高温超导电缆发展及其应用概述

随着高温超导技术的发展,高温超导电缆已经在输电系统中有了实际应用。与传统电缆相比,高温超导电缆具有传输容量大、损耗低、体积小、重量轻、可靠性高、节约资源、环境友好等优势,有望在未来电网发展中发挥重要作用。本文介绍了高温超导电缆的结构及特点、基本设计原理、传输电流与导体层电流分布及交流损耗等技术问题,并对高温超导电缆在交流和直流输电系统中的应用以及目前世界各国对高温超导电缆的研究及成果做了介绍。     

超导技术的发展及其应用

本文回顾了从 1 91 1年发现超导现象以来超导技术的发展历史和现状 ,包括超导材料、超导线、超导电缆和超导电气设备。对超导电缆和超导变压器作了重点介绍。文章最后提出了今后超导技术的应用前景     

Stabilization for thermomagnetic instability of CuNi/NbTi superconducting wire in spatially distributed magnetic field

Thermomagnetic instability in superconducting wires composing multistrand cables is a problem in the development of cables with large current capacity. This paper elucidates the quenching properties of ac superconducting wires in a distributed magnetic field applied to the strands in the cable, and the stabilization of the ac superconducting wires considering the effect of the longitudinal magnetic field or the fraction of copper embedded in each strand. First, the degradation of the quench current of CuNi/NbTi superconducting wires in a distributed magnetic field is exhibited with simple test samples. Second, the quench properties of the strand in a (6 + 1)³ cable and the optimal twist pitch of the cable for high stabilization are discussed. Last, the effect of copper on the quench properties of the strand and the appropriate fraction of copper for suppression of quench current degradation in a distributed magnetic field are discussed. © 2001 Scripta Technica, Electr Eng Jpn, 135(4): 26–34, 2001     

低温绝缘（CD）高温超导电缆屏蔽层电流对超导电缆导体和屏蔽电流分布的影响

文中首次提出低温绝缘（CD）高温超导电缆在屏蔽层通过与导体电流相等的反向电流条件下,屏蔽层自感、屏蔽层层间互感、屏蔽层与导体间互感的计算式,以及CD绝缘高温超导电统屏蔽和导体电流均匀分布的设计计算方法。通过对几种典型的屏蔽和导体结构的CD绝缘高温超导电缆屏蔽电流和导体电流分布计算,分析研究屏蔽层电流对CD绝缘高温超导电缆的导体和屏蔽电流分布的影响,并推荐将文中提出的计算方法作为CD绝缘高温超导电缆导体和屏蔽结构的设计基础。完善的计算机程序已缟制完成,可作为实际应用。     

高温超导电缆发展的概况

本文首先讨论了超导体的基本概念、性能和种类 ,介绍了超导材料研究的进展情况、超导电缆的设计方案、结构和特性参数 ,并与普通电缆作了比较。文章最后报道了高温超导线材和导体的结构和特性参数     

An over‐current withstanding design of superconducting power cables

In a design of HTS power cables, the over‐current withstanding design is very important. In a conventional case, when one of the 2‐circuit power cables failed, the other cable should transport the previous total power continuously. If we adopt this idea also in case of superconducting power cables, the rating current should be decided carefully. In this paper, the authors show a fundamental idea for a short‐time withstanding over‐current design of HTS power cables. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 141(2): 34–40, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10051     

海底超导电缆交流损耗的抗损伤特性研究

海上新能源发电的快速发展急需大容量高效率的海上电力传输网络与之匹配。为促进海底超导电缆的发展,需要研究局部损伤对超导电缆的影响,尤其是对其损耗特性的影响。这关系到损伤是否会导致损耗骤升而冷却系统无法及时排出多余热量,进而导致低温平衡被破坏,超导电缆无法继续工作,甚至发生进一步大范围损伤。基于陆上超导电缆建立了包含单层到多层电缆的物理模型,并使用有限元方法分析电缆的电流分布、内部磁场分布和输电损耗。通过比较损伤前后电缆损耗特性的变化,分析并总结得出了最适宜用于海底输电的超导电缆结构。结果表明,在单根带材损伤的情况下,一层和二层电缆的损耗大幅度提升,而六层电缆的损耗不到5%。因此六层电缆较为适应海底环境。     

