Multi-physics design of a novel turbine permanent magnet generator used for downhole high-pressure high-temperature environment

Conventional turbine generator with magnetic coupling is becoming difficult to meet large electric power demand because of complex structure, low-efficiency and lower-power density in the downhole environment. In this study, a novel stator-sealed downhole turbine permanent magnet generator is presented. Conventional magnetic coupling is replaced by the separate seals of stator and magnet, allowing drilling fluid flow from the air gap of the generator through the sliding bearings. Then the effective lubrication of bearings and cooling of generator are achieved as well as high power density and pressure balance of the generator. The Halbach array and fractional slot winding are both utilised to further improve the power density, reduce the loss, and keep a lower voltage regulation. A multi-physics design procedure is proposed in this study involving the electromagnetic, thermal, fluid and stress field for downhole harsh environment. In the design process, the coupling electromagnetic-thermal analysis based on two-way multiple iterations and the coupling thermal-fluid analysis based on conjugate heat transfer is incorporated to guarantee high accuracy. The experimental data are compared with simulation results to verify the correctness of proposed method and the feasibility of this novel turbine generator for downhole application.