SMES System Research Articles

A Study of SMES Control Logic for Power System Stabilization

The authors have addressed developments of SMES system effective for power system stabilizing control. Focused on control logics that can be used to efficiently regulate SMES, a number of unique control logics were devised by combining the popularly used power deviation (DeltaP) of a generator with the angular velocity deviation (Deltaomega) of a generator or the phase correction. We practiced a digital simulation analysis for the created logics under both conditions of one- and multi-machine infinite-bus systems using the Y-method power system dynamics analysis program, which was compiled by the CRIEPI. As a result, it was revealed that the rated capacity and the amount stored energy of SMES necessary for power system stabilizing can be reduced by approximately 3 to 5% when compared to that obtained by employing the conventionally used DeltaP control method alone.

Design of SMES System With Liquid Hydrogen for Emergency Purpose

The emergency power supply system, which is composed of a SMES system cooled by liquid hydrogen and a fuel cell (FC), is proposed as a backup for supplying electricity to hospitals, high-rise office buildings, and intelligent equipment. The capacity of the system is 2 MW for 10 hours. At a power failure, the SMES immediately functions to supply electric power at start-up for 60 seconds, and then after the FC generates electricity for 10 hours. Since the system is designed to be driven with liquid hydrogen and oxygen, it can be installed to any isolated spaces like spaceships, tunnels, and so on. The development scenario, that an 1-kW prototype, an 100-kW module as a basic unit and then a practical system will be developed step by step, is proposed. The system can be rather flexible for load requirements by adjusting the composition of the basic modules.

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.

SMES for Electric Power Compensation of the J-PARC High Intensity Proton Synchrotron

A new proton accelerator complex for a high intensity beam (Japan Particle Accelerator Research Complex-J-PARC) is under construction at the Tokai campus of Japan Atomic Energy Research Institute as a joint project between KEK and JAERI. The accelerator complex is composed of a 600 MeV linac, a 3 GeV rapid cycling synchrotron, and a 50 GeV main synchrotron. In Phase I, the main synchrotron will be operated at energy of 40 GeV with pulse operation. The proton energy is to be increased up to 50 GeV in Phase II, and a large amount of pulse electric power, which is +115 MW and -55 MW peak-to-peak with 3.4-second repetition, will be demanded. Such large pulse power will give un-allowed disturbances to the power network. Some means will be required for compensating the pulse electric power and reducing the disturbances. A SMES system is one of the promising means. We have studied a SMES system for this purpose, designed the SMES coils using a force-balanced coil and a solenoid with a capacity of 100 MJ/55 MW, and proposed a new circuit scheme. The cost estimation of the SMES system is also described

Test Results on Experimental SMES System With Normal Conducting Shielding Coils

A shielding coil system is effective to reduce pulse losses of the superconducting coil of the SMES system for power system control, such as power line stabilization and compensation of power fluctuation. The shielding coil system is consisted of a main superconducting coil and a normal conducting shielding coil connected in parallel. If a mutual inductance between them is equal to a self inductance of the latter, fluctuated current at energy transfer is diverted to the shielding coil and constant current flows in the main superconducting coil. In addition to the above inductance condition, to work the shielding operation completely, it is necessary to compensate the voltage decent due to the normal resistance of the shielding coil. We have been studying about the compensation system for the voltage decent in the shielding coil and have made an experimental shielding coil system to verify the operation of the voltage compensator. The experimental shielding coil system is composed of coaxial solenoid type coils which are a main superconducting coil, a shielding coil and a pair of correction shielding coils to achieve the inductance condition. Here, results of performance tests on the shielding coil system including work of the voltage compensator are presented

