Search

Ionized field strength on the ground level is one of the fundamental electromagnetic environment parameters of ultrahigh voltage direct current (UHVdc) transmission lines. An algorithm of an upstream boundary element method is presented in this paper to calculate the ionized field on the boundary with a high accuracy. The ionized field is generated and measured in an experimental platform with an HV conductor to a grounded cylindrical corona cage. The relations between ionized field strength and applied voltage, conductor position, and conductor diameter are investigated. Calculations show that the relative error of the ionized field on the HV electrode could be reduced to 0.1% when compared with the analytical solution. Ionized field distribution under the typical ±1100 kV UHVdc transmission lines is also analyzed as the application. [ABSTRACT FROM AUTHOR]

Ion mobility is one of fundamental parameters to describe the motion of ions in an electric field and a significant quantity to calculate the ionized field and ion current density of ultrahigh-voltage direct current (UHVDC) power lines. This paper presents a measurement method for atmospheric ion mobilities in a DC corona discharge. An apparatus with coaxial cylindrical electrodes is designed and utilized. A vibrating electric field meter is employed to measure the ionized field of the electrode. Experimental results show that under atmospheric conditions, the average positive and negative ion mobilities are 1.76 × 10−4 and 1.88 × 10−4m2·V−1·s−1, respectively. The proposed method is compared with previous works of others. The impact of fluctuations of the measured ionized field and ion current density on the results of ion mobilities is also analyzed. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

The ionized field is one of significant parameters to evaluate the electromagnetic environment of ultra-high-voltage direct current (UHVDC) transmission lines. The field mill is usually utilized to measure the ionized field on the ground level under the UHVDC power lines. In order to investigate the distortion characteristics of the ionized field with the presence of spaces charges near the probe of the field mill, Poisson's equation and current continuity equation are solved, respectively, based on the finite-element method and Gauss's law in the cylindrical coordinate system. The ionized fields on the surface of the probe are calculated under different ion current densities. An experimental apparatus with corona wire net and ground plate is designed and used to measure the ionized field and ion current density. Experimental results have shown that the measured data are consistent with the calculated ones, which verify the validity of the algorithm presented. The impact of the space charges on the field mill may provide valuable reference for the measurement of the electromagnetic environment of UHVDC projects. [ABSTRACT FROM PUBLISHER]

Ionic mobilities are characteristic parameters for describing the motion of charges in electric field and also basic parameters for the calculation of ionized field and ion current density of ultra high voltage direct current (UHVDC) transmission lines. This paper presents a measurement method of ionic mobilities in air. The analytical solution of ion mobility was derived from the equations of the ionized field and the ion current density. A circular parallel plate apparatus was applied to measure the ionic mobilities. Experimental results show that in direct current corona discharge of room temperature, the measured result of negative ion mobility was 2.23 to 2.51 ×10−4 m2·V−1 s−1, and the average value was 2.39 ×10−4 m2-V−1·s−1; the measurement of positive ion mobility was 1.54 to 1.93 × 10−4m2·V−1·s−1, with the average of 1.71 × 10−4 m2·V−1·s−1. [ABSTRACT FROM PUBLISHER]

Ions generated by corona discharge of high‐voltage direct current (HVDC) transmission lines exist in the space between conductors and the ground. Electric field strength, ion current density, and space charge density are significant electromagnetic environment parameters of HVDC transmission lines. To measure the charge densities at ground level under the HVDC power lines, an aspirator‐type charge meter is designed and utilised. The charge meter is calibrated in the ionised field generated by parallel metal mesh and plate. Charge densities on the ground under the unipolar HVDC conductor are measured by the calibrated devices in the laboratory. Experimental results show that reasonable agreement between measured data by the devices and the ones by field mills and ion current plates could be obtained, which establishes a foundation to research the charge characteristics of ions near the ground. [ABSTRACT FROM AUTHOR]

Although transverse wind exerts an important influence on the distribution of the ion current density under HVDC transmission lines, very few experiments involving stable wind have been used to verify the numerical model. To overcome the variability of natural wind, a low-speed wind tunnel was used to produce stable wind in this research. An experimental platform was set up in the wind tunnel, to measure the ion current density of dc wires. Based on the experiment, transverse wind exerted a significant influence over the distribution of the ion current. The numerical model was discussed and the results showed reasonable agreement with the measured values for different wind speeds. [ABSTRACT FROM PUBLISHER]

