On Liquid-Nitrogen-Cooled Copper-Wound Machines With Soft Magnetic Composite Core

This paper illustrates the potential and the convenience of copper-wound electrical machines with liquid nitrogen (LN) cooling. Natural convection heat exchange coefficients in LN are very high. Moreover, the resistivity of copper decreases remarkably at cryogenic temperature, subsequently reducing Joule loss in copper windings. Hence, cryogenic copper-wound electrical machines use less copper to carry the same current compared to airor water-cooled machines, thereby improving the powerto-weight ratio. An experimental study is made of some practical issues related to the design of an LN-cooled machine using as an example the construction of a 220-N permanent magnet tubular linear actuator with a soft magnetic composite stator core.