Development of MVA Class HTS SMES System for Bridging Instantaneous Voltage Dips

A SMES system of MVA class for bridging instantaneous voltage dips has been developed using Bi-2212 wire. The Bi-2212 wire has high-performance conductive characteristics that do not deteriorate at a low temperature in high magnetic fields beyond 10 T. These characteristics enable a compact design of a SMES system of the Bi-2212 wire. In addition, coils of the Bi-2212 wire can be adequately insulated due to a high temperature margin. Therefore, the SMES system designed by using the coils has advantages to enhance dielectric strength and output power of the system. In our previous study, a SMES system consisting of 4 unit coils was constructed and the various properties were examined. Up to the present, the total 18 unit coils were stacked to make a coil system (outer diameter: 700 mm, height: 554 mm, stored energy: 984 kJ) and installed into a SMES system of 1 MVA for bridging instantaneous voltage dips. Also, the cooling system of the HTS SMES has been improved. The characteristics of the conduction cooled HTS coils of 1 MJ class were investigated in the operations of 1 MVA SMES system for bridging instantaneous voltage dips. Thermal reliability was verified during each operations of exciting, standby, bridging and current damping. Moreover, the repetitive bridging operations even worked out every 5 minutes. Advantages of the conduction cooled HTS coils for SMES were verified.

Wind Farms Linked by SMES Systems

The objective of this paper is to introduce the concept of wind farms linked by SMES systems. In this work, the SMES system is applied to a wind farm that is interconnected with a grid through a back-to-back DC link for the variable speed operation of the wind turbines. This system enables the output power leveling of the wind farm depending on the power demand and can reduce the capacity of the converter system by selecting an optimal discharge/charge rate of the SMES. By using the stored energy of the SMES, this system can also compensate the inertia of the blades so that the wind turbine speed can be rapidly controlled depending on the wind condition. This paper describes the design condition of the SMES for the output power leveling of the wind farm and discusses the SMES configuration for a 100-MW class wind farm.

Research and Development of High-<tex>$rm T_c$</tex>SMES

High-T/sub c/ superconducting technology is thought to provide many merits for SMES systems. For example, a cryocooled system can be used as a cooling system for High-T/sub c/ superconducting coils, indicating that an operation temperature can be selected from a wide-temperature range below critical temperatures. Refrigerator cooling operation temperature for High-T/sub c/ SMES can be elevated more than 20 K from conventional 4.2 K. As a result, the heat capacity of coil system becomes much larger than that at 4.2 K, indicating that thermal diffusion time constant becomes much longer. If we could absorb transient heat generation with heat capacity of the coil, SMES systems can be designed under the over current state of critical current for a short duration. As a cooling capacity for an average heat load will be enough to cool High-T/sub c/ superconducting coil system for SMES, the refrigerator system cost can be much lower than that for a SMES system using Low-T/sub c/ superconductors. Moreover, we are developing high critical current superconducting wire for SMES system. The Bi2212 Rutherford conductors can carry 4 kA at 26 K under cryocooling. We also estimate the superconducting wire cost of the whole coil system, which is designed to minimize the superconductor volume. The conclusion is that the cost of High-T/sub c/ SMES system will be reduced by using the low-cost YBCO superconducting wires in the future.

On-Line Steady State Security Assessment of Power Systems by SMES

The response-based on-line steady state security assessment method of power systems can prevent influences of inaccuracy of models and parameters used in theoretical calculations and numerical simulations. With the aid of a grid model SMES system producing the specially designed disturbance signals, experiments were carried out in a simple power system to demonstrate the feasibility of the method. The results of experiments are then compared with that of calculations and simulations. The study indicates that the response signal of the power system being disturbed contains information of low-frequency oscillation modes and can be used as an index to the degree of steady state security of power systems.

高温超電導ＳＭＥＳの技術調査

High-Tc superconducting technology is thought to provide many merits for SMES systems. For example, a cryo-cooled system can be used as a cooling system for high-Tc superconducting coils, indicating that a wide range of operation temperatures can be selected. As a result, the heat capacity of the coil system becomes much larger than that at 4.2 K. If we could absorb transient heat generation with the heat capacity of the coil, SMES systems can be designed under the over-current state of critical current for a short duration. As the cooling capacity for an average heat load will be enough to cool the High-Tc superconducting coil system for an SMES, it is expected that refrigeration system cost can be reduced. Moreover, we are developing a high critical-current superconducting wire for the SMES system. The Bi2212 Rutherford conductors can carry 4 kA at 26 K under cryo-cooling. We also estimate the superconducting wire cost of the whole coil system, which is designed to minimize the superconductor volume. The conclusion is that the cost of a high-Tc SMES system can be reduced remarkably by using low-cost YBCO superconducting wires in the future.

