HTS SMES Research Articles

Design of HTS Modular Magnets for a 2.5 MJ Toroidal SMES: ReBCO vs. BSCCO

A 2.5 MJ HTS SMES is being developed as a national program in Korea. This paper presents design results of modular HTS magnets for the 2.5 MJ toroidal SMES. We considered a choice of BSCCO-2223 or ReBCO tapes as the conductors for the HTS magnets of the SMES. Operating temperature was decided to be 20 K which could be accomplished by conduction cooling with a couple of GM cryo-coolers. Key design factors may include minimization of total conductor requirement and low AC loss.

A study on insulation characteristics according to cooling methods of the HTS SMES

The high temperature superconducting magnetic energy storage (HTS SMES) stores electric power in the form of magnetic energy, and then converts it to electric energy. For the operation, the HTS SMES must have a cryogenic temperature.The cooling methods for a cryogenic temperature are divided into an immersed method and a conduction cooled method. The immersed method is a direct cooling method that immerses the superconducting magnet into a cryogen. On the other hand, the conduction cooled method is an indirect cooling method that cools a superconductor through thermal conduction with a cryocooler.This paper classified the structures of insulation according to cooling methods, and studied the insulation characteristics of each insulation factor.

Mobile conduction-cooled HTS SMES

An immovable 35kJ/7kW high-Tc superconducting magnetic energy storage (HTS SMES) system had been developed in the Electric Power System Dynamic Simulation Laboratory, Huazhong University of Science and Technology in 2005. In order to adapt for on-site experimental conditions, the mechanical configuration of the magnet is reinforced and the SMES system is assembled in a special container to be freighted to the actual power system for the feasibility study on different applications at different sites. The mobile HTS SMES system had withstood various kinds of poor road surfaces and then arrived at the experimental site on August 18, 2009. In this paper, the reconstructed configuration and the shock absorption of the magnet are presented. The field test results show that the mobile SMES system can operate on the power network at different locations and suppress effectively power fluctuation of the generator terminal.

Basic Insulation Characteristics of 2.5 MJ Class HTS SMES

The basic electrical insulation design of 2.5 MJ conduction cooling high temperature superconducting magnetic energy storage (HTS SMES) have been studied in this paper. The high voltage is generated both ends of magnet of HTS SMES by quench or energy discharge. Therefore, the insulation design of the high voltage needs for commercialization, stability, reliability and so on. In this study, we analyzed the insulation composition of a HTS SMES, and investigated about the insulation characteristics of the materials such as Polyimide, Al2O3 , GFRP and vacuum at cryogenic temperature. Base on these results, the basic insulation design for 2.5 MJ conduction cooling HTS SMES was performed.

Design of HTS Magnets for a 2.5 MJ SMES

A 600 kJ HTS SMES system has been developed for power system stabilization as a national project in Korea. Successful operating tests of the 600 kJ were recently completed. In this paper, a 2.5 MJ class SMES with HTS magnets of single solenoid, multiple solenoid and modular toroid type were optimized using a recently developed multi-modal optimization technique named multi-grouped particle swarm optimization (MGPSO). The objective of the optimization was to minimize the total length of HTS superconductor wires satisfying some equality and inequality constraints. The stored energy and constraints were calculated using 3-D magnetic field analysis techniques and an automatic tetrahedral mesh generator. Optimized results were verified by 3D finite element method (FEM).

Temperature Characteristic of a Conduction-Cooled HTS SMES Magnet

A 35 kJ/7 kW conduction-cooled HTS SMES is developed. The magnet of the SMES is a solenoid type coil, made of Bi2223/Ag tapes, and cooled to about 20 K by a cryocooler through conduction-cooled method. To evaluate the performance of the 35 kJ/7 kW SMES, system characteristics such as current carrying ability, power conditioning capability and dynamic operation for stabilizing power systems are investigated by experiments. In this paper, the temperature characteristic of the conduction-cooled HTS magnet for 35 kJ/7 kW SMES is analyzed. Experimental results verify that the thermal stability of the HTS magnet can meet the requirement of dynamic power compensation. Integrating with the analysis of the energy loss in dynamic operation of the magnet, the methods to reduce the energy loss and improve the thermal stability of the conduction-cooled HTS SMES magnet are discussed.

Dynamic Thermal Characteristics of HTS Coil for Conduction-Cooled SMES

In this paper, we investigate the thermal runaway characteristics of a BSCCO HTS single pancake coil conduction-cooled with a 4 K-GM cryo-cooler system. We also evaluate the static and dynamic characteristics of the HTS coil by measuring the temporal evolution of the temperature and the voltage for steady current and the typical current patterns of the load fluctuation compensation at different ambient temperatures T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> in the range of 20-50 K. Moreover, we experimentally discuss the criterion for monitoring the conduction-cooled HTS SMES system during compensating operation for load fluctuations.

