Haeryong Jeon

Experimental Analysis on AC Loss and Fault Current Test of HTS Coils Co-Wound With Various Inserted Materials

A significant number of recent studies have explored the impact of many kinds of winding insulation conditions on high-temperature superconducting (HTS) coils for the application of electric devices. HTS coil co-wound with turn-to-turn inserted materials could be an appropriate alternative to the no-insulation coil because of the poor charge-discharge delay and unexpected quench behavior of the no-insulation coil. In addition, the co-wound HTS coil has good thermal stability and mechanical integrity, making it useful for superconducting applications such as superconducting magnetic energy storage (SMES) and superconducting fault current limiter (SFCL). However, studies of the co-wound HTS coil have explored dc electrical characteristics, but not ac electrical characteristics. Research into ac electrical characteristics is essential because of the operation sequence of the SMES and fault occurrence for the SFCL. In this paper, the ac electrical characteristics of HTS coils co-wound with various inserted materials were experimentally analyzed. Tested coils were co-wound with either Kapton, stainless steel, or copper tape at every turn of the winding, and one no-insulation coil served as a reference. AC loss, fault current, and recovery time were measured at 77 K, self-field.

Methods for Increasing the Saturation Current and Charging Speed of a Rotary HTS Flux-Pump to Charge the Field Coil of a Synchronous Motor

The rotary flux-pump using HTS tape has been studied for superconducting rotating machinery application. The charging speed and saturation current of the rotary HTS flux-pump is closely related to magnetic flux linkage passing through the HTS tape. To analyze charging parameters that effect pumping rate and saturation current of the flux-pump, methods of changing the rotating speed, shape of permanent magnet, width of HTS tape, and magnetic flux intensity have been investigated in previous studies [1]– [3]. In this paper, we have tried to test three cases to investigate the pumping rate and saturation current: 1) two different background materials, iron and Bakelite, were used to compare the magnetic flux linkage reinforcement; 2) two HTS tapes were overlapped to extend the magnetic flux linkage area, and each HTS tape was connected to an HTS coil; and 3) the parallel joint was conducted between the flux-pump and the HTS coil to compose a closed loop for persistent current mode. In order to measure the charging speed and pumping rate, a Hall sensor was installed at the center of the HTS coil.

Magnetic Field Stability Analysis on No-Insulation and Turn-to-Turn Soldered HTS Magnets Under Sinusoidal Noise Operation

The field stability of a no-insulation and a turn-to-turn soldered high-temperature superconducting (HTS) magnet is analyzed under sinusoidal noise operation. The stability of the magnetic field is a critical factor for some applications such as nuclear magnetic resonance (NMR) spectrometer. The no-insulation and turn-to-turn soldered HTS magnets have intrinsic residual resistance which acts like a low-pass filter attached to the main magnet. The intrinsic low-pass filter can improve the time stability of the magnetic field by reducing ac noises generated by the power supply. In this paper, the improved field stability is analyzed with a no-insulation and a turn-to-turn soldered HTS magnet sample. The sample magnets are operated under sinusoidal power supply noise. Qualitative analysis is conducted by simulating the virtual NMR lineshapes based on the field mapping results obtained during sample magnet operation. Both the no-insulation and turn-to-turn soldered magnets demonstrated improved field stability, but the field stability in the turn-to-turn soldered case is greater.

Analysis of the Notch Effect on Flux Diverters for High-Temperature Superconducting Magnets

Flux diverters made of ferromagnetic materials can be used in high-temperature superconducting (HTS) magnets to change the magnetic field distribution and increase the critical current of the magnet. In this paper, the notch-shaped flux diverter increases the critical current of the HTS magnet by detouring the magnetic flux more effectively than the flat surface-shaped (simple) flux diverter. Numerical analyses are carried out to calculate the critical current using the simple-shaped and the notch-shaped flux diverters. Then, experiments are conducted to verify the results of the numerical analyses. As a result, the HTS coil with a notch-shaped flux diverter shows the increased critical current.