New approach to the ac loss measurement in the superconducting secondary circuit of an iron-core transformer

We have developed a transformer technique to supply currents over 500 A into a tape from a high-temperature superconductor (HTS). The superconducting tape under test could form either the whole or a part of the secondary circuit winding. The ferromagnetic core, as well as the copper primary, is immersed in an LN 2 bath. This results in a simple and compact design of the whole system. Our approach to the loss determination is based on the fact that the voltage on the entire secondary circuit can be easily registered with the help of a loop embracing the transformer core. In practice, it will also contain the signal from a resistive part of the secondary circuit (joint). We show how this voltage can be subtracted to obtain the pure superconductor loss signal. In our method, the problem of correctly placing the voltage signal wires in the vicinity of the superconducting object, carrying transport current, is avoided. This could be of substantial advantage in the case when the loss of a HTS object that is more complicated than the single tape (e.g. superconducting cable or coil) needs to be measured.