Electro-thermal-flow coupled analysis of thermal ageing patterns in steam turbine generator insulation under deep peak shaving conditions

Steam turbine generators frequently experience deep peak shaving conditions, in which the performance of insulation is significantly impacted by extreme fluctuations in operating temperature. The degradation of water-internally cooled stator bar insulation under repeated temperature variations is investigated in this study. This study examines the progression of winding insulation characteristics by Frequency Domain Spectroscopy (FDS) test and electro-thermal-hydraulic coupled simulations throughout various thermal ageing cycles. Accelerated thermal ageing experiments are conducted on stator bar specimens. Dielectric parameters are captured by FDS across various thermal ageing cycles to assess the effect of thermal ageing on the electrical properties of primary insulation materials. A stator bar model rated at 22 kV is constructed. Electro-thermal-fluid multiphysics simulations based on the Finite Element Method are performed to compare and analyze electric field strength and temperature distribution under different thermal ageing cycles. Experimental results demonstrate that dielectric properties of the main insulation material deteriorate as thermal ageing progresses, leading to gradual insulation performance degradation. Simulation analysis indicates that the resulting insulation decline increases surface electric fields and temperatures on the stator bar, accelerating thermal aging and establishing a positive feedback mechanism. These findings support optimised design of the stator bar's anti-corona structure to delay insulation aging, offering a theoretical basis for insulation design optimization and equipment lifespan extension in steam turbine generators.