AC Power Cables Research Articles

Optimal Design and Development of Magnetic Field Detection Sensor for AC Power Cable.

The state detection of power cables is very important to ensure the reliability of the power supply. Traditional sensors are mostly based on electric field detection. The operation is complex, and its efficiency needs to be improved. This paper optimizes the design and development of the magnetic field detection sensor for AC power cables. First, through the establishment of the magnetic field sensor model, it is determined that permalloy is the material of the magnetic core, the optimal aspect ratio of the magnetic core is 20, and the ratio of coil length to core length is 0.3. Second, the coil-simulation model is established, and it is determined that the optimal number of turns of the coil is 11,000 turns, the diameter of the enameled copper wire is 0.08 mm, and the equivalent magnetic field noise of the sensor is 0.06 pT. Finally, the amplifying circuit based on negative magnetic flux feedback is designed, the sensor is assembled, and the experimental circuit is built for the sensitivity test. The results show that the sensitivity of the magnetic field sensor is 327.6 mV/μT. The sensor designed in this paper has the advantages of small size, high sensitivity, ease of carry, and high reliability.

Thermal Characteristics of the Main Structural Schemes of AC Power Cables Based on High-Temperature Superconductors

Thermal Characteristics of the Main Structural Schemes of AC Power Cables Based on High-Temperature Superconductors

Measurement of critical current of superconducting cable

The critical current of a coaxial cable made of Bi-2223 tapes was investigated to survey underlying problems, especially for the resistive voltage caused by current transfer, for the standardization of test method of the critical current of superconducting AC power cables. Five voltage taps were attached on the copper sheath of 80 mm long, which is used as a part of the current lead, on both ends for the inner conductor layer and outer shield layer. The current transfer was theoretically examined especially for the outer shield layer of a simple structure. The resistive component in the measured voltage was calculated as a function of the position of the voltage tap, and it can be shown that the critical current is correctly obtained using the electric field criterion after subtracting the resistive component, as is usually done in experiments. These results are compared with the observed results.

Optimization and Cold Test of a Triaxial 2G HTS Power Cable With High Current Capacity

Triaxial HTS AC power cables, that incorporates three HTS phases wound around a single core within a single cable is considering the optimal solution for low and medium voltages. Such a design permits to save expensive HTS conductor and to increase the power density transmitted. It is difficult to increase the transmission capacity of a triaxial cable by increasing its operating voltage and therefore, insulation thickness between phases. The other way is to increase the operation current by using a multilayer structure in each phase of the triaxial cable. This task demands a complicated optimization analysis and a precise manufacturing technology. Following our previous studies, we developed and tested the triaxial cable prototype with two layers per phase made of ReBCO wire. The optimal parameters of the cable (twist pitch, diameters of phases, etc.) have been determined using the numerical simulation methods developed. DC and AC tests of the cable has been performed. In the result, the feasibility to provide a uniform current distribution in a triaxial cable, each phase of which consists of two layers, has been demonstrated. With the outer diameter of ∼24 mm only, this is the most compact triaxial HTS power cable manufactured and tested up to date with currents up to 4 kA per phase. The anticipated power transfer with three phases of this cable can be as large as ∼34 MW.

First-principles study on superconductive properties of compressive strain-engineered cryogenic superconducting heavy metal lead (Pb)

As one of the main materials in the practical application of superconductor, lead (Pb) has been used to manufacture superconducting AC power cable and some weak current fields. With the development of manufacturing technology, more and more researchers focus on exploring the physical and chemical properties of cryogenic superconducting materials, instead of blindly pursuing the improvement of the superconducting transition temperature (T c ). In this paper, the structural properties and superconducting transition temperature under high pressure of Pb have been studied by first-principles calculations. It has shown that Pb can withstand the compressive strain up to 10% while the lattice structure remains stable, indicated by the calculations of phonon band structures. From 0% to 10% compressive strain, there is neither a band-gap nor changing of the band structure. The changing of electronic DOS at the Fermi level leads to a decreasing of T c . Our calculations show that Pb is a stable elemental metallic superconductor even under high pressure, which explains the reason why it has been used in practical productions.

