| Submersible motor is the core drive component of downhole rodless pumping equipment in oil field, which has wide application prospect in oil and gas resources development of heavy oil well, horizontal well, and offshore platform cluster well. With the background of the national 863 program "Technology and Equipment of well downhole oil-water separation and reinjection(project number:2012AA061303) ", this dissertation proposed a submersible direct driven unit combination ultra slender permanent magnet motor(SPMM). Aiming at replacing the complex driven structure of "two-poles and three-phases squirrel-cage asynchronous motor + gear reducer" in traditional submersible screw pump, realizing direct driven with low speed and solving the bottleneck in existing submersible motor technology such as manufacturing process, the difficulties in operation and maintenance. The main research contents are as follows:Firstly, based on the characteristics of ultra slender structure of submersible motor, the total connection structure of unit combination permanent magnet motor is designed, which can be separated to many permanent magnet motors(unit motors) with normal slenderness ratio that operated in parallel. Electromagnetic design method of unit motor is summarized, and the optimization design of the stator, rotor magnetic circuit structure is carried out Using field-circuit coupled and curve fitting method, the analytical expression of the relationship between the leakage flux coefficient of rotor magnet and the width of flux barrier is got. The influence of the stator yoke groove depth on magnetic flux density limit is studied using finite element method(FEM). The effect of different slotting dimensions in rotor magnetic pole surface on torque ripple is analyzed, and the curve of slotting dimensions on torque ripple is given. Based on the difficulty degree of processing technology realization, a simplified pole eccentric structure is proposed, which realized the waveform of no-load back electro motive force(EMF) sinusoidal. The accurate analytical expression of unit motor torque angle characteristics is derived, and the electromagnetic validation test for tangential structure 114 mm series prototype is carried out.Secondly, arming at the complicated working condition of high temperature and high pressure, indoor flow-thermal coupled temperature rise model and downhole flow-thermal coupled temperature model are established for submersible motor. By using prototype indoor temperature test data, the related thermal conductivity and heat transfer coefficients of components of temperature rising model are modified, which improving the accuracy of the fluent-thermal coupled temperature rise model. The cooling condition of the downhole submersible motor is evaluated by using well fluid physical properties limit method. Through the comparison of downhole temperature calculation result and indoor temperature test data, it can been seen that the downhole relative cooling condition is superior to the indoor air cooling condition when the flow rate of well fluid isn’t less than 0.3 m/sThirdly, the rule of electromagnetic vibration for ultra slender SPMM with close pole-slot combination is studied. Based on the generating principle of electromagnetic force wave of permanent magnet motor, the radial air gap flux density and electromagnetic force wave spectrum for different series SPMM with 12 slots and 10 poles are obtained using FEM. The relation curve of electromagnetic wave spectrum with the switching frequency of inverter PWM supply is given. The static and dynamic eccentricities of slender permanent magnet rotor are calculated, and the quantitative variation histogram of electromagnetic force harmonic amplitudes vs. different eccentricity is got. The prototypes with different air gap lengths, different iron core lengths and different rotor magnetic pole structures are developed. Through the comparison of test and FEM results for electromagnetic vibration of radial structure series prototypes that the air gap length isn’t less than 0.8mm for 114 mm series motor and iron core length is no more than 400 mm for 98 mm series motor are recommend.Finally, For the phenomenon of the electromagnetic torque decline caused by twisting deformation of submersible motor super slender shaft within allowable twisting angle range, the analytic calculation curve of electromagnetic torque reduction coefficient is deduced. Based on mechanical stress field and electromagnetic field coupled 3D model for unit combination super slender permanent magnet rotor with equivalent skewing-pole, finite element simulation curve of electromagnetic torque reduction coefficient is obtained. The accuracy of torque reduction coefficient is verified by shaft twisting simulation test and combination operation load tests for 98 mm series prototypes. For ultra slender structure of SPMM, the shaft twisting deformation under the allowable stress and the combination process deviation of unit motor rotor are the main reasons for the reduction of the electromagnetic torque output ability and the rising of the power supply current. The combination operation efficiency with rated load under the speed of 300-500r/min for 98 mm series motors, which have 10 unit motors, achieves 0.8, which is 10% higher than the existing two-poles three-phases squirrel cage asynchronous submersible motor’s. |
PDF Full Text Request