Bundle Conductors Research Articles

Calculation of Ion-Flow Field Near the Crossing of HVdc Transmission Lines Using Equivalent Corona Conductors

The crossing of two-circuit high-voltage direct current (HVdc) overhead lines will happen with the increasing number of HVdc transmission projects. The 3-D calculation is needed to predict the ion-flow field near the crossed HVdc lines. In order to decrease the difficulty of meshing near the bundle conductors, the equivalent single conductors are applied in the modeling. A roughness coefficient converting approach for equivalent conductor in Peek’s formula is presented. Thus, the corona degree of bundle conductors can be reflected by the equivalent single conductor. Afterward, the effectiveness of equivalent corona conductors in ion-flow field calculation is checked by a series of experiments and simulation. Finally, the 3-D ion-flow field distribution near the crossing of ±800 and ±500 kV HVdc overhead lines is calculated using equivalent corona conductors.

The Optimum Method for Determining the Corona Onset Voltage Gradient of Bundle Conductors on UHV AC Power Line

The COG (Corona Onset Voltage Gradient) of bundle conductors, as an important parameter in the design of transmission lines, is related to the electromagnetic environment around the transmission lines. Therefore, it is important to accurately determine the COG. At present, there are several methods to determine the COG, the values of COG obtained by different methods are quite different, and the reasonableness of these methods is still not clear. In this paper, combined with the UHV corona cage set in Ping’an County, Xining city (elevation 2200 m), the corona characteristic measurement system and UV imager, the platform for measuring corona discharge characteristics of bundle conductors was built. For the 8 × LGJ-630 bundle conductors commonly used on UHV transmission lines, the change of corona discharge intensity was observed by UV imager. Then, the E (field intensity)–I (resistance current), the E–√P (square root of corona loss), E–PH (UV photon number), E–RI (radio interference), E–AN (audible noise) curves were measured. By using the tangent method, the experimental values of COG were obtained. Finally, the COG obtained by the five methods are analyzed and discussed, the COG values obtained by the E–I curve and E–√P curve are basically the same, with a deviation of about 1.5%, it has clear physical significance. While the deviation of the COG obtained by the E–PH, E–RI, and E–AN curves are about 10.4%, 29.9%, and 5.7%, respectively. And the optimal method proposed for determining the COG is E–I curve or E–√P curve.

Corona onset voltage gradient of bundle conductors for EHV/UHV AC power lines in corona cages considering the altitude correction

The corona onset voltage gradient (COG) of conductors is a key parameter in the design of overhead transmission lines. The commonly used semi-empirical calculation formula proposed by Peek (1910s) at present can roughly estimate the COG of single conductors and is not applicable to large cross-section bundle conductors. In this paper, experiments are conducted to investigate the corona characteristics of a whole series of bundle conductors at different altitudes, and a prediction formula is proposed for the COG of large cross-section bundle conductors on AC transmission lines considering the altitude correction. The calculated values using the proposed prediction formula are compared with the experimental values of the COG in two cases: UHV eight-bundle conductors at an altitude of 19 m; 500 kV UHV four-bundle conductors in Wuhan, Xining, Geermu, and Nachitai at four different altitudes. The results show that the use of the formula can predict the COG of bundle conductors with the radius of 1.34 cm to 1.995 cm and the number of sub-conductors of 4 to 12 at altitudes of 19 m to 4000 m above the mean sea level. The research findings can provide a reference for the design of EHV and UHV overhead transmission lines and even those in higher voltage levels.

Wind Tunnel Test Investigation on Unsteady Aerodynamic Coefficients of Iced 4‐Bundle Conductors

Iced conductor motion is induced by the aerodynamic instability of these conductors. The unsteady aerodynamic characteristics are different from the steady aerodynamic characteristics. The unsteady aerodynamic coefficients of typical iced conductors’ models under torsional motion are measured by the unsteady wind tunnel test. The unsteady aerodynamic coefficients of crescent‐shape and sector‐shape iced 4‐bundle conductors under different torsional motion frequencies, wind velocities, and ice thicknesses are obtained. Wind test results show that there are significant differences between the unsteady and steady aerodynamic coefficients. The unsteady aerodynamic coefficients curve is a loop which is different from the steady aerodynamic coefficients. In addition, the obvious differences exist between unsteady aerodynamic coefficients of crescent‐shape and sector‐shape iced bundle conductors. Critical parameters, including torsional motion frequencies, wind velocity, ice shape, and ice thickness, have significant influences on unsteady aerodynamic coefficients. It shows that the wind tunnel experiment results are able to provide necessary data for the investigation of iced bundle conductor motion and their prevention techniques.