Line Voltage Detector for SMES System Designed to Protect From Momentary Voltage Drop

For the precision industrial plants, a stable electrical power source is the one of the key components as known as well. Usually, a battery type UPS is used to protect computers from the power failure, but it cannot protect the whole plant because its capacity is too small to supply for all facilities. A short time SMES system is suitable to cover this problem. It will supply the enough power to the plant while the line voltage is momentary dropped. The target plant may be sensitive for the line voltage drop, a high-speed detection of voltage drop is required and a detector that uses two detect method in parallel, was developed. This paper introduces the voltage detector developed for the SMES system.

Development of SMES for power system control: present status and perspective

A present Japanese national project for SMES development focuses on the development of cost reduction technologies for a small-scale SMES for power system control. Optimal SMES system concepts were developed for power system stabilization and for load fluctuation compensation or frequency regulation. Performance of the designed superconductors was analyzed through fabrication and tests of short sample superconductors. Then, two kinds of model coil systems were manufactured and tested for evaluation of the design concepts and cost reduction technology developments. A multi-pole solenoid coil set as a model coil system for load fluctuation compensation SMES was successfully tested, for example, in 10 000-pulse iterative charge–discharge operations. In addition, application of high- T C superconductors to SMES has been studied for further cost reduction, more reliable operation, etc.

Power Controllable Region of a Power Conversion System for SMES by Use of a Single Natural Commutation Converter and an ICB Energy Transfer Circuit

Highly efficient current type power conversion system (PCS) is the key component for realizing SMES of the large scale. PCS by use of the inverter-converter bridge (ICB) energy transfer circuit has been proposed to achieve the above requirement, and the experimental studies have been carried out. This PCS can control the power supplying to the utility well when the power factor is small one, however, the system goes out of control in the high power factor operations. In this study, it is theoretically analyzed the reason why the system goes into the unstable states. The experimental results are examined for confirming the theoretical analysis.

Toroidal-Type Shielding Coil Systems for the Power System Control SMES

SMES systems for applications of power system control, such as power line stabilization and compensation of power fluctuation, attract interest recently. In these applications, the use of low-loss type conductors as strand cables are necessary to reduce AC losses accompanied with rapid changes of magnetic fields; however, it brings some difficulties of high cost and low mechanical strength of the superconducting coil. To solve the above problems, the shielding coil system, which is composed of a main superconducting coil and a normal shielding coil connected in parallel, were proposed. In the shielding coil system, the fluctuated current at energy input and output is diverted to the shielding coil and only the constant current flows in the main superconducting coil. In this paper, we propose a new shielding coil system of toroidal arrangement, which has low stray magnetic fields in ambient areas. Results of the optimization of coil configurations in the toroidal shielding system are presented. Besides the toroidal systems of the circular elementary coil, those of D-shaped elementary coils, which have lower electromagnetic stress than circular one, are also studied.

Quench in a conduction-cooled Nb3Sn SMES magnet

Due to the rapid development of cryocoolers, conduction-cooled Nb3Sn devices are nowadays enabled. A 0.2 MJ conduction-cooled Nb3Sn SMES system has been designed and constructed. The nominal current of the coil was 275 A at 10 K. The quench tests have been performed and in this paper the experimental data are compared to the computational one. Due to a slow normal zone propagation, Nb3Sn magnets are not necessarily self-protective. In conduction-cooled coils, a thermal interface provides a protection method known as a quench back. The temperature rise in the coil during a quench was measured with a sensor located on the inner radius of the coil. The current decay was also monitored. The measured temperature increased for approximately 15 s after the current had already decayed. This temperature rise is due to the heat conduction from the hot spot. Thus, the measured temperature does not represent the hot-spot temperature. A computational quench model which takes into account quench back and heat conduction after the current decay was developed in order to understand the measured temperatures. According to the results, a quench back due to the eddy current induced heating of the thermal interface of an LTS coil was an adequate protection method.

