A study on a coreless superconducting transformer

A conceptual design for a 1000-MVA-class coreless superconducting autotransformer (CLSCAT) has been developed. For a preliminary experimental study, a small 2.5-kVA CLSCAT has been manufactured and tested. The test result shows that though the exciting current of the CLSCAT is very large, its voltage drop is relatively small compared with the cored transformer. The dielectric strength of liquid helium has been tested using an insulation model. From the insulation test, the availability of the fundamental insulation structure composed of the lamination of small liquid helium gaps separated by solid barriers has been confirmed. From the conceptual design of a 1000-MVA-class CLSCAT, it becomes clear that the CLSCAT has an additional reactive power of about one-third of its rated capacity. This large reactive power can be utilized for the compensation of the capacitive charging current of a cable line or a UHV transmission line. The operating loss, was calculated to be about two-thirds of the conventional transformer. However, this figure is reduced to one-half if the additional reactive power of the CLSCAT is considered.<>