Charles-Henri Bonnard

A New Direct Magnetic Method for Determining

The knowing the critical current density J_C is important to calculate AC losses in superconducting applications. Usually can be obtained from magnetization measurements or electric measurements based on global quantities as the magnetic flux or the voltage. In this paper a quick and direct magnetic method for determining J_C is proposed. It is based on direct measurements of local magnetic field in the gap between two bulk HTS pellets. Field penetration measurements were carried out on HTS pellets at 77 K by applying increasing axial magnetic fields with a quasi constant sweep rate. This determination of J_C is theoretically based on Bean model. J_C is deduced from the complete penetration magnetic field B_P. B_P is deduced from the delay T_P between the applied magnetic field B_a(t)and the magnetic field at the center between the two pellets B₀(t). Numerical calculations allow deducing J_C more precisely from theoretical calculations and measurements. The numerical calculations are made with the power law E = E_C(J/J_C)ⁿ. For the determination of J_C the influence of the gap due to Hall probe sensor and the applied magnetic field rise rate are taken into account. The influence of thermal is also studied.

{\rm J}_{\rm C}

Complete penetration magnetic field BP is a feature of a superconducting sample submitted to an applied magnetic field. It is very important to know this for applications such as an electrical motor or levitation. The electric E-J characteristics of a high-temperature superconductor (HTS) bulk is generally described by a power law. The main purpose of this paper is to investigate the influence of the n-value and the applied magnetic field rise rate Vb on the BP of a cylindrical HTS pellet. The numerical results presented come from the resolution of a nonlinear diffusion problem with commercial software. In this paper, cylindrical HTS pellets are submitted to an axial applied magnetic field. With the help of these simulations, a linear relationship between BP , Vb, and the n-value has been found. A comparison between measurements and simulations is done for the magnetization of cylindrical bulk superconducting samples. This comparison allows to determine the critical current density JC and n-value of the power law E(J) = EC(J/JC)n. The experiment is based on the direct measurement of the local magnetic field in the gap between two bulk HTS pellets. The field penetration measurements have been carried out on HTS pellets at 77 K by applying increasing magnetic fields with a quasi-constant sweep rate for the axial direction of the applied magnetic field. Two values of complete penetration magnetic field BP have been measured at two different rise rates Vb. The n-value of the real HTS pellet has been deduced.

in Bulk Superconductors From Magnetic Field Diffusion Measurements

Planning the integration of a Superconducting Fault Current Limiter (SFCL) in an electric power network mainly consists in predicting the current limiting characteristics in any fault condition, in order to set the protection relays accordingly. Due to the very non linear behavior of the SFCL, modifications to the settings of existing protection relays are expected. To explore the potential changes, we used a Real-Time Simulation (RTS) methodology with Power-Hardware-In-the-Loop (PHIL) capabilities (i.e. circuit simulator coupled with power amplifiers for driving external physical power devices). The RTS-PHIL is a powerful approach that makes it possible to incorporate the actual transient reaction of the hardware under study without the need for developing a complicated numerical model, while the power system circuit, generally simpler in nature, can be purely simulated. In this project, the response of a commercial protection relay in the presence of a SFCL was investigated. Both the relay and a small scale shielded-core inductive limiter were coupled to the real time simulator (HYPERSIM) through single-phase linear power amplifiers and a variety of faults were applied. So far, this setup has allowed us to evaluate the impact of inserting a SFCL on overcurrent relays (OCR), in a simple radial distribution network. The results show that coordination has indeed to be slightly revised.

Determination of

The complete penetration magnetic field BP is the main feature of a superconducting pellet submitted to an axial applied magnetic field. The electric E-J characteristics of HTS bulk is generally described by a power law E(J) = E_C(J/J_C)ⁿ. The influence of the n-value and applied magnetic field rise rate V_b on the B_P of a HTS cylindrical pellet has been presented in a previous paper. The numerical results presented come from a numerical resolution of a nonlinear diffusion problem. With the help of these simulations, a linear relationship between B_P, ln V_b, and n-value has been deduced. This comparison allows determining the critical current density J_C and the n-value of the power law based on direct measurement of B_P in the gap between two bulk HTS pellets. In this paper, an improvement of this method is presented. The influence of geometric parameters R and L is studied to give generality to the relationship between B_P, V_b, and n-value. A previous B_P formula is confirmed by these new simulations. To correctly connect simulation and experimental results, the influence of spacing e between bulks is studied and presented. A relationship between B_P and measured complete penetration magnetic field B_PM is determined.