Abstract: The surface damage of conductors is an important factor in affecting the mechanical and
electrical performances of overhead transmission lines. Thus, it is important to study the surface
damage features of conductors for the durability design and safety assessment of transmission
conductors. Firstly, several typical conductors (aluminium conductor steel reinforced, ACSR) in
different regions and voltage levels are selected as the objects of study in this paper. Then the image
information of the damaged surface of conductors is extracted by image processing technology. An
improved pixel covering algorithm is proposed to make up for the shortcomings of the traditional
pixel covering method, and thus the relations between surface damage features and fractal dimensions
of conductors can be established. Research results show that there is obvious fractal rule in the
conductor surface topography. The fractal dimensions can measure the surface damage characteristics
of conductors. The two-dimensional (2D) fractal dimension tends to become smaller with the
decrease in the conductor surface damage. The increase in the unevenness of conductor surface will
improve the 3D fractal dimensions. When the damage of the conductor surface is a scar, the 2D
fractal dimension is between 1.5 and 1.7. If the damage is characterized with wear, the fractal
dimension spans from 1.2 to 1.4; whereas the damage is characterized with corrosion, the fractal dimension ranges from 1.4 to 1.5.

Key words: image processing, damage features, fractal, transmission line, aluminium conductor steel reinforced