Young Sik Jo

Thermal Design of a Cryogenics Cooling System for a 10 MW-Class High-Temperature Superconducting Rotating Machine

A cooling system is an essential part of high-temperature superconducting (HTS) rotating machine manufacturing. Moreover, thermal behavior is a crucial parameter of the cooling system that shows unique characteristics of superconductivity below a specific temperature to maintain a superconducting state. Therefore, many experiments have been performed to investigate new reliable cryogenic cooling systems for a large-scale HTS rotating machine. The motivation for the study is our recent development of the cryogenic cooling system using thermal trigger switches; it effectively minimizes non-operational downtime of the HTS machine in cases of power supply or cryocooler failure. This paper focuses on two main targets. First, the thermal design of the cooling system for the 10 MW-class HTS rotating machine is enhanced. Second, the performance of the cooling system is observed for various cryogens to investigate the feasibility of using solid cryogen.

Study of Magnetomotive Force Control Type Superconducting Magnet Using BSCCO HTS Wire

In this study, a method for controlling the magnetomotive force using the current bypass of no-insulation magnets was developed, and the characteristics of 1G high-temperature superconductivity (HTS) no-insulation magnets were elucidated through experiments. The experiments were performed using a magnet designed with bismuth strontium calcium copper oxide HTS wires. Film-type heaters were used to control the MMF. The analysis of the experimental results was carried out in conjunction with an analysis using finite elements method.

Improvement in Stability and Operating Characteristics of HTS Coil Using MIT Material

This paper proposes a new method of achieving electrical stability and controllability of a high-temperature superconductor (HTS) coil. The proposed method applied a material with a metal–insulator transition (MIT) property to the turn-to-turn resistance of an HTS coil. As a result, the turn-to-turn resistance remained at the insulator level in the normal state, thus removing delay during charging and discharging. During transient state, the turn-to-turn resistance dropped to the metal level, and current bypass occurs similar to that in a noinsulation coil, thus preventing the coil from burning out. The validity of the MIT characteristic and the proposed method were verified through experiments.

Effects of Stabilizer Thickness of 2G HTS Wire on the Design of a 1.5-MW-Class HTS Synchronous Machine

In general, a metallic stabilization layer is overcoated on the outermost layer of a second-generation high-temperature superconducting (2G HTS) wire to stably transfer current against thermal and magnetic disturbances. Stabilizer thickness Ts is one of the key issues in an HTS synchronous machine (HTSSM) application because it strongly affects the electrical output performance of the machine and the stable operation and reliable protection of the HTS field coil. In this paper, a design and characteristic analysis for manufacturing a 1.5-MW-class HTSSM was performed using a 2-D analytical design code and a 3-D finite-element method. Various Ts values were considered in the HTS field-coil design to investigate their effects on the stability and protection of the HTS coil and the back-electromotive force of the machine. The design parameters are also discussed to determine suitable Ts for the 2G HTS wire.

Characteristic Analysis of Various Structural Shapes of Superconducting Field Coils

Superconducting field coils consist of race-track-type double pancake (DP) coil modules fabricated using high-temperature superconducting (HTS) wire with high current density and zero resistance. The structural shape of race-track-type DP coils strongly influences the intensity and the shape of the magnetic flux density in the air-gap, which determines the generator electrical output and the superconducting field coil performance. Hence, the structural shape of a superconducting field coil is very important in designing a large-scale superconducting generator. We analyze the characteristics of a 10-MW-class HTS generator using 3-D finite-element analysis software to investigate the electromagnetic effects due to the structural-shape changes in the superconducting field coil.

Electrical Characteristic Analysis According to Contact Resistance Between Turns of HTS Coil

This paper presents our analysis of the output characteristics of a high-temperature superconductor (HTS) coil depending on the turn-to-turn contact resistance. Important design factors were investigated by taking into account the turn-to-turn contact resistance based on the analysis results. Analyses were performed on five self-fabricated coil models with different turn-to-turn contact resistances. To consider only the turn-to-turn contact resistance, we used a first-generation HTS BSCCO wire with simpler architecture and mechanical properties than the second-generation HTS wire. From this study, it was confirmed by experiment that as the turn-to-turn contact resistance decreases, the electrical stability increases but the output efficiency decreases compared with the input.

Design and Analysis of Cooling Structure on Advanced Air-Core Stator for Megawatt-Class HTS Synchronous Motor

A general high-temperature superconducting synchronous motor (HTSSM) is designed and manufactured with an air-core structure, which eliminates the laminated iron core to concentrate the linkage flux in conventional rotor and stator. In an air-core structure, a nonmagnetic material such as glass fiber-reinforced plastic (GFRP) is used as an armature winding supports to avoid saturation of magnetic field density in the stator core and to reduce the weight and harmonics of the motor. However, GFRP air-core supporters make heat dissipation difficult due to the very low thermal conductivity of GFRP, which makes sustainable and stable operation of HTSSMs impossible. Therefore, in this paper, the concept of advanced air-core stator (AACS) is presented to enhance the cooling performance of a conventional GFRP air-core stator. The AACS concept pertains to the introduction of thermal conductive materials on an armature supporter to replace the GFRP material of a conventional air-core stator. The AACS concept structure for a 1.5-MW-class HTSSM was designed and analyzed using three-dimensional electromagnetic and thermal finite element method.

Design of Indirect Closed-Cycle Cooling Scheme Coupled With a Cryocooler for a 3-MW-Class High-Temperature Superconducting Synchronous Motor

The increase in the heat generated from high-temperature superconducting (HTS) rotating components limits the applicability of a cooling method. Hence, a liquid cooling and convection cooling scheme for high-heat-flux applications has gained interest. An indirect closed-cycle cooling scheme coupled with a cryocooler is an alternative cooling technique, in which the heat of vaporization is transferred from an evaporator to a condenser with a relatively small temperature difference. The cooling system of a demonstrative 3-MW-class HTS motor is presented in this paper. A cryogen was used to maintain uniform temperature of the field coil; the maximum temperature of the HTS coils was approximately 30 K during normal operation. The operation process of the cooling system is illustrated, and the main circulation parameters, namely, cryogen flow rate and the heat flux of cooling system, are investigated.