Kyung Yong Yoon

Experimental Study of the New Type of HTS Elements for Current Leads to be Applied to the Nuclear Fusion Devices

This paper describes new kind of HTS (High Temperature Superconducting) element for current leads, which can transfer large electric current in the nuclear fusion system. Since the HTS tapes have no resistance and the generated Joule heat is also very small compared to the conventional current leads, cooling costs of the current leads can be reduced. For this reason, the various feasibility researches for HTS current leads have been promisingly progressed in the superconducting power applications. However, there is a limitation on the capability of current carrying for single HTS tape. In addition, the cross-sectional area of the current leads should be small enough to minimize the heat conducted through the HTS current leads. In order to improve the current carrying capacity of the current leads, multiple HTS tapes are required. In this paper, we proposed several structures of compact HTS current leads and compare them other 2 kA class current leads. We report on the calculated characteristics of stabilized HTS current leads and on the performance measured during critical current measurement tests.

Economic Analysis of a 1.5-MW-Class HTS Synchronous Machine Considering Various Commercial 2G CC Tapes

We present the comparative design results of a 1.5-MW-class high-temperature superconducting synchronous machine (HTSSM) by considering various commercial 2G coated conductors (CCs). We focus on the estimation of economic factors to manufacture a more cost-effective HTSSM. A key design issue in HTSSM development is the adoption of superconducting wire among various types of recent commercial 2G CC tapes with different dimensions, critical current performance, and cost-performance ratio that affect the HTSSM performance, thermal losses, and CC tape-length usage. Therefore, we first perform the electromagnetic and thermal design of a 1.5-MW-class HTSSM considering three types of 2G CC tapes. Then, we present the comparative analysis results related to economic factors.

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.

Analysis of a High-Tc Superconducting Power Converting System

This paper presents the analysis of a high-Tc superconducting (HTS) power converting system, as well as its operational characteristics. The converting system can be used to charge and discharge a magnet made of series-connected pancake coils. The HTS converting system consists of two heaters, a primary copper winding, a secondary HTS winding, a series-connected HTS pancake coil, an iron core and a conventional copper load. In the experiments, the charging and discharging periods were 7.5 and 2 s, respectively. A partial region of the superconducting tape in a secondary HTS winding is switched to a normal region by a buried heating coil. To measure the converting-current with respect to the magnet flux changes, a hall sensor was installed at the center of the pancake coil. In this experiment, the charging-current and discharging-energy reached about 51.7 A and 36.8 J, respectively. The experimental results have been compared with theoretical predictions by using the finite difference method.

Quench Propagation Characteristics of the Liquid Nitrogen Cooled HTS Wires by Externally Injected Heat Energy

With the successful commercialization of Bi-2223 powder-in-tube wire, many attempts to the R & D of the high-Tc superconducting (HTS) magnets for high magnetic field applications are now being implemented actively. Although operating temperature of HTS magnet must be kept in the designed level, the magnetic energy and mechanical disturbance can make the operational temperature of HTS magnet unstable. Especially, generated heat energy of inner HTS winding is apt to accumulate, so the normal region appears in HTS winding. This paper deals with the quenching characteristic of reinforced Bi-2223 wire and two bare Bi-2223 wires in adiabatic condition. The minimum quench energy (MQE) of HTS wires was affected by the material and ratio of their matrix. In the same condition, the normal zone propagation (NZP) energy of nonreinforced HTS wire was smaller than that of reinforced HTS wire

Test and Analysis of Electromagnetic and Mechanical Properties of HTS Coil During Quench State

This paper deals with the analysis of the electromagnetic and mechanical properties of a high-temperature superconducting (HTS) coil, as well as its characteristic as determined through tests using strain gauges. When an operating current is applied to an HTS coil, strain is generated by electromagnetic force. However, additional strain effects in the HTS coil are formed by the Joule heating during quench. Strain was measured with a full-bridge strain gauge mounted directly over the turns. We fabricated an HTS coil wound in a single pancake type to investigate strain characteristics. We also investigated structural analysis by a finite-element method to calculate the strain of the HTS coil. In tests, the strain in the HTS coil was measured during excitation. Test results of the HTS coil have been compared with the theoretical results. Finally, we performed quench propagation tests and could verify the strain effect during quench. The reaction times of the strain gauge at 30 and 80 A are 31.8 and 4.3 s, respectively.

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.

Experimental Analysis of Thermally and Magnetically Triggered Switch for High-Tc Superconducting Power Converting System

In this paper, characteristics of a thermally and magnetically triggered switch for a high-Tc superconducting (HTS) power converting system are experimentally analyzed. For verifying the efficiency of the suggested switch, current charging and discharging tests using heater-triggered switch with or without an external magnetic field are performed. Charging tests are performed with two charging sequences, i.e., CS1 and CS2. Each sequence is experimented with two kinds of heater currents to maintain different temperatures. Saturation current and saturation time are detected to calculate the pumping rate. Two discharging sequences, i.e., DS1 and DS2, are used for discharging tests with heater current to maintain 120 K. From the results, normalized load energies are calculated and compared.