| As a key subsystem of oil-gas resources development equipment in the middle and deep sea,the performance of underwater asynchronous motor cooling system has significant effects on the operation life of the motor and the whole equipment,crude oil production and drilling costs.Due to the complex working environment of underwater asynchronous motor,the cooling system must be specially designed.However,there is less in-depth research on underwater asynchronous motor cooling system at home and abroad,and there has not yet been a molding design method.The conventional motor cooling system analysis method and design method cannot be directly applied to underwater asynchronous motor.At the same time,the existing cooling system scheme has problems such as complex structure,low reliability and difficult design.Therefore,a new cooling system scheme with a forced circulation cooling impeller is designed.Based on the research of motor heating mechanism and cooling system characteristics,the coupling analysis method of the magnetic field,the flow field and the temperature field and the design method of structural parameters of the cooling system are proposed,which provides the necessary theoretical basis and technical support for the research and development of similar motor cooling system in the future.The main contents of this thesis include the following aspects:Aiming at the problem that the influence factors and calculation of iron loss mathematical model are not comprehensive and the research status that only unidirectional coupling is considered in the traditional asynchronous motor temperature field analysis,a heat source loading method is proposed,which reflects the unidirectional and bidirectional coupling between the physical fields of oil-filled underwater asynchronous motor.In the unidirectional coupling of the magnetic field and the temperature field,iron loss mathematical model considering the effects of alternating magnetization,rotating magnetization,harmonic magnetic field and local hysteresis loop is established.The time-stepping finite element method(T-S FEM)and Fourier analysis method(FAM)are used to calculate the iron loss of the stator and rotor.In the bidirectional coupling of the magnetic field,the air gap flow field,and the temperature field,T-S FEM and finite volume method(FVM)are respectively used to obtain the influence of temperature on copper loss and oil friction loss.The temperature field of oil-filled underwater asynchronous motor is studied.The influence of equivalent thermal resistance network method(ETRNM)and FVM on the temperature field of motor oil without forced flow are compared and analyzed,and the most reasonable temperature analysis method is determined.The UDF programs of copper loss,oil friction loss and convective heat transfer coefficient of shell surface are written.The temperature field of the motor under natural convective heat transfer is solved by iterative method.It is concluded that the temperature obtained under variable parameters can be closer to its reasonable working range,and it is revealed that the temperature obtained under different equivalent ways of convective heat transfer of shell surface is quite different,which draw forth the motor oil forced flow.The effects of different internal flow field inlet velocity,iron loss and unidirectional coupling between the magnetic field and the temperature field on the temperature field of the motor oil forced flow are studied.The design interval of circulation flow rate is obtained,and it is shown that calculating the rotor iron loss and considering the stray loss have a significant influence on the rotor temperature.The cooling system is actually a special centrifugal pump closed circulation system.The interaction among the cooling system temperature,circulation flow rate and motor oil viscosity is explained.The internal flow field inlet temperature and circulation flow rate are obtained as the variable parameters of the motor oil forced circulating flow.The characteristics of cooling system are studied.In the characteristics of pipeline heat transfer,the mathematical model of total convective heat transfer coefficient is given,and the calculation model of pipeline inlet and outlet temperature is established,which reflects the unidirectional coupling between the temperature field of pipeline and its internal flow field.In the characteristics of pipeline pressure loss,the influence laws of different pipeline structure parameters on the characteristic curve are obtained,and a calculation method of pressure loss considering the variation of motor oil viscosity is proposed.In the characteristics of cooling pump(impeller),the influence of structural parameters of cooling impeller,motor speed and motor oil viscosity on the characteristic curve are analyzed by using similarity theory and viscosity conversion method.In the joint working characteristics of cooling system,the calculation method of the relationship between the circulation flow rate at operating point and the pipeline inlet and outlet temperature is proposed based on the analysis of the above three characteristics,and the calculation model of the circulation flow rate at operating point is derived,which reflects the unidirectional coupling between the motor flow field and the pipeline temperature field.The calculation program for determining the operating point is written and the software is developed by this method.The parameter design of cooling system is studied.The coupling analysis method is mainly composed of heat source loading method,pipeline inlet and outlet temperature calculation method and the circulation flow rate at operating point calculation method.Compared with the conventional motor cooling system analysis method,the key of this method is the bidirectional coupling between the magnetic field,the flow field and the temperature field.The structural parameter design method solves the problem that the complex influence relationship between variable parameters leads to the difficulty of accurate design of structural parameters.The structural parameters of radiator and cooling impeller that meet the cooling system design conditions are obtained by using this method.In the design method,the calculation methods of pipeline inlet and outlet temperature and pipeline pressure loss are used to analyze the change law of pipeline performance parameters,and the fitting coefficient of the calculation model in the coupling analysis method is obtained by combining with the operating point calculation program.The matching interval between the constant circulation flow rate and the radiator structure parameters is obtained by using the coupling analysis method.The design interval of cooling system structural parameters is determined.The influence of structural parameters on cooling performance is studied,and the structural parameter matching analysis process is established.The experimental study of cooling system is carried out.The cooling system test-bed is built,and the no-load type test and temperature test are carried out.The experimental value is compared with the calculated value or the simulation value,and the causes of error under load are analyzed.The experimental research shows that the analysis method and the design method are reasonable.The scheme and method of the cooling system are applied to high-power oil-filled underwater asynchronous motor,which further shows that the scheme and method are reasonable and feasible. |
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