The electric field strength beneath 1000 kV ultra-high-voltage transmission lines is relatively high, posing a risk of excessive electric field exposure in the presence of nearby buildings. Shielding wires are an effective technical measure to mitigate excessive electric field strength at sensitive locations; however, optimal performance depends on the appropriate selection of shielding parameters such as wire size and placement. In this study, a 6 m × 6 m building platform was constructed beneath a 1000 kV double-circuit transmission line mounted on a single tower. Shielding wires with heights of 5 m, 6 m, and 7 m were installed. The electric field distribution above the building, as well as the shielding effects, were analyzed. The optimal positioning of the shielding wires was also investigated. The results indicate that the electric field on the upper surface of the platform closest to the transmission line side can reach 5 kV/m, while the electric field on the second-level platform can reach up to 7.5 kV/m. A single shielding wire can reduce the electric field strength by 21.7%, whereas multiple wires can achieve reductions of more than 30%. We convert the above electric field model into a mathematical model and propose an optimization method for the shielding wires position. When the height of the shielding wire is less than 8 m, the optimal placement is approximately directly above the sensitive point. These findings provide practical guidance for mitigating electric fields near sensitive areas and offer a technical foundation for the design and installation of shielding wires.

Radio interference (RI) is a key environmental indicator of extra-high-voltage (EHV) AC transmission lines. In high-altitude regions, the harsh climate and thin air result in a more intense corona discharge of the conductors, making the effects of meteorological parameters on RI even more complex. In this study, we perform statistical analysis of RI data collected over 1-2 years from three EHV transmission line observation stations located at an altitude of 1854, 3320, and 3950 m to investigate the effects of meteorological parameters on the RI level of EHV AC transmission lines at high altitudes. The correlation coefficients between RI and meteorological parameters under different weather conditions were calculated, followed by an analysis of the effects of rainfall rate, relative humidity, temperature, dew point, and other meteorological factors on the RI level. The statistical values of RI under different seasons and weather conditions were then compared. The findings are of significant importance for the measurement, prediction, and control of RI in high-altitude AC transmission lines.

The corona inception field strength is a key factor in the corona discharge of transmission lines. Accurate discrimination is of great significance for the study of corona effects and the characteristics of the electromagnetic environment. To this end, this study theoretically analyzes the linear relationships between radio interference (RI), audible noise (AN), and the voltage applied to the conductor after the conductor initiates corona. It improves the previous methods for discriminating the corona inception field strength and proposes a method for discriminating the corona inception field strength of conductors based on the RI voltage and sound pressure of AN. Corona discharge tests of smooth and multistranded conductors were carried out in the laboratory and in a ultrahigh voltage (UHV) corona cage at an altitude of 4300 m, respectively. For the smooth conductors in the laboratory, after the conductors initiated corona, the goodness-of-fit between the RI voltage, the sound pressure value of AN, and the applied voltage are 0.987 and 0.992, respectively. The relative errors between the calculated results of the corona inception field strength and the Peek formula are 3.74% and 2.18%, respectively, which verifies the effectiveness of the method. The method is extended and applied to four types of large cross section multistranded conductors: 6 & times; LGJ 720/50, 8 & times; LGJ 1000/45, 8 & times; LGJ 1250/70, and 12 & times; LGJ 500/45 in the UHV corona cage test, and corona inception field strengths under dry and rainy conditions are obtained. The results show that the proposed method can be effectively applied to the discrimination of the corona inception field strength of alternating current (AC) conductors, providing a basis for the selection of UHV AC conductors and other work.

Audible noise (AN) is a critical parameter in the economic and environmental design of extra-high voltage (EHV) AC transmission lines, especially in high-altitude regions. Although several altitude correction factors and AN prediction methods have been proposed based on corona cage tests and long-term observations, the accuracy remains uncertain owing to the limited measurement data from high-altitude transmission lines. This study addresses this gap through long-term observations of four EHV transmission lines on the Tibetan Plateau, combined with existing corona cage test results. The cumulative distribution of AN in rainy weather was obtained from various observation stations. By comparing measured values from stations at different altitudes and combining the experimental results from a movable corona cage, an altitude correction method for AN was developed. Subsequently, by comparing statistical data from four high-altitude observation stations with predicted results from different approaches, the predicted values were found to be overestimated. An improved prediction method for AN in rainy weather was proposed. Additionally, based on the statistical differences observed over one year at multiple long-term observation stations, a method for evaluating AN under varying weather conditions was investigated. A predictive model for AN under different rainfall conditions was developed based on correlation and multiple regression analyses, and its accuracy was validated. The findings of this study provide a crucial reference for the prediction and evaluation of AN from EHV AC transmission lines in high-altitude regions.

