Conductor Height Research Articles

Study on the Interference Law of AC Transmission Lines on the Cathodic Protection Potential of Long-Distance Transmission Pipelines

Through inductive coupling, AC transmission lines can generate large amounts of voltage to buried oil and gas pipelines in areas with common corridors, posing a threat to the cathodic protection effect of pipelines. Therefore, this paper investigates the effect of AC transmission lines on the cathodic protection of long-distance pipelines through inductive coupling. COMSOL Multiphysics finite element simulation software is used to calculate the distribution of cathodic protection potential of long-distance pipelines under different voltage levels, parallel spacing, conductor-to-ground height, conductor arrangement and pipeline burial depth for normal operation of AC transmission lines. Comparison and analysis of the AC transmission line on the pipeline cathodic protection potential interference law is conducted. The results show that: 1. AC transmission lines cause serious electromagnetic interference with the pipeline cathodic protection system, which will cause the pipeline cathodic protection potential to shift out of the effective protection area. 2. The maximum value of the induced voltage of the pipeline will appear at the two ends of the pipeline, and the induced voltage of the pipeline in the middle position is 0. 3. The shift of the pipeline cathodic protection potential increases with the increase of voltage level and decreases with the increase of parallel spacing, conductor height and burial depth. The pipeline cathodic protection potential shift is highest when the wires are arranged horizontally and lowest when they are arranged in an umbrella shape.

Study on the Maximum Ice-Shedding Height of Conductor Based on Energy Method

Study on the Maximum Ice-Shedding Height of Conductor Based on Energy Method

Novel Solution to Back Flashovers on High Voltage Transmission Lines: The Embedded Ground Conductor

It is well known that for high voltage transmission lines in the range of 245 kV–525 kV, particularly in regions of high ground resistivity, lightning back flashover problems could be a major concern. Line arresters have been used successfully to address the problem. Underbuilt ground wires have been proposed as a viable alternative. The present paper shows that the full potential of additional ground wires could be achieved by optimizing their position on the tower. Such optimization often results in a preferred position at the level, or higher than the attachment height of the lower phase conductors; therefore the designation Embedded Ground Conductor. An essential requirement is that such positioning does not infringe in any way on the dielectric integrity of the electrical clearances and, under the influence of induced charge, does not become a source of positive streamers that may lead to additional radio or audible noise. It is found that a streamer- inhibited conductor, when properly placed, fully satisfies the above requirements. It is determined that for 245 kV, 345 kV and 420 kV lines, a streamer-inhibited embedded conductor could improve the back flashover rate by a factor of 10 or more

Research on Risk Assessment and Suppression Measures for Ice-Shedding on 500 kV Compact Overhead Lines

Overhead line ice-shedding causes line breakage and results in electrical faults occurring between transmission lines, which seriously affects the safe operation of the power grid. In this paper, a risk assessment method for ice-shedding on 500 kV compact overhead lines is proposed. Two ratios were used to assess the discharge risk and mechanical failure risk of a line. A 500 kV compact overhead line in southern China was taken as an example, the proposed risk assessment method was used to carry out a risk assessment of the ice-shedding line with an ice thickness of 15 mm, and the suppression effects of different spacer arrangement schemes on the ice-shedding line were analyzed. The results showed that the impact coefficient of the conductor reached 1.88, the maximum jump height of the lower phase conductor reached 22.596 m, and the interphase clearance of the conductor decreased sharply when the lower phase conductor of 500 kV case line underwent full-span ice-shedding synchronously. The ice-shedding line displayed both a discharge risk and a mechanical failure risk. When interphase spacers were installed at L/3 from both ends of the span for the upper-left phase and the lower phase, the upper-right phase, and the lower phase, the impact coefficient of the line became 1.76, which was lower than the recommended value of 1.8; there was no mechanical failure risk; and the maximum jump height became 10.266 m. This study verified the effectiveness of this spacer arrangement scheme.

Jump height of an iced transmission conductor considering joint action of ice-shedding and wind

Ice shedding from conductors may cause a significant vertical vibration of a transmission line, which may lead to interphase flashover and thereby endanger power transmission. To design a reasonable electric insulation clearance, it requires an accurate estimation of the largest jump height of a conductor following ice shedding, which might be affected by wind actions. This study investigates the coupling effects of wind action and ice shedding on the jump height of an iced conductor. Wind tunnel tests were carried out to obtain aerodynamic force coefficients of the iced conductor with crescent sections. The dynamic responses of a practical extra-high voltage (EHV) transmission line subject to joint actions of ice-shedding and wind were analyzed by numerical simulation. The influence of wind actions, accreted ice thickness, and ice shedding rate were investigated and discussed on the largest jump height of conductors. An empirical formula for estimating the largest jump height was proposed considering the ice-wind joint effects. The accuracy and applicability of the proposed formula were validated through experimental and simulation data.

