Conductor Radius Research Articles

ATP-EMTP simulation of lightning protection system for multi-storey building

Multi-storey buildings with occupied highly technological instruments have more attraction possibilities of a lightning stroke than ordinary residential buildings. A protection system against lightning is necessary for these buildings and the level of the protection system performance is an issue to be examined. In this study, a protection system for a three-storey building is simulated in Alternative Transient Program-Electromagnetic Transients Program (ATP-EMTP). Distributed-parameter line models are used for the conductors of the protective system by modelling vertical conductors as nonuniform lines. The currents flowing in the critical conductors and the voltages at some critical points resulting by a lightning stroke are computed. The conventional lighting parameters required for structural protection such as lightning peak current, current rise time and time interval for the current flowing are determined. The effect of the radius of conductors in the protection system on the surge response is investigated.

Evaluation of ground conductor corrosion based on EMI technique with asymmetric sensor layout

ABSTRACT The ground conductor is prone to corrosion, which affects its ability to diverge current and the normal operation of the power system. The traditional detection method can’t detect its corrosion degree intuitively. This paper proposes a novel method based on Electromechanical impedance (EMI) technique to evaluate the corrosion degree of the grounding conductor. Firstly, based on the analysis of corrosion of metals. The change of ground conductor radius Δr is used as the corrosion parameter. A linear model of peak frequency Δf m and corrosion parameter Δr in asymmetric layout is established by analysing EMI and conductor mechanical admittance. Secondly, the EMI coupling models with different sensor layouts were built on the finite element software. It is verified that the asymmetric sensor layout effectively improves the sensitivity to corrosion. The linear model greatly improves the assessment accuracy compared with the Mean Absolute Percentage Deviation (MAPD) and Root Mean Square Deviation (RMSD) damage index. Thirdly, the proposed method is verified in a real grounding conductor corrosion experiment. The method based on the EMI technique with asymmetric sensor layout can evaluate the corrosion of the grounding conductor well.

Insulation design of -800 kV gas insulation transmission line for negative ion based neutral beam injector

The high-voltage transmission line carries electricity, water, and gas for the high-potential components in the NNBI system. High voltage transmission lines used in -800 kV acceleration grade NNBI systems require the transmission of multiple high voltages of different voltage levels. Its insulation design not only guarantees the reliability of insulation but also requires a small occupation volume. The FEA method is used for insulation design of multi-conductor transmission lines. In the design of -800 kV transmission line, coaxial and non-coaxial structures are mainly considered. In the case of SF6 filling space, conductor radius and conductor position are the main factors affecting insulation strength. Both structures can make its insulation strength meet the requirements. However, it is found that the coaxial transmission line is more compact and concise when it meets the insulation requirements, but it is difficult to install and maintain.

A Numerical Simulation Study on DC Positive Corona Discharge Characteristics at the Conductor’s Tip Defect

For investigating the relationship between the surface corona discharge of a DC wire and other influencing factors, a hybrid numerical model based on a fluid-chemical reaction was proposed to simulate the discharge process at the tip defect of the wire. Under different defect geometries and gas pressures achieved via simulation, the microscopic process of the reaction and movement of electrons and heavy particles during a positive corona discharge was studied, and characteristic parameters such as corona inception voltage and discharge current were analyzed. Furthermore, through the corona cage test, for a specific electrode configuration, corona inception voltages under different pressures were compared and verified, which showed that the model was reasonable. The results showed that the maximum electron density of the streamer head was about 1 × 1020 m−3, the rise time of the pulse current was about 10 ns, and the decay time was about 300–500 ns. The corona inception voltage decreased with an increase in the tip height and decreases in the tip curvature radius, conductor radius, and background air pressure; the amplitude of the pulse current increased with increases in the wire radius and curvature radius of the defect tip and decreases in tip height and background air pressure. The experimental results are consistent with the simulation results, which verifies the reasonability of the model.