Development of Nb-Ti cable with ultrafine filament and high-resistivity matrix for ac use

Superconducting ac machines such as transformers and reactors are expected to have an important role in future electric power transport lines. In these machines, superconducting coils are wound with superconducting cables that have low ac loss, stable ac quenching current, and high normal resistivity. We have developed Nb-Ti superconducting cables with ultrafine filaments and high-resistivity matrix for these coils. One such cable is a double-stranded round structure using 0.2-mm strands with 0.14-μm filaments and Cu-30wt%Ni as a matrix material. The 50-Hz quenching current without external magnetic field exceeds 1400 Arms. The ac loss is 15 kW/m³ at a transverse external magnetic field of 0.5 T, 50 Hz, and the normal resistivity is 0.21 Ω/m at 0 T, 10 K. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 120(2): 8–18, 1997     

高温超导电缆的研发现状和发展趋势

与常规电缆相比,高温超导电缆具有体积小、重量轻、容量大、电流密度高、损耗低、环境友好等优势,为未来电网提供了一种新的电力传输方式。随着高温超导线材取得的重要研究进展,国际上相继开展了高温超导电缆的研发,已有多条超导电缆工程成功地进行了挂网示范运行。本文介绍高温超导电缆的研发进展情况,并简单对高温超导电缆的发展趋势和关键技术做出展望。     

BSCCO超导带材的工艺要点与应用

高温超导材料的发现,推进了超导技术的实用化。作为典型的高温超导材料,铋系(BSCCO)超导带材目前已在超导电缆、超导限流器和超导储能等领域实现商用。粉末套管法是制备BSCCO超导带材最常用的方法,主要工艺步骤包括装粉、拉拔、轧制和热处理等。本文介绍了粉末套管法的工艺,重点介绍了各工艺步骤中的关键点,阐述了超导带材在超导限流器和超导储能系统中的应用,提出了BSCCO超导带材未来的发展方向。     

Research and development of electrical insulation ofsuperconducting cables by extruded polymers

This is a review to show the importance of electrical insulation in ac superconducting cables. An attractive superconducting cable has to be designed for the voltage range of 60-270 kV. Therefore, a reliable insulation design is imperative. Two types of insulation have been compared. One is composite insulation, namely laminar paper or plastic tape, impregnated with coolant. The other is solid insulation of extruded polymer on the conductor. The composite insulation has a lengthy history and, in the constructions to date, has been the insulation design used for superconducting cables. Some prototype superconducting cables with this type of insulation have been developed and successfully tested. However, the partial discharge in butt gaps may affect their long-term reliability. The solid insulation, on the other hand, can separate the coolant from the electrical insulation and can exploit the benefit of the super electrical insulation characteristics of polymers in the cryogenic region. Some attempts have been made to use this design with liquid nitrogen and liquid helium. One example incorporating extruded ethylenepropylene rubber (EPR) for insulation was found to satisfactorily go through the cool-down to a liquid helium temperature and to endure the simultaneous voltage and current tests. EPR, and possibly some other polymers, seem to be promising materials for solid insulation in the cryogenic region     

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     

Magnetic instability of ac multifilamentary superconductors in spatially distributed magnetic field

Alternating current (ac) superconducting machines such as superconducting generators, transformers, or resistive current limiters need large‐current‐capacity conductors. These conductors are generally fabricated as multistrand cables stacked with multifilamentary NbTi superconductors whose current capacity is a few tens of amperes. ac quench current degradation has often been observed in ac use of such multistrand cables. Several reasons for this degradation have been pointed out: nonuniformity of each strand current, mechanical disturbances, thermomagnetic instability, and ac losses. However, it has not as yet been overcome. Since the angle between the strand axis and the cable axis changes along the cable axis in multistrand cables, the strands are exposed to a spatially (axially) distributed magnetic field, which has longitudinal and transverse components changing periodically due to multiple cabling. This paper mainly discusses the thermomagnetic instability due to the distributed transverse magnetic field, which was compared with the self‐field instability and the longitudinal field instability experimentally and theoretically. It was confirmed that the ac quench current degradation due to the distributed transverse field could be induced by the following: nonlinear E–j characteristic, strong dependence of E–j characteristic on magnetic field in low field region, uniformity of the axial current profile inside the superconductor with the high resistive matrix, and the poor thermal diffusion of CuNi/NbTi composites. © 2000 Scripta Technica, Electr Eng Jpn, 131(1): 45–55, 2000     

