Over-fluxing capability of Large capacity Turbo Generators

Large capacity Turbo Generator (TG) in conventional power plants is meant for base load operation. Continuous operation of TG sets is inevitable to meet the load demands. The Stator core of the large TG comprises a cylinder of laminated steel sheets supported by Key Bars and Core end plates. Abnormal operation of the machine like over voltage and under frequency constitutes in over fluxing. This phenomenon leads to critical heating of the key bars. Excessive heating of the key bar results in core failure and a forced shut down of the TG set. The aim of this work is to implement novel analytical approach to estimate the Key bar heating. A reliable analytical model is developed for the assessment of enhanced efficient operation of the Turbo Generators connected to grid during any momentary variations in the terminal voltage and frequency. The impact of shape, position and material properties of the key bar are dealt in detail. Time taken by the key bar to reach its maximum temperature limit during over fluxing is derived. The analytical results are validated with the Finite Element simulation results. The relay settings for generator protection are decided on the basis of these calculation methodologies. The application of the developed model on a design is outlined.