S.T. Dai

Chinese Academy of Sciences, Peping, Beijing, China

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Publications (21)10.69 Total impact

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    ABSTRACT: An 1 MJ/0.5 MVA high-Tc SMES has been developed by the Institute of Electrical Engineering, Chinese Academy of Sciences. It has been operating in a real power grid since February 16, 2011 in Baiyin City, Gansu Province in northwest China. The SMES magnet is immersed in liquid helium and cooled by four G-M cryo-coolers to keep zero helium vaporization. To ensure safe operation of the system, protection of the HTS magnet is a necessity, which, however, cannot be complemented by only single protection. In this paper, coordinate protection of the system is introduced by an online measuring and control system and a power conversion unit, and the control principle is described in detail. By means of the coordinate protection, the temperature and pressure inside the SMES Dewar are controlled in the range of 4.3-4.5 K and 0.01~0.025 MPa, respectively. Long term demonstration of the SMES during a period of more than two years shows that the coordinate protection can ensure a stable and reliable operation of the HTS magnet.
    No preview · Article · Feb 2014
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    ABSTRACT: A 360 m/10 kA high-temperature superconducting (HTS) cable has been put into demonstration operation on September 26, 2012, which is used to supply to the electrolytic aluminum workshop 10000 A. A real-time measuring and control system for the 10 kA HTS cable is developed and completed. The critical current test and data analysis are finished before the demonstration operation of the 10 kA HTS cable. The parameters of the HTS cable are monitored in demonstration operation. The inlet and outlet temperatures of the HTS cable, which are used to calculate the loss of the HTS cable, are measured accurately.
    No preview · Article · Feb 2014
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    ABSTRACT: The 75 m/1.5 kA AC high-temperature superconducting cable(75 m HTS cable) and the 360 m/10 kA DC HTS power cable (10 kA HTS cable), which are supported by Chinese State 863 projects, are both of the demonstration projects facing to industrialization application. The characteristic in structure of warm dielectric (WD) insulated HTS cable is introduced. The electric field distribution characteristic at the cryogenic envelope body, the end-point of metallic shield layer at the end of the HTS cable and the connection sections are analyzed; the controlling method for electric field stress is introduced; there is serious concentration of electric field both in the termination and the connection sections between the termination and the cryogenic envelope. It is difficult to calculate the electric field of the part with irregular or special structure by resolution analytical methods, and the numerical analysis method is effective to analyze the electric field of the shaped structural part for HTS cable. The electric analysis, simulation, the design and processing of insulation for the two cables are finished based upon these two cables run well by now.
    No preview · Article · Aug 2013
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    ABSTRACT: A 10 kA HTS cable for the most transmission current in the world has been successfully demonstration developed on Sep. 26, 2012 in Gongyi, Henan Province of China. The 10 kV HTS cable is 360 meters long. This paper described the temperature measuring for the 10 kA HTS cable and the calibrated error is 0.1 K. The temperature signals of the 10 kA HTS cable conclude the high-voltage temperature signals and the low-voltage temperature signals which use the different high-precision digital voltmeters to test. Software is developed by using GENESIS 64 program.
    No preview · Article · Aug 2013
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    ABSTRACT: Semiconductor thermoelectric generators have a series of advantages, such as compact volume, high-level reliability, and effective power generation in the presence of temperature difference. In many occasions, as a result of high voltage, electrical equipments can't be measured by the way of direct contact. In order to avoid equipment faults caused by low-voltage contact, a thermoelectric generator which uses waste heat of electrical equipments in service was designed. Electrical equipments often operate below 400K, and in this condition Bi2Te3 shows an outstanding performance of power generation. In order to solve the problems of little temperature difference and output power on steady-state, two methods were introduced. On the one hand, the temperature difference can be increased by filling with thermal insulation padding between the p-n junctions and using a heat sink in the cold side, and on the other hand, the output voltage and power will be augmented by increasing the number of p-n junctions. These methods have been proved effectively by simulation and experiment with promising outcomes.
