Zhenghe Han

Introduction of China's first live grid installed HTS power cable system

Chinas first HTS power cable project was started in the second half of 2002 and on site system installation was finished at Puji Substation of China Southern Power Grid in March, 2004. This cable system consists of three 33.5 m, 35 kV/2 kA/sub rms/ cables, six terminations, and a closed cycle liquid nitrogen cooling station. The conductors of the cables were made of 4 layers of BSCCO 2223 HTS tapes. Off grid field testing and live grid trial operation has been carried out since the completion of the installation. In this paper, we will report the key technical parameters of the system. Descriptions of the installation site, demonstration of the system installation, and results of testing and trial operation will also be presented and discussed.

Measurement and Calculation of Residual Magnetic Field in a Bi2223/Ag Magnet

Residual magnetic field in a high temperature superconductor (HTS) magnet is a factor which should be avoided when the field of the magnet is being operated under a high uniformity and high accurate control. In this paper, the residual field in a Bi2223/Ag pancake magnet at 77 K is systematically studied. The amplitude of the residual field as a function of maximum charging current and the relaxation of the residual field are measured. For a magnet with an inner diameter of 60 mm, an outer diameter of 80 mm and a height of 30 mm, the maximum residual field is about 14.5 G after ramping the charging current up to 15 A, followed by dropping the current to zero. A simple model is proposed, from which the residual field can be estimated as along as the configurations of the magnet and the critical current (Ic) of the original short sample are given.

China’s 30 m, 35 kV/2 kA ac HTS power cable project

A project for a 30 m, 35 kV /2 kArms, 3 phase, warm dielectric HTS power cable system is underway in China. This system will be installed in the China Southern Power Grid at the Puji substation in Kunming, Yunan province, in 2004. We have carried out a series of experiments to investigate the possible winding angles and layer configurations of the cable conductor with Ag sheathed Bi-2223 tapes, different LN2 cooling mechanisms, termination configurations, and fabrication techniques. For better understanding of the basics of an HTS cable system and practising new fabrication techniques, a 4 m superconductor cable with terminations and a closed cycle cryogenic system was built and tested. In this paper, we give the detailed parameters of the 30 m cable system and the work plan of the project.

A rapid process of YBa2Cu3O7−δ thin film fabrication using trifluoroacetate metal–organic deposition with polyethylene glycol additive

Trifluoroacetate metal–organic deposition (TFA-MOD) is a promising technique to fabricate YBa2Cu3O7−δ (YBCO) superconducting films. However, its slow pyrolysis process, which usually takes more than 10 h, constitutes a barrier for industrial production. In this study, polyethylene glycol (PEG) was utilized to reduce the stress generation inside the coated films when the strong pyrolysis reactions happen. With the addition of 30 wt% PEG2000 to the precursor solution, a smooth film surface could be obtained through a rapid pyrolysis process of 15 min. After the optimizations of the crystallization and oxygenation processes, mass percentage and molecular weight of PEG additive, YBCO thin films with Jc of about 4.5 MA cm−2 (77 K, self-field) could be routinely fabricated using (20–30) wt% PEG(1000–2000) additive with a total treatment time of about 2 h including the 15 min pyrolysis process time. The effects of PEG additive were discussed using one of the mechanisms of buckling formation. The reduction of compressive stress by PEG additive was suggested to be the reason for preventing buckling.

Calculation of AC losses in HTS tape with FEA program ANSYS

The commercially available finite element analysis program ANSYS, primarily designed for solving problems for ferromagnetic materials and conventional conductors, has been used for simulating the ac losses in HTS tape carrying transport current or exposed to a perpendicular field. Details on how to develop the program as a calculation tool for HTS materials are presented; in particular some factors related to the numerical accuracy and efficiency are discussed. The approach is based on a 2D electromagnetic transient analysis, where the conductivity of the HTS material is simulated in terms of a power law. The commonly used flux creep model and Bean model can be realized by adjusting the power law index value from 2 to /spl infin/. For the Bean model, the simulated results are verified by comparison with the analytical formulas given by Norris, which shows the error to be less than 0.5%. For the flux creep model, the accuracy is estimated by comparison with Brandts method for a basic cylinder geometry, showing a good agreement.

Development and testing of a 2.5?kW synchronous generator with a high temperature superconducting stator and permanent magnet rotor

High temperature superconducting (HTS) armature windings have the potential for increasing the electric loading of a synchronous generator due to their high current transport capacity, which could increase the power density of an HTS rotating machine. In this work, a novel synchronous generator prototype with an HTS stator and permanent magnet rotor has been developed. It has a basic structure of four poles and six slots. The armature winding was constructed from six double-pancake race-track coils with 44 turns each. It was designed to deliver 2.5 kW at 300 rpm. A concentrated winding configuration was proposed, to prevent interference at the ends of adjacent HTS coils. The HTS stator was pressure mounted into a hollow Dewar cooled with liquid nitrogen. The whole stator could be cooled down to around 82 K by conduction cooling. In the preliminary testing, the machine worked properly and could deliver 1.8 kW power when the armature current was 14.4 A. Ic for the HTS coils was found to be suppressed due to the influence of the temperature and the leakage field.

