Xuebao Li

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.

Detailed characteristics of intermittent current pulses due to positive corona

In order to get detailed characteristics of intermittent current pulses due to positive corona such as the repetition rate of burst-pulse trains, the peak value ratio of the primary pulse to the secondary pulse, the number of pulses per burst, and the interval of the secondary pulses, a systematic study was carried out in a coaxial conductor-cylinder electrode system with the conductor electrode being set with a discharge point. Empirical formulae for the number of pulses per burst and the interval of the secondary pulses are first presented. A theoretical model based on the motion of the space-charge clouds is proposed. Analysis with the model gives explanations to the experimental results and reveals some new insights into the physical mechanism of positive intermittent corona.

Impact Factors in Measurements of Ion-Current Density Produced by High-Voltage DC Wire's Corona

The reduced-scale model of HVDC transmission lines in the laboratory is widely used to investigate the ionized fields. This paper is aimed at analyzing impact factors of the ion-current density measurement system based on Wilson plates in the laboratory. Both experimental and numerical simulation methods are used to obtain the characteristics of the measurement system. The results show that measurement data can be calibrated with different Wilson plates, and suitable parameters are proposed in this paper to meet the requirement of measurements. The measurement system described in this paper can be used in other similar applications.

Shielding Effect of HVAC Transmission Lines on the Ion-Flow Field of HVDC Transmission Lines

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 ±800-kV HVDC and 500-kV HVAC transmission lines running on the same tower are calculated.

The Ionized Fields and the Ion Current on a Human Model Under

The ultra-high-voltage direct-current (UHVDC) system has many advantages in long-distance power transmission. This paper is aimed at analyzing the distributions of the ionized fields and the ion current on the human model under ±800-kV UHVDC transmission lines; therefore, a numerical method which combines the 3-D charge simulation method and Deutschs assumption is used. And the validity of the presented method is demonstrated through a test in the laboratory. For ±800-kV UHVDC transmission lines, the ionized fields and the ion current on the human model are calculated, and numerical results show that the ionized fields and the ion current density on the top of the human model increase evidently when the human model stands under ±800-kV UHVDC transmission lines. And the total ion current flowing on the human model is far lower than the permitted limit.

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The corona-generated audible noise (AN) factor is an important consideration in the design and operation of ultrahigh voltage direct current (DC) and alternate current (AC) transmission lines. Due to the differences in discharge process and corona-generated space charges between the DC and AC corona discharge, the audible noise from DC and AC corona has different characteristics. This paper conducts a series of experiments by measuring the time-domain waveforms of the audible noise from a single corona source under DC and AC voltage. Sound pressure pulses are extracted from a correlation analysis, and then a detailed comparison of the basic characteristics of DC and AC corona-generated AN in time-domain and frequency spectrum is given. Results from this paper stand to contribute to an explanation of existing results in AN measurement and analysis from DC and AC transmission lines.

800-kV HVDC Transmission Lines

The corona-generated audible noise (AN) has become one of decisive factors in the design of high voltage direct current (HVDC) transmission lines. The AN from transmission lines can be attributed to sound pressure pulses which are generated by the multiple corona sources formed on the conductor, i.e., transmission lines. In this paper, a detailed time-domain characteristics of the sound pressure pulses, which are generated by the DC corona discharges formed over the surfaces of a stranded conductors, are investigated systematically in a laboratory settings using a corona cage structure. The amplitude of sound pressure pulse and its time intervals are extracted by observing a direct correlation between corona current pulses and corona-generated sound pressure pulses. Based on the statistical characteristics, a stochastic model is presented for simulating the sound pressure pulses due to DC corona discharges occurring on conductors. The proposed stochastic model is validated by comparing the calculated and ...

Comparison between the audible noises generated from single corona source under DC and AC corona discharge

This paper aims at developing a simulation method for the ion-flow field when HVDC transmission lines cross over HVAC transmission lines. A time-domain 3-D method is proposed in this paper, where the 3-D finite-element method and 3-D finite volume method are used to solve the Poissons equation and the charge conservation law, respectively. The implicit temporal discretization scheme is used to accelerate the computation. An indoor test model is set up in this work, and the simulation results agree well with the measured results from this test model, which validates the proposed method. The proposed method is then used to calculate the ground-level electric field and ion current density under the crossing of ± 800-kV HVDC transmission lines and 500-kV HVAC transmission lines. The presence of HVAC transmission lines is found to have a significant influence on the ion-flow field under the crossing.

Statistical characteristic in time-domain of direct current corona-generated audible noise from conductor in corona cage

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.