Conductor Strands Research Articles

Intermittent Audio Failure Analysis of a Remote Speaker-Microphone for a Two-Way Radio

This paper presents a case study of an intermittent audio failure analysis of a remote speaker-microphone module for a two-way radio. A root cause analysis was undertaken to identify probable causes of the intermittent failure, followed by a series of experiments to determine the strength and the intermittent audio failure load of cable components and the fully assembled cable. The combined experimental and finite element results demonstrated that the main contributor of the intermittent audio failure was the micro surface cracks on the copper conductor strands. In addition, the combination of the component materials and design of the cable have also contributed to the non-uniform state of residual stress induced in the copper conductors which have reduced the ability of the copper conductors to withstand the normal handling load under the influence of micro surface cracks.

Cable-in-Conduit Conductor Fabrication for the Hybrid Magnet of CHMFL

The superconducting magnet for a 40-T hybrid magnet is being developed at the High Magnetic Field Laboratory, Chinese Academy of Sciences. The hybrid magnet consists of a resistive insert and a superconducting outsert providing 29 and 11 T, respectively. The superconducting magnet was designed to be wound with four grades of cable-in-conduit conductors (CICCs). The superconducting coils contain over 5000 kg of $\hbox{Nb}_{3}\hbox{Sn/Cu}$ CICC in seven piece lengths. Three dummy conductors and seven prototype conductors have been successfully fabricated without incident. The conductor design, strand cabling, and conductor fabrication details will be introduced in this paper.

LineScout Technology Opens the Way to Robotic Inspection and Maintenance of High-Voltage Power Lines

Historically, the inspection and maintenance of high-voltage power lines have been performed by linemen using various traditional means. In recent years, the use of robots appeared as a new and complementary method of performing such tasks, as several initiatives have been explored around the world. Among them is the teleoperated robotic platform called LineScout Technology, developed by Hydro-Québec, which has the capacity to clear most obstacles found on the grid. Since its 2006 introduction in the operations, it is considered by many utilities as the pioneer project in the domain. This paper's purpose is to present the mobile platform design and its main mechatronics subsystems to support a comprehensive description of the main functions and application modules it offers. This includes sensors and a compact modular arm equipped with tools to repair cables and broken conductor strands. This system has now been used on many occasions to assess the condition of power line infrastructure and some results are presented. Finally, future developments and potential technologies roadmap are briefly discussed.

Investigation of Frictional Force Applied to Strands Surrounded by Other Strands and Tribological Analysis of Contact Surface in CIC Conductor

At the SULTAN test facility, the assessment of the performance of toroidal field coils has been progressing. Unpredictable strand buckling was observed during the destructive investigation of the conductor after significant degradation of the current sharing temperature. The buckling direction was perpendicular to the Lorentz force (LF), and the mechanism causing this was due to the thermal shrinkage occurring because of the difference in the thermal contraction between the strand material and the stainless steel conduit. Our previous research was based on a two-dimensional string model and demonstrated that the observed 2 mm strand bending could have led to strand buckling if the total amount of slide at the contact crossover was assumed to be 80 μm. To verify this assumption, we fabricated a device for the measurement of the friction force (shear force) between strands under a constriction force comparable to the LF of several hundred of kilonewtons per meter. The results for a Cr-coated 0.89 mm diameter strand surrounded by bare Cu strands indicated that the thermal contraction force would be sufficient to overcome the static friction force when the contraction force is reduced to a tenth of the maximum LF. The mechanism of the slide motion could be divided into two processes: separation of the inner wall of the conduit and the gradual separation from other strands due to a gradual reduction of the LF. A tribological analysis revealed that the real contact area increases by 10% when the shear force is applied; this result would help us evaluate the contact resistance between strands of conductors.

Torsional Stability of Research and Discussion on the Conductor-Spacers System

According to the instance of turnover and twist of conductor-spacers system,a question of torsional stability of conductor-spacers system is proposed.The paper analyzes the reason why the torsional instability of the entire system occurs and puts forward that the residual torque moment has existed during the process of conductor stranding,which creates a security risk to the stability of the system.In addition,the torque moment caused by the uneven ice-covering and different periods of ice-shedding will leave the system unbalanced.Finally, methods of improving the stability of conductor-spacers system is discussed.

