Determination of thermal and thermo-mechanical stresses in stator insulation of wind turbine generator based on online monitoring temperatures

The high thermal and thermo-mechanical stresses caused by the cut-in and cut-off of wind turbine generator (WTG) frequently occurred in the stator insulation of generator. In order to quantitatively determine these stresses in practice, the annual real-time temperatures were firstly collected and then analyzed by statistical methods from the two double-fed asynchronous generators respectively located in representative geographical or climate conditions in the paper. Then a typical simulating calculation of temperature distributions in stator insulation were carried out based on the on-line monitoring temperatures. All the essential thermodynamic properties of insulating materials used in stator insulation system of WTG, such as thermal conductivity, elasticity modulus and coefficient of thermal expansion, were measured also. The numerical calculation of thermal and mechanical coupling field with the finite element method (FEM) was conducted. The results of simulating calculation and statistical analysis indicate the highest temperature rise of stator insulation in the operation can exceed 100K, and the annually cumulative operation times with the temperature rise of more than 80K was over 400 hrs. When the temperature changed from the highest 142°C to the lowest -20°C, the maximum thermo-mechanical stress in the stator insulation system of WTG locates in the inner edge of the iron slot bottom. The maximum normal and shear stresses are 14MPa and 6.5MPa, respectively.