Young Gun Park

Experimental Analysis on Initial Current Decay Characteristics of Persistent-Mode HTS Coil by External Alternating Magnetic Field

This paper deals with the current decay characteristics of a high-Tc superconducting (HTS) coil operated in persistent current mode (PCM) under alternating magnetic field. In superconducting synchronous machine applications, such as linear synchronous motor (LSM), the superconducting coils are designed to operate in PCM to obtain steady-magnetic field with DC transport current. This superconducting coil operates on a direct current, but it can be exposed to alternating magnetic field due to the armature winding. When the field coils are subjected to an external time-varying magnetic field, it is possible to result in a current decay for those coils in PCM operation due to electrical AC loss. In this research, a current decay measurement system, which consists of field coil and armature coil, was fabricated to verify current decay characteristics of field coil in PCM operation against external alternating magnetic field. The current decay rate for the field coil was measured by using a hall sensor as a function of amplitude and frequency of armature coil.

A Novel and Smart Design of Superconducting Fault Current Controller: Implementation and Verification for Various Fault Condition

By the advent of the Smart Grid and integration of distributed generators, electrical networks are facing uncountable challenges. The existing protection schemes that simply limit the fault current to the predetermined set values may not perform optimally, and even the existing protection coordination schemes fail and lead to catastrophic failures in the increasingly complex and unpredictable grid operation. This paper proposes a novel and smart design of fault current controller constituting a full-bridge thyristor rectifier embedding a superconducting coil. When a fault occurs and the resulting current through the superconducting coil exceeds a certain preset value based on the current operating conditions of the grid to maintain the grid integrity, the magnitude of the fault current is regulated to a desired value by automatic controlling of the thyristor. This research also implements a lab-scale Smart FCC with smart current control capability and demonstrates the desired functionality and efficacy of design by changing the fault conditions. This proposed Smart FCC design will make the Smart Power Grid capable of self-healing against current faults.

Design and Test of a High-Tc Superconducting Power Conversion System With the GdBCO Magnet

This paper describes the design and test of a high-Tc Superconducting (HTS) power conversion system with the GdBCO magnet and presents its operational characteristics through tests. The HTS power conversion system can be employed to charge and discharge an Energy Storage Magnet (ESM). The HTS power conversion system consists of two heaters, a transformer, and a GdBCO pancake magnet. The energy stored in the dc magnet is converted to ac power via a transformer consisting of an HTS secondary and a normal copper primary. The timing sequential control and thermal transition of heaters are important factors to generate charging and discharging in ESM. In this paper, we verified the feasibility of the HTS power conversion system and obtained the design and manufacturing techniques for scale-up of the system. Based upon the tests, the operating current of 12 A in the transformer and the heater current was optimally derived. The magnetic energy was stored about 46.7 J. In discharging test, the system was converted from dc to ac power at 0.5 Hz and 1 Hz. The efficiency of the system reached about 96%.

Design Considerations of Superconducting Wireless Power Transfer for Electric Vehicle at Different Inserted Resonators

The wireless power transfer (WPT) technology based on strongly resonance coupled method realizes large power charging without any wires through the air. Recently, the WPT systems have started to be applied to the wireless charging for electrical vehicles (EVs) because of their advantages compared with the wired counterparts, such as convenient, safety, and fearless transmission of power. However, there are challenges in its commercialization, such as delivery distance and efficiency. To solve the problems, we proposed the technical fusion using high-temperature superconducting (HTS) resonance coil in the WPT system, which is called superconducting wireless power transfer for electric vehicle (SUWPT4EV) system. Since the superconducting wire has merits, i.e., a larger current density and a higher Q value than normal conducting wire, the HTS antenna coil enables to deliver a mass amount of electric energy in spite of a small-scale antenna, as well as is possible to keep much stronger magnetic fields out in the peripheral regions. Thus, the SUWPT4EV system has been expected as a reasonable option to improve the transfer efficiency of large electric power. In this study, as an advanced approach, we proposed the advanced SUWPT4EV system with inserted resonator using noncooled copper, cooled copper, and HTS resonators, respectively, in order to expand the transfer distance and improve the transfer ratio. In this paper, we presented operating characteristics of the advanced SUWPT4EV system and achieved the improvement and effects of transmission power for inserted resonators within 40-cm distance under radio frequency power of 370 kHz below 600 W.