Analysis of the Influence of Harmonics on Energy Efficiency of Typical Equipment in Distribution Network

With the continuous development of power systems, the number of non-linear loads is increasing. When harmonics flow through wires, transformers, filters, and other devices, additional harmonic losses will be generated, which will cause power loss and safety problems such as equipment overheating. However, there are few studies on loss in complex power quality environments. Considering the influence of skin effect when harmonics flow through the conductor, this paper studies the distribution of current density, explores the influence of conductor material, radius, and frequency of the current flowing through the metal on the current distribution, and proposes a calculation method of conductor harmonic resistance considering the influence of skin effect. Furthermore, the electrical energy consumption of typical devices in the distribution network is considered. Based on the theoretical calculation model, a simulation platform was established to carry out the equipment loss measurement experiment under each harmonic current, and the mutual verification between the theoretical calculation model and the experimental measurement was realized.

Study on the effective measurement area of an open-ended coaxial probe for the dielectric measurement of biological tissues.

The dielectric properties of tissues are very important physical factors for the investigation and application of bio-electromagnetism. However, the size of the active sample tissue is usually limited in actual measurement, making it difficult to meet the requirements of the existing high-frequency measurement methods, thus influencing the measurement results. The present study aimed to systematically investigate the various factors influencing the effective measurement area of the open-ended coaxial probe, including the design size of the probe and the dielectric properties of the object to be measured. The simplified material mixing model, in which several types of materials were set as the material under test (MUT) and the perfect conductor (PEC) was set as the specific material, was used in the simulation to study the effective measurement area of eight types of probes with different sizes for the dielectric measurement of different MUTs. Different concentrations of NaCl solutions and three types of coaxial probes were used in the actual measurement to verify the simulation results. According to the simulation results, the effective measurement area, especially the effective measurement radius, was closely related to the outer conductor radius of the probe. The effective measurement area of the probe decreased when the outer conductor radius of the probe reduced. Moreover, the change in the effective measurement area of the probe was independent of the MUT when the cross-sectional size of the probe was smaller than a certain threshold value. The experimental results also confirmed this conclusion. According to the research results, the independent variable dimension could be effectively reduced and the modeling difficulty was reduced when the analysis model of the effective measurement area of the probe was established.

Coupling model for time-domain analysis of nonparallel overhead wires and buried conductors in the presence of lossy ground

Buried conductors crossing paths with overhead transmission lines is a common occurrence. Interference caused by overhead lines has been found capable of affecting the safe, sustainable operation of the buried conductors. Such occurrences introduce an electromagnetic problem of a nonparallel structure with conductors present in both air and ground half-spaces. Electromagnetic transient (EMT) simulations of such structures are vital in predicting the behaviour of modern power networks. This paper develops a novel EMT compatible time-domain model for nonparallel overhead wires and conductors that are buried in a frequency-dependent lossy (finitely-conducting) ground. Analytical expressions are derived for the per-unit-length (PUL) impedance and admittance matrices based on thin-wire electromagnetic scattering theory. The closed-form formulations derived in this work can be easily incorporated in an EMT simulator to calculate the coupling effect between nonparallel overhead lines and buried conductors. The validity of the proposed approach is examined for various values of the ground conductivity, the radius of the buried conductor, the crossing angle, and burial depth of the conductor by comparing with results with those obtained using a full-wave approach. A case study on the induced voltage in buried conductors due to typical lightning transients in overhead lines has also been performed. • A novel closed-form formulation has been obtained for the mutual coupling of a nonparallel overhead and buried conductors. • Results obtained using the proposed model has been compared with those calculated using a commercial full-wave solver. • Case studies on the induced voltage in buried conductors due to typical lightning and switching transients in overhead lines have also been performed. • Results indicate that hazardous voltages might be induced in buried conductors at such occurrences.