Radio interference (RI) is a critical factor in the design of extra-high voltage (EHV) transmission lines at high altitudes. To address the insufficient field data of RI on high-altitude transmission lines, the lack of adequate validation for existing RI prediction methods, and the difficulty in assessing RI levels under various meteorological parameters, this study investigated prediction methods for RI in high-altitude AC transmission lines based on long-term observations. First, the altitude correction factors for RI were investigated by comparing long-term observational data from different altitudes and results of movable corona cage tests. Second, a more accurate RI prediction method for high-altitude transmission lines was proposed by comparing the long-term measured data from four high-altitude observation stations with the predicted values derived from various formulae. Finally, correlation and multiple regression analyses were employed to develop RI prediction models considering the effects of different meteorological parameters under both rainy and fair weather conditions. The accuracy of these models was validated using actual measurement data. The findings provide important references for the prediction and evaluation of RI from EHV AC transmission lines at high altitudes.

Audible noise has become a critical constraint in the construction of high-altitude ultra-high-voltage alternating current (UHV AC) projects. Currently, there is a lack of research on audible noise from UHV AC transmission conductors under extreme altitudes above 4000 m. This study, conducted at the Yangbajing High-Altitude Test Base in Tibet (4300m), employed a UHV corona cage and a BK sound measurement system to investigate the audible noise characteristics of three typical conductor configurations—8 × LGJ-1000, 10 × LGJ-630, and 12 × LGJ-500—under both dry and rain conditions. The audible noise levels under varying surface electric field strengths were systematically measured, and the coupling effects of rainfall and electric field intensity on noise generation at extreme altitudes were analyzed. Furthermore, using a typical 1000kV UHV AC single-circuit transmission tower configuration, a sound power calculation method was applied to evaluate the audible noise of transmission lines at 4300 m altitude. The findings provide essential references for the design and construction of UHV AC transmission lines in extremely high-altitude regions.

The attenuation of corona current pulses in overhead transmission lines is key to understanding radio frequency interference. Previous studies focused on specific frequency spectra and complex calculations, lacking practical engineering applicability and time-domain pulse attenuation data. This article uses typical positive and negative corona current pulse waveform and ATP-EMTP program to simulate the attenuation of these pulses on 1000kV UHVAC overhead transmission lines, and obtained the corresponding attenuation law. This simulation method can quickly assess corona current pulse attenuation for any overhead transmission line.

Audible noise (AN) is a critical factor in determining the conductor size and phase-to-phase distance for AC transmission lines in high-altitude areas. To obtain the characteristics of the AN from extra-high voltage transmission lines in such regions, a two-year long-term measurement was conducted at the 750-kV Guanting Observation Station, located at an altitude of 1854 m on the Tibetan Plateau. The annual AN data were categorized into six weather types, and normality tests were performed on the data. The results showed that pure sound was most prominent during rainy and heavy snow weather, the L50 values of AN under different weather conditions and their interrelationships were obtained. The probability of AN being below 55 dB(A) during rainy days was 98.5 %, while 97.8 % below 45 dB(A) across all weather types. The two-year L50 values were consistent with those from two independent one-year observations, indicating that a single year of observation is sufficient to determine the AN levels. A more efficient method to estimate the annual L50 value for rainy days through short-term observations was also proposed. Additionally, the measured AN values were more consistent with the Bonneville Power Administration formula predictions after subtracting 2 dB. The research findings are important for the measurement, prediction, and control of AN in high-altitude AC transmission lines.

The corona onset field strength is a critical factor for corona discharge in transmission lines, and accurately discriminating it is crucial for studying the corona effect and electromagnetic environment characteristics. In this paper, corona cage tests were conducted to determine the corona onset field strength of conductors. The relationship between radio interference (RI), audible noise (AN), and applied voltage was analyzed, and a method for discriminating the corona onset field strength based on RI voltage and AN sound pressure was proposed. For smooth fine copper wires tested in the laboratory, the regression coefficients R 2 between RI voltage, sound pressure, and applied voltage exceeded 0.98. The maximum relative error between the calculated corona onset field strength and the Peek formula was 6.04%, validating the effectiveness of the method. The results indicate that this method is more accurate than traditional methods and can be effectively applied to determine the corona onset field strength of AC conductors.

The development of electric vehicle charging facilities has been extremely rapid in recent years. The power quality issues of charging facilities have also become increasingly important. Traditionally, it was believed that the performance of charging piles based on PWM rectification technology was excellent, with no harmonic components in the AC current waveform and the current phase fully tracking the corresponding phase voltage. As a result, it was thought that there were no power quality problems. However, the charging piles and stations that have actually been put into operation have exhibited characteristics such as current waveform distortion and the current phase leading the voltage. At present, there is no clear research conclusion on whether these problems are isolated phenomena or common issues. This paper selects several typical DC charging piles and large-scale charging stations for field measurements. Through extensive data analysis, it has been clarified harmonic current and capacitive reactive power are common phenomena in charging piles and stations. A method using the APF device is proposed to solve the harmonic and reactive power problems of charging piles and stations, and the correctness and feasibility of the proposed method has been verified by the simulation results.