Design Consideration and Efficiency Comparison of Wireless Power Transfer With HTS and Cooled Copper Antennas for Electric Vehicle

The wireless power transfer (WPT) technology based on strongly resonance coupled method realizes large power charging without any wires through the air. Recently, the WPT systems have started to be applied to the wireless charging for electrical vehicles (EVs) because of their advantages compared with the wired counterparts, such as convenience, safety, and fearless transmission of power. However, it has obstacles to commercialize such as delivery distance and efficiency. To solve the problems, we proposed the technical fusion using a high-temperature superconducting (HTS) antenna in the WPT system, which is called superconducting WPT for electric vehicle (SUWPT4EV) system. Since the superconducting wire has the merits of a larger current density and higher Q value than a normal conducting wire, the HTS antenna enables to deliver a mass amount of electric energy in spite of a small-scale antenna. To apply copper-stabilizer HTS (GdBCO) coil for EV charging system practically, the transfer efficiency characteristics for the HTS wires should be investigated. In this study, we examined transfer characteristics with copper-stabilizer HTS antenna at 77 K and copper antenna at 77 K, respectively. The transfer distance is at 30 cm, and RF power of 370 kHz below 500 W is adopted. Moreover, in order to improve the transfer efficiency, the design considerations for the SUWPT system were described.

Development and Experimental Evaluation of a Prototype of the TF Secondary Quench Detection System for KSTAR Device

A prototype of the toroidal field (TF) secondary quench detection (SQD) system was developed and implemented with the Korea Superconducting Tokamak Advanced Research (KSTAR) device to carry out the design verification of the SQD. The SQD can detect a quench based on the change of absolute pressures (APs) and mass flow rates of helium in the cooling lines of the TF coils. If the primary quench detection system of the TF coils cannot detect a quench or the fast discharge of the TF coils cannot be carried out as planned, SQD should work to prevent the TF coils and the peripheral structures from severe damages. In addition, SQD should operate in the reliable and stable condition against the disturbances caused by the poloidal field coil discharge, plasma perturbation, and any faults of subsystems of the KSTAR device. The 2-out-of-3 (2oo3) voting configuration was applied to the SQD to enhance the reliability and stability of quench detection. The prototype SQD consists of AP and differential pressure transducers, signal interfaces, logic solvers, and interlock systems. All the transducers were selected from metallic types with no electronic circuit in order to reduce the failure rates caused by strong electromagnetic field and radiation around the tokamak. The transducers were installed in the manifolds of the helium inlet lines of the KSTAR TF coils. Their signals were amplified and compared with the reference voltage for quench decision in the signal interface unit. The quench signal generated by the signal interface unit was transmitted to the 2oo3 voting modules of the logic solvers. The design requirements of SQD were verified through testing the prototype SQD in the 2014 KSTAR campaign.

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.

Evaluation on Electrical and Thermal Characteristics of Multi-Stacked HTS Coated Conductor With Various Stabilizers

Transporting large currents through High- Tc (HTS) current leads (CLs) inevitably involves using several HTS tapes in multi-stacked form to obtain a high current density. For safe operation of HTS CLs, the thermal stability of stacked HTS tapes should be considered. In this paper, we investigated electrical and thermal properties of multi-stacked HTS tapes using 2G coated conductor (CC). Three kinds of commercial CC with different specification of stabilizer were used for the experiment. Each stack sample was fabricated by soldering together CC tapes using In-Bi alloy. To verify the effects of a stabilizer on thermal stability for multi-stacked CC tapes, we performed an experiment of minimum quench energy measurements. In addition, transient electrical and thermal behavior were measured as a function of the external heat input energy. Each stack sample has a heater made of nickel-chromium (Ni-Cr) wire to make the external heat disturbance and a type-E thermocouple to measure the temperature. Based on the test results, electrical and thermal characteristics of multi-stacked CC tapes were evaluated.

Conceptual Design and Operating Characteristics of Multi-Resonance Antennas in the Wireless Power Charging System for Superconducting MAGLEV Train

Recently super high-speed magnetic levitation (MAGLEV) using high-temperature superconducting (HTS) magnet has been expected as next-generation transportation since superconducting magnet can keep mighty levitation force. The superconducting magnet at MAGLEV train should be continually charged with high power in order to keep stronger and stable levitation force. Practically, since conventional power supply unit should be attached to HTS magnet in the MAGLEV, a large thermal loss is indispensably caused by power transfer wires and joints, those have been one of essential obstacles in the superconducting MAGLEV train. As the wireless power transfer (WPT) technology based on strongly resonance-coupled method realizes large power charging without any wires through the air, there are advantages compared with the wired counterparts, such as convenient, safety, and fearless transmission of power. From this reason, the WPT systems have started to be applied to the wireless charging for various power applications, such as transportations (train, underwater ship, electric vehicle). However, it has obstacles to commercialize, such as delivery distance and efficiency. To solve the problems, authors proposed the technical fusion using HTS resonance coil in the WPT system since the superconducting wire has merits a larger current density and higher Q -value than normal conducting wire. In this study, authors described the conceptual design of HTS receiver (Rx) coil with multi-copper antenna (Tx) coils. The priority characteristics of moving HTS receivers under multi-copper Tx coils are compared with and various copper Rx coils with radio frequency power of 370 kHz below 300 W.

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.