Heat transfer analysis of an air-cooled turbine generator Stator under ground-wall insulation multi-direction shelling

Abstract

Insulation aging in large generators is one of critical fault sources for machines. About 1/3 of generator faults are caused by critical temperature under stator winding insulation faults, especially stator ground-wall insulation shelling fault. To determine stator ground-wall insulation aging mechanism under influences of electric-thermal-mechanical stresses, the 3-D temperature field mathematic models considering different stator ground-wall insulation shellings are established. Based on calculated additional copper losses, turbulent movement in the ventilation ducts and boundary conditions of the model, stator temperature field in the generator normal operating is calculated via finite volume method (FVM). The obtained results are compared with the measurements to verify the accuracy of the calculation method. Then, the stator temperature field considering ground-wall insulation non-transfixion shelling, 1/4 lamination stacking in axial direction and 0.5 mm in circular direction, is calculated. Next, stator temperature fields under multiple ground-wall insulation shelling faults are also investigated. Moreover, the heat transfer laws within the stator components such as strands, ground-wall insulation both in shelling side and non-shelling side, row insulation, and air in the shelling gap, etc., are analyzed. The comparative analysis on the heat transfer laws under different shellings are addressed to provide practical reference in insulation failure diagnosis.