The development of ultra-high-voltage direct current (UHVDC) projects in China has led to the consideration of ground-level total electric fields of DC transmission lines in the selection of conductors. The total electric field is intimately linked to line corona and is substantially impacted by the surrounding environment. Despite ongoing scientific research, the theoretical relationship between total electric field and weather parameters remains incompletely understood. Furthermore, the investigation of the effects of weather parameters on total electric fields is still inadequate for operating UHVDC lines. To address this knowledge gap, we analyze the impact of air temperature, humidity, and wind speed using prevailing theories in the literature. Furthermore, we apply the Random Forest method to measured data collected over approximately 13 months from an operating ±800 k V bipolar DC line to ascertain the essential ranking of weather parameters that impact the total electric field. Our research outcomes enhance our understanding of the statistical impact of weather parameters on total electric fields at a macroscopic level.

AbstractBuildings near direct current transmission lines are sensitive to the electromagnetic environment, and the measurement of the electric field above them is important in engineering design and environmental assessment in China. The models of buildings and probes in the ion flow field were established to explore the accurate measurement method of the electric field above the building. Based on the upstream finite element method and the predictor–corrector method, the influence of whether the probe was grounded or not above the building was studied. On this basis, simulation experiments and real‐type experiments were carried out. The results show that when the electrical conductivity of the building was greater than 10−10 S/m, being grounded or not would not change the results. When the building conductivity was between 10−11 and 10−12 S/m, the electric field measurement results would be increased by 30% to 120% after grounding. In the real‐type experiments on the platform with a plywood roof, the relative error in the electric field when grounded or not was only 2.6%. This proved the reliability of the calculated results. In this paper, the measuring method of the DC space charge‐modified electric field above buildings was analyzed first, and the conclusion that ground wire can be cancelled above buildings with general materials was presented. The research results can provide a technical basis for the accurate measurement of the electric field above the buildings near DC transmission lines.

China is now rapidly developing ultra-high voltage (UHV) AC transmission lines to meet the needs of national economic development. Due to the limited land resources, the choice of line corridor has become a design problem The proximity of lines to be close to residential area causes the electric field distortion and partial exceedances at residential buildings, which causes public concern. This paper uses the finite element method to calculate the distortion field intensity distribution law of the roof and platform observation surface near the 1000kV AC double-circuit transmission line, and explores the effect of reduction of the trees on the power frequency electric field by establishing different heights of the cypress tree model The results show that the maximum value of the distortion field is generally found at the top corners and edges near the line. When the tree is higher than the house, the effect of reduction for trees on the electric field becomes better, as the distance between tree and house decreases.

From the design point of view, the audible noise(AN) on rainy days is the most concerned parameter. For 1000kV UHV AC lines, many prediction methods for rainy days are mainly based on the statistical data of the test lines, and do not take into account the variation of rainfall deeply. In this paper, the first long-term observation station has been established under the Huainan-Shanghai 1000kV UHV AC double-circuit transmission line which has been in operation for 2 years, and the AN test has been carried out for one year. The statistical results during rain in different seasons and the influence of rain rate are analyzed, and compared with the longterm test statistical results of 1000kV UHV AC single circuit line. The statistical prediction method for AN of 1000kV UHV AC transmission lines during rainy days is proposed.

The electromagnetic environment of UHV AC transmission project mainly considers the electric field, magnetic field, radio interference (RI) and audible noise. Based on the condition of electrified test of UHV AC Gas insulated line (GIL) test line, the measurement of electromagnetic environment was carried out, the limits of these impact factors were sorted out, the field measurement was carried out, and the conformity to the limits was analyzed. The electromagnetic environment around GIL was measured under different conditions of current and voltage. The measurement results have shown as follows: The electric field strength increased significantly after voltage was applied, and the electric field strength generated by line structure above GIL and VFTO device was dominant. After current and voltage were applied, the magnetic flux density around GIL increased significantly, and the maximum value was near the middle of the straight line or at the corner. The farther away the GIL is, and the higher the GIL is from the ground, the lower the magnetic flux density is. While voltage was applied and no current was applied, RI increased significantly, and RI generated by line architecture above GIL and VFTO was dominant. Considering the horizontal attenuation, the distance above 20 m can meet the limit requirements. After applying voltage and current, even if there were buildings under construction nearby, the Zone-0 daytime limit of 50 dB(A) was not exceeded. In general, the electromagnetic environment level of UHV AC GIL test line meets the requirements of relevant limits.

