Submerged cryogenic motor materials development

A unique application for three-phase random and form-wound squirrel-cage motors and generators and their insulation systems is their operation while submerged in liquefied gases at cryogenic temperatures. Motors utilized for this service initially appeared in the late 1950s using standard air-motor designs and insulation systems. More specialized systems and designs were developed throughout the 1970s and 1980s and, as more extensive testing was conducted on motors in these applications, a better understanding of the properties of materials operating in dielectric fluids at cryogenic temperatures was gained. It was found that many of the problems associated with air motors, such as partial discharge, corona, thermal life, and oxidation, were absent on submerged motors. This has enabled engineers to better tailor each motor to its specific application. Over the years, end users have been steadily increasing the demands on these motors, and their sizes have grown ever larger. Today, submerged electric motors are used at loads as high as 2,500 kW, 7 kV, and in a wide variety of liquids, many much warmer than the cryogenic temperatures of earlier designs.