Experimental research on stator insulation system of 5 MW offshore Wind turbine generator under simulated marine environments

The stator insulation system of offshore wind turbine generator (WTG) will be subjected to marine environment, such as high humility and heavy salt fog. In order to study its resistance to this hostile environment, the marine environmental conditions in the coast regions along China´s coastline have been firstly examined in this paper. The specimens for modeling stator insulation system of 5MW/3kV class offshore wind turbine generator were prepared. The environmental tests, including the change of temperature, steady damp heat and salt mist, have been carried out. At each interval of periodic tests, some nondestructive diagnoses such as dissipation factor and insulation resistance have also been carried out to monitor the change. After the simulated marine environmental test of 4 periods, the residual breakdown voltages of specimens were measured and the micro-structures of insulating material were observed by microscope. The test results show that, even though micro-cracks have been generated on the interface between the coil main insulation and the iron core, and resulted in the brine permeated into the inner surface of the core slot, the dielectric properties of insulation system of the specimens still kept in the range of normal specifications. The insulation system of specimen has performed an excellent resistance to the marine environment due to the electrical shielding effect of the semi-conductive slot coating.