Robust and Long-Term High-Speed Operational Status Inspection of Pantograph-OCS in Complex Environments

Good contact conditions between the pantograph and catenary ensure the safety of electrified railways. However, the relevant state-of-the-art status inspection methods cannot achieve high speed, and robust effects under complex conditions, such as multi-suspended line interference, unknown complex backgrounds, and light and dark changes. Therefore, a two-module contact status diagnosis methodology, consisted of long-term tracking and 3D reconstruction, is proposed in this study. This long-term tracking method is a combination of tracking, detection and discrimination, focusing on locating the contact area of high-speed movement in complex environments. First, a brand-new tracking paradigm, namely, GMSTrack, based on feature matching is developed to adapt to complex background changes. Second, we modify the loss function via GloU-plus loss for box regression and via adaptive wing loss for landmark regression on CenterNet and realize a dramatic improvement in detection accuracy at 125 FPS. Third, sequential information is collected for the transformer-based discriminator to evaluate the correctness of the current tracking result. Experimental results show that the optimal strategy that combines tracking, detection, and discrimination can locate the contact area in complex environments with an accuracy higher than 93% and with a speed higher than 84 FPS. Lastly, dynamic stagger value and height of conductor that can reflect contact status are analyzed though 3D reconstruction of the binocular contact points. The overall status inspection methodology can be applied to the on-site high-speed trains at speeds exceeding 80 FPS.

Dynamic Response Analysis of Asynchronous Deicing of Quad Bundle Conductor Spacer System During DC Ice Melting

In order to study the melting and falling off of the iced conductor under DC ice melting process by considering a lgj-400 / 50 transmission conductor as a research object, Ansys LS-DYNA model is used for simulating the response of materials under short periods of high-intensity loads and a nonlinear structural dynamics model is used to establish the finite element model of split conductor system in the actual process. In the process of finite element analysis, solid45 element is used to model the conductor layer by layer. During the calculation process, the life and death element method is used to transform its element stiffness matrix to near zero icing element for accurately simulating the actual situation during ice melting. Currently, the research on the deicing of the split conductor mostly equates the split conductor to a single conductor for calculation. In the actual ice melting operation, the split conductor system has a phenomenon of asynchronous deicing, so it is necessary to analyze the deicing of different sub-conductors. The results show that the jump height of the deicing conductor under DC deicing is smaller than that of the normal deicing. The jump height and tension of conductor deicing decrease with an increase in the deicing current. When the sub-conductors of the four-bundle conductor spacer system are not deiced synchronously, the two sub-conductors on the diagonal and two sub-conductors below are deiced, the split conductor system is relatively stable. When the sub-conductors under other working conditions are not deiced synchronously, the four-bundle conductor spacer system has lateral swing, resulting in torsional risk, which causes conductor wear and strand breaking accidents.

Propagation Characteristics of Partial Discharge Pulse Current on 10kV Covered Conductor

With the application of covered conductor in distribution overhead lines, the grounding and short circuit faults caused by foreign objects have been eliminated. But new partial discharge problem has appeared on the surface of the covered conductors around tower head. It may cause the single-phase grounding fault and affect the power supply reliability. To increase the reliability, status monitoring must be used to prevent the faults from beginning. Currently, the partial discharge on overhead lines is usually measured by coils. It utilizes pulse currents to check whether there is a partial discharge. However, it cannot be used in status monitoring as the propagation characteristics is not clear. This paper carried out a simulation study on the propagation characteristics. By constructing a simulation model of overhead lines with covered conductor by the distribution parameters, the initial pulse current amplitude and front time transformation rule in different transmission distance is obtained. Considering different conditions such as pulse current frequency domain (10~50MHz), covered conductor height (4.5~8.0m), covered conductors’ phase spacing (0.6~1.0m), and conductor cross-sectional area (50~185mm2), simulation results show that the amplitude attenuation rate is between 1.5% and 6.3% per 100m, and the front time growth rate is between 1.5% and 5.7% per 100m. The height of covered conductor has the greatest influence on the pulse current waveform transformation, and the main frequency of the pulse current takes the second place, while the difference between the phase spacing and the cross-sectional area has less than 1% influence on transformation.

