Conductor Size Research Articles

Thermal and Mechanical Design of Error Field Correction Coil for JT-60SA

The inhomogeneous poloidal magnetic field of tokamak device, which is called error field, has to be reduced because the error field degrades the plasma performance. There are 18 sets of EFC coils installed inside the vacuum vessel for JT-60SA to compensate the error field. The conceptual design of EFC coils has been completed. The water-cooled hollow copper conductor was selected to reduce the conductor size since the available space for EFC coils is small. The outer size of the conductor and the diameter of the cooling channel were optimized in considering hydraulic and thermal characteristics. The design of the conductor was validated by the testing of a mock-up coil. The bar springs are used for the structure of EFC coils. The structural analysis was performed to optimize the parameters of bar springs. The results of structural analysis suggest that the structure of EFC coils can be used for both the conditions of plasma operation and baking operation with the use of Inconel625 for bar springs. In this paper, the specification of the JT-60SA EFC coils, the test results of mock-up coils, and the structural analysis results of the EFC coil structure are described. The manufacture of EFC coils has started based on these designs.

Planning of unbalanced radial distribution systems using differential evolution algorithm

This paper presents a planning approach for unbalanced radial distribution systems using differential evolution algorithm (DE) so as to determine the optimal phase balancing and conductor sizes. The objective functions used in the planning are minimization of: (1) total complex power unbalance, (2) total power loss, (3) average voltage drop, (4) voltage unbalance factor, and (5) total neutral current. The optimization is done under the constraints of minimum and maximum voltage limits for each bus voltage and thermal limit of each line. A three phase forward–backward sweep load flow algorithm is developed and used for the determination of these objective functions. The effectiveness of the proposed planning algorithm is corroborated on 19-bus and IEEE 25-bus unbalanced radial distribution systems. The results show that significant improvements in power loss and voltage drop with simultaneous optimization for phase balancing and conductor sizes. The performance of DE is found to be better and consistent as compared to some other meta-heuristic algorithms studied here.

Voltage distribution constant versus losses in medium-voltage distribution transformer: A polynomial interpolation approach

This paper aims to calculate an estimate of the initial stress voltage distribution in the transformer windings through their losses (that can be reduced by varying the construction parameters such as conductor section and size of the core window) through the numerical interpolation applied in capacitances of distribution transformers 30, 45, 75 and 112.5kVA, 15kV class. The calculations of the projects were organized into sets, with simultaneous variation of three construction parameters, totaling analysis of 10,648 projects of each power transformers arranged in three-dimensional arrays. The equation of the constant voltage distribution (α-factor) according to the losses through the quadratic polynomial and cubic splines for the of LV and HV windings is formulated.

Limits of lightning protection systems

Positive first strokes, less frequent but more powerful than negative return strokes, require a larger conductor. If the skin effect is accounted for, a near maximum value of the action integral of positive lightning can be estimated from the sizes of conductors specified by established building codes. The conductor size for watercraft could be increased: (1) to match that used for structures on land; (2) to avoid exceeding the maximum operating temperature of a dielectric hull; and (3) to limit magnetic stresses caused by 90° bends in conductor paths predicted by Ampere's law. Connecting a conductor at right angles to a ground plate may be problematic; a linear grounding electrode alternative is discussed. Destructive magnetic force can be caused by surface current on: a solid conductor; a hollow conducting mast; or a horizontal ground plate. Electric shielding, unless struck directly, might protect a dielectric hull, except from a subsequent stroke with a short current risetime. Thus, lightning protection systems do not always work, and lightning is best avoided.

Analyzing of AC Corona Discharge Parameters of Atmospheric Air

Corona on transmission line conductors is a significant source of electromagnetic interference and corona loss. In order to analyze variable atmospheric condition on corona inception voltage gradient of bundle conductors a calculation model was established. The voltage gradient around stranded conductors for calculating corona inception voltage gradient is required. For the high voltage transmission lines, it is necessary to know the electric field in vicinity of the conductor's surface to determine the conditions for corona inception. The conditions under which corona discharge occurs for any arrangement of conductors are an important design consideration since corona can limit the performance of any given configuration of transmission line conductors. The AC corona inception voltage gradient criterion should involve the line characteristics, i.e., arrangement and size of conductors as well as atmospheric condition of the air in which the conductor is immersed. The numerical calculation method, as well as empirical equations, combined with gas discharge theory is adopted to investigate corona inception voltage gradient. The electrical field enhancement at the tip of each strand is about 14% higher than the electrical field for a cylindrical conductor of the same overall diameter. According to self-sustained corona discharge criterion in a severe non-uniform electric field, variations of pressure, temperature and humidity on corona inception voltage gradient of bundle conductors are analyzed. Increased voltages in 400kV electric power network of Bosnia and Herzegovina causes increase the value of voltage gradient and higher power losses due to AC corona. Therefore, it is important to determine the value of the voltage gradient in vicinity of conductor's surface as well as corona inception voltage gradient to accurate determined power losses due to AC corona.