Curvature Analysis of ${\rm Nb}_{3}{\rm Sn}$ Strands in React and Wind CIC Conductor for Fusion Magnets

The Cable-In-Conduit Conductor (CICC) is the most promising one for large scale fusion magnets. Now it has been adopted as conductors for ITER magnets. Although the conductor has good mechanical strength against large electromagnetic force, the performance is not so good because the Nb3Sn strands are fragile and the critical current density is sensitive to strain. Because conductor is composed of hundreds or thousands of strands which are twisted and become tangled, the strands experience extra-bending during energizing magnets. It seems so difficult to analyse plastic deformation of the strands of whole conductor. Our approach to calculate it is unique in terms of using structural mechanics called “Beam Model” based on the measured strand traces inside the conduit. The calculated traces provide us the local curvatures of strands under electromagnetic force. This leads to the evaluate the conductor performance such as Ic degradation.

Theoretical Study on Ac Loss Properties of REBCO Superconducting Two-Strand Parallel Conductors Exposed to a Non-Uniform Magnetic Field

Abstract RE1Ba2Cu3O7-δ(RE: Rare Earth, Y Gd and so on, REBCO) superconducting tapes have great performance in critical current density, J c, property even at liquid nitrogen temperature. However, it is necessary to enhance a current capacity for practical use. We proposed the configuration of parallel conductors and adopted it to several pieces of test transformers, e.g. a 66kV-2MVA one for a power grid, 25kV-4MVA one for a Shinkansen rolling stock, and so on. The constituent strands of parallel conductors need to be insulated and transposed for the sake of uniform current distribution and low ac loss. In case the transposition points deviate from the optimum ones, shielding current is induced according to the interlinkage magnetic flux of the twisted loop enclosed by the insulated strands and the contact resistances at the terminals. It produces an additional ac loss. Up to now, we have studied in the simple situation where parallel conductors are exposed to a uniform ac magnetic field. In this study, we studied the additional ac losses in the case that two-strand parallel conductors are located in non-uniform magnetic field. We derived theoretical expressions of the additional ac losses and discussed the dependences of them on the non-uniformity in magnetic field, the deviation length of the transposition point from the optimum one, and so on.

Thermal characterization of mica–epoxy composite used as insulation material for high voltage machines

The study of mica–epoxy-based composite has a great role in high voltage machines industry. Beside electric properties, this composite should present compatible mechanical and chemical, in this case thermal characteristics to insulate properly the conductor strand, avoiding short-circuits, and leading electrical current with minimal losses. Improvement of the quality is possible through the knowledge of raw materials and system. This study aims to list a complete thermal characterization of mica composite, its components, epoxy resin, anhydride methylhexahydrophtalic, mica tape and zinc naphthenate, and thermoanalytical interactions between them. These data shows intrinsic properties of the system, which is so relevant to its great electrical and thermal performance. Thermal analysis allows the detailed study of curing process and thermal decomposition, predicting and suggesting mechanisms, beside future and possible optimization to the system. Composite system glass transition (Tg) was obtained through an important and very respected methodology, presenting the value of Tg = 138 ± 2 °C, finally characterizing the material.

Current carrying capability of HTS Roebel cable

We have developed a numerical technique to estimate the current carrying capability of HTS Roebel cable composed from coated conductor strands. The influence of self-field on the critical current density is studied computationally for a Roebel cable using a realistic field and angle dependence behaviour of critical current. The computations are carried out for N/2 (number of strands/strand width in mm), and N/5 Roebel cable for N = 2–15. The local current distribution in each strand satisfies the self-consistent criteria J = J c( B( J)) except for a small region where the current density is set to zero to maintain the condition of equal currents in all strands. The variation of critical current with vertical and horizontal separation between the strands is also investigated. Results are compared with the measured values of critical current for some of our cables. The comparison shows an error of up to 10% which we attribute mostly to the model not accounting for the spread in I c values of the constituent strands.

