Power Transmission Cables Research Articles

AC Loss Reduction of Superconducting Power Transmission Cables Composed of Coated Conductors

AC losses in power transmission cables composed of coated conductors could be potentially small. A strategy to approach their potentially small AC loss was studied. AC losses in mono-layer conductors for cables were calculated numerically in order to show the principle for AC loss reduction: use of narrower coated conductors and/or decrease in space between conductors reduce the magnetic field component perpendicular to the wide face of coated conductors, and they are effective for AC loss reduction. This principle was confirmed experimentally by using short mono-layer conductors. Based on the principle, 1 kArms-class three-layer conductors were fabricated, and AC loss of 0.054 W/m at 1 kArms was achieved in a three-layer conductor whose outer diameter is 19.6 mm. The influence of a magnetic substrate on the AC losses in a single coated conductor and a mono-layer conductor for a cable was studied numerically.

Numerical study on AC loss characteristics of superconducting power transmission cables comprising coated conductors with magnetic substrates

Electromagnetic field analyses were made for mono-layer conductors comprising coated conductors for superconducting power transmission cables in order to evaluate their AC loss characteristics. We focused on the magnetic properties of the substrates of coated conductors. The current distribution in each coated conductor and the magnetic flux profile around each coated conductor were visualized. The influence of relative permeability and the space between coated conductors on the AC loss characteristics of mono-layer conductors were studied based on the visualized current and magnetic flux distributions. The influence of a saturated magnetic property on a calculated AC loss was also discussed.

Influence of Ethylene Ionomers on the Electrical Properties of Crosslinked Polyethylene

AbstractSummary: Water treeing is a deterioration mechanism observed in the polymeric insulation of extruded cables, which can affect the service life of the transmission and distribution XLPE power cables. To improve the water‐tree resistance of XLPE, it was blended with sodium‐neutralized EAA‐Na ionomers which were formed by neutralization of EAA with NaOH. A series of XLPE/EAA‐Na ionomer blends were investigated for their electrical properties, such as water treeing, electrical breakdown strength, dielectric constant, and dissipation factor. The results strongly suggest that EAA‐Na ionomers can improve the water‐tree resistance of XLPE, and the XLPE/EAA‐Na blends retain excellent dielectric properties. Characterization of XLPE/EAA‐Na blends by using FTIR indicates that the neutralization reaction is effectively achieved. In addition, it can be found that XLPE/EAA‐Na blends are partially compatible from observing morphology observations made by SEM and, therefore, EAA‐Na ionomers can be well dispersed in the matrix.Water tree length of the XLPE/EAA‐0.5Na blends.magnified imageWater tree length of the XLPE/EAA‐0.5Na blends.

Analysis on Current Distribution of Four-Layer HTSC Power Transmission Cable with a Shield Layer

The inductance difference between conducting layers of high-T c superconducting (HTSC) power transmission cable causes the current sharing of each conducting layer to be unequal, which decreases the current transmission capacity of HTSC power cable. Therefore, the design for even current sharing in HTSC power transmission cable is required. In this paper, we investigated the current distribution of HTSC power cable with a shield layer dependent on the pitch length and the winding direction of each layer. To analyze the effect of the shield layer on the current sharing of the conducting layers of HTSC power cable, the current distribution of HTSC power cable without a shield layer was compared with the case of HTSC power cable with a shield layer. It could be found through the analysis from the computer simulations that the shield layer of HTSC power cable could be contributed to the improvement of current distribution of conducting layers at the specific pitch length and the winding direction of conducting layer. The result and discussion for the current distribution calculated for HTSC power transmission cable with a shield layer were presented and compared with the cable without a shield layer.

Transient analysis for alternating over-current characteristics of HTSC power transmission cable

In this paper, the transient analysis for the alternating over-current distribution in case that the over-current was applied for a high-TC superconducting (HTSC) power transmission cable was performed. The transient analysis for the alternating over-current characteristics of HTSC power transmission cable with multi-layer is required to estimate the redistribution of the over-current between its conducting layers and to protect the cable system from the over-current in case that the quench in one or two layers of the HTSC power cable happens. For its transient analysis, the resistance generation of the conducting layers for the alternating over-current was reflected on its equivalent circuit, based on the resistance equation obtained by applying discrete Fourier transform (DFT) for the voltage and the current waveforms of the HTSC tape, which comprises each layer of the HTSC power transmission cable. It was confirmed through the numerical analysis on its equivalent circuit that after the current redistribution from the outermost layer into the inner layers first happened, the fast current redistribution between the inner layers developed as the amplitude of the alternating over-current increased.