A Systematic Approach to Safe and Effective Earthing System Design for High Voltage Substation

In high voltage substation, earthing system is an essential part not only for providing the protection to people who are working or walking in the vicinity of earthed facilities and equipment against the danger of electric shock, but also for maintaining the proper function of the entire electrical system. By selecting a proper conductor and electrode size based on standard criteria, the existence of large potential differences during fault or lightning conditions will able to be avoided. Standard equations for earthing are used in the design to obtain the desired parameters such as tolerable touch and step voltage, earth resistance, grid resistance, minimum size of earthing conductor and electrode, as well as resistivity of soil. Therefore, it would enable the establishment of the safe limits of potential differences under both normal and fault conditions. The main objective of this research work is to perform a necessary background information pertinent step by step approach for safe and reliable earthing system design for high voltage distribution substation in Malaysia. It including a set of applicable standard to be used as well as demonstrate an earthing design simulation developed using Microsoft Excel auto mathematical functions. The case study for high voltage substation design and simulation at two locations with different soil resistivity and properties is also performed in this research work. The results revealed that the design of high voltage substation earting system is much dependent on the property and resistivity of soil where the substation will be constructed.

Preliminary conductor layouts for the detectors of the Future Circular Collider

For the Future Circular Collider (FCC) presently under the conceptual design at the European Council for Nuclear Research (CERN), very large conductors are needed for the detector magnets. The requested critical current is an order of magnitude higher than that of the previous generation, corresponding to about 250 kA at 4.2 K and 5 T. Characteristic conductor layouts, particularly the type and fraction of structural materials, are reviewed in order to extrapolate to the most promising designs and adapt those to the requirements imposed for the FCC detector magnets. The nominal currents required at characteristic operating conditions of 6.5 T and 4.6 K, conductor dimensions, production unit lengths and mass are investigated for defining the design of the conductor. For comparing various conductor layout options, and as a first step in the conductor R&D, it is proposed to study the conductor sizing according to relevant material characteristics.

Design optimization of RF lines in vacuum environment for the MITICA experiment.

This contribution regards the Radio Frequency (RF) transmission line of the Megavolt ITER Injector and Concept Advancement (MITICA) experiment. The original design considered copper coaxial lines of 1″ 5/8, but thermal simulations under operating conditions showed maximum temperatures of the lines at regime not compatible with the prescription of the component manufacturer. Hence, an optimization of the design was necessary. Enhancing thermal radiation and increasing the conductor size were considered for design optimization: thermal analyses were carried out to calculate the temperature of MITICA RF lines during operation, as a function of the emissivity value and of other geometrical parameters. Five coating products to increase the conductor surface emissivity were tested, measuring the outgassing behavior of the selected products and the obtained emissivity values.

Coil Block Designs With Good Homogeneity for MRI Magnets Based on SVD Eigenmode Strengths

This paper describes an improved method to determine coil block (CB) placements with good homogeneities for magnetic resonance imaging magnets. Each magnet has a main coil (MC) for strong magnetic fields in a volume of interest and a shield coil (SC) to make the magnetic fields weak outside the magnet. The CB placements are done in three steps and at every step, the SC magnetic moments are tuned. In step 1, approximate placements are done with axially distributed circular filament loop currents. According to the distribution, rough placements of CBs are done for the MC. In step 2, the CB cross-sectional shapes and positions are optimized to get good homogeneity with real numbers of winding turns. In step 3, the CB shapes are approximated with integer numbers of winding turns and conductor sizes, and the CB positions are tuned to get as good homogeneities as the step 1 result. In all steps, optimizations are done through truncated singular value decompositions. In steps 2 and 3, the placements are done with respect to eigenmode strengths, which are obtained in step 1. For a magnet with six MC-CBs, seven symmetric eigenmode strengths are tuned. The CB placements for magnets can be obtained with good homogeneities and integerized CB winding turns using the method.

Neutral Conductor Size Selection for Electrical Supply with Harmonic

Presence of harmonic current brings adverse impacts on electrical system. Among others, it can derate rated ampacity of conductors. In a perfectly balanced 3-phase system, harmonics existence gives rise to harmonic-rich neutral current. In this paper, two alternative methods are compared with a technique from standard. Results show that the alternative methods are comparable with method from a standard.

