金属杂质侵蚀下的大型发电机定子线棒绝缘劣化机理

To reveal the coupling mechanism of metal impurities eroding the epoxy mica insulation layer of the stator bar in the whole working condition of large generators, the dielectric loss of metal impurity particles and stator insulation layer under high strain was subject to electromagnetic-mechanical-temperature multi-field finite element simulation and experimental analysis. Firstly, the electromagnetic-mechanical parametric model of bar and core slot containing spherical metal impurities is constructed under the swirl field of vector magnetic potential, and the characteristic element type and air domain odd symmetry boundary conditions are assigned. Then, the force density value and nonlinear transient force application behavior of the model are analyzed by the interactive sequence coupling method such as the matrix method. By studying the phase transition and microscopic loss increment of the epoxy insulating layer at the end of the stator bar, the characteristic value range of stress and deformation of the metal impurity grinding insulating layer are obtained. Furthermore, an electromagnetic-temperature model containing spherical metal impurities is established and the thermal erosion calculation is carried out by using the unidirectional magneto-thermal coupling method. Based on this model, the temperature field range of the impurity contact surface is rigorously analyzed. Finally, the metal grinding experiment under the alternating magnetic field is conducted on the insulating layer of the bar section for simulated force application verification and the samples were observed by the scanning electron microscope in detail. The experimental and simulation results show that the abnormal temperature rise caused by joule loss of metal impurities is not enough to cause short-term thermal erosion of the epoxy insulation layer, and the mechanical process of sheet mica's defect being aggravated due to the breakage of the epoxy molecular chain ground and eroded by impurities is the main cause of insulation deterioration of the stator bar. The conclusion provides a reference for the state monitoring and fault diagnosis of the main insulation of generator stator bars.