Modeling, Investigation, and Mitigation of AC Losses in IPM Machines with Hairpin Windings for EV Applications

Interior permanent magnet (IPM) machines with hairpin windings have attracted significant attention in EV applications owing to their low DC resistance and excellent thermal capabilities. In this paper, we present a comprehensive investigation of AC winding losses in IPM machines for traction applications, including analytical modeling, the influence of design parameters, and finite element (FE) verification. The proposed analytical model can predict the trends in AC winding losses for any number of bar conductors and slot/pole combinations. The results of the parametric study, obtained via the analytical model, are presented to examine the effects of key design parameters, such as conductor width and height, phase arrangement, and slot-per-pole-per-phase (SPP). To incorporate more practical issues into the analysis of IPM machines with hairpin windings, extensive FE simulations were conducted. The results indicated that the AC winding losses decrease with an increasing number of conductor layers and phases inside the slot.

Calculation of Electric Field on Substation Equipment considering AC Ion Flow Field

With the increase of voltage levels in substation corona discharge on the surface of high voltage conductors and equipment in substations becoming more and more severe, the influence on the electromagnetic environment around substations is becoming more and more obvious. In order to study the influence of corona discharge on the ground electric field under substation equipment in AC substations, this paper proposes an improved method based on Abdel-Salam’s calculation of the ion flow field on AC power lines. By redefining the criterion of corona onset and the amount of emission charge and combining with the migration, motion, and recombination of the space charge, a new model which can be applied to the calculation of AC ion flow field electric field of multiphase bundle conductors in substations is established. The calculation results of the ground power frequency electric field of the conductor at the typical tower in the light, medium, and heavy ice regions of 750 kV typical AC transmission project show that the ground electric field gradually decreases with the increase of conductor height. At the same conductor height, the ground electric field strength in the heavy ice region is the largest, while under the conductor in a light ice region, it is the smallest, and the minimum allowable conductor-to-ground distance can be concluded that the national standard limit value is not exceeded when the conductor-to-ground distance in light ice region is 24.5 m, the conductor-to-ground distance in medium ice region is 25.5 m, and the conductor-to-ground distance in heavy ice region is 26 m.

A Simplified Method for Quick Calculation of Corona I–V Characteristics of Unipolar Transmission-Line Configurations

This article is concerned with the calculation of the corona current-voltage characteristics of a unipolar high-voltage direct current (HVDC) transmission line with a single conductor stretched above the ground plane. In light of justified assumptions, the corona charge density around the conductor surface is obtained using an iterative procedure. This makes it possible to calculate the corona current for a given applied voltage. It is interesting to note that the per-unit charge density around the conductor surface with reference to its value at the gap axis has the same distribution irrespective of the conductor radius and height above the ground plane as well as of the applied voltage. Along this axis, Deutsch's assumption is waived and the charge density is calculated as being dependent on the conductor radius, conductor height, onset voltage, and applied voltage. A curve-fitting polynomial is made for the per-unit distribution of charge density around the conductor surface. Determination of the surface charge density at the gap axis and the polynomial describing the per-unit charge density distribution represent the basis of a proposed simplified method for quick calculation of the I-V characteristics, irrespective of the conductor radius and height above the ground plane. The corona current-voltage characteristics, as calculated by the proposed simplified approach, are compared with those calculated before and with those measured in different laboratories. The computation time is drastically reduced when using the proposed simplified method.

Asymmetric Bar Winding for High-Speed Traction Electric Machines

A new asymmetric bar winding concept along with the analysis and benefits for high-speed traction electric machines is presented. The objective is to reduce the ac losses, especially at high speeds, utilizing optimized and asymmetric conductor heights within a slot for bar-wound stators. Detailed winding diagram, height optimization, ac loss analysis, and thermal performance are presented for both symmetric, i.e., conventional, and asymmetric bar windings. The proposed idea is validated using the closed-form analytical equation and 2-D time-stepped finite-element analysis (FEA). A substantial reduction of ac losses and improvement in continuous power over the wide operation range is achieved as demonstrated for a 12-pole, 100-kW high-speed (15 000 r/min) PM traction machine. Thermal performance analysis using forced liquid cooling is also included. The design and analysis methodology is presented to support high-speed traction electric machine designers meet the ever-increasing demand on efficiency and performance with bar-type windings.