System-Based Safety Tenets Applied to the Extra-High Voltage Transmission Line Design for Common Uses of Highway Right-of-Way

The rapidly increasing demand for electricity in recent years resulted in increasing needs of electrical system capacity and deployment for alternate uses of highway right-of-way (ROW) for the purpose of electric power generation, transmission, and distribution. In this framework, a systems approach—fundamental principles of system dynamics for identifying, understanding, and analyzing safety requirements of the extra-high voltage power line (EHV)—is used to objectively focus on two main safety issues related to the design and the risk of the EHV transmission line within highway ROW: (1) assess the design and the operation, and (2) evaluate causally related impacts on the public and workers’ safety that matter. A generalized model of the electromagnetic fields distribution and the clearance model are developed for the analysis of the causally related impacts of a conceptual design and the reliability of materials of construction of the electric systems by introducing the number of exposed individuals and the level of the environmental impacts as a second dimension in addition to the risk factors. A worst-case design scenario is evaluated. Sensitivity analysis of effects of the design attributes such as the route configuration, over voltages, and conductor clearance is performed by determining the magnitude of the electromagnetic field strengths and predicting the resulting maximum voltage. Information obtained on the structural design scenario, conductor size and configuration, insulators, and connectors is of value in determining the safety of the design for operation at extra-high voltages within highway ROW.

A Mathematical Expression to Determine Copper Losses in Switching-Mode Power Supplies Transformers Including Geometry and Frequency Effects

High-frequency copper losses, or copper losses produced during switching in switching-mode power supplies, are very much related to variations of the magnetic field distribution within the core window. When operating at high frequency, the current flowing through the windings of a magnetic component experiences redistribution across the section of the conductor due to skin and proximity effects. Current redistribution depends not only on actual frequency, but also on conductor size and layer distribution. While previous works aim to optimize windings size by considering just the current flowing through that winding, this paper shows that, in most of the cases, current redistribution is strongly affected by the currents at the other transformer windings, which should also be taken into account. This paper derives a mathematical expression to calculate the evolution, in the time domain, of the magnetic field during the switching, which will be later used to obtain the current density distribution and copper losses in the component. An easy-to-calculate expression will be derived that allows magnetic windings to be analyzed and/or optimized, because losses are expressed as a function of the winding geometry and position. An application example is also included. All the equations derived are verified by comparing them with the results obtained from a differential equations solver, and with previous works when applicable. Experimental results are also provided.

Finite element analysis of deepwater conductor bearing capacity to analyze the subsea wellhead stability with consideration of contact interface models between pile and soil

Bearing capacity of deep-water conductor belongs to the research category of pile soil mutual interaction, which indicated that reasonable pile soil contact interface model is of great significance to calculate the bearing capacity correctly. In this paper, theoretical models have been established to calculate the lateral displacement and vertical bearing capacity. Two different pile and soil contact interface models are taken into consideration to calculate conductor lateral displacement and vertical bearing capacity using ABAQUS software by writing corresponding computer programs of constitutive model of interface model. The two different models calculating lateral displacement are contact mechanics model and contact element model. The two different models calculating vertical bearing capacity are coulomb friction model and Goodman element contact model. The results show that the lateral displacement calculated with the contact element method is greater than that calculated with contact mechanics model. However, the vertical bearing capacity calculated by Goodman model is greater than that calculated by the coulomb friction model. Moreover, the variation of vertical bearing capacity with jetted depth calculated by theoretical model, coulomb friction model and Goodman element contact model are different with one another. The variation of conductor lateral displacement with wellhead load and the variation of conductor vertical maximum bearing capacity with conductor size have also been figured out. In order to improve the subsea wellhead stability, the suggestion is calculating conductor bearing capacity with different contact models between pile and soil and take the minimum value as conductor design bases. The method introduced in this paper has a significant reference value to analyze the safety of subsea wellhead.

An Energy-efficient Switching Scheme with Reduced Switching Transients for a Wind-driven Induction Generator

This article presents a scheme for improving the power output of grid-connected induction generator commonly used in wind energy conversion systems. Generally, the stator of the induction generator is connected in a star with a line voltage of √3 times the rated winding voltage to reduce the line current and, hence, conductor size. To extend the generating operation over a wider speed range, delta-star switchable stator windings are also in vogue. In such cases, the stator is star connected in the lower speed range and switched to a delta connection above a threshold speed. In this study, a new switching scheme is proposed wherein the stator coils are always connected in a star, while the stator is connected to different voltages in low- and high-speed conditions. At low wind speeds, nominal winding voltage is applied to the stator, whereas at higher speeds, the stator applied voltage is √3 times higher than the rated winding voltage. The efficacy of the scheme is demonstrated experimentally with a suitable microcontroller-based switching arrangement. Typical results indicate an increase in output with reduced switching transients. A case study on a 3-Φ, 50-kW induction generator is presented to emphasize the performance improvement with the proposed scheme.

A 1 kA-class cryogen-free critical current characterization system for superconducting coated conductors.

