two conditions of endurance test under combined thermal and repetitive impulse stresses were established, in which the repetitive impulse stress were dominated. The specimens were prepared modeling the stator insulation system of 1.5 MW WTG. During the test duration of 1000 h in total, the dielectric and characteristic parameters of specimens were periodically diagnosed to monitor the change. After the test, the residual breakdown voltage were measured, the micro-structures of insulating materials of specimen were analyzed by means of the infrared spectroscopy, and compared with the initial specimens. The test results demonstrate that, after the high repetitive impulse stress up to 6 kV peak with high repetition rate up to 15 kHz having been applied, the apparent of insulating material near model slot edge of the specimen was destroyed, while the deterioration of the specimens in terms of dielectric properties was detectable, which indicate the capacity to withstand the combined thermal and repetitive impulse stress.