Variable-resistance conductors (VRC) for power-line de-icing

Abstract Ice storms can result in accumulation of ice on structures, including overhead power transmission and distribution lines and associated poles and towers; this ice may reach thicknesses of many tens of millimeters. Icing can cause catastrophic damage which disrupts power transmission and is expensive to repair. Normal operation of a power transmission or distribution line entails Joule heating of the conductor as current flows through it. Lines are normally designed to have a constant, low resistance, so as to avoid excessive power losses and avoid excessive operating temperatures. Because the normal heating is low (by design), it is of limited value in preventing or recovering from an icing event. This paper describes power conductors that can switch their electrical resistance from a very low value, to transmit electric energy, to a much higher value, for de-icing. The switching in between two conductor resistances does not disturb the main conductor function, which is to provide a customer with uninterrupted electric power. A variable-resistance conductor (VRC) is built of N strands (or groups of strands) insulated from each other, where N is any odd integer greater than one. For instance, N = 3, 5 or 7, etc. In normal energy-transmission operations all the conductor strands (or strand groups) are connected in parallel, whereas in de-icing mode they all are connected in series. Switching from parallel to series connection increases the line resistance by a large factor of N2, making the resistance sufficiently high for heating the line above the ice melting point. One important advantage of the method is that it uses low-voltage and, thus, low-cost switches. The design of a VRC de-icing system is described, including considerations for switches, conductors, control and deployment strategy. We also describe safety devices to return the line to normal operation if the electronics get damaged. Laboratory and full-scale prototypes have both successfully demonstrated the capability of VRC de-icing.

Investigation of Irregular Strand Positions Causing Additional AC Losses in CIC Conductor

AC losses with long time constants can not be simply estimated from a short sample conductor because there are many irregular loops formed by strands strongly displaced from their original positions. In our previous work, we measured trajectories of 81 strands of NbTi conductor and it was proved that strongly displaced strands produced many line contacts with other strands, and thereby caused low contact resistance and long time constants. Long loops due to the displacement of strands should also produce large AC loss because the time constant of the loss is proportional to the inductance, i.e., the length of coupling current loops. In order to investigate the long loops in practical conductors, we developed a method to estimate the strand positions over the entire length. In this method, only one cross section of the conductor is required to calculate gravities of each sub-cable. The strand trajectories are obtained in a manner that the same order sub-cables rotate around the gravity to form one order higher sub-cable. The estimated trajectories are in good agreement with the measured ones, with errors of 1 mm.

Results of magnet tests as a basis for the design of ITER magnets

To ensure the availability of the ITER magnets an extensive development programme has been executed to demonstrate that the technology is available on industrial scale. This programme included two major projects, firstly the development and testing of a central solenoid model coil (CSMC) with additional testing of high field inserts and secondly the development and testing of a toroidal field model coil (TFMC), both supported by investigations on conductors, structural material and critical components. The model coils have been successfully developed, fabricated and tested in dedicated test facilities at JAERI/Naka (CSMC) and Forschungszentrum Karlsruhe (TFMC), respectively. The tests confirmed that the design criteria are met by the model coils and the ITER coils can be built on this basis. Of course, the tests showed also in which areas improvements should be implemented. One concerns the Nb 3Sn conductor. To guarantee the defined margin of the current sharing temperature, advanced conductor strands with higher critical current density than those used in the model coils have to be used and are available now. The codes for mechanical behaviour, ac loss predictions and thermohydraulic behaviour gave rather good agreement with the measurements, but can still be improved. Quality assurance issues concern high voltage properties and leak tightness.