A shell type superconducting transformer for experiments using Nb3Sn superconducting cables

A shell-type superconducting transformer was developed for experiments using Nb₃Sn superconducting cables. The designed capacity is 667 kVA (single phase), the voltage is 440/220 V, the current is 1515/3030 A and the percent impedance is 16 percent. Main features of the transformer are as follows: (1) Magnetic field in superconducting coils is decreased by increasing the number of high and low coil groups. (2) Large-scale superconducting cables are not needed when the number of high and low coil groups is increased. (3) Epoxy impregnated coils are used to withstand an electromagnetic force at 120 Hz. The Nb₃Sn basic strand was manufactured by the internal tin diffusion process. The cable consists of seven insulated subcables, and the subcable consists of seven strands. The primary (HV) coil of the transformer was excited, in which the secondary (LV) coil was shortened. The primary current reached 1618 A_rms without quenching, and the reached capacity corresponds to 712 KA. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 118 (3): 13–21, 1997     

单相高温超导电缆屏蔽层电流仿真及实验研究

高温超导电缆的屏蔽层在非对称故障情况下会在变电站间产生入地电流,影响系统的零序阻抗。采用数值模拟与实验相结合的方法,研究单相高温超导电缆的屏蔽层电流的影响因素。首先建立了超导电缆的电磁数值仿真模型,通过解析公式对模型进行验证,然后仿真计算不同屏蔽层等效电阻下,屏蔽层感应电流和感应电压大小。结果表明,感应电流和感应电压的主要影响因素是屏蔽层电阻的大小,且屏蔽层与导电层间的电磁关系可以采用变压器模型进行定性分析。同时,搭建了超导电缆屏蔽层电流的测试实验平台,初步验证了屏蔽层阻抗对屏蔽层电流的影响规律。     

First trial of the electric power transmission of 3.8 kV–460 kVA through the prospective power transmission model system integrated under superconducting environment (PROMISE)

Superconducting technology is regarded as a breakthrough to future electric power transmission because of its highly densified and large transmission capability. This paper proposes a concept of the future power system composed of various superconducting apparatuses. A prototype model system called “PROMISE (PROspective power transmission Model system Integrated under Superconducting Environment)” is constructed to prove the realization of the above concept. PROMISE is composed of a superconducting transformer (60 Hz, 6/3 kV, 1000 kVA class), superconducting fault current limiter (6 kV, 200 A class), and superconducting power cable (5 m, 6 kV, 650 A class). This paper also shows that PROMISE realized the transmission of the electric power of 3.8 kV–460 kVA (50 Hz). This is the first achievement in the world. The voltage-current synthetic test verified that PROMISE can withstand ac voltage of 6 kV while carrying ac current of 170 A (60 Hz). The ac loss of superconducting cables, the heat leak of cryostat and the core loss of the superconducting transformer are measured to estimate the transmission loss of PROMISE. These fundamental performances of PROMISE may indicate the feasibility of the future introduction of superconducting technology for electric power systems.     