    No preview · Article · Jan 2013 · Materials Science Forum
  • Y. Liu · W. Du · H.F. Wang · L.Y. Xiao · S.T. Dai
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    ABSTRACT: China's renewable energy resource such as wind and solar energy resources mainly distributed in the northeast, northwest, north China, while China's electricity load centre is in the eastern and central regions. Therefore, longdistance, large-capacity and cross-regional transmission of wind power is one of the significant challenges for China's renewable power development and utilisation. Based on a certain optimization method for the transmission capacity determination the transmission cost can be minimized due to the spatiotemporal complementarities of dispersed renewable energy resources, which has been well known for a long time but never been studied in terms of the capacity optimization of transmission lines. Hence, base on the real wind data provided by China Meteorological Administration (CMA) and the idea that this paper investigates the complementary effect of dispersed renewable energy resources on the capacity optimization of ultra HVDC lines.
    No preview · Conference Paper · Jan 2012
  • Y. Liu · W. Du · H.F. Wang · L.Y. Xiao · S.T. Dai
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    ABSTRACT: China has begun to build eight 10-million-kilowatt wind power bases and the wind power can reach 230 GW of installed capacity by 2020. Such large-scale integration of wind power will have significant impacts on the power system, such as increasingly outstanding difficulties of peak load regulating, the bottleneck of grid integrating capability, and so on. But keeping view of geographically dispersed wind energy resources in a larger scope or even countrywide scope may be an effective way to solve those above problems. In this case, due to the spatiotemporal complementarities of dispersed wind generation, electricity power from wind energy changes slowly, thus to benefit the safe and economic operation of the power system. Hence, based on real wind data which is provided by the China Meteorological Administration (CMA), this paper investigates the impacts of the complementary effect of countrywide dispersed wind energy on the power system. Both short term and long term effects of wind power on the power system are investigated. The results show that the countrywide complementary effect of dispersed wind energy resources could bring various benefits to operation of China electricity system.
    No preview · Conference Paper · Jan 2012
  • F.-Z. Ding · H.-W. Gu · T. Zhang · S.-T. Dai · X.-Y. Peng · W.-W. Zhou
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    ABSTRACT: The surface condition of substrate tape is an important factor to obtain epitaxial buffer layer on biaxially textured Ni tape for YBa 2Cu 3O 7-x coated conductors. We prepare ceria films on Ni single crystal, biaxially textured Ni tape and sulfured Ni substrates by direct current magnetron sputtering. The results show that the ceria films prepared on Ni single crystal and sulfured Ni substrates each have a poor-textured grain structure. However, the ceria film fabricated on rolling assisted biaxially textured substrate (RABiTS) exhibits a good c-axis texture and desirable surface morphology. Reflection high-energy electron diffraction analysis indicates that the c(2×2) superstructure on the RABiTS Ni surface has a dramatic effect on the heteroepitaxial growth of oxide buffer layer.
    No preview · Article · Dec 2011
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    ABSTRACT: Magnesium diboride shows a wide appli- cation prospect in the field of low field DC application for its relatively simple structure and rather higher critical temperature than LTS. With the development of composite super- conductor manufacturing technology and cryogenic technology, developing conduction cooled superconducting MRI system with composite superconductor is becoming increasingly feasible. An superconducting magnet for MRI was devel- oped. The superconducting magnet is used to investigate the fundamental scientific problem of the MRI main magnet, including field uniformity and stability, influencing factors of composite superconductor on field uniformity and sta- bility. The superconducting magnet consists of 2 solenoids wound with wire with the length of 60 m. The magnet has an outer diameter of 169 mm, an iron core diameter of 135 mm, and air gap of 32 mm. The superconducting magnet is fabricated and tested. The central magnetic field reaches 1.0 T when the current of the magnet is 290 A. The central magnetic field is 0.39 T when the current of the magnet is 100 A. In this paper, the minimum quench energy, the quench propagation velocity and the minimum propagation zone of the composite conductor are measured. Main magnet for MRI with composite superconductor is analysed and proposed, including magnet de- sign and test results. By theoretical modeling and simulation, the detailed quench propagation of the magnet is further analysed. Finally, the stability criteria of conduction-cooled MRI magnet are established.
