基于第二代高温超导带材的高载流超导导体研究进展

由于其高临界电流密度以及优越的机械性能和电磁特性,第二代高温超导带材(也叫涂层导体)在高温低场的电力传输和低温高场下的磁体应用具有广阔的应用前景。在电力传输的低场应用中,高温超导导体在低电压大容量场合需要几千安培甚至上万安培的传输电流。在大型高场磁体应用方面,为了避免由于过高电感在磁体失超和快速关断过程中的感应高压问题,大载流容量、高电流密度高温超导导体在运行于4.2K及以下温度的大型高场超导磁体方面具有很好的应用前景。近年来,基于第二代高温超导带材,国际上相继提出了几种高载流容量的高温超导导体,本文介绍几种高温超导导体的结构及研发现状和进展,并对其结构、性能和工艺进行简单的比较和评述。     

Study on dependence of AC transport current losses in YBCO‐coated conductors on distribution of critical current density and n value

We measured AC transport current losses in three kinds of thin‐film YBCO‐coated conductors made by different processes. The results showed that the loss characteristics were different and that some of the conductors did not follow the Norris strip model which is generally believed to well explain the loss characteristics of YBCO conductors. In the paper, an analytical model in which distribution of critical current density and n value of the conductor are taken into consideration is proposed to describe the AC transport current loss characteristics more generally than the Norris strip and elliptical models. It is shown that the analytical model explains well the measured loss characteristics of the three kinds of conductors. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 152(2): 26–38, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20056     

Development of long‐span‐type overhead rigid‐conductor line of a catenary system

An overhead rigid conductor line in a tunnel is free from the fear of disconnection because the contact wire is not tensioned, and it is superior in maintenance saving. In order to introduce this in open sections, we have developed “a long‐span‐type overhead rigid conductor line of catenary system.” This contact line structure consists of a contact wire of no tension attached to a supporter that has a small drag coefficient suspended from the messenger wire. We have now developed a “square supporter” to make the drag smaller and have put it to various tests with support point intervals of 50 and 10 m. As the testing results show, the contact loss is 1 to 2% at 130 km/h, and this overhead rigid conductor line can collect the current with a stability equal to that of the normal catenary system. © 2000 Scripta Technica, Electr Eng Jpn, 131(1): 94–102, 2000     

Development of HTS (high-temperature-superconductor) current leads for 1-MW/1-kWh modular SMES system

We are developing high-temperature-superconductor (HTS) current loads for a 1-MW/1-kWh modular SMES system. In the modular SMES system, a pair of current leads would be installed in each module so that the heat load to the low-temperature end through the leads is minimized. Design study of the lead configuration including the safety lead and its thermal characteristics is presented herein. The safety lead composed of stainless steel is placed in parallel to the bulk HTS. A test unit for verification of safe operation has been developed and the simulated bulk HTS quench test has been demonstrated. The maximum temperature of the safety lead reached 200 K and the terminal voltage of the safety lead was only 1.2 V in the case of a 1000-A quench test. This temperature rise was well below the designed value. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 120(1): 23–32, 1997     

Experiments on a tokamak device with force‐balanced coils

High field is very favorable for magnetically confined fusion devices such as a tokamak, but the electromagnetic force derived from the field becomes a fatal problem. In particular, the largest in‐plane centering force hinders toroidal field coils from operating at higher fields. Although variable‐pitch multihelical coils, which we term force‐balanced coils (FBCs), by which this force is drastically reduced, were proposed for the coil system of tokamaks, there had been no actual tokamak device with FBCs. Therefore, Todoroki‐1, a small tokamak device with FBCs has been manufactured and experiments started. In this paper, the structure of Todoroki‐1 is indicated, and the stray magnetic field and centering force on FBCs are investigated. The plasmas have been generated in the device, and attempts at better plasmas are beginning. © 1999 Scripta Technica, Electr Eng Jpn, 130(3): 19–29, 2000     

Development of NbTi superconducting strands and cables for the field winding of a 200‐MW‐class high‐energy‐density superconducting generator

