Determination of Iron Loss Coefficients of Ferromagnetic Materials Used in Cryogenic Motors

Cryogenic motors are the main motivation parts in submerged liquefied natural gas (LNG) pumps in LNG transportation industry. As the environment temperature is lower than 110K, the performances of cryogenic motors should be greatly different from that of ordinary motors, as well as the calculation method should be. Currently there exist obvious confusions in the calculation of iron-losses of cryogenic motors. There are studies claiming the iron losses calculated increased to 8 times at the cryogenic temperature, while some other studies claiming the iron losses would maintain the same from the cryogenic temperature to room temperatures. Thus, the temperature characteristics and the calculation methods of iron losses should be addressed in-depth and can be explained clearly. An accurate calculation method of iron losses of cryogenic motors is the key to the study of cryogenic motors. By comparing and summarizing the prior studies of the magnetic and loss characteristics of ferromagnetic materials under room temperature and cryogenic conditions, this paper tries to determine the rough changing tendencies of the key parameters of the soft ferromagnetic materials commonly for the cryogenic motors. It can be roughly conclude that not only the conductivity but also the specific loss of ferromagnetic materials increase an average of 20% in the cryogenic environment. Further study shows that the proportion of the hysteresis loss maintains basically unchanged while the eddy current losses increases. And the increasing percentages are basically consistent with that of conductivity ratio, so the loss coefficients can be approximatively determined.