Tunable Coaxial Cavity Resonator-Based Filters Using Actuated Liquid Metal Posts

This letter presents a new tuning method for coaxial cavity resonator-based bandpass filters (BPFs). The proposed tuning mechanism lays its foundations on pneumatically-actuated Galinstan that functionalizes the inner conductor of a capacitively-loaded coaxial cavity resonator. By altering the volume of Galinstan (i.e., height of inner conductor), ultrawide (>octave) and low loss RF tuning can be obtained without the need for small capacitive gaps that typically limit the RF performance of coaxial BPFs. To validate the concept, a coaxial cavity resonator with frequency tuning between 2.9 and 9.9 GHz (3.4:1 tuning range), and unloaded quality factor between 120 and 625 was manufactured and measured. Furthermore, the RF performance of a two-pole BPF with: 1) tunable frequency between 3.4 and 7.5 GHz (2.2:1); 2) an intrinsically switched-off state; 3) insertion loss <1 dB; and 4) return loss <10.5 dB was experimentally validated.

Wind-induced conductor response considering the nonproportionality of generalized aerodynamic damping

Aerodynamic damping is a key factor that influences the wind-induced responses of transmission conductors. The inaccurate estimation of aerodynamic damping leads to misunderstanding of conductor response to wind actions. For dynamic response analysis in the frequency domain, the generalized aerodynamic damping matrix used to solve conductor motion is diagonal. This study reanalyzed the conductor generalized aerodynamic damping matrix by considering its horizontal and vertical motions and the coupling effects of different modes. The derived generalized aerodynamic damping was a nondiagonal matrix, and we defined it as nonproportional generalized aerodynamic damping. Variations in the aerodynamic damping ratio and the nonproportionality of generalized aerodynamic damping with wind speed were investigated through numerical studies of single- and triple-span conductors. Triple-span conductors with different span lengths, hanging heights, and initial pretension forces were adopted to discuss the effects of the nonproportionality of generalized aerodynamic damping on estimating the dynamic responses of conductors. Results showed that neglecting the vertical motion of a conductor leads to an overestimation of the aerodynamic damping ratio, especially under high wind speed conditions. The nonproportionality of generalized aerodynamic damping is highest when the incoming wind speed at 10 m is 25 m/s. Ignoring such nonproportionality leads to an overestimation of the resonant responses of conductors but exerts minimal effects on total fluctuating responses mainly contributed by background components. Therefore, for a transmission conductor with a significant resonant response, the nonproportionality effect of generalized aerodynamic damping must be considered. Increasing span length and conductor height or reducing initial pretension force seems to enhance nonproportionality effects on conductor responses.

Analysis of Electromagnetic Environment and Influencing Factors of Yihua DC Transmission Lines

The electromagnetic environment of transmission lines is one of the major constraints to the design and construction of HVDC transmission lines. In this paper, the charge simulation method and the analytic method based on the Deutsch hypothesis are used to calculate the total electric field strength and ion current density of the 500 kV Yihua DC transmission lines, and the correctness of the calculation is verified by the actual measurement results. Then the EPRI formula and CISPR formula are applied to analyse the audible noise and radio interference of HVDC transmission lines. At last, the influence of factors such as the pole spacing of HVDC lines, the conductor height to the ground, the splitting spacing and the roughness coefficient on the electromagnetic environment of HVDC transmission lines are analysed. Among them, the height of conductor has effective impact on the total electric field strength, while the control of polar spacing is limited. The height of the conductor and the distance between the poles affect the level of audible noise and radio interference mostly, but the control effect of the two is opposite.

Modeling of microstrip line characteristics with side grounded conductors near air–substrate boundary

The modeling of the microstrip line with side grounded conductors located near air-substrate boundary is performed. The dependences of per-unit-length delay and the characteristic impedance on a distance between the grounded conductors are calculated with a change in the height above the boundary and the burying into the substrate. The change of the points of zero sensitivity of the per-unit-length delay to the position of the side grounding conductors over and under the air-substrate boundary is investigated. The possibility of obtaining a minimum (up to zero) sensitivity of the impedance to the height of the side grounding conductors near the air-substrate boundary is revealed.

