HTS Cable Research Articles

Experimental Evaluation of AC Losses in the Cold Dielectric High-Temperature Superconducting Cable

The alternating-current (AC) losses in the 20-cm Bi-2223/Ag tape cold dielectric high-temperature superconducting (CD HTS) test cable are experimentally evaluated. The method used is the electrical method which is based on a lock-in amplifier. Firstly, the AC losses of the CD HTS cable which has two conductor layers and one shield layer are measured. Then, in order to eliminate the error caused by joint resistance, a test is designed to measure the joint resistance of each layer. The measured losses that eliminated the error due to joint resistance are found to be in good agreement with calculated ones with the monoblock model, Carr, and Magnusson equations at the frequencies of 50 ∼ 300 Hz. Finally, the errors caused by joint resistance and other uncertain factors are discussed.

Status of 275 kV REBCO HTS Cable Development in the NEDO Project

A 275kV 3 kA high temperature superconducting cable (HTS cable), which could be used as a backbone power line in the future, was developed in the NEDO project called M-PACC. One of the most important developments of a high voltage HTS cable was the high voltage insulation technology. A design guideline and a test specification that was necessary to design, product and demonstrate of a 275kV, 3 kA HTS cable have been studied by obtaining the various experimental data such as AC withstand voltage, impulse withstand voltage, partial discharge inception stress, and the V-t characteristics of the insulation, on the basis of the Japan Electrical Standards (JEC) and the International Electrotechnical Commission (IEC). Moreover, the 275kV, 3 kA HTS cable with a length of 30 m was demonstrated under a long-term voltage and current loading test.

사고전류 제한형 초전도케이블 제작을 위한 초전도 선재 선정에 관한 연구

When an abnormal condition occurs due to a fault current at a consumer location where electricity is supplied through a high-capacity and high-<TEX>$T_c$</TEX> superconducting(HTS) cable, the HTS cable would be damaged if there is no appropriate measure to protect it. Therefore, appropriate measures are needed to protect HTS cables. The fault-current-limiting HTS cable that was suggested in this study performs an ideal transport current function in normal operations and plays a role in limiting a fault current in abnormal operation (i.e., when a fault current is applied). It has a structure that facilitated its self-current-limiting ability through device change and reconfiguration in the existing HTS cable without extra switching equipment. To complete this structure, it is essential to investigate about the selection of the superconducting wire. Therefore, in this paper, HTS wire using two types of different stabilization layer is compared and examined the stability and current limiting properties under the existence of a fault current.

The Electric Field Analysis of the Warm Dielectric HTS Power Cable

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.

The Temperature Measurement for the 10 kA HTS Cable

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.

Status of a 200-Meter DC Superconducting Power Transmission Cable After Cooling Cycles

We constructed a facility of a 200-m HTS power transmission test cable (CASER-II) in 2010. Generally, an HTS cable contracts about 0.3% when it is cooled from room temperature to liquid nitrogen (LN2) temperature. The contraction of the 200-m HTS cable corresponds to 0.6 m. In order to realize the HTS power transmission system, it is an essential issue to absorb the mechanical stress of the HTS cable during the cycles of cooling-down and heating-up. The CASER-II uses smooth pipes as the cryogenic pipe for the cable line to reduce the pressure drop of the liquid nitrogen flow, whereas the other HTS cables use corrugated pipes to absorb the mechanical stress. The CASER-II employed (1) the movable terminals at the cable end, and (2) the extendable bellows inserted in the cryogenic pipe, to absorb the contraction of 0.6 m in cooling cycles. Even at the 4th cooling-down test, no damage was observed in the CASER-II. Use of the smooth cryogenic pipe enabled low pressure drop with low LN2 flow rate, and negative pressure drop appeared at less than 5 L/sec of the LN2 flow rate. This negative pressure drop was caused by the LN2 flow assisted by siphon effect due to the difference of LN2 density along the cryogenic pipe line with elevation of 2.6 m.

