The Surface Damage Features Of Overhead Conductors And Its Effect On Corona Characters

Overhead transmission conductor is an important part of China’s UHV transmission line.In EHV/UHV transmission line,the actual overhead transmission conductor is complex aluminum cable steel reinforced(ACSR)which is often hinged by many strands of round conductor.The conductors running in the atmospheric environment have been under harsh natural environment and construction conditions for a long time,which will inevitable cause the surface damage.The damage of conductor surface is an important source of corona discharge,which not only increases the corona energy loss but also threatens the safe operation of transmission lines.Therefore,it is of great engineering value and academic significance to study the effect of conductor surface damage features on corona discharge.Firstly,the features of actual conductor surface damage are observed and extracted by means of experiment and image processing in this thesis.Fractal dimension is used to describe the damage of conductor surface.Then,the corona characteristics on the surface of non-damaged conductor are studied by using the hybrid numerical model of corona discharge.Finally,the corona characteristics of damaged conductor surface are studied by PIC-MCC method.The specific research content is as follows:1.The actual transmission lines are selected as the research object.The surface damage characteristics of typical conductors with different voltage levels intercepted in different regions are observed through experiments.Image processing technology is used to extract image information of damaged surface of different conductors.The damage characteristics of conductor surface are studied by pixel point covering method,differential box dimension method and wavelet transform.An improved pixel covering method is proposed for the shortcomings of traditional pixel covering method,and the relationships between fractal dimension and surface damage of conductor are established.2.A hybrid numerical model for quantitatively analyzing the microcosmic process of plasma discharge on smooth conductor surface is proposed.Then the electron density and electric field intensity of circular conductor and aluminum conductor steel reinforced(ACSR)are numerically investigated under different discharge time.Moreover,the influences of the number of outer strands for conductors on the corona discharge performance are also discussed.Research results show that the electron densities around the ACSR are higher than that around the circular conductor at initial discharge stage.But the electron density around conductors with different cross sections varies little in the phases of streamer.The electric field intensity of ACSR is significantly higher than that of circular conductor at initial discharge.The electric field and electron density will decrease with the number of outer strands for conductors.3.PIC-MCC method is used to establish the discharge model on the conductor surface with protrusion,and the corona characteristics of common damage characteristics(protrusion)on the conductor surface caused by indentation are studied.The change processes of electric field intensity and microscopic particles on the surface of the conductor with a protrusion and smooth surface are analyzed with a constant conductor radius,and the influence rules of different radius and distribution of protrusions on discharge are given.It is found that the protrusion radius has an important influence on the corona discharge characters in different discharge stages.When there are multiple protrusions on the surface of conductor,they will affect each other.With the increase of the protrusion number,the maximum electric field intensity on the conductor surface gradually decreases.