12. Super conducting transformers
12.4 Other losses
The followings have to be considered.:
1) Iron loss is same as normal temperature conventional transformer's. Iron core less type is, due to very high magnetizing current, not applicable to general use. To reduce the magnetizing current, tremendous amount of conductor material is necessary, resulting in higher loss in the conductor and too high short-circuit impedance of the transformer due to the increase of winding turn. Furthermore, except in case of Toroidal type, magnetic shield core shall be equipped out side of the coil in order to reduce the strong magnetic field. For the case with iron core, the iron core is to be located out side of the ultralow temperature region (normal temperature region) and cooled separately for avoiding excess cooling energy.
2) The performance of the thermal insulation case (Cryostats) can be almost perfect. So, the heat penetration through the cryostats can be negligible. On the other hand, the heat penetration through the electric bushings shall be considered and added as the losses in the ultra-low temperature region.
3) Some significant stray losses may exist but little has been studied.
4) Losses in insulation materials are, hopefully, negligible.
To produce fine diameter of filaments, metal super conductive materials are only applicable by today's technology. These have to be kept in liquid helium level temperature (4K) for keeping super conductivity. Theoretically the efficiency of the refrigerator to produce such temperature is extremely low and practically furthermore low (in the order of 1/500 --- 1/1000). That means to refrigerate 1kW of loss, 500 --- 1000kW of electric power is necessary.
This page is based on Prof. E.Haginomori's lectures
in Tokyo Institute of Technology, and edited by Japanese ATP User Group.
Copyright (C) Eiichi Haginomori and Japanese ATP User Group.