The NbTi superconducting strands and cables for the field winding of the 200‐MW‐class high‐energy‐density‐type superconducting generator are developed. They are composed of Cu/Cu‐10wt%Ni/Nb‐46.5wt%Ti superconducting strands and the 10‐kA (at 5 T)‐class 9‐strand compacted cables. The diameter of strands is 1.33 mm, and the 9‐strand compacted cables are 2.4 mm thick and 6.0 mm wide. In order to produce high‐current‐density NbTi strands, we made strands under controlled aging heat treatments, the total and final strains, and the strains between heat treatments, by using large‐scale extruder. Moreover, in order to produce high‐stability and low‐AC‐loss NbTi strands and cables, the matrix ratio of strands and the cross sections of strands are optimized. The current density of NbTi filaments for the four‐time‐aging manufactured 1.33‐mm‐diameter strands was J_C=3150 A/mm² at 5 T, 1150 A/mm² at 8 T. The critical current of the 9‐strand compacted cable is 10.7 kA at 5 T. The AC losses of the final compacted cables are less than 100 kW/m³ at 5 T, 5 T/s, that is, decreased to less than half of the target of the AC loss value (< at 5 T, 5 T/s). Compared with the strand (Cu ratio 1.77), the minimum quench energy (MQE) of the strand (Cu ratio>2) increased about 40% at the operation mode current of the superconducting generator. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 156(3): 24– 31, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20266     

Eddy current flaw testing probe with high performance in detecting flaws during in‐service inspection of tubing

Eddy current flaw testing that uses changes in the impedance of the test coil as an electromagnetic field interacts with the test material is a nondestructive testing method. It can be used to inspect test material at high speed without bringing the test coil into contact with the test material. Therefore, it is widely used for product inspection. In the inspection of heat exchanger tubing in power plants and chemical plants, eddy current flaw testing is performed by using an inner probe, because of the structural restrictions of such plants. However, high levels of wobble noise and support plate noise occur in the conventional method using a rotating pancake coil. The authors therefore propose new minimal‐noise eddy current inner probes. Two new types of probes have been developed: one for detecting axial flaws and the other for detecting circumference flaws. These probes can detect flaws with a low level of noise. The phase of the flaw signal by the new probes changes according to the flaw depth. As a result, the signal phase by the new probes can be used for evaluating the depth of surface flaws. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 161(2): 52–61, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20605     

Development of 3‐in‐one high‐temperature superconducting cable

A three‐in‐one HTS cable has been developed. Its cable core is composed of a conductor and a shield wound with BSCCO and electrical insulation of the PPLP. The three cable cores are covered in thermal insulated stainless corrugated pipes. The BSCCO wires represent a dramatic innovation by virtue of a newly developed process named Controlled Over‐Pressure (CT‐OP). As a new cable technology, a 350‐m thermal insulation pipe was tested for 7 months to find that the life of the vacuum intensity is more than 10 years. The HTS cable with tension members was designed for installation into an underground duct. In addition, a fault current of 23 kA, 0.63 s, was applied to a sample cable with no damage to the BSCCO wires or the cable insulation. These technologies will be applied to the Albany project in the USA. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 162(1): 15–24, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20577     

新型电缆导体直流电阻测量仪的研制

采用小电流电压比率法测量原理 ,研制了一种智能型的电缆导体直流电阻测量仪。它能够快速精密地测量导体的直流电阻 ,并能自动转换显示其 2 0°C、单位长度 (1km)的电阻和 2 0°C时的电阻率。该仪器还具有液晶汉字化显示、蓄电池供电和便于现场使用等特点。     

面向实用化的第二代高温超导带材研究进展

自20世纪80年代钇钡铜氧化合物被发现具有超导电性以来,它受到了世界范围内研究者的广泛关注。该材料具有高不可逆场、高超导转变温度、高临界电流密度等本征物理优势。这种材料以薄膜外延沉积在织构柔性金属基带上,被称为第二代高温超导带材。近年来,国内外数家科研机构和公司解决了生产公里级超导带材的技术瓶颈,已能够批量生产第二代高温超导带材,极大地推动了超导示范工程的开展。此外,超导带材用户单位也从应用角度向超导带材性能提出新的要求,拉动了超导带材材料的发展。本文结合国内外二代超导带材发展的主要趋势,重点介绍面向实用化第二代高温超导带材研发取得的主要进展。     

调容式消弧线圈的谐波电流放大问题分析

通过试验数据和设备原理分析,对调容式消弧线圈性能试验中所出现的接地电流谐波放大问题进行了研究,并提出了相应的建议和措施.     