Analysis and optimization of a micro SMES system using multiple parallel solenoids

The micro superconducting magnetic energy storage system is becoming a powerful tool for application in power systems. Nowadays, devices include active shielding systems instead of passive ferromagnetic shields. This calls for sophisticated analysis and design techniques able to provide satisfactory performance in terms of stored energy efficiency, reduced stray field, and/or minimal superconductor's volume. In this paper, the features of an active shielding system using multiple parallel solenoid configurations for superconducting magnets are analyzed and the results of their corresponding stray fields are compared. Two optimization strategies are briefly presented. The results using the proposed optimization strategies for magnet systems of energy capacity of 1 MJ, 5 MJ, and 10 MJ are given, respectively.

Test results of long-term and over-load operation for a 1 kWh/1 MW module-type SMES

The authors have developed a 1 kWh/1 MW module-type SMES system (ESK), linked to the actual power system, that was tested at Imajuku Substation in Fukuoka. The practical use of SMES at field sites requires ensuring its reliability, as well as reducing costs with minimum component set-ups. In order to quantitatively verify its reliability and performance limit, two kinds of tests were conducted on ESK: a long-term and over-load operation. In the long-term operation test, a DC500 triangle waveform up to 1000 A was applied to ESK 10,000 times. Further, the compensation ability for distribution line load fluctuation was observed for three days. The results revealed that ESK functioned adequately and in a stable manner. In the other test, a power output 1.2 times that of the rated output was attained, along with an energy storage capacity 1.44 times the rated value. This allowed us to confirm the over-load operation limit of ESK.

Interaction between a superconducting coil and the power electronics interface on a 100 MJ SMES system

Although numerous studies have focused on the connection of SMES to the utility power grid, fewer have addressed in detail the interactions between the power electronics interface and the SMES coil. While electromagnetic transient models are available from classical transformer studies, little work has been done on how these models apply to SMES coils. This paper presents the computer modeling of the interaction between a 100 MJ/100 MW LTS SMES coil now under construction and its power electronics interface. It is concluded that frequency domain modeling methods are applicable to study SMES coil-converter interactions and to recommend preferred operating frequencies of the power converter provided that certain characteristics unique to SMES systems are accounted for.

Fabrication and test of a 4 kjJ Bi-2223 pulse coil for smes

We designed and fabricated a 4 kJ conduction-cooled high-Tc superconducting (HTS) pulse coil. The coil is wound with an interlayer-transposed 6-strand parallel conductor which is composed of Bi-2223 silver alloy-sheathed multi-filamentary wires. We had developed a complete 3.6 MJ/1 MW low-Tc superconducting (LTS) SMES system for testing on a power line at Imajuku substation. Aiming at the feasible operation of SMES applying a HTS coil, we made a SMES system set-up in which HTS coils were serially connected to 3 LTS coils of the SMES. The SMES including the HTS coil was connected to Imajuku substation's power system, to made operational tests of compensation for load fluctuation at the 6 kV power line. The test results lead to the feasibility of the HTS SMES for practical use in future power systems.

Demonstration of the stress-minimized force-balanced coil concept for SMES

Strong electromagnetic force caused by high magnetic field and coil current is a serious problem in SMES systems. In facing this problem, we proposed the concept of Force-Balanced Coil (FBC) which is a helically wound toroidal coil. Based on the virial theorem, the FBC can minimize structure requirements for energy storage by selecting an optimal number of poloidal turns. We designed and fabricated a small experimental device which is composed of inner and outer helical coils mutually wound in opposite toroidal directions using NbTi superconductors. The distribution of the working stresses in this device can be changed by selecting the optimal current ratios between inner and outer coil currents. From the experimental results, we demonstrated the validity of the FBC concept.