The construction of energy efficient electric power equipment using high-temperature superconductivity (HTSC) is one of the priority research and development directions in electric power engineering. This is true for power transformers as important elements of power supply systems. In the windings of HTSC transformer with dense arrangement of superconducting turns and layers, magnetic induction in the magnetic leakage flux path between the primary and secondary windings is generated by total ampere-turns of the windings and attains a high level. As this takes place, in the windings themselves each turn is affected not only by the magnetic field generated by the current in the turn, but also by the magnetic field generated by currents in adjacent turns of the winding. Also, the edge effect occurs, and, as a result, there is an excess increase in the current density on the edges of cylindrical windings. All this results in increased loss in transformer windings, reduction in the current-carrying capacity of the windings, and reduction in the transformer efficiency. Such an effect of deterioration of superconducting transformer parameters that considerably degrades their cost/performance ratio is more important to be prevented in HTSC transformers than in low-temperature superconducting (LTSC) ones, because a HTSC winding material has appreciably lower current-carrying capacity in the magnetic fields as compared to a LTSC material. In the Krzhizhanovsky Power Engineering Institute in order to eliminate these drawbacks there have been developed, constructed, and tested laboratory scale prototypes of core type and toroidally wound superconducting transformers with the localized magnetic field operating with pulsed magnetic field, and transformers of electrical machine-type exploiting rotating magnetic field, including transformers with the core made of amorphous electrical steel. The essential difference between the superconducting transformers that have been developed and similar conventional superconducting transformers is that each turn of windings of the transformer is located in its self-magnetic field, which is generated by the current in the turn and is localized in its vicinity. The effect of the external magnetic field generated by currents in the other turns of the windings of the transformer is minimal; and in this case the influence of the self-magnetic field of a turn on other turns of windings of the transformer is negligible. Therefore, superconducting windings of the transformer are located in their self-magnetic field, which is equal to a magnetic field of one turn taken separately. In accordance with the design superconducting windings of the transformer are wound loosely with a predetermined pitch. The principles of design of multistranded superconducting wires with the localized magnetic field have been substantiated theoretically. Such wires can find application in superconducting electric power equipment. In the Krzhizhanovsky Power Engineering Institute there was designed, manufactured, and tested a prototype single-phase 10 kVA HTSC transformer with rated voltages 1,0/0,04 kV, with the magnetic core made of amorphous electrical steel. It was found that no-load losses were reduced by a factor of about 5, and short-circuit losses by a factor of about 50 as compared to the losses in conventional transformers having the same power rating.
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