In consideration of the allowable torsion deformation of the thin motor shaft resulting in a output torque decline and a input current rise with submersible motor for screw pump, analytical expression of the allowable torsion angle was derived and the electromagnetic torque weakened coefficient, the quantita-tive relation curve of torsion angle was established and electromagnetic torque was weakened, which pro-vides the theory basis for the failure of submersible screw pump. Unit combination permanent magnet di-rect-drive submersible motor was developed. The tension stress strength of thin shaft was analyzed by 3D finite element simulation, then 2D and 3D rotor-skewing equivalent motor model for the mechanical stress field and electromagnetic field coupling calculation were established to get the output torque decline. Pro-totype combination operation experiment was carried out. Accuracy of analytical expression is verified.%针对潜油电机在负载运行时，其细长的电机转轴发生许用扭转变形导致输出转矩下降、电流上升等问题，推导许用扭转角与电磁转矩削弱系数的解析表达式，建立细长转轴扭转角与电磁转矩下降的定量关系曲线，为潜油螺杆泵机组故障原因提供了理论依据。研制单元组合式永磁直驱潜油电机，对其细长转轴进行3D有限元扭转变形应力分析。基于转轴扭转变形结果建立电机2D和3D斜极等效有限元模型，进行机械应力场和电磁场耦合计算，得出电机电磁转矩的下降情况。研制样机进行单元电机组合运行试验，验证了转矩削弱系数表达式的正确性。
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