Zhengying Chen

Conductor Surface Conditions Effects on the Ion-Flow Field of Long-Term Operating Conductors of the HVDC Transmission Line

The influence of conductor surface conditions of new and aged conductors on ground-level resultant electric field and ion current density is analyzed in this paper. The surface roughness and morphology of conductors are measured and analyzed by 3-D phase shift Micro-Xam (MicroXAM-3D) and scanning electron microscopy. Calculations are made using the upstream finite-element-finite difference method for the corona cage model to obtain the influence of surface conditions on the ion-flow field, consequently, changing the resulting electric field and ion current density. An indoor corona cage platform is build up to check the impact of surface conditions on the ground-level resultant electric field and ion current density in the laboratory. Considering the aging characteristics of the conductor surface, a typical

Influence of surface contamination of conductor on positive corona-generated audible noise spectrum characteristics of HVDC system

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A full hydrodynamic steady-state model of positive dc corona in coaxial cylindrical electrode

800 kV ultra-high voltage direct current transmission line is analyzed. The calculated results show that compared with the new conductor, the electric field and ion current density of the long-term operation conductors increase very significantly.

On the radiated EMI current extraction of dc transmission line based on corona current statistical measurements

Surface contamination of high-voltage direct-current power transmission lines has a large influence on corona characteristics. The audible noise of the polluted conductors is much higher than clean conductors. Little is known about the effect of the surface conditions of conductors on spectrum characteristics of the positive corona-generated audible noise under a high voltage. In order to investigate the influence of surface contamination produced by atmospheric pollution on the spectrum of the audible noise, this paper presented the measurement of spectrum characteristics of the audible noise of positive corona discharge in a laboratory corona cage. We researched the influence of deposition and relative permittivity of the contamination on the spectrum characteristics of the positive corona-generated audible noise. The relationships among these factors were consequently acquired. The results revealed that the spectral components of the audible noise of clean conductor were obviously different with the increase of the applied voltage. The spectral components (>1kHz) of the polluted conductors were much higher than those of the clean conductors. The contamination adhering to the surface of conductors affected spectral components (>1kHz) much more obviously than low spectral components, and the results were analyzed in this paper. The conclusion lays a foundation for researching the influence of the surface conditions on the corona-generated audible noise.

Inception threshold conditions for positive dc corona in a rod-plane electrode at low atmospheric temperatures

The predictions of the steady-state distributions of the space charge and electric field in the coaxial cylindrical electrode are significant in many industrial applications. The positive dc corona in the coaxial cylindrical electrode is modeled by a full hydro-dynamic steady-state model and solved by the fourth-order Runge-Kutta method and the central finite difference approach. The new model predicts the distributions of the space charge and electric field in the whole electrode space. The effects of the electron diffusion, positive and negative charge recombination, and space photoionization are compared with the simplified model. The results present that the calculation accuracy of the new model is superior to that of the simplified model especially under large current. The simulation results also exhibit the influence of the corona current and conductor radius on the distribution of space charge and electric field and voltage-current characteristics.The predictions of the steady-state distributions of the space charge and electric field in the coaxial cylindrical electrode are significant in many industrial applications. The positive dc corona in the coaxial cylindrical electrode is modeled by a full hydro-dynamic steady-state model and solved by the fourth-order Runge-Kutta method and the central finite difference approach. The new model predicts the distributions of the space charge and electric field in the whole electrode space. The effects of the electron diffusion, positive and negative charge recombination, and space photoionization are compared with the simplified model. The results present that the calculation accuracy of the new model is superior to that of the simplified model especially under large current. The simulation results also exhibit the influence of the corona current and conductor radius on the distribution of space charge and electric field and voltage-current characteristics.

