Tiebing Lu

The correlation between audible noise and corona current in time domain caused by single positive corona source on the conductor

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 time-domain 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.

Time-domain characteristics of the audible noise generated by single corona source under positive voltage

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.

A Laboratory Study on the Ion-Flow Field Model of the DC Wires in Stable Wind

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.

Statistical characteristics and stochastic model of DC corona-generated sound pressure pulses from single corona source

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.

Time-domain and frequency-domain characteristics of audible noise from single corona source

In this paper, the time-domain measurement method for audible noise is employed to study the time and frequency domains characteristics of audible noise generated by single corona discharge under DC and AC voltage in a coaxial geometry. The results show that in time-domain the audible noise from positive and negative corona discharge both consist of a series of random sound pressure pulses and the amplitudes of sound pressure pulses from positive corona discharge are larger than those from negative corona discharge. As for the audible noise from AC corona discharge in the test, it has a periodic component with a 50Hz fundamental frequency accompanied by sound pressure pulse trains mainly near the negative peaks of AC voltage. When the applied voltage is further increased, sound pressure pulses may be generated at the positive half-cycle. The asymmetrical waveforms in positive and negative half-cycle of AC voltage may attribute to the influence of the space charges. Besides, the discrete wavelet transform (DWT) is used to analyze the detailed characteristics and the difference of corona-generated noise and the background noise. Furthermore, the frequency-domain characteristics of audible noise from DC and AC corona are analyzed based on the time-domain results. This presented work hopefully will be a useful reference for further theoretical studies of the audible noise caused by corona discharge.

The impact of composite AC-DC voltage on characteristics of corona discharge in rod-plane air gaps

In order to obtain the corona characteristics of electrodes under positive DC and AC composite voltages, the experiment platform of series circuit was established by using a stainless rod-plane electrode, in which rod electrode was applied with positive DC voltage, and plane electrode was applied with AC voltage. The change of ultraviolet photon counting was used as the corona criterion and the characteristics of corona inception voltages were studied. Besides, the influences of composite voltages and geometrical size on the electric field distribution were also investigated. It was found that, in the same atmospheric conditions and electrode arrangement, there exists the minimum corona inception voltage under a certain combination of AC and DC voltage. On the basis of the simulation results of electric field, the variation of composite electric field strength agrees well with that of corona inception voltage under composite voltages. The maximum electric field strength of electrodes decreases with the increase of rod radius or air gaps when fixing the composite voltages of AC and DC.

The features of positive dc corona discharge on the surface of the conductor with different contaminations

HVDC transmission lines operating in polluted areas may absorb a large amount of contamination, which seriously affects the corona discharge and its associated audible noise, electric field, ion current density from the transmission lines. To fully study the effects of conductor surface condition on photon count and dc electric field, conductors coated with different kinds of contamination were investigated and compared with a clean one. Scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) analysis and SPIP were employed to characterize the surface morphology of the conductor samples. To fully study the effects of conductor surface condition on photon count and dc electric field, conductors coated with different kinds of contamination were investigated and compared with a clean one. Kaolin, salt and carbon were used as the coating contamination during the experiment. Experimental results illustrated by both ultraviolet photographs and measurement data reveal the dielectric coating resists corona discharge and enhances the onset voltage when the contamination is uniform enough, while electrical conductive contaminations have less impact when the coating is uniform enough.

A platform for multiple DC corona effects measurements and analysis

This paper describes a platform for measuring the multiple DC corona-generated effects, i.e. audible noise, ionized fields, ion current density and steady corona current simultaneously. The platform includes the corona cage for generating the corona discharge, the corresponding measuring equipment for each corona effect, and the acquisition and analysis system based on LabVIEW. The system can acquire four channels of signal simultaneously with maximum sampling rate 100kS/s. The processing of the measured signals is performed based on the LabVIEW. Based on this platform, some experiments were conducted and some results are presented in this paper.

Study of the contamination thicknesses effects on DC corona streamer pulses based on a corona cage

The previous research work has dealt with corona characteristics of conductors coated with different types of contaminations, while the thickness is rarely considered. To fully study the effects of conductor surface condition on photon count and corona streamer pulses, conductors coated with different thicknesses of contamination are investigated and compared with a clean one. An experimental system based on an indoor corona cage was established to exclude the interference from environmental factors. In the experiment, kaolin was used as the coating contamination on the surface of the conductors. Experimental results illustrated by both ultraviolet photographs and measurement data reveal that the effects of contamination thicknesses on corona characteristics and current pulses are obvious. It can be inferred that the dielectric coating resists corona discharge and enhances the onset voltage when the contamination is uniform enough.

Measurement of corona-generated space charge density under DC test wire

Corona-generated space charge density is an important quantity that helps describe the electrical environment in the vicinity of High Voltage Direct Current (HVDC) transmission lines. This paper develops a device based on the ion counter method to measure space charge density under a DC test wire, which is used to simulate a HVDC transmission line. An experiment is carried out to analyze the various factors affecting the measurement. Another experiment, comparing the device with the indirect rotating field-mill method which is often used to measure space charge density at the ground level, is conducted to verify the feasibility and validity of the device and to calibrate its accuracy. Based on the device, the space charge distributions under the test wire are measured and analyzed.