AC loss characteristics of Bi-2223 HTS tapes under bending

Superconductor is developed for applications in high-power devices such as power-transmission cables, transformers, motors and generators. In such applications, HTS tapes are subjected to various kinds of stress or strain. AC loss is also important consideration for many large-scale superconducting devices. In the fabrication of the devices, the critical current (Ic) of the high temperature superconductor degrades due to many reasons including the tension applied by bending and thermal contraction. These mechanical loads reduce the Ic of superconducting wire and the Ic degradation affects the AC loss of the wire. The Ic degradation and AC loss of Bi-2223 HTS tape were measured under tension and bending conditions at 77K and self-field. Moreover, the frequency characteristics of AC loss was measured at the 30–480Hz. As a result, self-field penetrates the deeper into the conductor at the lower frequency, which means higher self-field losses per cycle.

Feasibility study on a new three-phase power transmission cable with radial arrangement of superconducting tapes

A new type of superconducting power transmission cable is proposed to fulfill both the conditions of low AC loss and rare leakage magnetic flux. A lot of superconducting tapes are arranged radially, and three-phase currents are applied one by another in the azimuthal direction. If the number of tapes is a multiple of three, the leakage flux can become very small. The AC loss in the superconducting tapes can also be suppressed because of the reduction of a magnetic field applied perpendicular to the tape face with increasing the number of tapes. The numerical estimation of AC losses in the proposed power cables is carried out by means of a finite element method as well as those in the conventional types of cables.

Magnetization Loss and Shield Effect in Multi-Stacked Tapes With Various Stacking Configurations

AC loss is one of the major topics in large AC power applications using high temperature superconductor such as power transformers, transmission cables and fault current limiters because it is closely related to operation efficiency. Multi-stacked tape conductors should be used to transport the large current in those power applications. A research of various arrangements of HTS tapes for multi-stacked tapes has been performed to increase the capacity of transport current in HTS power applications. In this paper, we studied magnetization loss and shield effect from several different arrangements of BSCCO tapes such as Face-to-Face type, regular matrix type (m <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$times$</tex> 2) and irregular matrix type. The results show that the magnetization loss of the Face-to-Face arrangement was lower than those of the other matrix types for the same stacking numbers. We think that the result was due to the shield effect by demagnetization of adjacent HTS tapes which were located as face to face.

The design and construction of a controllable reactor with a HTS control winding

Reactive power compensation is vital for obtaining efficient operation of long transmission power lines or cables. The need of reactive power changes with the load of the transmission line. Discrete units of conventional reactors are therefore switched in and out in order to obtain more efficient reactive power compensation. A continuous reactive compensation will reduce the transmission losses and increase the transmission capacity of active power. We have designed and constructed a one phase small scale prototype of a controllable shunt reactor with a high temperature superconducting control winding. The reactor consists basically of two windings and an iron core. The control winding is placed so that it generates a DC magnetic field perpendicular to the main AC magnetic field. Thus the DC current in the control winding can control the direction of the magnetization of the iron core and thereby the reactance of the reactor. Such a control winding will have low losses and give the reactor a large dynamic range. For this small scale reactor we found that the reactive power could be varied with a factor six. We have demonstrated the feasibility to design large scale controllable shunt reactors with large dynamic range and low losses utilizing a control winding made of a high temperature superconductor.

Fault Management of a Cold Dielectric HTS Power Transmission Cable

High temperature superconductor (HTS) power transmission cables offer significant advantages in power density over conventional copper-based cables. As with conventional cables, HTS cables must be safe and reliable when abnormal conditions, such as local and through faults, occur in the power grid. Due to the unique characteristics of HTS power cables, the fault management of an HTS cable is different from that of a conventional cable. Issues, such as nitrogen bubble formation within lapped dielectric material, need to be addressed. This paper reviews the efforts that have been performed to study the fault conditions of a cold dielectric HTS power cable. As a result of the efforts, a fault management scheme has been developed, which provides both local and through faults system protection. Details of the fault management scheme with examples are presented

