Thermal Evaluation of Air Cooled Generators to Investigate the Generator Rotor Overheating - A Pre-rewind Evaluation Case Study

摘要

Rewinding of generators stator and rotor is a common practice for life extension of the generators being followed by power utilities. This is the stage when the latent defects can be addressed without much of an additional cost. To address these defects strong engineering tools like thermal modeling supported with online site measurements is required to do reverse engineering. This presents a case study of a unique investigation carried out on a gas turbine driven air-cooled 20 MW generator to find out the cause of overheating at central part of the generator rotor. For investigation a thermal model devised for Air Cooled generators was used. The model was developed for design development and for engineering application tool for generators. It was re-configured for this specific application. The program of the model calculates temperature of air, stator core, stator windings and rotor body and air pressures, velocities, air flows and ventilation losses in the generator. The actual operating data such as static and dynamic air pressure, air temperature was collected online by installing additional measurement devices on the generator. The measurements were carried out at different operating load conditions and transient operating conditions were simulated. The results of the model have added value to the refurbishment plan as has highlighted various efficiency improvement aspects.