A Conjugate Heat Transfer Approach to Analyze the Thermal Performance of a 1 MW Synchronous Motor–Generator

This study used a 3D numerical model to investigate the heat-flow behavior of a 1 MW synchronous motor–generator by creating a conjugate heat transfer model that included the rotating parts. The computational model involved complex solid/fluid interfaces, a rotor–stator gap, and a fan-driven cooling path that passes through a stator’s external flow path in order to identify local temperature fields and flow distributions. Under design conditions, localized high-temperature regions were observed in the rotor coil because the cooling air was heated, and the airflow then diverged through the stator’s internal channels. On the contrary, periodic low-temperature areas were formed around the stator’s circumference as a result of conductive heat diffusion into the outer casing. A correlation was derived describing a relationship where the peak temperature decreased in a clear logarithmic manner as the cooling air mass flow rate increased. We confirmed that a cooling flow rate of at least 2.0 kg/s is needed to keep the rotor coil temperature below 120 °C within its operational limit under design points. Furthermore, the functional form of the temperature–flow rate relationship remained logarithmic, and the correlation coefficients in this relationship changed linearly with heat generation, even under off-design conditions, where the total heat generation was reduced to 88% of the design value and the ambient temperature was lowered. The study results will provide a practical basis for swiftly estimating peak temperature for various operating scenarios and for determining cooling paths and fan geometry to avoid repeating expensive simulations.