Effective bending strain estimated from Ic test results of a D-shaped Nb 3Al CICC coil fabricated with a react-and-wind process for the National Centralized Tokamak

Japan National Centralized Tokamak (NCT) is a superconducting tokamak proposed as a modification to JT-60U. As part of the R&D for the National Centralized Tokamak, a two-turn, approximately 2 m tall, D-shaped Nb 3Al coil was wound and tested using a full-size cable-in-conduit conductor (CICC). The Nb 3Al cable-in-conductor was bent following the heat treatment reaction with a maximum bending strain of 0.4% to simulate the react-and-wind fabrication. The comparison of the coil performance to the measured strand data shows that the effective axial strain of the conductor strands is essentially zero despite the 0.4% bending strain of the conductor. This suggests that the strands in the cable slipped relatively to each other during bending of the conduit, thus reducing the effective strain transmitted to the strands. This result is very encouraging for the low-cost fabrication of high-current-density fusion coils using the react-and-wind method.

Effect of micro and macrononhomogeneity of Nb3Sn strands on E–I characteristics

Abstract The peculiar feature of Nb 3 Sn diffusion grown layers is the presence of intrinsic regions, which differ by the composition and microstructure. These regions can be treated as Nb 3 Sn macrononhomogeneity. Internal stresses and composition fluctuations in Nb 3 Sn grains can be associated with the micrononhomogeneity. Both types of the inhomogeneites exhibit itself in the shape of superconducting transition characteristics. In the present work voltage–current and voltage–temperature curves were studied for Nb 3 Sn model flat conductor and ITER type multifilamentary strands.

Practical neutral-axis conductor geometries for coated conductor composite wire

To optimize mechanical properties, particularly under bending deformation, a composite laminated architecture is proposed for second generation high temperature superconducting (HTS) coated conductor wire in which the superconductor layer is located at or near the neutral mechanical axis. ‘Neutral-axis’ conductors, each approximately 7 cm long, were fabricated by solder-laminating copper strip onto silver-coated HTS coated conductor strands. ‘Neutral-axis’ and non-laminated samples were bend/reverse-bend tested on mandrels of successively smaller diameters while measuring critical current after each reduction in mandrel size. The ‘neutral-axis’ samples showed significantly improved Ic retention compared to the non-laminated strands.

Forensic Engineering - Testing Of Hostile Electrical Connections In A Residential Clothes Dryer

A Fire Occurred In A Residence That Was Being Utilized As A Day Care Center. All Parties Involved In The Initial Investigations Into The Fire Cause Agreed That The Fire Originated In The Laundry Room In The Vicinity Of The Electric Clothes Dryer. The Plaintiffs Expert Opined That The Dryer Was Defectively Designed And Hence Caused The Fire. This Writer Was Retained By The Manufacturer Of The Dryer And Asked To Determine The Most Probable Failure Mode And To Test An Exemplar Dryer In Order To Validate Those Observations. The Ignition Point Appeared To Be At A High Resistance Electrical Connection At The Dryer Heater Box Involving Both Copper And Steel. (See Figure 1) Initial Examination Of The Clothes Dryer At The Residence Revealed That The Dryer Heater Circuitry Connection Had Been Modified. One Of The Male Prongs Had Been Removed, The Insulating Material Stripped Back And The #10 Awg Stranded Copper Wire Was Partially Inserted And Held In Place By A Common Steel Wood Screw. (See Figure 2) The Conductor Strands And The Wood Screw Appeared Heavily Heat Stressed And Appeared To Be A Viable Ignition Source. A Few Inches Away Black Electrical Tape Was Deformed By Heat But Not Fully Combusted. (See Figure 3) This Connection Was Duplicated On An Exemplar Dryer Test Stand And Under Operating Conditions Ignited Lightweight Fabrics.

HTS transposed cable conductor and round shape strand

Bi-2223 round shaped strands were developed for realizing a HTS transposed cable conductor. The maximum critical current density ( J c) of a short sample was 3.2×10 8 A/m 2 without external magnetic field at 77 K, and the J c of 50 m class long length strands was 1.6×10 8 A/m 2 at the same condition. We prepared subcables consisted of the round shape strands. Using subcables, a HTS transposed conductor was fabricated, and investigated the DC and AC performance. The conductor I c was 900 A as 10 −4 V/m (77 K, 0 T) criterion. Measured AC loss was compared with the theoretical loss considering of the magnetic field distribution and J c– B dependence of the strand. It was confirmed that the experimental and theoretical values were nearly identical.