Базовые технологии изготовления силовых кабелей на основе высокотемпературных сверхпроводников второго поколения

Power cables made of high temperature superconductors (HTS) are considered to be the most advanced application field of superconductivity in the electric power industry. Cables made of the first-generation (1G) HTS wires have already been put in use in electrical grids in a number of countries around the world. Active efforts are presently being taken to develop power cables made of second-generation HTS wires (2G or Coated Conductors). The basic principles for designing coaxial HTS power cables have been known since 1990s. New methods for developing compact 2G HTS AC power cables are considered. Methods to optimize the design of these cable aimed to ensure uniform distribution of the current among the cable layers and the technology for manufacturing such cables are presented. The test program and a setup for testing HTS cable models are described. Some problems pertinent to the development of small-diameter 2G HTS power cables are discussed. Examples of the development, manufacture, and test results of two basic designs of compact coaxial HTS cables, namely, a single-phase (a cable core and a shield) and a three-phase (so-called triaxial with three coaxial phases) versions, are given.

Thermal characteristics of the main structural schemes of AC power cables based on high-temperature superconductors

Thermal characteristics of the main structural schemes of AC power cables based on high-temperature superconductors

Design and Model of Series-Connected High-Voltage DC Multipliers

The generation of high dc voltages is necessary for feeding many technical applications and testing the insulation material of high-voltage dc transmission lines and ac power cables with long lengths. The article proposes a modular multiplier high-voltage dc generator with integrated Cockcroft-Walton (CW) circuits. In this new topology, CW circuits are connected in series to produce a high dc output voltage with low regulation factor (<; 2%) and a negligible ripple factor without the need for costly filters to produce a nearly constant output voltage. The modules are fed by low input ac voltage sources that have the same magnitude and frequency. Numerical simulations using MATLAB/Simulink confirm the viability of the proposed generator. The generator is finally validated by experimental tests on a kV-size prototype.

Installation of XLPE-Insulated 400 kV Submarine AC Power Cables under the Dardanelles Strait: A 4 GW Turkish Grid Reinforcement

This paper describes the 400 kV AC submarine link under the Dardanelles Strait composed of 12 submarine armoured single-core cross-linked polyethylene (XLPE)-insulated cables (plus a back-up power cable). The link consists of two parallel-operated double-circuit links named Lâpseki–Sütlüce I and Lâpseki–Sütlüce II. The transmissible power is 4000 MW (1000 MW per circuit) and the average length for a single-core cable is about 4.6 km: the submarine cables are part of overhead lines. This paper gives a wide account of the cable installations and, chiefly, of the cable protections on the seabed: different protection choices were extensively used (i.e., water jetting and mattressing).

Investigation of necessary modeling detail of a large scale EHV transmission network for slow front transients

Traditionally, extra high voltage (EHV) transmission systems consist exclusively of overhead lines (OHL) but in the recent years the utilization of high voltage AC (HVAC) power cables is increasing due to environmental, political and operational aspects. To study the impact of HVAC power cables on temporary overvoltages and slow front transients, a simulation model of the large-scale network is required. Guidelines concerning the modeling detail for the surrounding network need to be established to ensure sufficient accurate results. Existing guidelines for purely OHL transmission networks may not be adequate since the integration of HVAC power cables shift the harmonic impedance of the network to lower frequencies and that can affect the extent of the needed simulation model. Much effort can be saved from obtaining detailed data for an extensive but proper model, but a less detailed model might not describe the network behavior with sufficient accuracy. In this study, simplification options are considered, for which the time to construct and analyze a simulation model can be reduced. The simplification options are compared with the reference model (full detail), and judged based on three indicators for the level of accuracy: frequency and amplitude of the main resonance, and maximum over-voltage. As a result, guidelines on the extent of the simulated network and in which detail the model has to be built are proposed. The inverse approach, i.e. increasing level of detail until simulation results hardly change leads to similar results, but requires equivalent short-circuit networks for the rest of the grid. The method is tested for the Dutch 380kV grid where an underground cable connection of 10.8km length is introduced in 2013 and a second connection is planned for 2017.

