Research On Design And Operation Characteristics Of Cryogenic High Speed Permanent Magnet Motor For Submerged Liquefied Natural Gas Pump

In the transportation of liquefied natural gas(LNG),the use of submerged LNG pumps provides a guarantee for the safe transportation of liquefied natural gas.As one of the core components of the LNG pump,the cryogenic motor provides power for the normal operation of the LNG pump.Cryogenic motors mainly include into cryogenic permanent magnet motors and cryogenic asynchronous motors.The rotors of cryogenic permanent magnet motors use permanent magnets to replace the rotor windings or cage bars of cryogenic asynchronous motors.The efficiency and power factor of the motors are relatively high,which is conducive to the efficient operation of the LNG pump.It has important research significance.In this dissertation,a cryogenic high speed permanent magnet motor for submerged LNG pump with a rated power of 40 k W is taken as an example,and the cryogenic motor is designed and studied.Cryogenic motor is sealed in LNG pump and operates in LNG at a temperature of-161?.Considering the influence of liquefied natural gas on the material properties of the motor,the design scheme of the conventional high speed permanent magnet motor is modified,the basic structural parameters of the cryogenic high speed permanent magnet motor are determined,and the design steps and various parameter calculation methods of the motor are given.Based on the time-step finite element method,the electromagnetic characteristics of the motor in liquefied natural gas were calculated,and the electromagnetic fields of the motor under no-load condition and load condition are obtained,magnetic density in the air gap of the motor is extracted for Fourier decomposition.Compared with the electromagnetic parameters of the motor at room temperature,the influence of liquefied natural gas on the electromagnetic characteristics of the motor wasclarified.In view of the complexity of the working environment of the rotor permanent magnets of the cryogenic motor for submerged LNG pumps and the operating characteristics of the motor in LNG,the operating performance of the motor when the permanent magnet of the motor rotor is demagnetized under complex working conditions is studied,and the distribution law of stator and rotor magnetic density and other parameters with the degree of demagnetization of the rotor permanent magnet is obtained.Establish a 1/24 three-dimensional fluid field physical model based on the motor structure,the rotor LNG friction loss at different speeds was calculated,and the effects of the axial flow velocity of the medium,the temperature of the medium,and the surface roughness of the rotor on the rotor LNG friction loss are considered separately.The numerical relationship between the rotor LNG friction loss and various influencing factors is obtained.At the same time,it is compared with the rotor air friction loss.It provides a reference for the electromagnetic design of the cryogenic high speed permanent magnet motor for submerged LNG pump.