Effect analysis of angular momentum on coaxial multipactor with 1D3V statistical modeling

How does the multipactor threshold voltage vary when two semi-infinite parallel plates are bent into coaxial lines? This topic with respect to the geometric effect on multipactor formation is essential for the optimal design of multipactor-free microwave systems. It requires accurate multipactor threshold analysis of the coaxial lines with the consideration of electron angular momentum, which is not considered in most multipactor theoretical approaches for efficient threshold calculations. To address this effect from the perspective of multipactor threshold analysis, this work presents an improved implementation of the multipactor statistical modeling (1D3V modeling) by constructing the joint probability density function with angular emissions and impacts of secondary electrons included. On that basis, a multipactor susceptibility chart of coaxial lines is conducted and compared with the experimental results, and multipactor threshold voltage for varying ratios of outer to inner conductor radii (radius ratio) is calculated to quantitatively investigate the effect of electron angular momentum. The results indicate that the 1D3V modeling can achieve fairly good agreement with the experimental result and relatively better accuracy of threshold calculation at first multipactor orders with comparison to the 1D1V result which only regards the radial momentum. With different variations of the threshold voltage from the 1D1V result, the 1D3V result reaches its minimum at a specific radius ratio before the sudden rise, and the discrepancy becomes more significant for the high-order multipactor, revealing the indispensable effect of angular momentum on the coaxial multipactor. The intricacies of the mechanism analysis will be further explored in the paper.

Experimental and numerical study on corona onset threshold under combined AC-DC voltages in Wire-Plane electrodes

With the large-scale application of hybrid HVDC/HVAC transmission technology, the phenomenon of corona discharge is also intensified. This paper attempts to provide a comprehensive understanding of the variation of corona onset voltage under combined AC-DC voltages. In this paper, an experimental platform for measuring corona onset voltage and current pulses of wire-plane electrode under combined AC-DC voltages was built. A new corona model of wire-plane electrode under combined AC-DC voltages was also established by using the fluid model and the ion flow field model. The corona onset voltages of wire-plane electrode under different ratios of AC and DC voltages, conductor radius and conductor spacing were measured. It turned out that the conductor radius affected the intercept of the corona onset curve, while the conductor spacing affected the slope. In addition, the type of corona only affected the intercept of the corona onset curve, not the slope. With the same fixed voltage of non-corona conductor, the corona onset voltage of the DC-side positive corona was the largest, followed by the DC-side negative corona, then was the AC-side positive half-cycle corona, and the smallest was the AC-side negative half-cycle corona. The interaction between AC voltage and DC voltage was approximately linear. The calculations of the model illustrated that the residual space charges had a blocking effect on corona discharge. Therefore, the more residual space charge was, the higher corona onset voltage would be.

Analysis of Hemispherical Dielectric Resonator Antenna With an Imperfect Concentric Conductor

This work presents a full-wave Green’s function approach for the rigorous investigation of a probe-coupled dielectric resonator antenna (DRA) configuration with an imperfect inner conductor. The impedance boundary condition is applied over the imperfect conductor in the formulation to derive the fields inside and outside the dielectric region, considering all higher-order modes. The technique enhances the applicability of the full-wave Green’s function in the evaluation of input impedance and radiation characteristics for an antenna structure with imperfectly conducting spherical surface, which to the best of our knowledge has not been reported before in the DRA literature. The role of the surface impedance on the antenna resonance and quality factor is thoroughly characterized. A suitable choice of the surface reactance depending on the radius of the imperfect conductor and dielectric-coating thickness enables the simultaneous reduction in the resonant frequency and quality factor for the antenna configuration. The effect of the surface reactance with varying coating permittivities is also investigated. The parametric variations in the input impedance, reflection coefficient, and antenna bandwidth with change in the surface impedance and coating permittivity for the antenna configuration are analyzed. The radiation characteristics for the antenna configuration are also examined.