Molecular modeling and electron transport in polyethylene

Polyethylene is commonly used as an insulator for AC power cables. However it is known to undergo chemical and physical change which can lead to dielectric breakdown. Despite almost eighty years of experimental characterization of its electrical properties, very little is known about the details of the electrical behaviour of this material at the molecular level. An understanding of the mechanisms of charge trapping and transport could help in the development of materials with better insulating properties required for the next generation of high voltage AC and DC cables. Molecular simulation techniques provide a unique tool with which to study dielectric processes at the atomic and electronic level. Here we summarise simulation methodologies which have been used to study the properties of PE at the molecular level, elucidating the role of morphology in the trapping of excess electrons. We find that polyethylene has localised states due to conformational trapping extending below the mobility edge (above which the electrons are delocalised), at -0.1±0.1eV with respect to the vacuum level. These trap states with localisation lengths between 0.3 and 1.2nm have energies as low as -0.4±0.1eV in the amorphous and interfacial regions of polyethylene with more positive values in lamella structures. Crystalline regions have a mobility edge at +0.46 ±0.1eV, so we would expect transport by electrons excited above the mobility edge to delocalised states to be predominantly through amorphous regions if they percolate the sample.

Measurements of Medium-Frequency Propagation Characteristics of a Transmission Line in an Underground Coal Mine

In underground coal mines, medium frequency (MF) communication systems couple their signals to metal infrastructures such as ac power cables and wire-based telephone lines, which guide the signals to propagate for a long distance. To better understand the propagation characteristics of MF signals, an easy-to-use measurement method was recently developed at the National Institute for Occupational Safety and Health. The method will be introduced along with an equivalent transmission line model for a long metallic infrastructure in underground coal mines. The model serves as the fundamental driver for the method development. Propagation measurements on a twisted pair of telephone lines in an underground mine were made using this method. The measurements confirmed the low MF signal attenuation rate and the dependence of the propagation characteristics of the line on the electrical properties of surrounding coal and rock as theoretical studies predicted.

Flux-transfer losses in helically wound superconducting power cables

Minimization of ac losses is essential for economic operation of high-temperature superconductor (HTS) ac power cables. A favorable configuration for the phase conductor of such cables has two counter-wound layers of HTS tape-shaped wires lying next to each other and helically wound around a flexible cylindrical former. However, if magnetic materials such as magnetic substrates of the tapes lie between the two layers, or if the winding pitch angles are not opposite and essentially equal in magnitude to each other, current distributes unequally between the two layers. Then, if at some point in the ac cycle the current of either of the two layers exceeds its critical current, a large ac loss arises from the transfer of flux between the two layers. A detailed review of the formalism, and its application to the case of paramagnetic substrates including the calculation of this flux-transfer loss, is presented.

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.

ENDESA Supercable, a 3.2 kA, 138 MVA, Medium Voltage Superconducting Power Cable

Nexans, ICMAB-CSIC, Tecnalia and UAB have collaborated on the ENDESA Supercable, a 30 m long, medium-voltage superconducting ac power cable. The cable was developed and manufactured within the framework of the ENDESA Novare program. With a rated current of 3200 A, a 3-phase system based on this cable is able to transmit 138 MVA at its envisioned operating voltage of 25 kV. While the cable was designed for 25 kV, the terminations avail able for cable testing were rated for the 20-kV class. Consequently the high voltage tests were carried out at the levels appropriate for 20 kV cable systems. The cable has successfully passed all high voltage and load cycle tests. The load cycles consisted of ten 24-hour cycles during which, with a voltage of 2 - UO applied for the full duration of the 10 test cycles, the rated current of 3200 A was applied for 8 hours. The ac losses of the cable were also measured. The successful prototype testing of the cable confirmed the de sign, manufacturing, and performance of this high transmission capacity cable: To our knowledge, it is the highest ampacity power cable so far that has passed the rigorous load cycle test protocol of a similarly rated conventional cable.