Study on wind tunnel test and galloping of iced quad bundle conductor

Conductor galloping is a common phenomenon during the operation of the transmission line, which can easily result in electrical and mechanical accidents such as tower collapses and interphase flashover. And aerodynamic parameters are key factors to study galloping. In this paper, the aerodynamic parameters of crescent-shaped and D-shaped conductors, which are two typical iced conductors, are studied by wind tunnel test. The instability analysis is carried out according to Den Hartog instability mechanism and the linear galloping model. The results indicate that wind velocity, ice thickness, conductor type, bundle spacing and splitting number all have a great influence on aerodynamic parameters and conductor galloping. Then the galloping situation of a 500 kV quad bundle conductor are simulated according to the parameters obtained from wind tunnel test. The calculating results correspond with the actual situation. The results obtained in this paper are important to predict the galloping amplitudes under different weather conditions and investigate anti-galloping technology of iced quad bundle conductor.

A Novel Method for High-Voltage Bundle Conductor Reconstruction from Airborne LiDAR Data

The security of high-voltage power transmission corridors is significantly vital to the national economy and daily life. With its rapid development, LiDAR (Light Detection and Ranging) technology has been widely applied in the inspection of transmission lines. As the basis of potential hazard detection, a robust and precise power line model is a necessary requirement for rapid and correct clearance. Thus, this paper proposes a novel method for high-voltage bundle conductor reconstruction, which can precisely reconstruct each sub-conductor. First, points in high-voltage power transmission corridors are detected and classified into four categories; second, for classified power lines, single power line spans are extracted, and bundle conductors are identified by analyzing the single spans’ fitting residuals; and then, each sub-conductor of bundle conductors is extracted by a projected dichotomy method on the XOY and XOZ planes, respectively; finally, a double-RANSAC (random sample consensus)-based algorithm was introduced to reconstruct each power line. The proposed method makes use of the distribution of bundle conductors in high-voltage transmission lines, and our experiments showed that it could preferably reconstruct the real structure of bundle conductors robustly with a high precision better than 0.2 m.

Research on overvoltage and minimum air clearance on 1000 kV AC side of converter transformer in ±1100 kV Guquan converter station

In the hierarchically connected ultra-high voltage (UHV) DC projects, the minimum air clearance on the 1000 kV AC side of converter transformer directly affects the layout and area of the valve hall. The minimum air clearance is determined by the overvoltage and the flashover characteristics of different electrodes. Since the UHV DC projects are hierarchically connected to the AC power grid, the overvoltage and the electrode flashover characteristics are different from that of general UHV AC projects, necessitating the relevant overvoltage calculation and test studies. The electromagnetic transients software PSCAD is used for modelling of the ±1100 kV Wannan convertor station and the related AC system. The power frequency overvoltage, switching overvoltage, time-to-crest value, and coefficient α of phase-to-phase overvoltage on the AC side of the 1000 kV converter transformer are calculated. Tests are carried out on air clearances between bundle conductors, tubular buses, and equipment grading rings under switching impulse with 1000 μs long wave-front. The minimum phase-to-earth and phase-to-phase air clearances on the 1000 kV AC side of the converter transformer are given.

Study on the Effect of Altitude on the Corona Inception Field and the Ground-Level Total Electric Field Under HVdc Lines Using Bipolar Test Lines

With the growing public awareness of environmental protection, the dc ground-level total electric field (TEF) is attracting increasing attention. Especially in high-altitude areas, it has become a key technical factor in deciding conductor types and the height of the transmission line. To determine the altitude effect and correction of the ground-level TEF for HVdc transmission lines, four short bipolar test lines with bundle conductors with the same parameters were built in China at altitudes of 50, 1700, 3400, and 4300 m. Using the test facilities, the dc ground-level TEF was measured over a long period of time, from Jan. 2010 to Nov. 2015. Through a statistical analysis of a large amount of data, the ground-level TEF characteristics of short bipolar test lines at different altitudes were obtained. By comparing the statistical results from different altitudes, it is determined that the dc ground-level TEF and corona inception field strength are linearly dependent on the altitude. Finally, the ground-level TEF and corona inception field strength altitude correction formulas of HVdc transmission lines are proposed.