    No preview · Article · Jun 2011 · IEEE Transactions on Applied Superconductivity
  • Wen Yong Guo · Li Ye Xiao · Shao Tao Dai
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    ABSTRACT: The superconducting magnetic energy storage system (SMES) has good characteristics such as high efficiency, quick response, no deteriorations, etc. However it is still far from wide application. The main obstacle is due to its high cost. One of the most effective ways to reduce the cost of SMES is to make it multifunctional. In this paper, a dual mode control strategy is proposed. With the proposed control strategy, The SMES can compensate voltage dip, current harmonics, reactive power, and active power fluctuation with a simple topology. The efficacy of the proposed control strategy is verified by simulation results.
    No preview · Article · Apr 2011
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    ABSTRACT: Magnesium diboride shows a wide application prospect in the field of low field DC application for its relatively simple structure and rather higher critical temperature than LTS. With the development of composite superconductor manufacturing technology and cryogenic technology, developing conduction cooled superconducting MRI system with composite superconductor is becoming increasingly feasible. An superconducting magnet for MRI was developed. The superconducting magnet is used to investigate the fundamental scientific problem of the MRI main magnet, including field uniformity and stability, influencing factors of composite superconductor on field uniformity and stability. The superconducting magnet consists of 2 solenoids wound with wire with the length of 60 m. The magnet has an outer diameter of 169 mm, an iron core diameter of 135 mm, and air gap of 32 mm. The superconducting magnet is fabricated and tested. The central magnetic field reaches 1.0 T when the current of the magnet is 290 A. The central magnetic field is 0.39 T when the current of the magnet is 100 A. In this paper, main magnet for MRI with composite superconductor is analysed and proposed, including magnet design, test results, and field uniformity.
    No preview · Article · Jul 2010 · IEEE Transactions on Applied Superconductivity
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    ABSTRACT: The critical performance of YBCO tape with inhomogeneous superconducting properties was simulated by use of a bad point distribution model and the Gaussian distribution model. The critical current and n value of the whole HTS tape was analysed. The reliability of the simulation was verified with the experimental data. The results of the two simulation models were compared each other. The influence of inhomogeneous properties on the critical performance of YBCO HTS tape was proved by simulation results which are helpful for the simulation of superconducting devices based on YBCO HTS tapes.
    No preview · Article · Jul 2010 · IEEE Transactions on Applied Superconductivity
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    ABSTRACT: Close circuits made of Fe and composite sheathed, mono- and multi-filament MgB2 wires were fabricated and tested in liquid He and conduction cooling environments for the demonstration of persistent current operation in such as the magnetic resonance imaging (MRI) magnets. Persistent current switches and superconducting joints were designed and installed in the circuits. The decay time of the captured magnetic field in the coil and joint resistance were measured. According to the results, the resistance of the closed circuit at low temperature can be less than 10-13 Omega, showing a potential for application in the currently develop MgB2 MRI systems. The causes of the circuit resistance were also discussed.
    Full-text · Article · Jun 2010 · Journal of Physics Conference Series
  • Y.-S. Wang · S.-T. Dai · L.-Y. Xiao · L.-Z. Lin
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    ABSTRACT: The quench behavior of YBCO coated conductors subjected to over-critical current with different puise durations at 50 Hz is researched in order to explore their prospects for power apphcation in liquid nitrogen. YBCO samples, in parallel with a resistor, are connected in series with a transformer whose current is controlled by thyristors. Current with amplitude of several tens of the critical current are fed through the samples for up to several cycles. The voltage and current profiles along the sample are recorded during its quenching. The results show that samples with high resistivity substrates have stronger current-hmited capability fhan those of lower resistivity substrates during the first half cycle of over-current duration.
    No preview · Article · Dec 2007 · Zhongguo Dianji Gongcheng Xuebao/Proceedings of the Chinese Society of Electrical Engineering
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    ABSTRACT: A 0.1MJ superconducting magnetic energy storage (SMES) is designed with low stray field by FEM. By applying a shield magnet, the stray field of SMES is reduced effectively. By analyzing the magnetic field of magnet, equipotential line, distributions of magnetic flux density are obtained. The SMES magnet is tested in the liquid helium and the calculated results and the measured results are compared. Based on above analyses, a design scheme, which has both acceptable technical performance and low stray field, is derived.