A low-fluorine solution with a 2:1 F/Ba mole ratio for the fabrication of YBCO films

In previously reported low-fluorine MOD-YBCO studies, the lowest F/Ba mole ratio of the precursor solution was 4.5. Further lowering the F/Ba ratio would bring benefits for the environment, thick film deposition, and an understanding of the heat treatment process. On the other hand, the F/Ba ratio must be at least 2 for full conversion of the Ba-precursor to BaF2 to avoid the formation of BaCO3, which is detrimental to the superconducting performance of YBCO films. In this study, a solution with a 2:1 F/Ba mole ratio was developed, and the fluorine content of this solution was approximately only 10.3% of that used in the conventional TFA-MOD method. Attenuated total reflectance-Fourier transform-infrared spectra (ATR-FT-IR) revealed that BaCO3 was remarkably suppressed in the as-pyrolyzed film?and eliminated at 700??C. Thus, YBCO films with a critical current density (Jc) of over 5?MA?cm?2 (77?K, 0?T, 200?nm thickness) could be obtained on lanthanum aluminate single-crystal substrates. In?situ FT-IR spectra showed that no obvious fluorinated gaseous by-products were detected in the pyrolysis step, which indicated that all F atoms might remain in the film as fluorides. X-ray diffraction ?/2? scans showed the presence of BaF2?but not of Y F3 or CuF2?in films quenched at 400?800??C. The formation priority of BaF2 over Y F3 and CuF2 was interpreted by examining the chemical equilibrium of the potential reactions. Our study could enlarge the synthesis window of precursor solutions for MOD-YBCO fabrication, and serve as a foundation for continuously and systematically studying the influence of fluorine content in the precursor solutions.

Simulation of AC Loss in Small HTS Coils With Iron Core

AC loss is one of the key problems in HTS applications. This study focuses on the AC loss in small Bi-2223/Ag and YBCO coils, with an emphasis on the presence of an iron core. HTS coils with an iron core can be used in a number of applications, including induction heaters, motors, fault current limiters, controllable reactors and transformers. The major concern of the study is the interaction between the iron core and the HTS coil. This study first provides a brief introduction of the resistivity-adaption algorithm (RAA) method, which is used to simulate the field penetration, based on a given flux motion theory. A general model is then proposed, with a discussion on the effect of the iron core. Results showed that a well-designed iron core is beneficial for the AC loss reduction.

AC Losses in HTS Tapes and Devices With Transport Current Solved Through the Resistivity-Adaption Algorithm

Alternating current (ac) losses in high-temperature superconductor tapes and devices with transport current are solved by using the resistivity-adaption algorithm (RAA). The most advanced feature of the RAA is that it enables the simulation of any model derived from the flux motion theory on finite-element analysis (FEA) packages that have an eddy current solver. The principle of the RAA, as well as its realization on the ANSYS FEA package, is introduced. The simulation begins with the calculation of the ac loss of an ellipse and of strips with aspect ratios ranging from 50 to 2000. The accuracy and efficiency of the calculation are verified through comparisons with the Norris theoretical curves. The possible errors and the method to overcome such errors are discussed. The most significant improvement in the proposed RAA from that discussed in a previous study is that the RAA was proven to be valid for calculating the field-dependent critical state model by using the descendant process from +Im to -Im. We then extend this method to calculate the transport ac loss of a stack of ellipses with Jc(B) characteristic from a typical Bi2223/Ag tape and the transport ac loss of a stack of strips with Jc(B) characteristic from a typical YBCO-coated conductor.

Method and Apparatus for Continuous

A new method based on the principle of magnetic circuits is proposed and realized for continuous <i>I</i>_c examination of HTS tapes. The greatest advantages of the new method are that it first eliminates all the noise caused by mechanical fluctuations, and thus makes high speed and high stability measurement possible, and second has a natural ability to measure HTS tape with a magnetic substrate. The principle of the method is introduced with the help of Finite Element Analysis. An apparatus for examination of kilometer long tapes has been constructed, by which continuous <i>I</i>_c examination for a YBa₂Cu₃O_7-<i>x</i> tape with and without a magnetic substrate and a Bi₂Si₂Ca₂Cu₃O<i>x</i> multi-filamentary tape is reported.