Inductive Method for the Determination of the Critical Current $I_{c}$ of HTS Stators in Axial Flux Configuration

This work presents the evaluation and determination of the critical current (I_c) of HTS stators in axial flux configuration. The stator construction was done considering the previously definite and optimized geometry, by cutting and soldering the sections of HTS tape in order to get the axial flux poles configuration. By this reason and due to the construction method, a reduction value of the initial critical current was presented. This reduction increases because of the stator pole numbers or the number of the welded joints. If the method of the four-lead is used, this one can introduce an additional error to the measurement of I_c, which can present confusion. The inductive sensors used in the present work are based on the use of a Rogowski coil placed at the terminal end in order to observe the behavior of the circulating current in the superconductor stator. When the current flows through a superconductive tape and this one is increased, the behavior of the tension of the third harmonic also increases (V₃) and it is induced in the coil. By this reason the tension value of the critical state V₃ can be determined and it is proportional to the amplitude of the driven current I_o. Due to the characteristics of the signal to measure, it is necessary to make a signal conditioning. This conditioning was obtained using a filtering circuit and an integrator, connected to a data acquisition system (DAQS). The design of the filtrate parameters and the circuit of integration are presented altogether with the comparative results of the inductive measurement method and the four-lead method on tapes and stator.