Modeling of Second Generation HTS Cables for Grid Fault Analysis Applied to Power System Simulation

HTS power cable systems are an emerging technology aimed at competing with XLPE cable systems. Knowledge on the thermal operating conditions of HTS power devices is needed to estimate their availability when connected to a power system, because the HTS material must remain below its critical temperature to transport current. In this work, a simple finite difference method is used to assess the temperature distribution at certain cross-section of a second-generation coaxial HTS cable. This method has been implemented in MATLAB and its proper functioning has been verified with the software package FLUX. This method is a tool to establish temperature distributions among HTS cable layers under normal operating conditions. Additionally, the aim of this work is to serve as basis for future simulations including heat generation changes within the cable layers typically caused by grid fault events.

Influence of Various Voltage Leads on AC Loss Measurement in a Double Layer BSCCO Conductor

We have operated the two 22.9 kV/50 MVA HTS cable systems installed at Gochang Test Yard and Icheon Substation of Korea Electric Power Corporation (KEPCO), respectively; they have a double layer conductor and a single layer shield, consisting of BSCCO and YBCO-NiW wires. In general, the ac loss of a multilayer cylindrical conductor like the KEPCO HTS cables is evaluated from the conductor's current and the loss voltage of a lead soldered onto its outermost layer. To experimentally investigate what the voltage lead on the outermost layer picks up in this study, we prepared a double layer BSCCO conductor sample, and attached the four voltage leads of the outer, inner, contactless, and total leads. Then its ac loss for these leads was examined for different layer current distribution, and finally compared with a numerically calculated one. The results show that the outer-lead, which is often used in the double layer conductors, takes only the outer layer's loss voltage like the contactless-lead. Therefore, for ac loss evaluation of our double layer sample, a new voltage lead, total-lead, is presented besides the conventionally used outer-lead. The total-lead best fits with the numerical calculations, regardless of layer current distribution. However, the outer-lead is not suitable, especially for nonuniform distribution, although it still now is valid only for uniform distribution.

Assessment of Improved Power Quality Due to Fault Current Limiting HTS Cable

Fault current limiting high-temperature superconductor (FCL-HTS) cable not only provides effective power transmission, but also reduces the negative impact of fault current. As the demand grows rapidly, distributed generation (DG) is being implemented into the power grids. The integration of DG into the existing power grid causes an increase in short circuit current. In order to facilitate reliable planning and operation of future power systems, power system planners and operators will need to avoid the potential threat of increased fault current. The superconductor cable is considered as an enabling technology because it can raise power transmission capability and effectiveness with minimal loss. However, high fault current through the superconductor cable may seriously damage the power system. However, FCL-HTS cables can reduce the impact from unexpected high fault current. The FCL-HTS cable helps avoid interruption and voltage sag without harming existing coordination of protection devices. This study addresses the power quality issues for increased fault current that will be caused by the DG. We also analyze the response of FCL-HTS cable in perspective of power quality, when the fault occurs with DG.

Numerical analysis of the stability of HTS power cable under fault current considering the gaps in the cable

During the operation of a high temperature superconducting power cable in a real grid, the power cable can be impacted inevitably by large fault current. The study on current distribution and thermal characteristics in the cable under fault current is the foundation to analyze its stability. To analyze the operation situation of 110kV/3kA class superconducting cable under the fault current of 25kArms for 3s, the equivalent circuit equations and heat balance equations were established. The current distribution curves and the temperature distribution curves were obtained. The liquid nitrogen which exists in the gaps of HTS cable was taken into consideration, the influence of gap liquid nitrogen on the thermal characteristics was investigated. The analysis results can be used to estimate the security and stability of the superconducting cable.

Calculation of critical current in DC HTS cable using longitudinal magnetic field effect

It is known from experimental data that the critical current of superconducting wires in a longitudinal magnetic field is higher than that in a transverse magnetic field. This property was proposed to apply to DC superconducting cables in our previous paper. Here, we propose a new calculation method of the current-carrying capacity for a new DC superconducting cable. An iteration method is used to calculate the magnetic field and critical current density in each layer and the current-carrying capacity of the cable. This enables us to calculate these quantities even for the cable with a different structure from the force-free one. When the critical current density increases with a longitudinal magnetic field, the optimal structure is found to be close to that of the force free cable. The optimal structure is obtained also when the critical current density decreases slightly with the longitudinal magnetic field. The reason for the enhanced current-carrying capacity even for such a case is a sufficiently larger critical current density in the longitudinal magnetic field than that in the transverse magnetic field.