Field Test and Short-circuit Test of HTS Power Cable

In order to cope with the increase in the electric power demand and an alternative technology to the conventional electric power transmission cables, it's hoped that high temperature superconducting (HTS) cable is developed. In case the HTS cable is introduced into the actual power grid, its length can extend up to several kilometers. The flow properties of liquid nitrogen (LN2) that is a coolant of the HTS cable have not been understood yet. Thus, CRIEPI, Furukawa Electric and Super-GM had constructed an HTS cable test system with its length of 500 m. The rated voltage is 77 kV corresponding to one of the major voltage level of medium-voltage transmission lines. The rated current is 1 kA. We had carried out a numerous set of tests such as measurement of LN2 flow properties, current flow properties, electrical insulation properties, thermal insulation properties and so forth. In addition, short-circuit test was carried out using 10 m HTS cables that is same structure as the 500 m HTS power cable. The test was conducted with the supply voltage of 16 kV and the prospective short-circuit current of 31.5 kA using a short-circuit generator.

Influence of gaps in monolayer superconducting cable on AC losses

AC transport loss in a core of superconducting power transmission cable has been investigated by numerical simulations. We assumed that the core consists of superconducting tapes distributed symmetrically on a cylindrical surface. It is well-known that the ideal geometry, from the point of AC-losses, would be a single uniform superconducting layer. However, the manufacturing of cable requires that superconducting tapes are separated from each other. On that account, the Brandt's method was used to study and evaluate how the size of gaps between tapes would influence the AC losses. The considered tapes have rectangular shape with aspect ratio similar to the filamentary zone of commercial Bi2223/Ag tapes. For this material the critical current density sharply decreases with magnetic field. Therefore, we have assumed a dependence of the critical current density on magnetic field in our calculations (jc(B) dependence). Our simulations show how the increasing of the gaps size results in an increasing of AC-losses. This can be used to find the compromise between an easy manufacturing of cable and the low AC-losses.

Sheath fault detection and classification based on wavelet analysis

AbstractThis paper presents a wavelet based algorithm to detect and classify sheath insulation faults on underground transmission cables. This algorithm can detect a high impedance sheath to earth fault, classify it, and discriminate it from other phenomena, such as load change, harmonics and surges on the cores. For the development of the algorithm, a simplified fault model is introduced to simulate a sheath to earth fault on a power transmission cable. Before applying wavelet analysis, an ‘adaptive noise cancelling’ (ANC) technique is used to extract the fault signal. Simulation studies are reported on a 300 mm2 concentric copper PVC insulated bonding lead. Copyright © 2006 John Wiley &amp; Sons, Ltd.

Development of a single-phase 30 m HTS power cable

HTS power transmission cables appear to be the replacement and retrofitting of underground cables in urban areas and HTS power transmission cable offers a number of technical and economic merits compared to the normal conductor cable system. A 30 m long, single-phase 22.9 kV class HTS power transmission cable system has been developed by Korea Electrotechnology Research Institute (KERI), LS Cable Ltd., and Korea Institute of Machinery and Materials (KIMM), which is one of the 21st century frontier project in Korea since 2001. The HTS power cable has been developed, cooled down and tested to obtain realistic thermal and electrical data on HTS power cable system. The evaluation results clarified such good performance of HTS cable that DC critical current of the HTS cable was 3.6 kA and AC loss was 0.98 W/m at 1260 Arms and shield current was 1000 Arms. These results proved the basic properties for 22.9 kV HTS power cable. As a next step, we have been developing a 30 m, three-phase 22.9 kV, 50 MV A HTS power cable system and long term evaluation is in progress now.

Magnetic circuit for a controllable reactor

Reactive power compensation is vital for obtaining efficient operation of long transmission power lines or cables. A controllable shunt reactor that controls the transmission of power by continuous reactive power compensation will reduce the transmission losses and increase the transmission capacity of active power. We show that the saturation phenomena of iron and the high current density of a high-temperature superconductor can be utilized to design controllable reactors with large dynamic range, low losses, and limited harmonic distortion. We have designed and constructed a small-scale prototype of a controllable shunt reactor with a high-temperature superconductor control winding. We present a simple model of the magnetic circuit of the controllable reactor and we compare calculations from the model to experimental measurements on the controllable reactor