The sound pressure level (SPL) has been generally accepted in the measurement and evaluation of degree of nuisance to the corona-generated audible noise from transmission lines. Quite many scholars have studied the spectrum and statistical characteristics of the SPL from transmission lines through the long-term frequency measurement. In fact, the corona sources on the transmission lines usually act as sound sources emitting sound pressure pulses with random amplitudes and random time intervals, yet the statistical characteristics of the random sound pressure pulses and their correlation to the SPL have barely been investigated. In this paper, a series of experiments with single positive corona source in a coaxial cylindrical structure were carried out to investigate the statistical characteristics of the pulse amplitudes and time intervals of sound pressure pulses. In the experiment, time-domain measurement for the audible noise was employed. Based on the statistical results, a stochastic model was developed to simulate the sound pressure pulses. The validity of the stochastic model was testified by comparing the simulated and measured A-weighted sound pressure levels. On the basis of the stochastic model, the influence of random pulse amplitudes and time intervals of the sound pressure pulses on the resultant SPL was demonstrated. [ABSTRACT FROM AUTHOR]

Audible noise and corona current are two main DC corona effects, and they may both highly depend on the characteristics of space charges generated during corona discharge. However, relatively little investigation has previously been done on the correlation between them especially in time-domain. In the present work, the timedomain waveforms of audible noise and corona current generated by single positive corona source were recorded simultaneously. Their characteristics were carefully analyzed and found to be closely related. It was found that both the audible noise and the corona current consisted of repetitive pulses, and one-to-one relationship in time could be observed and confirmed between them. Furthermore, a linear correlation between the peak-to-peak values of audible noise pulses and the amplitude of corona current pulses was obtained. Empirical formulas with the same forms for them were derived to further prove the linear correlation. The close correlation between the audible noise and the corona current was interpreted qualitatively in the presented work and found to be highly related to the generated space charges. [ABSTRACT FROM AUTHOR]

This paper aims to investigate time-domain characteristics of the audible noise caused by single corona source under positive corona discharge. The obtained time-domain waveform of the audible noise consisted of a series of bipolar sound pressure pulses. After the background noise was successfully removed, the characteristics of audible noise pulses, such as amplitudes of each pulse, pulse rate and apparent duration time, were analyzed in this paper. Using the applied voltage and the onset voltage as variables, empirical formulas were derived from the measured results to predict the pulse rate and the amplitudes of the pulses. Furthermore, a typical waveform in the form of segmented double exponential function was developed to simulate the audible noise pulse. The rationality of the typical waveform was confirmed both in time domain and in frequency domain. Finally, some qualitative explanations for the generation of the bipolar pulse waveform of audible noise were given. Based on the remaining space charges characteristics, the influences of the applied voltage on the amplitude and pulse rate of the audible noise pulses were studied qualitatively. [ABSTRACT FROM AUTHOR]

With more HVDC transmission lines being built in China, the situation of the plastic greenhouses existing underneath the HVDC lines is becoming more common when the transmission lines pass over the farmland. The ionic space charges generated by corona discharge of HVDC transmission lines strengthen the electric field at the ground level. And with the accumulation of the ionic space charges on the surface of the plastic greenhouses, the ion-flow fields are highly perturbed. In this paper, a set of single conductor experiments is performed in the laboratory. Extensive measurements are carried out for different voltages and polarities with different types of plastic greenhouse models. The main goal of this work is to make it clear that whether or not the presence of greenhouses would affect the ion-flow fields and ion current density inside the greenhouse models. And through the analysis and discussion, we find out the differences of the ion-flow fields when the greenhouse models exist or not, which is the foundation of the future research. [ABSTRACT FROM AUTHOR]

The HVDC and HVAC transmission lines running on the same tower is a promising technology to improve the transmission capacity of an existing corridor. The ions generated by corona discharge of HVDC transmission lines will strengthen the ground-level electric field, which may endanger human exposure. To investigate how the presence of HVAC transmission lines changes the ion-flow field, experiments are carried out on an indoor test model with bipolar dc and three-phase ac lines. The experiment results are then compared with the simulation results. The experiment and simulation results show that the HVAC transmission lines have a shielding effect on the ion-flow field from the HVDC transmission lines running above. Finally, the ground-level electric field and ion current density of the \pm 800–kV HVDC and 500-kV HVAC transmission lines running on the same tower are calculated. [ABSTRACT FROM PUBLISHER]