Corona loss characteristics of bundle conductors in UHV AC transmission lines at 2200 m altitude

Corona loss is the key parameter for evaluating operating economy of ultra-high voltage (UHV) and extra-high voltage (EHV) alternating current (AC) transmission lines and is one of important factors that need to be considered in line design and operation. At present, corona losses of 8×LGJ-630 conductors, which are commonly used in ultra-high voltage alternating current (UHV AC) double-circuit transmission lines on the same tower, and 8×LGJ-720, and 10×LGJ-720 bundle conductors with a larger cross-section and more bundle number in high-altitude areas have not yet been studied. In the paper, the corona losses of the 8×LGJ-630, 8×LGJ-720, and 10×LGJ-720 conductors were measured under conditions of dryness, artificial moderate rain, heavy rain and a wet conductor, based on the UHV corona cage built in Ping’an County, Xi’ning, China at an altitude of 2,200m. By taking typical 1,000kV UHV-AC double-circuit transmission lines on the same tower as an example, the electric field strengths on the surface of conductors in the corona cage and the actual lines were calculated. On this basis, the corona loss of the UHV-AC double-circuit transmission line in a high-altitude area was analyzed. The research results can provide data reference for constructing UHV transmission lines in high-altitude areas.

Radio Interference Performance of HVAC Conductor Bundles at High-Altitude Location: Measured Data Analysis and Altitude Correction

Radio interference (RI) induced by the corona discharge of alternating current transmission lines is more severe at high altitudes than at low altitudes; hence, RI is a crucial limiting factor in the structural design of transmission lines and environmental impact assessments. To determine RI performance at high altitudes, the State Grid Corporation of China constructed an ultrahigh-voltage (UHV) corona cage in Xining in 2015 at an altitude of 2261 m. In this study, the cage was used to investigate a high number of bundled conductors under heavy rain. An RI excitation function was derived from Xining and the effects of several variables on RI performance were analyzed. In addition, RI altitude corrections were studied by comparing the Xining data with data obtained from a UHV corona cage in Wuhan located at an altitude of 23 m. The RI correction value was verified not to be a constant value but rather one that changed with the surface electric field and bundle size. The correction values obtained in this paper could enable the RI levels of high-voltage alternating current transmission lines at high altitudes to be evaluated more precisely.

Corona onset gradient of the bundle conductor on AC power lines under sand and dust weather condition at 2,200 m altitude

During spring and autumn, sand storms occur frequently in high-altitude areas of Northwest China. The presence of sand particles may affect the corona characteristics of the bundle conductor on AC power lines. A simulation system of sand and dust weather conditions was established to investigate the corona characteristics of 23 types of bundle conductors in Ping'an County (elevation 2200 m). By using tangent method, the corona onset gradient (COG) was obtained for the first time. Finally, the prediction formula for the COG was proposed considering the sub-conductor radius, bundle number, sand and dust concentration, and sand particle size.

Wake-induced oscillation behaviour of twin bundle conductor transmission lines.

A numerical method to simulate air flow around a bundle conductor line by means of the FLUENT software is presented and verified by a wind tunnel test for aerodynamic characteristics of a twin bundle conductor line. The lift and drag coefficients of the leeward sub-conductor of a twin bundle conductor varying with its relative position in the wake zone to the windward one under different wind velocities are numerically determined by the presented method. A user-defined subroutine of ABAQUS software is developed to apply the aerodynamic loads on each sub-conductor and the electromagnetic force between sub-conductors. The numerical simulation method for wake-induced oscillation of a bundle conductor line is proposed. By means of the numerical method, wake-induced oscillation processes of twin bundle conductor transmission lines under different parameters, including current intensity, spacer layout, span length and wind velocity, are numerically simulated. Moreover, the effects of those parameters on the oscillation characteristics of the lines, such as vibration mode, frequency, amplitude and motion trace, are discussed. The results obtained provide a fundamental basis for the understanding of wake-induced oscillation behaviour of twin bundle conductor transmission lines and the development of control technique for wake-induced oscillation.

Corona Onset Characteristics of Bundle Conductors in UHV AC Power Lines at 2200 m Altitude

The corona onset characteristic of bundle conductors is an important limiting factor for the design of UHV AC power lines in high-altitude areas. An experimental study on the corona characteristics of 8 × LGJ630, 6 × LGJ720, 8 × LGJ720 and 10 × LGJ720 bundle conductors commonly used in UHV power lines under dry and wet conductor conditions, as well as artificial moderate and heavy rain conditions, was conducted in Ping’an County, Xining City (elevation 2200 m). By using the tangent line method, the corona onset voltages and onset electric field of four types of conductors at high altitudes are obtained for the first time. In addition, the calculation model of corona onset voltage considering the outer strands’ effect on the electric field and the geometric factor in the corona cage in high altitude areas is established. The comparison of the calculation results and experimental results under dry conditions verifies the model’s correctness. Based on the results, an optimal selection scheme for high altitudes is proposed. The roughness coefficient was also calculated and analysed: the roughness coefficient of bundled conductors was between 0.59 and 0.77, and the roughness coefficient of the wet conductor was between the dry and rainy conditions. Both the experimental data and the calculation model can provide a reference for conductor selection for UHV AC power lines for use in high-altitude areas.