Considerations on the thrust‐to‐input ratio of a cylindrical moving‐coil‐type linear dc motor

Linear dc motors (LDMs) are widely used for servo‐actuators, compressors, and so on. High‐efficiency LDMs are strongly desired for compressors. To realize LDMs with high‐efficiency characteristics, decreasing the copper losses, namely, thrust‐to‐input ratio, F/P, must be increased. This paper describes an optimization method for the F/P of a moving‐coil‐type LDM. The following results are obtained:

• 1 Simplified expression for the F/P of the LDM is derived from the permeance analysis method. The effects of dimensions of the LDM on the F/P of the LDM are investigated through the simplified expression for the F/P. As a result, the optimum dimension of the LDM for maximizing the F/P exists.
• 2 When the static thrust is 100 N, the measured F/P of the initial LDM is 7.9 N/W, and the errors using the simplified expression for the F/P and the finite element method (FEM) are 33 and 8%, respectively. Derived simplified expression for the F/P is useful because the F/P can be calculated easily.
• 3 An improved LDM, which has 26% higher F/P than those of the initial LDM, is designed by using the permeance analysis method and the FEM. © 2000 Scripta Technica, Electr Eng Jpn, 131(1): 103–111, 2000

     

Operating tests with a 6.6‐kV reduced model of rectifying‐type fault current limiter system

Fault current limiters (FCL) are extensively needed to suppress fault currents, particularly for trunk power systems heavily connected to high‐voltage transmission lines, such as the 500‐kV‐class power system which constitutes the nucleus of the electric power system. In this paper, we propose a new FCL system, consisting of solid‐state diodes, a dc coil, and a bypass ac coil, and describe the specifications of the trunk electric power system and the 6.6‐kV reduction model. Also we propose a 6.6‐kV trial model and describe an efficiency test with a short circuit generator, which we have trial produced for the new FCL system. © 2001 Scripta Technica, Electr Eng Jpn, 137(3): 29–36, 2001     

Development and characteristics of superconductor for 70-MW class high-response excitation superconducting generator

The superconducting field winding of the 70-MW classhigh-response excitation superconducting generator requires a maximum operation current of 4.5 kA at the field of 6 T and needs to allow the field change of 10 T/s. In addition, superconductors have to meet the requirements of saddle-shape winding in the rotor slot and require the mechanical strength withstanding the centrifugal force as well as electromagnetic force. The developed conductor has the configuration of double stranded cable, consisting of NbTi, Cu and CuNi. An optimization was made, taking into account the requirement of low ac loss and high current density. The critical current of 13.6 kA was achieved at the field of 6 T and the ac loss was 6.9 kW/m³. The developed low-loss high-current density superconductor will be able to be applied to the field winding of the 70-MW class high-response excitation superconducting generator.     

Study of phase current measurement by the whole conductors clamping method for three‐phase cable

This paper describes a new measuring method for the phase current in a high‐voltage three‐phase cable. Twenty‐four pieces of independent coils wound around the coreless bobbins are used to make a CT sensor. The primary phase current may be calculated based on the output voltage of each coil. The certain correlation between the output voltage and primary phase current is observed by the experimental data. This new CT sensor enables the measurement of the phase current using the whole conductors clamping method for a three‐phase cable. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 165(2): 9–20, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20753     

Examination of a fault current limiter with conduction‐cooled Nb3Sn screen

We examined the possibility of the practical use of a conduction‐cooled magnetic shield type fault current limiter. A small superconducting fault current limiter was built and the current limiting characteristics were tested. Conceptual design of the conduction‐cooled fault current limiter for a distribution power system was carried out, and we calculated and discussed the temperature rise of shielding coil during a normal and a fault condition. We suggest a protection method for quench due to local disturbances during normal operation. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 145(1): 20–27, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10164     