This paper aims at investigating the mechanism of hybrid ac/dc corona which is usually accompanied with the hybrid HVAC/HVDC power transmission lines. A coaxial wire-cylinder corona cage is designed in this paper, and the combined ac/dc voltage is applied to the wire and cage. The low-frequency component of corona current from the hybrid ac/dc corona in this corona cage with five types of wires is measured. To obtain the detailed characteristic of the interaction between the space charge and ionized electric field, a 1-D method is developed to simulate the hybrid ac/dc corona in the symmetrical corona cage. This method is validated through the comparison with measurement results. Based on this simulation method, analysis of the evolution of space charge and ionized electric field in one time cycle is presented. The regular pattern of charge injection from the discharge electrode is summarized, where the charge injection is found not linearly dependent on the applied voltage. Finally, the corona loss of hybrid ac/dc corona is calculated, and the similar result with the quadratic law in ac corona is found from the calculation results. This research provides useful knowledge for the engineering computation of the effects of hybrid ac/dc corona. [ABSTRACT FROM AUTHOR]

Audible noise (AN) is very important for the construction of transmission lines for the sake of the environment. Especially, at high-altitude areas, it has become a key technical factor deciding conductor types and tower structures. In order to determine the altitude effect and the correction of AN for HVdc transmission lines, four reduced-scale test lines with the same parameters were built up at elevations of 50, 1700, 3400, and 4300 m in China, respectively. Simultaneously, two full-scale test lines were set up in Beijing and Tibet, whose altitudes were 50 m and 4300 m, respectively. Using the test facilities, the AN of HVdc transmission lines had been measured for a four-year period, from January 2010 to July 2014. Through a statistical analysis of a large amount of data, AN characteristics of HVdc transmission lines at different altitudes are obtained. By comparing the statistical results from different altitude areas, it is found that AN of HVdc transmission lines is nonlinearly dependent on altitude. Finally, an AN altitude correction formula of HVdc transmission lines is proposed. It shows that from 0 to 4300 m, the AN correction value of HVdc lines is far less than the predicted value by an HVac method. [ABSTRACT FROM AUTHOR]

An improved method to simulate the ion-flow field generated from the corona discharge on HVDC transmission lines is proposed. To remove the oscillations in simulation of charge conservation law, an upwind weighting function is adopted in the finite-element method. The Poisson's equation and the charge conservation law are solved simultaneously through Newton's method of iterations, which accelerates the convergence of the algorithm. A rule for charge density on boundary in the bipolar problem is proposed in this paper, which ensures the stability of the iterations. The computation time, convergence rate, and accuracy of the proposed method are analyzed. The proposed method is verified by analytical and experimental results, and then it is applied to the prediction of the ion-flow field from a \pm1100-kV HVDC transmission line. [ABSTRACT FROM AUTHOR]

A modified method based on the optimized charge simulation method (CSM) is used to predict the corona onset voltage and electric field when the space charges due to the corona are considered. Based on the streamer model of corona discharge, space charges generated near the conductors are predicted. In order to calculate the electric field at the conductor surface, space charges are replaced by some equivalent line charges near the conductor. Because of the existence of space charges, the corona onset electric field is changed a little. After a simplified model of actual power transmission lines is introduced with the help of rough coefficient, the corona onset voltage and corona onset electric field are calculated for different types of conductors finally. [ABSTRACT FROM PUBLISHER]

Corona-generated audible noise is induced by the collisions between space charges and air molecules. It has been proven that there is a close correlation between audible noise and corona current from DC corona discharge. Analysis on the correlation between audible noise and corona current can promote the cognition of the generation mechanism of corona discharge. In this paper, time-domain waveforms of AC corona-generated audible noise and corona current are measured simultaneously. The one-to-one relationship between sound pressure pulses and corona current pulses can be found and is used to remove the interferences from background noise. After the interferences are removed, the linear correlated relationships between sound pressure pulse amplitude and corona current pulse amplitude are obtained through statistical analysis. Besides, frequency components at the harmonics of power frequency (50 Hz) can be found both in the frequency spectrums of audible noise and corona current through frequency analysis. Furthermore, the self-correlation relationships between harmonic components below 400 Hz with the 50 Hz component are analyzed for audible noise and corona current and corresponding empirical formulas are proposed to calculate the harmonic components based on the 50 Hz component. Finally, based on the AC corona discharge process and generation mechanism of audible noise and corona current, the correlation between audible noise and corona current in time domain and frequency domain are interpreted qualitatively. Besides, with the aid of analytical expressions of periodic square waves, sound pressure pulses, and corona current pulses, the modulation effects from the AC voltage on the pulse trains are used to interpret the generation of the harmonic components of audible noise and corona current. [ABSTRACT FROM AUTHOR]