Negamax based optimization methods for current distribution of conducting materials

This paper proposes a novel Negamax based three optimization techniques for current distribution of conducting materials. Skin effect solver developed for current distribution of copper is extended for other materials with multiple frequency variation of AC supply. Current distribution in copper, silver, gold and aluminum conductors for 1 kHz and 10 kHz calculating using skin effective solver from existing scheme is extensively studied. Initialization of conductor properties for different frequency levels from the reference current start out the preliminary computation. The development of resistance of individual frequencies for every skin depth for the gradient of conductor radius. Min-Max function of the existing solver enhanced through the concept of Negamax applied based on maximizing the impact of skin depth. The categories of Negamax from base, pruning and transposition for the current distributions. The influence of frequency varies with radius of the conductor analyzed for individual points and impact in the current distribution in different conducting materials is extensively studied and simulation results shows the feasibility of the proposed scheme.

On equilibrium magnetoplasma configurations in “Galatea-Belt” magnetic traps

The computation results of equilibrium magnetoplasma configurations in magnetic Galatea-traps developed for solution of controlled thermonuclear fusion problem are presented in the paper. In traps of this type, electric current conductors creating a confining magnetic field are immersed into the plasma volume but do not come in contact with it. In numerical solution of two-dimensional boundary value problems with the elliptic Grad-Shafranov equation, distributions of the main parameters of the plasma and the magnetic field in the trap “Galatea-Belt” with two electric current conductors are obtained. In the series of numerical experiments, the research on how the problem parameters such as the maximum plasma pressure measured in magnetic units, the relative radius of the electric current conductors and the configuration transverse size influence on the properties and characteristics of the configurations is provided.

Transient impedance of grounding system with impulse superimposed sinewave

Investigating the transient performance of grounding systems subject to lightning (impulse or impulse superimposed sinewave) is valuable for protecting the power system and maintaining the system operation. In this work, the grounding system's impedance is computed when an impulse superimposed sinewave is applied to the grounding grid's proposed lumped circuit and grounding system can be simulated as an inductance in series with resistance, and all of them are in parallel with capacitance based on Thione's assumption. Several variables were investigated to study their effects on the grounding system's behavior. The variables were the soil resistivity, soil permittivity, main wire length, grid conductor radius, grid side length, grid configurationand its mesh number. The grounding system configuration varied between square and rectangular shapes, which connects to the protecting rod via the main wire conductor. A 3.69 kA peak of impulse current was applied to avoid soil ionization. The results indicated the performance of the grounding system when subjecting to impulse current.

Measurement and assessment of corona current density for HVDC bundle conductors by FDM integrated with full multigrid technique

This paper presents an intensive measurement and analysis of monopolar ionized fields in bundled high voltage direct current (HVDC) conductors using the finite difference method based on the full multigrid technique. The positive feature of this study is that it considers the comprehensive representation of the bundle conductor, unlike the existing studies that approximate the bundle conductor with an equivalent conductor radius. Firstly, the proposed method is compared with previous experimental results. Secondly, a flexible laboratory model for the bundled HVDC conductors is constructed. Thirdly, the laboratory model is exploited to validate the numerically computed current density distribution on the ground plane and corona current for different bundles’ numbers and different distances between bundles. Bundles of one, two, and four conductors are adopted in the experimental setup. For the same applied voltage, the results verified that the corona current decreases by increasing the bundles’ number and/or minimizing the spacing between bundles. Consequently, the obtained results confirmed that corona power losses can be minimized, without needing the traditional procedures that involve increasing either the conductor radius or its height above the ground. The results of the proposed numerical approach concurred well with the present and past laboratory results.