AC losses in multifilamentary Bi-2223/Ag tapes subjected to bending strains

Electrical power devices, e.g. motors, power transmission cables, transformers, etc. are the most promising, and nowadays the most technologically advanced, applications of high temperature superconductors (HTS). Multifilamentary HTS tapes (usually Bi-2223/Ag composites) are used in forms of various in shape coils, therefore are subjected to different kinds of mechanical stresses. This leads to some changes in physical parameters of superconducting material, mainly in the critical current density, and thus in the dissipated electromagnetic energy. In general, when a superconductor is carrying an AC transport current and simultaneously subjected to an external AC magnetic field, the total dissipated energy can be considered as a sum of components, the transport loss and the magnetization loss. In this work we report some experimental results related to the total AC loss characteristics of Bi-2223 tapes and their dependencies on bending strains. An external magnetic field, in phase with an AC transport current, was directed parallel to the wider surfaces of the samples. The total AC losses in the Bi-2223/Ag tapes were measured by means of a calorimetric method. Obtained experimental data are compared with the critical state model predictions for total losses behavior in presented here experimental conditions.

Demonstration and Verification Tests of 500 m Long HTS Power Cable

A high-temperature superconducting (HTS) power transmission cable is considered as one of the next-generation power transmission technologies. The introduction of HTS cables into the actual power grid requires a long-distance cooling tube, due to the location of the cooling stations at intervals of several kilometers along the cable length. Therefore, it is essential to understand the flow property of the liquid nitrogen as a coolant for the HTS cable, the current flow properties, electrical insulation characteristics, thermal insulation properties and mechanical behavior for the HTS cable taking into account its long length. This paper provides a brief summary of the HTS cable test system with a length of 500 m constructed in the Yokosuka area of CRIEPI.

Microstructures of High-&amp;lt;tex&amp;gt;$rm T_c$&amp;lt;/tex&amp;gt;Superconducting Films Having Artificial Pinning Centers

REBa/sub 2/Cu/sub 3/O/sub y/ (REBCO) is expected to be used in numerous applications, such as power transmission cables, high-field magnets and generators, due to the possibility of a high critical current density at 77 K under a high magnetic field. Biaxially textured REBCO superconducting tapes are developed to obtain high-J/sub c/. However, the J/sub c/-B characteristics of REBa/sub 2/Cu/sub 3/O/sub y/ films have a magnetic field angle dependency. When the magnetic field is applied parallel to the film surface, the reduction in J/sub c/ is not larger under a high magnetic field of 10 T. When the magnetic field is applied perpendicular to the film surface, the reduction in J/sub c/ is significantly large under a magnetic field of more than around 5 T at 77 K. From the viewpoint of realizing wide applications of high-T/sub c/ superconductors, it is important to improve the J/sub c/-B characteristics of REBCO films under magnetic fields higher than 5 T applied perpendicular to the film surface. Our group focuses on artificial pinning centers (APCs) introduced into REBCO films. The J/sub c/-B characteristics of certain films are improved by the introduction of APCs. The microstructures of these films are investigated using transmission electron microscopy (TEM). We report on the microstructures of REBCO films with APCs.

Influence of Pitch Length and Winding Direction on Four-Layer HTSC Power Transmission Cable With a Shield Layer

The design for even current sharing in high-T/sub C/ superconducting (HTSC) power transmission cable is required to increase the current transmission capacity and decrease the AC loss. Increasing the contact resistance of each layer is effective method for achieving the uniform current distribution among conducting layers. However, this method increases the power loss and causes the efficiency of HTSC cable system to decrease. Another method to adjust the pitch length and the winding direction of each layer is complicated, which is difficult for the cable designer to find a simple solution for the uniform current distribution. In this paper, we investigated the current distribution of HTSC cable dependent on the pitch length and the winding direction of each layer for two cases: four-layer HTSC cable with a shield layer and four-layer HTSC cable without a shield layer. It could be found through the analysis from the computer simulations that the shield layer of HTSC cable could contribute to the improvement of current distribution of each layer at the specific pitch length and winding direction. The result and discussion for the current distribution calculated for HTSC power transmission cable with a shield layer were presented and compared with the cable without a shield layer.

Development and Testing of 30 m HTS Power Transmission Cable

To obtain realistic data on HTS power cable, single-phase 30 m long, 22.9 kV class HTS power transmission cable system have been developed by Korea Electrotechnology Research Institute (KERI) and LG cable Ltd. that is one of 21st century frontier project in Korea. The HTS cable consists of Ag/Bi-2223 tapes, high voltage insulation paper which is impregnated by LN/sub 2/. The cable is rated at 22.9 kV, 50 MVA, 60 Hz and is cooled with pressured liquid nitrogen at temperature from 70 to 80 K. This paper describes the results of design, fabrication and evaluation of the single-phase, 30 m HTS power cable system.