Studies of superconducting or cryoresistive power transformer are summarized.
Since 1960, feasibility studies of superconducting transformer have been made by Mcfee, Wilkinson Jones, Lorch, Harrowell and the experimental models of superconducting transformers have also been constructed and tested by Mcfee and Jones.
Though Mcfee thought that a superconducting transformer could compete with a usual transformer at high power region more than several ten MVA, others reported that it would not be economic until a superconductor having the extremely low AC loss and the high critical current density under high magnetic field were developed.
In addition to the development of such a new superconductor, they pointed out that the improved winding construction having the low leakage magnetic field, superinsulation vessel for winding, and protection of the superconductor against fault conditions should be studied.
Feasibility studies of cryoresistive transformers have been made by Wilkinson. He has estimated economic terms power that could be saved if the conductor in several hundred MVA cryoresistive transformers were pure aluminium maintained at 20°K by liquid hydrogen or beryllium maintained at 77°K by liquid nitrogen. Compared the possible saving in conductor loss with the drive power used by refrigerators and with the cost of refrigeration plant, it was found that in cryoresistive transformers, there was no promise of net saving over conventional costs that would warrant the constructional and operational complexities entailed in deep refrigeration.
The experimental models of cryoresistive transformers have been made by Lair Liquid Ltd. and Hitachi Ltd..
In the former, a capacity of which was 253kVA, pure aluminium at 20°K have been used as the conductor.
In the latter, a capacity of which is 1, 200kVA, copper have been used as the conductor and maintained at 130°K by liquid fluorocarbon cooled by the heat of the evaporation of liquid natural gas, which have been used more and more as fuel of power plants. This type of the cooling systems would save the cooling cost of the cryoresistive transformer.