Lightning Impulse Impedance and Surface Potential Distribution of 10 kV Distribution Line Tower: Field Test and Simulation

The impulse grounding performance of distribution lines tower is the key factor to lightning protection. Few field high-current impulse test researches are conducted on distribution line tower. In this paper, we used a mobile high-current impulse generator to conduct test on a 10 kV distribution line tower. The peak value of the current injection is 6 kA to 16 kA. The impulse impedance and the surface potential distribution are measured and analyzed. Based on the CDEGS software, an equivalent modeling of the experiment was carried out. The influence of soil ionization was taken into account by the method of changing the conductor radius through two rounds of calculation. The simulation and measured results were basically consistent. Experiments have shown that the soil ionization effect has an important impact on lightning performance of distribution line tower. The graphite earthing modules (GEMs) and pulling wires can significantly reduce the impulse impedance of the tower. The potential rise of the earth surface at a distance of 30 m from the tower can reach 1 kV at peak, under an injection of 7.15 kA.

Design and numerical simulation of a microwave antenna with coaxial slots for preventing secondary formation of gas hydrate

Gas hydrate is a new clean energy resource with polar molecule. However due to the change of temperature and pressure during extraction process, there will be secondary formation of gas hydrate, which usually occurs in reservoirs or pipelines near the wellhead. It is significance to prevent secondary formation of hydrate because of safety issues or production rate reduction caused by it. Theoretically, microwave heating can accelerate the decomposition of gas hydrate. Therefore, it is possible to use microwave radiation to prevent secondary formation of hydrate. In this paper, a microwave antenna with special shaped coaxial-slots was designed. Based on electromagnetics and antenna transmission theories, the key parameters of the coaxial-slot antenna were calculated. The frequency is 2.45 GHz, the impedance is 50 ohms, and ratio of outer to inner conductor radius is 3.32. The slots were designed as ‘H’-shape with the width is 2 mm, the radial length is 12mm, the axial length is 14 mm and the interval is 35 mm. Teflon was used as filling material and the radome. Then the software HFSS and ANSYS were used to analyze the electromagnetic field and temperature field to further optimize the parameters. It will be proved that the microwave antenna can heat gas hydrate and prevent the secondary formation.

The Forming Parameters Study Based on ITER Prototypical Vertical Stability Coil Small Bending Arcs

The vertical stability (VS) coil is a set of circle-shaped multilayer in-vessel coil that is arranged in the vacuum vessel. For International Thermonuclear Experimental Reactor (ITER) prototypical VS coil, to avoid the interference with other in-vessel components some small bending arcs are designed. They are the R600 S-shaped bending arc with the angle of 9.2°, the R600 W-shaped bending arc with the angle of 20.3°, 38.1°, 20.3°, and the R215 S-shaped bending arc with the angle of 53.6°. The forming parameters of these arcs are studied in the article. Given the fact of conductor rebound after bending, the key issues of forming the arcs are to determine the suitable wheel mold radius and rotation angle. With regard to the determination of wheel mold radius, the forming deformation states of conductor under different wheel mold radius are simulated. Then the conductor displacement data after rebound are extracted to acquire the conductor inner and outer arcs fitting equations and the corresponding conductor radii are obtained simultaneously. If the calculated conductor central radius is different with the target value, the wheel mold radius will be adjusted and new simulation is employed. The reiteration work is terminated until the target radius is obtained. Subsequently, the wheel mold radius obtained in the data fitting process is referenced to fabricate the matching wheel mold. And the forming experiment is launched to verify the feasibility of conductor bending based on the above wheel mold radius. As to the determination of wheel mold rotation angle, the bending simulation and data fitting are carried out first. Then the process is repeated continuously until the target bending angle is obtained. Finally, the obtained wheel mold rotation angle is assigned as the preliminary bending angle in the forming experiment. If the forming results fail to satisfy the angle requirement, the preliminary bending angle is adjusted slightly and the forming experiment is performed again until the target bending angle is achieved. In addition, wrinkles are found during the forming process for the R215 S-shaped arc. To deal with the wrinkle issue a series of forming technology are attempted, while nearly all of them seem to be not feasible. Finally, bushing is installed at the outer surface of conductor jacket to reinforce its strength and resist the buckling impact from magnesium oxide (MgO). The forming experiments indicate bushing technology successfully eliminates the large wrinkles on the jacket.