Influence of measurement uncertainty of overhead power line conductor heights on electric and magnetic field calculation results

In this paper, it is analyzed how the measurement uncertainty of the overhead power line conductor heights influences the calculation results of electric field strength and magnetic flux density in the vicinity of the line. It is assumed that the conductor heights have been determined by measurements, by using a laser telemeter which has a certain measurement error. The laser telemeter measures the distance to the target object and inclination, and based on these two quantities and the manually entered data concerning the height on which the telemeter is placed it calculates the height of the target object, as well as the horizontal distance to it. Each of these measured quantities (distance and inclination) is measured with a defined error. The error of the height measurement has to be calculated based on the two defined errors. The procedure for calculating these errors is explained in detail in the paper, and the errors referring to typical heights of the overhead power line conductors are determined. If the calculations of electric field strength and magnetic flux density are made for the conductor heights with the established deviation in relation to the real heights, this will reflect on the calculated field results. The influence of this factor on the results of the electric field strength and magnetic flux density calculations is thoroughly analyzed.

Modeling of UHV and Double-Circuit EHV Transmission-Line Exposure to Direct Lightning Strikes

This paper comprises the first systematic investigation into the factors that render ultra-high voltage and double-circuit extremely high voltage transmission lines more vulnerable to direct lightning strikes by shielding failure. Such lines are typically characterized by one or more of the following features: massive conductor bundles, extreme conductor heights, and exceptionally high operating voltage. The model addresses the effects of the upward connecting leader onset of conductor proximity, ground field due to cloud charges prior to negative leader descent, positive space-charge generation at ground wires, as well as the operating voltage during the positive half cycle. It has been found that such factors have significant effects on the lateral attractive distance of both conductor bundles and ground wires. An agreement between model findings and field experience is found to be generally satisfactory.

A High-Precision Detection Approach for Catenary Geometry Parameters of Electrical Railway

This paper aims to develop a high-precision detection approach for catenary geometry parameters of electrical railway based on vision technology. The novel idea of the proposed detection method is that, the image coordinates of the spot formed on the contact line by a laser emitter are mapped to the world system to obtain the conductor height and stagger. In the proposed detection system, the key factors that affect the detection accuracy include two components, the localization of the spot and the correction of the detection value. To solve these problems, the genetic particle filter algorithm based on particle swarm optimization (PSO-GAPF) is presented to track and locate the spot in the image. Compared with the standard particle filter, PSO-GAPF can improve the particle deprivation and increase the accuracy of state estimation. In addition, Kalman filter (KF) is used for correcting the detected value of catenary geometry parameters. In this paper, first of all, the model of spot target is established according to the feature distribution of gray color histogram, and the tracking and locating of the spot in the image are realized by PSO-GAPF. Second, the detection formulas of catenary geometry parameters are deduced by utilizing the space coordinate transformation to compute the conductor height and stagger. At last, the correcting of the catenary geometry parameters is achieved by KF. The real-life detection results show that the proposed method has high precision, and can meet the requirements of real-time catenary geometry parameters detection system.

Coil optimisation for transcranial magnetic stimulation in realistic head geometry

BackgroundTranscranial magnetic stimulation (TMS) allows focal, non-invasive stimulation of the cortex. A TMS pulse is inherently weakly coupled to the cortex; thus, magnetic stimulation requires both high current and high voltage to reach sufficient intensity. These requirements limit, for example, the maximum repetition rate and the maximum number of consecutive pulses with the same coil due to the rise of its temperature. ObjectiveTo develop methods to optimise, design, and manufacture energy-efficient TMS coils in realistic head geometry with an arbitrary overall coil shape. MethodsWe derive a semi-analytical integration scheme for computing the magnetic field energy of an arbitrary surface current distribution, compute the electric field induced by this distribution with a boundary element method, and optimise a TMS coil for focal stimulation. Additionally, we introduce a method for manufacturing such a coil by using Litz wire and a coil former machined from polyvinyl chloride. ResultsWe designed, manufactured, and validated an optimised TMS coil and applied it to brain stimulation. Our simulations indicate that this coil requires less than half the power of a commercial figure-of-eight coil, with a 41% reduction due to the optimised winding geometry and a partial contribution due to our thinner coil former and reduced conductor height. With the optimised coil, the resting motor threshold of abductor pollicis brevis was reached with the capacitor voltage below 600 V and peak current below 3000 A. ConclusionThe described method allows designing practical TMS coils that have considerably higher efficiency than conventional figure-of-eight coils.