Influence of Repeated Mechanical Stresses on AC Losses in Multi-Filamentary Bi2223/Ag-Sheathed Wires

Influence of repeated mechanical stresses/strains on AC losses (transport current losses and magnetization losses) in two kinds of multi-filamentary Bi2223/Ag-sheathed wires (twisted and non-twisted) for AC power cables was experimentally investigated. Repeated uni-axial tensile stresses/strains were applied to the wires in the longitudinal direction and the AC losses were measured electrically at 77.3 K. It was found that the influence of the repeated mechanical stresses/strains on the AC losses was different in the twisted and non-twisted wires. In the paper it is shown that the differences can be characterized by assuming that there are two kinds of critical currents of a sample wire, overall critical current across whole length of the sample wire and local critical current within the sample. Those critical currents are affected differently by the repeated mechanical stresses/strains. It is also shown that differences in manners of relations between the AC loss characteristics and the two kinds of critical currents can be explained assuming that different types of defects are caused by the repeated stresses in the two kinds of the wires.

Evaluation of sea return impedance and mutual impedance between submarine AC power cables and pipelines

The paper presents a novel approach to calculate the sea return impedance related to submarine AC power cables. Moreover, in order to determine possible AC interferences generated on other submerged structures, like pipelines, also formulas for the mutual impedance are given. The approach, takes into account of the laying depth of the cable on the bottom of the sea, as well as of the sea resistivity and of the soil beneath it. Comparisons with simpler existing formulas show that, besides the sea resistivity, also the laying depth and the resistivity of the soil beneath the sea have to be taken into account for a correct evaluation of the impedances. Copyright © 2010 John Wiley & Sons, Ltd.

Sub‐sea power cables and the migration behaviour of the European eel

Abstract Coded acoustic tags and an array with moored receivers were used to study the effect of a sub‐sea AC power cable on migrating European eel, Anguilla anguilla (L.) in the Baltic Sea. Sixty eels were tagged and the migration speed was measured in a strait with a 130 kV AC power cable. Observed swimming speed over the ground was corrected for advection by the water current. Eel swimming speed was significantly lower around the cable than both north and south of the cable. No details on the behaviour during passage over the cable were possible and possible physiological mechanisms explaining the phenomenon are unknown. Further work is needed to understand the nature of the effect.

Development of HTS power cable using YBCO coated conductor

Reductions of AC losses and of cost of HTS power cables are important to put it into practical power networks. Since an YBCO-coated-conductor (YBCO tape) has higher Jc and better magnetic property than a Bi2223-Ag-sheathed-tape, an AC power cable using YBCO tapes will obtain higher performance than XLPE-cables and HTS cables using BSCCO tapes in future. Especially, an YBCO HTS cable will be expected to become a higher economical cable than a Bi cable because an YBCO tape reduced its AC losses and its wire cost. We have started developing HTS power cables using YBCO tapes. Mechanical properties, superconducting properties and other electro magnetic properties of YBCO tapes have been measured to estimate the applicability to the HTS cable. Moreover, we have developed some technologies to bring out latent potentials of YBCO tapes.

High-temperature superconducting tri-axial power cable

Encouraged by the positive test results of a 1.5-m long prototype tri-axial cable, the Southwire/ORNL team has conceived, designed and built a 5-m tri-axial cable with three-phase terminations. The three concentric superconducting phases are made of BSCCO-2223 HTS tapes, separated by layers of cold-dielectric tape. A copper braid is added as the grounding shield. The completed tri-axial cable is enclosed in a flexible cryostat. Cooling of the cable and terminations is achieved by liquid nitrogen flowing through the annulus between the cable and the cryostat. The terminations used in the cable tests are cooled by a separate liquid nitrogen stream. The resulting three-phase, cold dielectric, cable and termination design is nearly as compact as the single-phase, co-axial design developed previously by Southwire/ORNL and represents the highest known cable current density achievable in an electric AC power cable. DC testing of the 5-m cable includes V– I curves for each of the concentric HTS phases, cable heat loads at varying DC currents, liquid nitrogen flow-pressure measurements, and over-current tests. AC testing of the cable includes ac loss measurements, induced-current in the Cu-shield measurements and operation at the line voltage test. The ac losses are measured calorimetrically by measuring the temperature differential of the coolant across the cable length due to the ac loss in the superconductors. Both balanced and un-balanced currents among the three phases are used in ac loss and induced current measurements.