Rapid Thermal Life Assessment of Corrugated Plate Inside the Stator Slot of Large-Scale Turbogenerator

The corrugated plate with excellent bending resistance is one of the main fixing materials inside the stator slot of large-scale turbogenerator. Under the long-term effect of thermal ageing, the performance of corrugated plate will decline and finally affect the safe operation of the generator. Rapid thermal life assessment is of great significance for ensuring the reliability of corrugated plate. In this study, the actual ageing process of corrugated plate is simulated by thermogravimetric analysis (TGA) under an extremely slow heating rate and air atmosphere. The thermogravimetric kinetic analysis has been carried out to solve the activation energy of corrugated plate material using an improved integral method, where a new higher-accuracy temperature integral approximation in rational function form is proposed. In the meantime, a conventional thermal ageing test at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$220{ }^{\circ} \mathrm{C}$</tex> has also been performed in an oven on samples made from corrugated plate material, during which the bending strength of corrugated plate material is tested periodically. The ageing curve at 220° C is fitted using logistic regression model and the thermal life at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{2 2 0}$</tex> °C is obtained by taking 50 % decrease in bending strength as failure criterion. Then the Arrhenius lifespan model parameters of corrugated plate is determined according to its lifetime at 220 °C and activation energy. The results show that the improved kinetic analysis method can be used to accurately calculate the activation energy by comparison with traditional Flynn-WallOzawa (FWO) method and the estimated thermal life of corrugated plate is judged to be reasonable. This paper provides a rapid life assessment method based on thermo-oxidative ageing kinetic analysis for corrugated plate.