The numerical calculation of electromagnetic field has always played an important role in engineering practice. Different numerical methods, such as finite element method, simulated charge method, boundary element method and moment method, have been summarized for different applications. These numerical methods have led to their simulation because of their own mathematical model, theoretical basis and assumptions. The limitations of the occasion promote the rational application of different numerical calculation methods in different electromagnetic field projects. However, in the face of complex engineering applications, these limitations often expose the disadvantages of single numerical calculation method, reduce the efficiency of simulation work, reduce the accuracy of simulation calculation and even make it impossible to carry out simulation work. In this paper, the advantages and disadvantages of the finite element method and the charge simulation method used in the numerical calculation of electromagnetic field are compared and analyzed. The theory and method of coupling simulation calculation of complex electric field model are proposed. The method is used to calculate the distortion electric field model of UHV AC transmission line. The results show that the coupling method of finite element method and simulated charge method can significantly improve the efficiency and accuracy of simulation calculation, and is more suitable for engineering practice.

The ion-flow environment is an important corona design factor of HVDC transmission lines. The space charges generated by corona form a typical convection-dominated ion-flow field. For this special transport phenomenon, however, standard Galerkin FEM always presents serious deficiencies. In this study, a new approach is used to solve ion-flow field based on Petrov-Galerkin method derived from the theory of fluid computation. A high-order stabilisation technique is used to overcome the non-physical oscillations in the presence of highly convective effects. This algorithm is equivalent to the proper modification of weight function according to the direction and magnitude of local drift velocity. It reflects the characteristic of information propagation in flow problem. The establishment procedure of weak form and matrix gives a further explanation on the deficiency of Galerkin method. Moreover, to guarantee convergence of the iteration for this fully-coupled non-linear problem, a relaxation method is introduced in the iterative loop. Calculations with the Petrov-Galerkin least square method are in good agreement with analytical solution and experiment values of ground-level values and corona losses. Results show that the proposed stabilisation technique is able to preclude the numerical spurious oscillation and has a higher-order accuracy than the fully-upwind treatment.

Building HVdc and HVac transmission lines in the same corridor or even on the same tower is an attractive way to extend electricity transport capacity where getting the new right of way is difficult. The resulting hybrid lines produce a new corona performance, such as ground-level hybrid electric field and ion current density, which are quite different from those of pure ac or dc lines. In this paper, inherent space-time pattern and characteristics of the information propagation in Lagrangian description are presented for the ion transport problem, that is, the ion density at a certain point has a direct relationship with its drift time. Based on this, the theoretical explanation is provided for the decoupling algorithm, by which the ground-level dc component can be solved with the ac conductors assumed to be at zero potential and vice versa. The simulation results show that the sinusoidal ac field has negligible influence on the dc ion drift time from conductor surface to ground, whereas stationary electric field generated by the grounded ac lines has a dominant effect. Therefore, ac energization has a rather low impact on ground-level quantities and the simplification of grounded ac conductors is quite reasonable.

It is an attractive way to build the ac/dc hybrid overhead lines to increase the capability of scarce transmission corridors. In this paper, a new approach is present to solve the fully coupled ion-flow problem of ac/dc hybrid lines. The 2-D transport equation of ions is transferred to 1-D fully coupled characteristic equations along each flux line, based on the methodology of the flux tracing method (FTM). An iterative process is proposed to reduce the error due to Deutsch assumption used in FTM. The calculation is efficient as only 1-D transport equations are solved. The iteration converges within only a few times since all the boundary conditions can be satisfied at each step. Results coincide well with measurements and calculations in the previous literature. Comparison shows that Deutsch assumption may lead to significant errors for the hybrid models and the proposed modification should be used.

In order to investigate the effects of intermittent exposure extremely low frequency magnetic field on embryonic development of fish, Zebrafish was selected to serve as the study object to study the embryonic development effect of intermittent exposure to magnetic fields.Hatching fertilized eggs of zebrafish was placed in the magnetic field of 50Hz and 100μT, and divided into five groups which include control group, "1h exposure/5h intermittence", "2h exposure/4h intermittence", "3h exposure/3h intermittence" and full day exposure according to daily exposure time.Then, it was necessary to analyze the difference between relevant embryonic development indexes of each group.The results showed that at 96h of zebrafish embryonic development, there was no significant difference between survival rate, aberration rate, hatching rate of exposed embryos in each magnetic field and the control group (probability P>0.05); Heart rate gradually increased with the increase of embryo and there were no significant differences between groups (P>0.05).The study showed that the selected magnetic field exposure conditions had no significant effect on embryonic development of fish.