DC V-I characteristics of a HTS tape for a 600kJ SMES in an Oblique external magnetic field

The critical current and n-value of the HTS tape, which are important for the characteristic analysis of the 600kJ HTS SMES system, were studied, and based on the results of the study, the DC V-I characteristics of a model coil fabricated by the same HTS tape of a 500 m length conductor were analyzed. The result show that the measured critical current and n-value of the conductor for parallel field are constant in external magnetic fields less than about 0.2, whereas the characteristics decreased for the whole range of the oblique magnetic field. The critical current of the coil, which was calculated based on the results of the study on a short sample conductor, corresponded to the obtained value, which means that the critical current and n-value of a conductor for an oblique magnetic field in an arbitrary direction in the HTS SMES system can be estimated only by using the DC V-I characteristics of a short sample conductor for parallel and perpendicular magnetic fields.

Thermal characteristics of conduction cooled 600 kJ HTS SMES system

A 600kJ HTS SMES is developed and tested in Korea. The HTS SMES consists of 22 double pancake coils wound on each aluminum alloy bobbin. It is cooled by two GM cryocoolers down to around 6K and current is charged through HTS current leads up to 275A. Beside the heat penetration from room temperature structures, heat generation in the HTS coil is inevitable because of the joint resistances and the intrinsic property of the HTS tape such as index loss. Moreover, during the charging and discharging operation, AC loss of the HTS conductor and eddy current loss in the coil bobbin and metallic structures are generated. Therefore, the heat generation should be effectively removed by the cryocooler to ensure the stable operation of the coil. In the HTS SMES, aluminum alloy conduction plates outside the each coil are used as thermal paths to the cryocoolers. This paper describes the thermal characteristics of the HTS SMES for the charging and discharge operation.

Analysis of eddy current losses during discharging period in a 600 kJ SMES

The operation of the SMES system can be divided into three modes such as charging, operating and discharging. During the charging and the discharging modes, a magnetic field variation due to the current increase and decrease generate eddy current losses in the SMES system. The eddy current loss in discharging mode is the major factor to be considered because the operating time in the mode is fixed, whereas the charging mode has the arbitrary operating time which is not fixed. In this paper, we present the analysis results of the eddy current losses which are generated in the 600 kJ class HTS SMES system during the discharging mode.

The Electrical Insulation Design of 600 kJ Conduction Cooled HTS SMES

The electrical insulation design of 600 kJ conduction cooled high temperature superconducting magnetic energy storage (HTS SMES) has been studied in this paper. High voltage is generated to both ends of magnet of HTS SMES by quench or energy discharge. Therefore, the insulation design of the high voltage needs for stability and reliability to allow commercialization. In this study, we analyzed the insulation composition of a HTS SMES, and investigated about the insulation characteristics of materials such as Kapton, AlN,Al2O3, GFRP and vacuum at cryogenic temperatures. Based on these results, the insulation design for 600 kJ conduction cooled HTS SMES was performed.

First Tests of a 800 kJ HTS SMES

SMES using high critical temperature superconductors are interesting for high power pulsed sources. Operation at temperatures above 20 K makes cryogenics easier, enhances stability and improves operation as pulsed power source. In the context of a DGA (Delegation Generate pour l'Armement) project, we have designed and constructed a 800 kJ SMES. The coil is wound with Nexans conductors made of Bi-2212 PIT tapes soldered in parallel. The coil consists in 26 superposed simple pancakes wound and bonded on sliced copper plates coated with epoxy. The rated current is 315 A for an energy of 814 kJ. The external diameter of the coil is 814 mm and its height 222 mm. The cooling at 20 K is only performed by conduction from cryocoolers to make cryogenics very friendly and invisible for the SMES users. The cooling down has been successfully carried out and the thermal system works as designed. After a brief description of the SMES design and construction, some tests will be presented. From a current of 244 A, the SMES delivered 425 kJ to a resistance with a maximum power of 175 kW.

Development of a 600 kJ HTS SMES

This paper describes an overview of development on a 600 kJ high-temperature superconducting magnetic energy storage (HTS SMES). Our final goal will be the commercialization of MJ class HTS SMES system for the increase of power quality within 5 years. Hence, for this purpose, we have developed the research and development in 3 years. The purpose of this research is to develop a pilot system, which can protect the sensitivity loads from a momentary power interruption or a voltage sag.

A study on the operation analysis of the power conditioning system with real HTS SMES coil

Voltage sag from sudden increasing loads is one of the major problems in the utility network. In order to compensate the voltage sag problem, power compensation devices have widely been developed. In the case of voltage sag, it needs an energy source to overcome the energy caused by voltage sag. According as the SMES device is characterized by its very high response time of charge and discharge, it has widely been researched and developed for more than 20 years. However, before the installation of SMES into utility, the system analysis has to be carried out with a certain simulation tool. This paper presents a real-time simulation algorithm for the SMES system by using the miniaturized SMES model coil whose properties are same as those of real size SMES coil. With this method, researchers can easily analyse the performance of SMES connected into utility network by abstracting the properties from the real modeled SMES coil and using the virtual simulated power network in RSCAD/RTDS.