Magnet and superconductor development for a high power SMES based power modulator

A superconducting magnetic energy storage (SMES) based power modulator is being developed by the Forschungszentrum Karlsruhe for the proposed TESLA (TeV Superconducting Linear Accelerator) project, under development at the Research Centre DESY, Hamburg. Given the high power (25 MW), high dB/dt (above 50 T/s) pulses required for this application, a cored Rutherford cable with copper oxide insulated strands of mixed matrix NbTi conductor was chosen, to minimize AC losses. The modulator magnet will utilize a structure to provide good cooling of the liquid helium cooled conductor. Optimization of the magnet system with respect to stray magnetic field and costs has led us to choose two solenoids in antiparallel orientation. A test solenoid was constructed and tested, to measure conductor performance and AC losses. The current distribution in the individual strands of the cable was measured at different current ramp rates, through the use of low resistance shunts. Results of these tests and calculations are presented, along with details of the full sized magnets for the modulator.

Clinical evaluation of a thin bipolar pacing lead.

The main disadvantages of bipolar pacing leads have traditionally been related to their relative thickness and stiffness compared to unipolar leads. In a new "drawn filled tube" plus "coated wire" technology, each conductor strand is composed of MP35N tubing filled with silver core and coated with a thin ETFE polymer insulation material. This and parallel winding of single anode and cathode conductors into a single bifilar coil resulted in a bipolar lead (ThinLine, Intermedics) with a body diameter and flexibility similar to unipolar leads. The lead is tined, polyurethane, with the cathode and the anode made of iridium-oxide-coated titanium (IROX). The slotted 8-mm2 cathode tip is coated with polyethylene glycol, a blood soluble material. We present the clinical evaluation results from four pacemaker clinics, where 47 leads (23 atrial-J model 432-04 and 24 ventricular model 430-10) were implanted in 25 patients and followed for up to 2 years. The lead handling characteristics were found to be very satisfactory. Electrical parameters of the leads were measured at implant and noninvasively on postoperative days 1, 2, 21, 42, and months 3, 6, 12, and 24. Mean chronic pulse width thresholds at 2.5 V were 0.14 +/- 0.05 ms in the atrium and 0.10 +/- 0.02 ms in the ventricle, pacing impedances 443 +/- 104 omega and 520 +/- 241 omega, while median electrogram amplitudes were > or = 3.5 mV and > or = 7 mV, respectively. Pacing impedances and thresholds were found to be slightly but statistically significantly higher in unipolar than in bipolar configuration--the findings are explainable by the lead construction. One of 47 leads failed 3 weeks after implant; the conductors were short circuited due to an error during the manufacturing process. We conclude that the new lead thus far has demonstrated appropriate mechanical and electrical characteristics.

Accelerated cable life testing of EPR-insulated medium voltage distribution cables

This paper presents results aimed at developing a reliable accelerated aging tank test for EPR-insulated cables. Aging was performed at 2 to 4 times rated voltage on load cycling to temperatures of 45/spl deg/C, 60/spl deg/C, 75/spl deg/C, and 90/spl deg/C at the conductor with water in the conductor strands and outside the cable. Results show that cable failure is more rapid at the highest electrical stress and lowest conductor load cycle temperature. Cables aged at higher temperatures and various levels of electrical stress rarely failed and retained in excess of 40% of their original breakdown strength after 1500+ days of aging. Aging performed at 90/spl deg/C load cycle temperature and 4 times rated voltage with air on the outside and water at the conductor of the cable showed more rapid loss of life than with water outside. Results indicate the optimum aging conditions for EPR-insulated cables in the accelerated cable life test (ACLT) differ significantly from those previously observed for XLPE-insulated cables, and that the appropriate test methodology for EPR-insulated cables requires additional study.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>