The Structure of the Near-Surface Layer of the AAAC Overhead Power Line Wires after Operation and Its Effect on Their Elastic, Microplastic, and Electroresistance Properties

Abstract

Overhead power-transmission lines are one of the most important components of modern infrastructure. Their service life is determined by the state of the near-surface defect layers (NSDLs) of wires constituting these lines. Both the structure and microstructure of the NSDLs of wires of the AAAC type (All Aluminum Alloy Conductor), which were in operation during 0 (new) to 62 years, were investigated by methods of the X-ray (XRD) and electron back-scattering diffraction, optical microscopy, and resistivity measurements, as well as by means of densitometric and acoustic measurements with layer-by-layer removal of the near-surface material by etching. Two characteristic thicknesses of the NSDLs were obtained, different methods providing close results, namely, ~30–50 μm and ~56–140 μm. According to the mass-density distribution (XRD), these characteristic thicknesses correspond to the depths from the surface where they occur, respectively, ~70% and ~99% of the density drop in comparison with the bulk density value. The rate of increase in NSDL thickness is ~4 μm/year in the interval from 0 to 18 years. Results of investigation of elastic and microplastic properties of wires after removal of ~35 μm of the upper layer are also presented.

Pyrochlore phase in the Bi2O3-Fe2O3-WO3-(H2O) system: its stability field in the low-temperature region of the phase diagram and thermal stability

“…The preprocessing of the measured XRD patterns of samples in order to obtain the parameters of the observed XRD reflections necessary for unit cell and microstructure calculations was carried out using the EVA program, version 5.1.0.5 (Bruker AXS, Germany). To increase the precision of the analysis, the observed values of the Bragg angles obtained by EVA were corrected for zero shift and displacement (see [28] for details). Angular corrections (zero shift and displacement) were obtained by the external standard method based on additional measurements of a 5.12 powder sample mixed with NaCl powder, which was calibrated by the internal standard method using the Si640f powder XRD standard (NIST, USA).…”

Characteristics of Wires of the Long-Operated Aluminum-Steel Cable at Different Places on an Overhead Power Line Span

“…In the literature, stranded all-aluminum cables are referred to as all-aluminum alloy conductors (AAACs) [4,7,8,[20][21][22][23][24][25][26][27] or, separately, all-aluminum conductors (AACs) if all of the wires in the cable are made of high-purity aluminum or aluminum conductor alloy-reinforced (ACAR) if the wires are made of technical-grade aluminum [28]. Stranded steel-aluminum cables are called aluminum conductors (or cable or clad) steel-reinforced (ACSR) [4][5][6][7]11,12,14,15,26,[29][30][31][32][33][34].…”

“…Earlier, to investigate the processes occurring during the operation of cables, cables were studied not only immediately after operation in OPLs [5,11,12,14,15,[24][25][26]30,34] but also after fatigue tests [6,16,[20][21][22][23][27][28][29][31][32][33]35,36], which simulated "aging" of wires (changes in microstructural, structural, and other properties) under real operating conditions or after heat treatment [8][9][10]. Both AAAC [6,8,16,[20][21][22][23][24][25][26][27][28]36] and ACSR [5,6,11,12,14,15,26,[29][30]…”

“…A wide range of experimental methods were used for research, such as optical microscopy (OM) [5,11,12,14,15,[20][21][22][23]25,27,29,30], scanning electron microscopy (SEM) [5,11,12,14,15,[20][21][22][23]27,30,32], energy-dispersive X-ray microanalysis (EDX, also energydispersive X-ray spectroscopy in some articles, abbreviated as EDS) [5,11,14,20,24,25,27,30], X-ray diffraction (XRD) [14,15,[24][25][26][27], electron backscatter diffraction (EBSD) [24][25][26][27]34], densitometry [24][25][26][27]34], the acoustic-resonance ...…”

“…For instance, the effect of both tensile mechanical stress [20,21,28,29] and the amplitude of displacements at bending [6,[21][22][23]28,29,31,35] were investigated, as well as that of annealing temperature [8,9] and mechanical defects of Al wires during their production [7], effect of clamp material [23,31], elemental composition of Al wires [6,22], presence of a steel core [6,26], corrosion due to exposure to ambient air during operation in power lines [5,14,15,30], forest fires [10], and the environment during fatigue tests (either room atmosphere or NaCl solution) [32]. Changes in the microstructure, structure, chemical composition, and physical properties of wires from cables were also studied after their operation in OPLs for various service lives ranging from 8 to 62 years [5,11,12,14,15,[24][25][26]30,34] and after fatigue testing [27,36].…”