Experimental and analytical studies on electromagnetic behaviors of the GdBCO racetrack coils in a time-varying magnetic field

The electromagnetic responses of two GdBCO racetrack coils, one wound without turn-to-turn insulation (NI) and the other wound with Kapton tape (INS), were examined in a time-varying magnetic field generated by a permanent magnet mounted on a rotor, which was driven by a separate motor. The currents induced by the electromotive forces were measured with respect to the rotating speed, number of turns, and the distance (d) between the permanent magnet and the coil. In the case of the NI coil, delay of the induced current was observed in a time-varying magnetic field (5 rpm, d= 10mm) due to anisotropy of the current path, suggesting that delay of the induced current will affect the electromagnetic induction by dB/dt. Consequently, the maximum induced current (0.35 A) of the NI coil was 8.2 times lower than that of the INS coil (2.88 A). Moreover, the induced currents in the INS coil increased with increasing rotating speed and number of turns, as well as with decreasing d, while those of the NI coil were barely affected due to the anisotropic current path. The experimental results showed good agreement with the simulated ones, which validates the proposed approaches involving an NI equivalent circuit model.