The calculation and measurement of electromagnetic energy flows for investigation of critical current estimation for high-temperature superconducting coil by means of pick-up coils

Abstract

For practical operations of high-temperature superconducting (HTS) devices, we have proposed a monitoring and diagnosing system to detect the degradations of superconducting properties before normal transitions occur locally in the HTS winding. The proposed system estimates the distributions of critical current indirectly from measurement results of the active power components of the Poynting vector around the monitoring HTS devices conducting ac currents by means of pick-up coils pairs mounted surrounding the HTS devices. For this purpose, it is necessary to solve the inverse problem. In order to estimate the critical current distribution, therefore, it is first necessary to be able to calculate the measurement signal distribution from the critical current distribution of the monitoring coil. This paper first proposes the calculation method of signal distributions measured by our system, next reports the results of the experiments and analysis, which were carried out to verify the validity of the calculation method. A pancake coil wound with Bi-2223 multifilamentary tape exposed to a uniform AC magnetic field was assumed as a monitoring coil in the experiments and analyses. The good agreement between the measured signals obtained from the experiments and the numerical analysis demonstrates the effectiveness of the proposed calculation method of measured signals.