Development of a 22kV/6.9kV single-phase model for a 3MVA HTS power transformer

We have developed a 22kV16.9kV HTS single-phase transformer cooled by liqui d nitrogen for field test, which is a practical model for the single-phase part of a 3MVA HTS power transformer. First, we numerically simulated elect romagnetic, mechanical and thermal conditions of the windings in accidental cases of short-circuit and lightning impulse, and considered the winding s tructure withstanding the severe loads, We constructed a small-sized model coil of Bi-2223 Ag/Mn-sheathed tapes and confirmed applicability of the des ign concept for the over-current and high-withstand-voltage tests. We desig ned and constructed a single-phase HTS transformer on the basis of the mode l-coil-test results. The primary and secondary windings are transposed para llel conductors of two and six Bi-2223 Ag/Mn tapes, respectively. The same tests for the HTS transformer as for usual oil-filled ones indicated the re liable operation and high performance. The field test in a distribution gri d of Kyushu Electric Power Co. included inrush-current test and long-term o peration of the transformer cooled by a continuous supply system of subcool ed liquid nitrogen with cryocoolers.