A cryogenic electrical transport measurement system is described that is particularly designed to meet the requirements for routine and effective characterization of commercial second generation high-temperature superconducting (HTS) wires in the form of coated conductors based on YBa2Cu3O7. Specific design parameters include a base temperature of 20 K, an applied magnetic field capability of 8 T (provided by a HTS split-coil magnet), and a measurement current capacity approaching 1 kA. The system accommodates samples up to 12 mm in width (the widest conductor size presently commercially available) and 40 mm long, although this is not a limiting size. The sample is able to be rotated freely with respect to the magnetic field direction about an axis parallel to the current flow, producing field angle variations in the standard maximum Lorentz force configuration. The system is completely free of liquid cryogens for both sample cooling and magnet cool-down and operation. Software enables the system to conduct a full characterization of the temperature, magnetic field, and field angle dependence of the critical current of a sample without any user interaction. The system has successfully been used to measure a wide range of experimental and commercially-available superconducting wire samples sourced from different manufacturers across the full range of operating conditions. The system encapsulates significant advances in HTS magnet design and efficient cryogen-free cooling technologies together with the capability for routine and automated high-current electrical transport measurements at cryogenic temperatures. It will be of interest to both research scientists investigating superconductor behavior and commercial wire manufacturers seeking to accurately characterize the performance of their product under all desired operating conditions.

Optimized Power Distribution Planning A Review

Distribution system planning is extremely important for the end consumers of electricity; it is indeed become necessity to explore the area of real term planning of distribution system. The practical planning of distribution system incorporates the selection of optimal conductor size selection and capacitor placement in radial distribution network in distribution system. The load flow needs to carry out on the distributed system for power flow calculation at each node subjected to various system constraints to minimize total energy losses as well as cost. The capacitor placement includes the voltage constraint and load variation. Reactive power status needs to be investigated for the voltage profile on the feeder. In this paper, different techniques for distribution system planning have been presented based on previous literature to anticipate the future requirement and new hybrid techniques can be developed to enhance the current distribution system with the incorporation of more system constraints.

A population based approach to design multi-loop medium voltage distribution network

In this paper, a method is presented to design a multi-loop medium voltage network which supplies each mv/lv substation with an alternate feeding point from hv/mv substation to assure the reliability of the system while the total cost of installation, cost of energy losses and cost of unserved energy is minimized subject to operating constraints. A generalized technique for multi-loop mv network design has been developed. In the proposed technique, at first step, mv/lv substations are clustered corresponding to geographical coordinates using MSVM and K-means method. Then multi-loop are formed using population based approaches Ant Colony System and Genetic Algorithm (ACS–GA) in combination. The developed method can explore and exploit search space efficiently. In the next step, using economical criteria, conductor size is selected for each loop under worst operating condition (feeder segment outage near to source end) subject to constraint on voltage magnitude at each node and admissible current carrying capacity of the conductor. Finally, for radial operation of multi-loop, a heuristic approach is presented. The developed technique has been applied effectively on 45-bus test system.

Study on Slot Bottom Size of Stringing Pulley Based on Reducing Conductor Abrasion

Slot bottom size has directly effect on conductor abrasion,Chinese Technical Regulation of design for Stringing blocks of overhead transmission lines (DL/T371-2010) clearly states that slot bottom size should be no less than 20 times of the size of conductor to be extended. In this paper, based on effect of slot bottom size on conductor abrasion,the size of slot bottom of stringing pulley is analyzed. Some useful suggestions are given.

Thermal Sizing and Electric Shock Calculations for Equipment Grounding Conductors

This paper presents the thermal sizing procedure of equipment grounding (protective) conductors and the electric shock calculations as per the standard 60364 of the International Electrotechnical Committee (IEC) that is used worldwide. The application of IEC standards in the design of low-voltage systems (i.e., not exceeding 1 kV) governed by the National Electrical Code (NEC) and the American National Standards Institute (ANSI), which are adopted in the U.S., is discussed and proposed in this paper. The authors propose an interpretation of the NEC installations in light of the earthing definitions included in the IEC realm. On this premises, IEC sizing criteria are applied to typical North American installations to prove their general applicability and their legitimacy to NEC/ANSI-based electrical systems. Examples are also presented for both thermal sizing and electric shock calculation of equipment grounding conductors.

Current Leads for Conduction-Cooled Magnets at 20–30 K

Cryogenic current leads are designed and tested for conduction-cooled superconducting magnets operating at 20-30 K. These magnets are under development in Korea for electrical machinery with MgB2 wires or YBCO tapes. Since a single-stage cryocooler is employed, the current leads are made of metal over the entire length. Different sizes of copper conductor are fabricated for 80-100 A level and experimentally tested with a commercial Gifford-McMahon cryocooler. Temperature is measured at the coldhead and several axial locations along the conductor in order to estimate the cryogenic load. A geometric condition to minimize the cooling load is clearly demonstrated by the experiment. An analytical model is also presented to explain the optimal condition, taking into account the properties of copper and the refrigeration capacity of cryocooler.