Open source cable models for EMI simulations

One of the most significant coupling paths for electromagnetic interference into systems is via cables [1], This may be cable to cable coupling within a bundle of conductors or coupling from an illuminating electromagnetic field [2]–[4], These coupling effects may be enhanced by non-ideal cable terminations such as pigtail connections of shields or by crosstalk within connectors [5], In addition, imperfect cable shields allow coupling via transfer impedance and transfer admittance [6][7].

A helical charge simulation based 3-D calculation model for corona loss of AC stranded conductors in the corona cage

Corona loss generated from conductors is an indispensable factor in the design of alternating current(AC) transmission lines. Based on a helical charge simulation method, a 3-D calculation model for corona loss considering the outer strands of the conductor in the corona cage was established. Compared to the 2-D corona-loss calculation method, the calculation model proposed in this study incorporates the heterogeneity of the electric fields strength along the axial direction of the stranded conductor. Furthermore, it was also able to calculate the corona loss when the conductor had sagged. The calculation results of the LGJ-300/40 and LGJ-400/35 in the small corona cage show close agreement with the measurement results indicating that the corona-loss calculation model was accurate. In addition, the corona loss of the bundle conductors 4 × LGJ720 with sag in the UHV corona cage was also analyzed.

Evaluation of Corona Loss in 750 kV Four-Circuit Transmission Lines on the Same Tower Considering Complex Meteorological Conditions

As an important index for measuring the operational economy of EHV AC transmission lines, corona loss (CL) is one of important factors worth considering during the operation and design of transmission lines. The 750-kV transmission lines are mainly distributed in high-altitude areas in northwestern China, where sand storm occurs frequently in spring and autumn. At present, a few researches are available on the evaluation of CL in multi-circuit transmission lines on the same tower in sandy and dusty area at high altitudes. Based on a transmission project with four-circuit transmission lines on the same tower in the north of Xi’an, Shaanxi Province, China, the electric field distributions of bundle conductors under two types of arrangement structure, including six and four cross-arms tower, were investigated. Then, by using the CL equivalent theory, the CL under meteorological conditions of fair, rainy, snowy, foggy, and dusty weather were evaluated. Finally, the optimal phase-sequence arrangement under the optimal tower modes was proposed, and the CL and resistance loss under the selected arrangements were compared.

Current Reconstruction of Bundle Conductors Based on Tunneling Magnetoresistive Sensors

The current monitoring of bundle conductors is essential for precisely locating operation failures in transmission lines, leading to a more stable and reliable power grid. This paper proposed a novel method for current reconstruction of bundle conductors, utilizing tunneling magnetoresistive (TMR) sensors. Both the normal and abnormal situations are discussed. The optimal and sub-optimal measurement points for sensors were obtained for concise current measurement with only one uniaxial TMR sensor. The current in each bundle conductor was calculated separately based on the comprehensive algorithm. Validation experiment indicated the error of the measurement and calculation system was no more than 10%, proving the robustness and feasibility of the measurement system and the algorithm. The reconstruction process takes full advantages of TMR sensors and provides a promising solution for transmission line monitoring in power grid.

On the Generation Functions of DC Corona Performance

Definitions of generation functions of corona loss (CL), radio interference (RI), and audible noise (AN) traditionally used in the evaluation of ac corona performance were found to not be applicable to dc corona. Based on the results of CL calculations in cage and monopolar dc transmission-line configurations, proposals are made for a new definition of CL generation function that includes geometric parameters of the respective conductor configurations. Using published experimental data obtained for the same conductor bundle in two cages with different geometric parameters, it is shown that the same definition can be used for monopolar dc corona generated RI and AN. Calculations also show that the new definition applies to the case of CL from bipolar dc transmission-line configurations. Finally, the possibility and limitations of using cage tests for predicting the CL, RI, and AN performance of bipolar dc transmission lines are examined.

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.

Audible Noise Performance of Conductor Bundles Based on Cage Test Results and Comparison with Long Term Data

A reasonable acoustic power formula is vital to precisely evaluate the audible noise (AN) level of ultra-high-voltage (UHV) AC power lines. This study derived a formula by taking several AN measurements under heavy rain conditions, using multiple conductor bundles in a UHV corona cage, and then subjecting these measured values to least squares fitting. The validity of the proposed formula was subsequently verified with statistical data obtained from two long-term stations at Henan and Hubei Province, which are located under the Jindongnan-Nanyang-Jingmen UHV AC transmission lines operating at 1000 kV. The deviation between the prediction and the long-term (L50) value was 0.76 dB for the Henan station and 0.17 dB for the Hubei station. It shows that the acoustic power formula derived in this paper is more accurate than the widely used Bonneville Power Administration formula, in which the corresponding deviations are much larger (3.07 and 2.53 dB).