Preliminary insulation design for transmission line of CFETR NNBI test platform

Abstract In order to satisfy the requirements of China Fusion Engineering Test Reactor (CFETR) for neutral beam injector system, a Negative-ion Based Neutral Beam Injector system (NNBI) test platform will be established by Institute of Plasma Physics Chinese Academy of Sciences (ASIPP). The high voltage Transmission Line (TL) plays an important role in the NNBI system, connecting the ion source and the power supply system. The TL will be insulated by gas insulation technology, that is, Gas Insulated Transmission Line (GITL). This paper mainly focuses on the insulation dimension design of TL2, which is the longest and main section of the TL. Firstly, the method of determining the design criteria of TL2 gas insulation is given, the gap required by gas insulation is analyzed and the condition of electric field strength to prevent the movement of conductive particles is put forward; secondly, the basic design principles of TL2 insulation design are put forward and the design method of wall thickness of TL2 central conductor and grounding shell is given. Finally, according to the above insulation requirements and design methods, some basic structural parameters of TL2 of the NNBI test platform are determined, including the outer radius and wall thickness of the central conductor and the inner radius and wall thickness of the grounding shell. The outer radius and the wall thickness of the intermediate voltage (rated as −200 kV) conductor are selected as 50 mm and 5 mm, the outer radius and the wall thickness of the high voltage (rated as −400 kV) conductor are selected as 250 mm and 5 mm, while the inner radius and the wall thickness of the grounding shell with tolerated gas pressure from 0.45 MPa to 0.6 MPa, are selected as 525 mm and 10 mm, which lays a foundation for the subsequent detailed design of TL.

Improved and simplified design of the relativistic helitron resonator

One of the main trends in microwave electronics is the ultra-large power production. The electron stream energy is converted inside vacuum systems, where the key moment is increasing output power of microwave devices, which is possible only when using more and more powerful electron streams. Increasing electron stream power is possible due to either enhancing the carried currents or as a result of increasing the electron energy. Given the law that connects currents and voltages in electronic systems operating when the current is limited by a spatial charge, the production of ultra-high-power electron flows is associated with the usage of relativistic velocity electrons, i. e. approaching the light speed. Likewise, at present, relativistic electrovacuum devices (traveling-wave lamps and backward-wave lamps) use magnetic focusing for linear relativistic streams, which prevents the implementation of simple superconducting electrodynamic systems, because highfrequency metal superconductivity disappears in constant magnetic fields. Meanwhile, simplified ultra-highpower superconducting device structures can significantly increase the device energy due to the strong ohmic loss reduction, which just limits the device energy, destroying the working electrodynamic system surface by increasing power or pulse duration of the generator. The article outlines the modernized design of a new-type microwave generator – the relativistic helitron. The paper considers a simpler coaxial resonator design, obtained by using the supercritical narrowing of the inner conductor radius by the Hn1l mode of the electromagnetic field, rather than a coaxial resonator with notch filters.

Predicting the Sensing Radius of a Coaxial Probe Based on the Probe Dimensions

The coaxial probe technique is used to acquire the dielectric properties of biological tissues in the microwave frequency range. To dielectrically characterize heterogeneous samples, the sensing radius of the probe must be known. Thus, in this article, for the first time, both experimental and numerical investigations were conducted to analyze and model the sensing radius dependence on the probe dimensions. The results suggest that 1) the sensing radius increases linearly with the inner radius of the outer conductor and is not affected by the width of the outer conductor; 2) the inner conductor has higher impact than the insulator on the sensing radius; and 3) although the sensing radius depends on the dielectric properties of the investigated samples, the trend of the sensing radius relative to the probe dimensions is the same across different samples. Furthermore, a method for predicting the sensing radius, through use of neural networks, is proposed.