Proposal of flux‐lock‐type fault current limiter with high‐TC superconducting element

This paper proposes a new type of fault current limiter (FCL), which consists of a high‐T_C superconducting (HTS) element and two coils wound on the same core without any leakage magnetic flux. In this FCL, either the limiting impedance or the initial limiting current level can be controlled by adjusting the inductances and the winding direction of the coils. Therefore, this FCL could relax the material restrictions on high‐T_C superconducting FCL. A current‐limiting experiment by a model FCL was carried out, and the limiting performance was observed. The initial limiting current level of the model FCL was 1.7 times higher than the critical current of the HTS element, and the fault current is suppressed to 52% immediately after the short‐circuit in the test. Considering voltage–current characteristics of a high‐T_C superconductor in a computer simulation, the calculated results almost agreed with the experimental results. © 1999 Scripta Technica, Electr Eng Jpn, 127(1): 31–38, 1999     

Study of the Counterclockwise/Clockwise (CCW/CW) Rotational Losses Measured with a Two‐dimensional Vector Magnetic Property Measurement System

In the development of high‐efficiency actuators, high‐magnetic flux density conditions are applied to achieve higher torque, lower weight and smaller size. It is therefore very important to understand the magnetic properties under high‐magnetic flux conditions in the electrical steel sheets. However, it is very difficult to measure the two‐dimensional vector magnetic properties under high‐flux density conditions due to nonlinearity and anisotropy of the magnetic materials. The measured magnetic power loss under clockwise rotating fields differs from that of the counter‐clockwise direction, and the value in counter‐clockwise rotating fields sometimes becomes negative. It can be considered that angle errors of H‐coils and B‐coils are the main causes of the measurement errors. In this paper, the angle errors of the double B‐coil (search coils) and the double H‐coil (cross‐type H‐coil) are evaluated with a projector‐type magnifying scope and a calibration device. We have compensated the measured magnetic field vector components caused by the angle errors and made clear their influence on the two‐dimensional vector magnetic property measurements. Furthermore, we proposed a method to cancel out small angle errors that remained in the saturated region. Copyright © 2008 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Demonstration of Loss‐reduction Effect of the Amorphous Cores for Larger‐Capacity Transformers by Trial Manufacture

For the demonstration of feasibility and loss‐reduction effect of the larger‐capacity amorphous core transformers (AMT), this paper proposed the support structure and design method of the iron‐loss reduced amorphous wound cores with a weight of 7 tons. We designed and manufactured 10 MVA single‐phase test model with the cores inserted in a support cage having structures of the stress‐buffered core support, the proof electromagnetic force from the windings, and the stray loss‐reducing shields. The 50%‐loaded total loss of the test model estimated from the calculated and measured results has been reduced by 35% compared with a conventional silicon‐steel core transformer (SST) with the same power capacity.     

A new separate‐identification method of two stator equivalent core‐loss resistances corresponding to hysteresis and eddy‐current losses for parallel‐type mathematical models of AC motors

This paper proposes a new unified method for identifying equivalent stator core‐loss resistance of AC motors, which can be applied to both induction and synchronous motors. In order to realize AC motors that exhibit high performance such as precise torque generation and/or efficient energy transmission, stator core loss cannot be neglected in designing vector control systems. It is common to model stator core loss in magnetic circuits as loss caused by equivalent resistance in electrical circuit. One of the best mathematical models for controlling AC motors with core loss is a kind of parallel‐type model that succeeds in modeling both eddy‐current and hysteresis losses. The newly proposed method succeeds in identifying separately and simultaneously two kinds of equivalent core‐loss resistances on the model corresponding to eddy‐current and hysteresis losses. The practical usefulness of the method is evaluated and confirmed through experiments using two induction motors of 5.5 and 2.0 kW having relatively high core losses and a permanent magnet synchronous motor of 750 W having relatively low core losses. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 143(4): 50–63, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10152