Experiences Determining the AC Current Rating of HTS Tapes in Power Transformers

Two experimental high temperature superconducting transformers has been designed and built using Bi2223 HTS tape. The transformers are unique in that the magnetic circuit is comprised of air and a silicon steel partial core. The first transformer failed during a full load endurance run and an investigation was carried out to determine the cause of the failure. The cause was believed to be from operating the HTS windings close to critical conditions. A method of determining the ac current rating of the HTS tape was developed and applied to the second transformer. This second transformer was tested successfully under load for several hours