A Comprehensive Numerical Model of Steady-State Negative Corona for Coaxial Cylindrical Electrode in Atmosphere Air

Corona-originated discharge of DC transmission lines is the main reason for the radiated electromagnetic interference (EMI) field in the vicinity of transmission lines. A joint time-frequency analysis technique was proposed to extract the radiated EMI current (excitation current) of DC corona based on corona current statistical measurements. A reduced-scale experimental platform was setup to measure the statistical distributions of current waveform parameters of aluminum conductor steel reinforced. Based on the measured results, the peak value, root-mean-square value and average value with 9 kHz and 200 Hz band-with of 0.5 MHz radiated EMI current were calculated by the technique proposed and validated with conventional excitation function method. Radio interference (RI) was calculated based on the radiated EMI current and a wire-to-plate platform was built for the validity of the RI computation results. The reason for the certain deviation between the computations and measurements was detailed analyzed.

Surface aging effects of long-term energized conductors on spectrum characteristics of audible noise

The effects of low temperature on the inception threshold conditions of positive dc corona in a rod-plane electrode are investigated. The low-temperature platform, including the refrigeration system, air drying system, and inception threshold measurement system, is used to research the salient inception condition at a wide range of temperatures. This paper also attempts to use the numerical inception model to understand the effects of temperature on ionization coefficient, charge density, primary avalanche length, and radius. In a wide range of temperatures, the inception electric field strength is evaluated through approximate empirical formulas and a numerical model. Experimental results of corona inception are given for temperatures ranging from –80 °C to 40 °C, radii from 0.2 to 1.6 cm, and 20% relative humidity of air. The comparisons between the calculations and experiments of inception voltages under different temperatures are presented. Experimental results are consistent with inception corona vol...

Effect of surface aging on UV intensity characteristics for long-term energized conductors of HVDC transmission lines

Corona numerical model to predict the distributions of space charge and electric field is an important aspect in coaxial cylindrical electrode. Compared with the existing steady-state negative corona models, electron diffusion, space charge recombination, photoionization, and secondary electron emission mechanism are simultaneously considered in a comprehensive negative corona model. The 1-D hydrodynamic equations are calculated by the fourth-order Runge–Kutta method and the central finite difference method. The effects of these four terms in the conversation equations are analyzed quantitatively. In addition, the influence of corona current and conductor radius on the distribution of space charge and electric field and voltage–current characteristics has been discussed. The results from the comprehensive model show that under the high corona current, the comprehensive scheme is superior to the simplified model and the ion flow model in the accuracy.

Influence of humidity on spectrum characteristics of audible noise of DC transmission lines

The impact of surface aging level of long-term energized conductors on spectrum characteristics of audible noise is studied in this paper. It is found that the average roughness and root-mean-square roughness of conductors increase with the operating time, namely the aging degree, through the quantitative measurement. A-weighted equivalent continuous sound pressure level (LAeq) is found to increase with the aging level. As the aging aggravation, the LAeq and its high-frequency components (>1 kHz) increase substantially and high-frequency components are mainly contributing to the increasing of LAeq. The high-frequency components (>1 kHz) of the new and aged stranded conductors have a marked increasing trend as the surface potential gradient increases, while the low-frequency components are mainly environment noise.

Statistical evaluation and prediction of audible noise of HVDC transmission lines

In order to access the effect of surface aging on the corona UV characteristics, several groups with various aging level ACSR conductors have been collected from operating transmission lines and a laboratory scale corona cage has been constructed. A daytime UV detection based on solar blind bispectral UV technology is applied to visualize UV signals emitted on the aged ACSR conductors. Meanwhile, the surface roughness of the new and aged ACSR conductors has been measured by the three-dimensional confocal microscope phase shift. The results of surface roughness show that the average roughness and root mean square roughness increase as the aging degree. From the quantitative study of UV intensity, the UV photon number increases with the aging level. With the increase of the applied voltage, above inception level, the UV intensity enhances and the photon number soars. From the statistical measured results of UV intensity, it is found that the UV intensity is a function of the surface roughness level and surface contamination severity.