Electrical Insulation Performance of Paper–Ice Composite Insulation System at Cryogenic Temperature

In recent years, research on the development of high-temperature superconducting cables has advanced. The application of a composite insulating system made of insulating paper-liquid nitrogen has been studied as an electrical insulating system for high-temperature superconducting cables. In paper-liquid nitrogen composite insulating systems developed on the basis of conventional techniques, microscopic bubbles easily remain inside the paper, and the partial discharge are supposed to occur easily. In order to overcome this drawback, we formulated a paper-ice composite insulating system as a substitute for the paper-LN₂ of the cryogenic electrical insulating system in high-temperature superconducting cables. In this study, the breakdown strength, partial discharge, V-t characteristics, effect of pressure on breakdown characteristics, and the self-healing breakdown characteristics of a paper-ice composite insulating system were investigated in order to understand the basic properties of new insulating materials for applications to high-temperature superconducting cables. As a result, it was clarified that the AC breakdown strength of paper-ice composite insulating system was higher than that of paper-liquid nitrogen insulating system, and that of paper-ice composite insulating system exhibited a self-healing type. Copyright © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Current distribution in superconducting multistrands for ac use before and after quenching

A superconducting multistranded cable is used to realize high current capacity for ac use. The critical current value of the cable is reported to be less than the simple summation of the individual critical current value of each strand. The causes for such a degradation of the critical current value have not been revealed. This paper investigates the current distribution in multistrands before and after their quenching by using seven-strand superconducting cable and 7x7 cable. The following experimental results are derived: (1) the quenching is initiated at one strand in the cable; (2) the current in the quenched strand is transferred into the other strands; (3) an avalanche of quenching is induced among the strands; and (4) the central strand is quenched finally among the strands. The critical current values of the 7- and 7 × 7-stranded cables also are measured. These values are in good agreement with the predicted values based on the mutual inductance among the strands. It is concluded that the unbalance of the current distribution in the superconducting multistrands can be one of the promising causes for the degradation of the critical current value.     

高温超导电缆在城市地下输电系统应用的可行性研究

大城市有可能最先采用商业化运行高温超导电缆 ,用于城市地下交流输电系统。其主要应用目标是用于地下电缆工程改造 ,利用现有排管以高温超导电缆取代现有的常导电缆 ,增加地下电缆传输容量以及采用高温超导电缆将巨大电能 (1GVA以上 )输入到城市负荷中心。采用常导电力电缆传输 1GVA以上的电能进入中心城区 ,输电电压一般要求为 5 0 0 k V。在城市中心区不可能建设 5 0 0 k V变电站。 5 0 0 k V电缆线路所需的 5 0 0 k V大长度电缆和相应附件 ,目前尚未研制开发。采用高温超导电缆将有可能降低输电电压等级 ,可以采用 2 2 0 k V高温超导电缆将 1GVA以上的电能输入到城市负荷中心 ,满足特大型城市负荷中心供电需求。采用 110 k V高温超导电缆 ,亦有可能传输 1GVA左右电能。本文通过对交流高温超导电缆系列设计计算对额定电压 35 k V、110 k V、2 2 0 k V的高温超导电缆 ,按不同传输电流 (或传输容量 ) ,以高温超导电缆的传输效率 (损耗与传输容量比 )、高温超导电缆外径限值和超导导体绕制结构限制条件 ,确定高温超导电缆适用性界定条件 ,提出城市地下输电、配电系统用高温超导电缆可行方案。     

Tan δ of ethylene-propylene rubber in cryogenic temperature region–effects of additives and sample thickness

The authors have been developing extruded polymer insulated superconducting power cables. Dielectric loss in electrical insulation cannot be ignored in superconducting cables since conductor loss in the cables is minimal. Studies so far show that ethylene-propylene rubber (EPR) is suitable as an electrical insulating material in the extruded polymer insulated superconducting cable design because it demonstrates excellent mechanical and relatively good electrical qualities at a cryogenic temperature. Widely used EPR includes some kinds of additives; however, their effect on tan δ of EPR at cryogenic temperature remains unknown. The effect of additives such as crosslinking agent and fillers on tan δ of EPR was examined at temperatures of between 4.2 K and 300 K. Thickness dependence of tan δ was also measured using EPR films of different thickness and an extruded EPR insulated cable sample. The results show that additives increase tan δ of relatively thin films of EPR even in the cryogenic temperature region; however, they do not have an intolerable dielectric loss in comparison with conductor loss and heat inflow of the superconducting cable. The remedy to tan δ increase due to the polymer contraction relative to shielding wires has been established.