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Title: Structural health monitoring of compression connectors for overhead transmission lines

Abstract

Two-stage aluminum conductor steel-reinforced (ACSR) compression connectors are extensively used in US overhead transmission lines. The connectors are made by crimping a steel sleeve onto a steel core and an aluminum sleeve over aluminum conductive strands. The connectors are designed to operate at temperatures up to 125 C, but their performance is increasingly degrading because of overloading of lines. Currently, electric utilities conduct routine line inspections using thermal and electrical measurements. However, information about the structural integrity of connectors cannot be obtained. In this work, structural health monitoring (SHM) of compression connectors was studied using electromechanical impedance (EMI) analysis. Lead zirconate titanate (PZT)-5A was identified as a smart material for SHM. A flexible high-temperature bonding layer was used to address challenges in PZT integration due to a significant difference in the coefficients of thermal expansion of PZT and the aluminum substrate. The steel joint on the steel core was investigated because it is responsible for the ultimate tensile strength of the connector. Tensile testing was used to create structural damage to the joint, or steel core pullout, and thermal cycling introduced additional structural perturbations. EMI measurements were conducted between the tests. The root mean square deviation (RMSD) of EMI wasmore » identified as a damage index. The use of steel joints has been shown to enable SHM under simulated conditions. The EMI signature is sensitive to variations in structural conditions. RMSD can be correlated to the structural health of a connector and has potential for use in the SHM and structural integrity evaluation.« less

Authors:
 [1];  [1];  [1];  [1];  [2]
  1. ORNL
  2. Electric Power Research Institute (EPRI)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1352779
DOE Contract Number:
AC05-00OR22725
Resource Type:
Conference
Resource Relation:
Conference: SPIE Smart Structures/NDE 2017, Portland, OR, USA, 20170325, 20170329
Country of Publication:
United States
Language:
English
Subject:
PZT; electromechanical impedance; structural health monitoring; damage index; compression connectors; transmission lines

Citation Formats

Wang, Hong, Wang, Jy-An John, Swindeman, Joseph P, Ren, Fei, and Chan, John. Structural health monitoring of compression connectors for overhead transmission lines. United States: N. p., 2017. Web.
Wang, Hong, Wang, Jy-An John, Swindeman, Joseph P, Ren, Fei, & Chan, John. Structural health monitoring of compression connectors for overhead transmission lines. United States.
Wang, Hong, Wang, Jy-An John, Swindeman, Joseph P, Ren, Fei, and Chan, John. Sun . "Structural health monitoring of compression connectors for overhead transmission lines". United States. doi:.
@article{osti_1352779,
title = {Structural health monitoring of compression connectors for overhead transmission lines},
author = {Wang, Hong and Wang, Jy-An John and Swindeman, Joseph P and Ren, Fei and Chan, John},
abstractNote = {Two-stage aluminum conductor steel-reinforced (ACSR) compression connectors are extensively used in US overhead transmission lines. The connectors are made by crimping a steel sleeve onto a steel core and an aluminum sleeve over aluminum conductive strands. The connectors are designed to operate at temperatures up to 125 C, but their performance is increasingly degrading because of overloading of lines. Currently, electric utilities conduct routine line inspections using thermal and electrical measurements. However, information about the structural integrity of connectors cannot be obtained. In this work, structural health monitoring (SHM) of compression connectors was studied using electromechanical impedance (EMI) analysis. Lead zirconate titanate (PZT)-5A was identified as a smart material for SHM. A flexible high-temperature bonding layer was used to address challenges in PZT integration due to a significant difference in the coefficients of thermal expansion of PZT and the aluminum substrate. The steel joint on the steel core was investigated because it is responsible for the ultimate tensile strength of the connector. Tensile testing was used to create structural damage to the joint, or steel core pullout, and thermal cycling introduced additional structural perturbations. EMI measurements were conducted between the tests. The root mean square deviation (RMSD) of EMI was identified as a damage index. The use of steel joints has been shown to enable SHM under simulated conditions. The EMI signature is sensitive to variations in structural conditions. RMSD can be correlated to the structural health of a connector and has potential for use in the SHM and structural integrity evaluation.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2017},
month = {Sun Jan 01 00:00:00 EST 2017}
}

Conference:
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  • Integration of smart patches into full-tension splice connectors in overhead power transmission lines was investigated. Lead zirconate titanate (PZT) -5A was used as a smart material and an aluminum beam was used as a host structure. Negative electrode termination was examined by using copper adhesive tape and direct bonding methods. Various commercial adhesives were studied for PZT integration onto the host structure. Aluminum beam specimens with integrated PZT smart patches were tested under thermal cycling at a temperature of 125 C, which is the higher-end temperature experienced by in-service aluminum conductor steel-reinforced cables. Electromechanical impedance (EMI) measurements were conducted atmore » room temperature, and the root mean square deviation (RMSD) of the conductance signals was used to analyze the EMI data. It has been shown that the negative electrode method has an important effect on the performance of the integrated PZT. The PZT displayed more susceptibility to cracking when copper tape was used than when direct bonding was used. The reliability of PZT in direct bonding depended on the adhesives used in bonding layers. Although a hard alumina based adhesive can lead to cracking of the PZT, a high-temperature epoxy with adequate flexibility, such as Duralco 4538D, can provide the desired performance under target thermal cycling conditions. The RMSD parameter can characterize conductance signatures effectively. It also was demonstrated that RMSD can be used to quantify the fatigue of the PZT integration system, although RMSD is used primarily as a damage index in monitoring structural health.« less
  • The potential adverse public health and safety effects of the overhead transmission line electrical environment in Minnesota were explored. Primary emphasis was placed on the electric and magnetic field effects of extra high voltage (EHV) and high voltage direct current (HVDC) transmission lines. Coupling effects and safety were considered in relation to the transmission line field environment, electric shock, alternating current and direct current safety criteria, and regulatory controls. Adverse biological effects resulting from exposure to EHV and HVDC transmission lines were explored There was no evidence to suggest any effect on health or well-being from the intermittent exposure experiencedmore » in the transmission line environment. Alternating current electric fields, however, are of more environmental concern than direct current electric fields. These fields are not strong enough to cause tissue heating or nerve stimulation, but the possibility of more insidious effects has prompted research in this area. Various research studies and programs on the effects of electric and magnetic fields are reviewed. Recommendations are made for the State of Minnesota which deal with the application of performance standards in transmission line construction permits, follow-on research monitoring, and research projects that the State may wish to consider sponsoring. A generic public hearing by the Minnesota Environmental Quality Board is not recommended. Appendixes contain a selected bibliography and further information on the study.« less
  • Due to material discontinuity and inherited forming mechanism from a crimped-type splice connector, the associated conductor-connector system is highly sensitive to system components aging, especially during high-temperature operations. Furthermore, due to the increase in power demand and limited investment in new infrastructure, existing overhead power transmission lines often need to operate at temperatures higher than the original designed values. This has led to the accelerated aging and degradation of conductor-connector systems. The implications of connector aging are two-fold: (1) significant increase in resistivity of the splice connector and (2) significant reduction in the connector clamping strength. Therefore, splice connectors aremore » one of the weakest links in the electric power transmission infrastructure. In this paper we will discuss the reliability of splice connector systems, including both single stage and two stage splice connectors, used in ACSR conductor of transmission lines under high temperature operations.« less
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