A Quantitative Analysis on Future World Marketability of HTS Power Industry

This study estimates total world market volumes of HTS power industry, one of the main smart grid equipment in the future when the market penetration ratio reaches 100% in the future. The results of this paper are based on the GOULDEN Report providing the total market volumes of conventional power industry for the world market. This study determines the market penetration ratio using the judgment method with market penetration S-curve induced from Delphi method and Product Life Cycle from 2011 (expected to be a launching year, not the actual year) to 2050 (expected to be a final target year). For this purpose, HTS market penetration ratio of each stage, so called innovation, early adapters, early/late majority and laggard stage, is analyzed using S-curve and thus calculated the total future market volumes of HTS equipment. In conclusion, this paper shows the quantitative analysis for HTS cable, FCL, transformer and rotational machine in the world market.

高温超電導ケーブル用冷却システムおよび高性能冷凍機の開発

高温超電導ケーブル用冷却システムおよび高性能冷凍機の開発

Installation and Power Grid Demonstration of a 22.9 kV, 50 MVA, High Temperature Superconducting Cable for KEPCO

Korea Electric Power Corporation (KEPCO) has a great interest on the application of HTS cable to its network to relieve power congestion and enhance the reliability of the power system. Down through the years from 2005 to 2010, the 22.9 kV, 50 MVA HTS cable has been demonstrated by field test, showing affirmative results. With the financial support of Ministry of Knowledge and Economy (MKE), the new project to install and operate the HTS cable in electrical network of Korea was launched in 2008. An HTS cable with the 22.9 kV, 50 MVA, and 410 m length was installed in the KECPO grid in the end of 2010. After the integration of the HTS cable system, the commissioning items of the DC withstand voltage test, DC critical current test, and heat loss measurements were conducted in accordance with the Korean industrial standard, and self-defined specifications. The HTS cable was energized on the 154 kV Icheon substation of KEPCO on August 19th, 2011. The details of the project description, onsite installation, and commissioning tests are presented in this paper.

Novel Protection Scheme With the Superconducting Power Cables and Fault Current Limiters Through RTDS Test in Icheon Substation

This paper proposes a novel power system protection scheme in the power system including high temperature superconducting cables (HTS cables) and high temperature superconducting fault current limiters (HTSFCLs). The superconducting power system utilizes the large-capacity and environment-friendly characteristics of superconducting power equipment. Since the superconducting devices are one of the most optimal solutions to enhance the robustness of the power system, especially in Icheon substation in Korea, the protection of the conservative relays and additional relays, differential and instantaneous overcurrent relays, should be alternated with a new optimal protection coordination under the changed system configurations. To find the optimal protection scheme, the power system with existing power devices, conservative relays, HTS cables, and fault current limiter has to be modeled in Icheon substation and the novel protection scheme has been verified through RTDS test with real-time relay test.

Evaluation on Current Limiting Properties During 3-Phase Connection Between the Wires for SFCL and HTS Cable

Advantages of YBCO thin film type wires are as follows. First, their high critical current density allows effective handling of normal and fault currents. Second, high index values can lead to fast fault current limiting because of the rapid build-up of resistance. Third, a variety of stabilizing materials can be employed in YBCO thin film type wire, resulting in more flexible adjustment of limiting resistance after the quench. In this study, the wires for the current limiter and cable were selected through an over-current conducting (transport) test that took into account the characteristics of the YBCO thin film type wire. The current limiting characteristics of the wires for the current limiter and cable according to the fault type and fault angle were examined. The tests were conducted in three phases, and the fault type and fault angle were examined for single-line-to-ground fault, double-line-to-ground fault and triple-line-to-ground fault at the fault point of R-phase 0 that was defined as the fault standard in the test. The YBCO thin film type wire for the current limiter with a critical current of 80 Arms, critical temperature of 90 K and voltage rating of 0.6 Vrms/cm had stainless steel stabilization layer, while the Bi-2223Ag wire for HTS cable with a critical current of 110 Arms, critical temperature of 106 K and voltage rating of 2.5 Vrms/cm had silver stabilization layer. The required lengths were determined considering the voltage rating of wires, and the wires were respectively wound on a straight former and a spiral former.