    No preview · Article · Jul 2007 · Cryogenics
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    ABSTRACT: A 75 m, three-phase HTS power cable is successfully demonstrated in a distribution grid of Gansu Changtong Cable Science and Technology Joint Stock Co., Ltd. in northwest China. The HTS power cable operates at a local live distribution grid of 6.6 kV to supply electric power for Changtong's factory in Baiyin, Gansu Province. The cable was rated for voltages up to 10.5 kV, and has conducted up to 1600 A at 400 V, which was limited only by the load available at Changtong's factory. The critical current of cable was tested as high as 5300 A DC at 76 K. The cable was connected to a local distribution grid to supply the power for the workshops at Changtong's factory. The cable operates stably and reliably over 5500 h since December 2004.
    No preview · Article · Jul 2007 · Cryogenics
  • L.Y. Xiao · S.T. Dai · Y.B. Lin · Z.Y. Gao · F.Y. Zhang · X. Xu · L.Z. Lin
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    ABSTRACT: Along with the rapid growth of the national economy in China, the electric utility is faced with an ever rising demand for electricity and the problem to solve large capacity power transmission. Under the support of the High Technology Research & Development Program of China, a 1.5 kA/10.5 kV 10-m long 3-phases HTS transmission power cable and a 75-m long, 3-phase, 10.5 kV/1.5 kA HTS power cable have been developed successfully by the Institute of Electrical Engineering, Chinese Academy of Sciences. The 75-m long HTS power cable operates now at a local live distribution grid of 6.6 kV to supply electric power for Changtong's factory in Baiyin, Gansu Province. The cable operates stably and reliably over 7000 hours since December 2004.
    No preview · Article · Jul 2007 · IEEE Transactions on Applied Superconductivity
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    ABSTRACT: 75 m long 10.5 kV/1.5 kA three-phase high temperature superconducting (HTS) power cable has been developed successfully and put into operation in live power grid. Conductor of the power cable utilizes optimum design method and is wound by a stranding machine. Cryogenic envelope consists of two concentric corrugated stainless steel tubes with thermal insulation and high vacuum. Design and processing of cable insulation is compatible with that of conventional cable. Cryocooling system uses sub-cooled nitrogen pressurized to cool the power cable and its termination. Online monitoring system adopts fiber technique to insulate high voltage. The power cable can carry more than 3500 A AC current, and has been operating for almost 7000 h without any breakdown since December, 2004.
    No preview · Article · Apr 2007 · Zhongguo Dianji Gongcheng Xuebao/Proceedings of the Chinese Society of Electrical Engineering
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    ABSTRACT: Superconducting Fault Current Limiter (SFCL) is an attractive appliance for modern electrical power system. A 10.5kV/1.5 kA three-phase HTS fault current limiter was developed by IEE, CAS. This improved rectifier-type SFCL with HTS coil of 6.25 mH is going on a demonstrated long-term reliable operation in a real 10.5 kV substation located in Hunan, China. In a three-phase-to-ground short circuit test of grid, the prospective fault current of 3.5 kA was limited to 635 A at the pre-setup short-circuit point successfully
    No preview · Article · Jul 2006 · IEEE Transactions on Applied Superconductivity
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    ABSTRACT: We prepared 6 coils from the stainless steel-enforced multifilamentary Bi2223/Ag tapes and studied their electromagnetic behavior for a three-phase 26 kVA (400 V/16 V, 37.5 A/937.5 A) transformer. The primary windings were solenoid coils consisted of 4 helically wound layers, and the secondary windings were consisted of 24 double pancakes connected in parallel with 3 layers, the strand of 6 windings was consisted of two parallel transposed multifilamentary tapes. A numerical analysis has been developed to predict the DC and AC behavior of the coils based on measurements of short samples and tested coils at 77 K. A comparison is made between the experiment and model calculation.
    No preview · Article · Jul 2004 · IEEE Transactions on Applied Superconductivity