DEVELOPMENT OF ELECTRIC MOTORS AND GENERATORS FOR OPERATION IN LIQUID DIELECTRIC ENVIRONMENTS AT CRYOGENIC TEMPERATURES ETUDE SUR LA MISE AU POINT DE MOTEURS ET DE GENERATRICES ELECTRIQUES FONCTIONNANT EN MILIEU LIQUIDE DIELECTRIQUE A CRYOTEMPERATURE

摘要

This paper discusses the development, design and performance characteristics of 3- phase random wound and formwound squirrel-cage motors and generators while operating submerged in liquefied gases at cryogenic temperatures. Through a combination of field experience and laboratory testing, motors designed to operate in this unique environment have been evolving over the past 45 plus years. During this time, it has been determined that many of the problems normally associated with air motors, such as partial discharge, corona, thermal life and oxidation are absent on submerged motors. This has enabled engineers to select different materials and adapt designs to better tailor each motor to its specific application and to significantly reduce the physical size required for any given kW rating. It has been suggested that motors operating in submerged cryogenic applications are inherently less efficient than equivalent rated air cooled machines. This is based on the premise that the friction losses encountered by a rotating body in a viscous fluid will be much greater than a body rotating in air. However, a detailed analysis and comparison of the segmented losses of identically rated air-cooled and submerged cryogenic motors reveals this is not necessarily the case. In recent years new applications have been developed using submerged motor technology. One such use is motors being used as induction generators in applications where the isentropic thermodynamic properties of electricity generation can be effectively used to improve the efficiency of the gas liquefaction process.