Low Friction Cryostat for HTS Power Cable of Dutch Project

Particulars of 6 km long HTS AC power cable for Amsterdam project are: a cable has to fit in an annulus of 160 mm, with only two cooling stations at the cable ends [1] . Application of existing solutions for HTS cables would result in excessively high coolant pressure drop in the cable, possibly affecting public acceptance of the project. In order to solve this problem, a model cryostat was developed consisting of alternating rigid and flexible sections and hydraulic tests were conducted using sub-cooled liquid nitrogen. In the 47 m-long cryostat, containing a full-size HTS cable model, measured pressure drop amounts 11 mbar at the mass flow rate of 0.3 kg/s and temperature 65 K. For a 6 km-long HTS cable this gives a pressure drop below 2 bar, which is acceptable. In order to achieve this result, the cryostat was manufactured from alternating straight rigid sections and corrugated flexible sections. A flexible dummy HTS cable was inserted into this cryostat and sub-cooled liquid nitrogen was circulated in the annulus between the dummy cable surface and the inner cryostat surface. In the paper details are presented of the cryostat, of the measurement setup, of the experiment and of the results.

Development of 66kV class REBCO superconducting cable

Abstract Sumitomo Electric Industries (SEI) has been involved in the development of 66 kV/5 kA-class HTS cables using REBCO wires. One of the technical targets was to reduce the AC loss to less than 2 W/m/phase at 5 kA. SEI developed a clad-type textured metal substrate with lower magnetization loss than NiW substrates. REBCO wires of 30 mm wide were slit into 4 mm-wide strips, and these strips were wound spirally on a former with small gaps. The measured AC loss of the manufactured cable was 1.8 W/m/phase at 5 kA, achieving the AC loss goal. Another important target was to manage fault current. The copper protection layers were designed based on simulation findings. Fault current tests (max. 31.5 kA, 2 sec) showed that the designed HTS cable has the required withstanding performance. The development of the elemental technologies was finished on schedule, and a 15 m-long HTS cable system will be constructed to demonstrate that it meets all the required specifications.

Low AC Loss in a 3 kA HTS Cable of the Dutch Project

are: a cable has to fit in an annulus of 160 mm, with two cooling stations at the cable ends only. Existing solutions for HTS cables would lead to excessively high coolant pressure drop in the cable, potentially affecting public acceptance of the project. A way out would be to substantially reduce AC losses from 1 down to about 0.1 W/m per phase at rated current of 3 kArms, frequency of 50 Hz and temperature of 77 K. In this paper we discuss a strategy towards this ambitious goal, a concept design of the single phase cable 3 kA conductor made of YBCO tapes and present corresponding experimental and simulation data supporting the developed approach leading directly to this goal. HTS cable model was made that show a drastically reduced AC loss. The low loss was achieved by using appropriate pitch angles for two-layer cable conductor of relatively large diameter, by minimizing the gaps between the HTS tapes, and by using narrow HTS tapes that conform well to the roundness of the underlying former. AC loss of 0.12 W/m at 3 kArms was measured at a frequency of 60 Hz and at a temperature of 77 K.

Dynamic Model of an HTS Cable for Power Grid Simulation

Abstract Electric power utilities usually use conventional grid simulators to perform simulations for grid design, operation and maintenance studies. Connection of superconducting devices, such as HTS cables, to real grids addresses the need for including specially-designed models in such studies. A 1G HTS cable user-written model suitable for dynamic simulations is developed and it is applied in a sample test grid to analyze its dynamic behavior under fault conditions.