Effect of Low Temperature and High Pressure on Deep-Sea Oil-Filled Brushless DC Motors

Abstract

AbstractThe principle of electronic commutation makes brushless DC motors suitable for deep-sea application by sealing the motor in an oil-filled housing. However, if the oil-filled actuator is not designed properly, it will malfunction in the deep sea in spite of its excellent performance on land. In this paper, oil viscosity variations with pressure and temperature are reviewed because both factors vary with the operating depth, and a practical approach to estimate the viscous torque is advanced based on a viscous drag model of the selected motor and the properties of the oil. An experimental rig that can simulate the deep sea environment was developed, by which a series of experiments to study the motor efficiency and dynamic performance in different conditions were conducted. The values of viscous torque obtained in the experiments agreed well with our estimation. The low efficiency in the 2°C experimental group confirmed the influence of temperature, while the dramatic difference in the dynamic performance of the motor when filled with different oils verified the importance of analyzing the properties of the oil and of making a deliberate selection.<def-list>Nomenclature<def-item><term>T0</term><def>Normal temperature</def></def-item><def-item><term>P0</term><def>Atmospheric pressure</def></def-item><def-item><term>μ</term><def>Dynamic viscosity</def></def-item><def-item><term>μ0</term><def>Dynamic viscosity at given temperature T0 and pressure P0</def></def-item><def-item><term>ρ</term><def>Density</def></def-item><def-item><term>P</term><def>Pressure</def></def-item><def-item><term>T</term><def>Temperature</def></def-item><def-item><term>α</term><def>Pressure-viscosity coefficient</def></def-item><def-item><term>η</term><def>Kinetic viscosity</def></def-item><def-item><term><inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" mimetype="image" xlink:href="MTS50208e13.gif"/></term><def>Taylor number</def></def-item><def-item><term>Mv</term><def>Viscous drag moment</def></def-item><def-item><term>MC</term><def>Viscous drag moment acting on cylinder flank</def></def-item><def-item><term>CM</term><def>Moment coefficient</def></def-item><def-item><term>Ri</term><def>Rotor diameter</def></def-item><def-item><term>C</term><def>Air-gap clearance</def></def-item><def-item><term>L</term><def>Rotor length</def></def-item><def-item><term>B</term><def>Clearance between housing and end face of the motor</def></def-item><def-item><term>ω</term><def>Rotor angular velocity</def></def-item><def-item><term>Re</term><def>Reynolds number</def></def-item><def-item><term>k</term><def>Coefficient relating to the motor geometry</def></def-item><def-item><term>PeL</term><def>Input electric power</def></def-item><def-item><term>Pir</term><def>Iron power loss</def></def-item><def-item><term>Pme</term><def>Mechanical power</def></def-item><def-item><term>Pj</term><def>Joule power loss</def></def-item><def-item><term>R</term><def>Phase resistance</def></def-item><def-item><term>U</term><def>Input voltage</def></def-item><def-item><term>I</term><def>Input current</def></def-item></def-list>