Test result of the model coil for the conduction cooled HTS SMES

A 600kJ HTS SMES is under development in Korea. Before the specific design of the HTS SMES, its model coil is fabricated and tested to verify the thermal and electrical characteristics. The model coil consists of two single pancakes and one double pancake coil with copper conduction plates between the coils. Each pancake is fabricated with a soldered 4-ply HTS conductor to increase the coil current. The model coil is cooled by two GM-cryocoolers and cooled down to below 20K. Copper conducting plates between the coils are used as the thermal path to the cryocooler. With the model coil, experiments are performed to investigate the thermal stability related with the transport current and the charge/discharge rate. The results are used to develop the 600kJ HTS SMES by clarify the several source of the heat generation.

Thermal Runaway Characteristics of Bi2212 Coil for Conduction-Cooled SMES

In this paper, we investigated the thermal runaway characteristics of a conduction-cooled Bi2212 HTS coil with a 4 K-GM cryocooler system under compensating operation for load fluctuations. We measured the temporal evolutions of temperature and voltage distributions of the HTS solenoidal coil for typical current patterns of load fluctuation compensation at different ambient temperatures. On the basis of these experimental results, we constructed a thermal analysis model, and analysed the thermal runaway characteristics during and after the load fluctuation compensation. Based on the results of our experiments and the numerical simulations, we proposed criterion for the monitoring of an HTS SMES system during compensating operation for load fluctuations.

A Study on High Temperature Superconducting Coil of Different Coil Arrangements

As for the stored energy density, the solenoid coil has the larger value. On the other hand, the toroidal field coil has the least leakage flux. The primary concern of HTS SMES coil is the reduction of the cost, while securing superconducting coil performance. For this purpose, the required HTS tape length needs to be as short as possible. The critical current and n values of HTS tapes depends on the magnetic fields as well as its field angle to the tapes. Therefore, the performance of magnets wound with HTS tapes needs to be analyzed based on above factors. The current-voltage characteristics of the HTS coil were analyzed by means of fitting equations of the critical current and n value obtained from the measured values of the Bi2223/Ag tape. The stored energy of four kinds of coil arrangement was analyzed, thereby pursuing the shortest length of HTS tapes. The toroidal coil requires 58% longer HTS tapes than the solenoidal coil to store the energy of 100 kJ, but 0.01 T leakage field region at the mid-plane is about a half of the solenoid coil.

Design and First Tests of a 800 kJ HTS SMES

The SMES is an interesting way for a large power pulsed source. High critical temperature superconductors have brought the possibility to operate at higher temperatures when compared to conventional NbTi SMES. This makes cryogenics easier, enhances the coil stability and improves the power. In a context of a DGA (Delegation Generale pour l'Armement) project, we have fully designed and partly constructed a 800 kJ SMES. The coil is wound with Nexans Bi-2212 PIT conductor made of 3 or 4 PIT tapes soldered in parallel depending on the magnetic flux density. At some locations the conductor is reinforced by a stainless steel tape. The conductor is isolated with Kapton. The coil consists in 26 superposed simple pancakes wound and glued on cut and epoxy coated copper plates. The rated current is 315 A for an energy of 814 kJ. The external diameter of the coil is 814 mm and its height 222 mm. The maximum magnetic flux densities are 5.2 T and 2.5 T respectively in axial and radial directions. The cooling at 20 K is only performed by conduction from a cryocooler to make cryogenics very friendly and transparent for the SMES users. The SMES design and construction are presented as well as the first tests with 10 pancakes. The first cooling down was successful and the thermal system worked as designed. 6 pancakes carry 300 A without any voltage.

Study on electric insulation properties for development of conduction-cooled HTS SMES

The conduction-cooled HTS SMES magnet is operated in high vacuum and cryogenic condition. Thus, electric insulation design at high vacuum and cryogenic temperature is a key and important element that should be established to accomplish compact design that is a big advantage of HTS SMES. However, the performance of insulators under cryogenic conditions in air or vacuum is virtually unknown. Therefore, we need active research and development of insulation concerning application of the conduction-cooled HTS SMES. Specially, this paper will present the results of high vacuum and cryogenic temperature breakdown and flashover discharge characteristics between cryocooler and magnet-coil. The breakdown and surface flashover discharge characteristics are studied at cryogenic temperature and vacuum. Also, some materials such as aluminum nitride (AlN), Al 2O 3 that have high thermal conduction are taken up and the flashover discharge characteristics are investigated. From the results, we confirmed that basic database on the discharge between cryocooler and magnet-coil was established for the electric insulation design.

전도냉각형 고온초전도 에너지저장장치의 전기적 특성

The conduction-cooled HTS SMES is operated in cryogenic and high vacuum condition. Thus, Insulation design at cryogenic temperature and high vacuum is a key and an important element that should be established to accomplish miniaturization that is a big advantage of HTS SMES. However, the behaviors of insulators for cryogenic conditions in vacuum are virtually unknown. Therefore, we need active research and development of insulation concerning application of the conduction-cooled HTS SMES. Therefore, in this study, we experimented about insulation characteristic high vacuum and cryogenic similar to driving condition of SMES system. Also, investigated about insulation characteristic of suitable some materials to insulator for conduction-cooled HTS SMES. As this results, we possessed basis data for insulation materials selection and insulation design for development of 600 kJ class conduction-cooled HTS SMES.