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Ageing OPGW - LineVue™ Inspection

Complete Capabilities for OPGW Testing and Analysis

Introduction

 
Optical Ground Wire (OPGW) installed in the field may experience lightning arc damage and corrosion as the OPGW ages.  If lightning arc damage or corrosion affects the steel strands, the OPGW’s remaining tensile strength may be reduced.  With a lower tensile strength, the OPGW becomes susceptible to premature failure in heavy wind or ice loading events.  Unexpected failures can cause safety risks and result in costly fiber network outages.  The LineVue™ device, originally designed to inspect the condition of steel strands in overhead phase conductors, is now being investigated with respect to inspection of the mechanical condition of steel strands in OPGW lines. 
 
Project Objective
 
With a proven application for inspecting traditional overhead conductors, the Kinectrics LineVue™ was examined for its potential use in inspecting overhead OPGW lines as part of a mechanical inspection program. The objective of this case study was to investigate the feasibility of using the LineVue™ device to inspect the condition of steel strands in an OPGW, without affecting the OPGW optical performance.
 
Scope of Work
 
To investigate the feasibility of using the LineVue™ device to inspect the condition of the steel strands in an OPGW cable, the cable was first exposed to simulated lightning arc strikes in a laboratory setting.  The OPGW tested in this case study had an outside diameter of 16.3 mm.  The OPGW was constructed with 16 aluminum alloy (AA) strands, 10 aluminum-clad steel (ACS) strands, and a central aluminum-clad stainless steel tube.   
 
Lightning Arc Test
The intent of the Lightning Arc Test is to subject the OPGW cable to simulated lightning strikes that it may experience in the field.  Lightning arc damage may reduce the tensile strength of the individual strands as a result of melting or softening due to extremely high temperatures. The optical signals may also be adversely affected by lightning conditions.
 
For this case study, the OPGW was subjected to a Lightning Arc Test (LAT) based on conditions outlined in IEEE 1139-2009 “Standard for Testing and Performance for Optical Ground Wire (OPGW) for Use on Electric Utility Power Lines”, Paragraph 6.4.3.4.  Upon completion of the LAT, a length of the OPGW with two (2) lightning arc strikes was installed in a tension frame. 
 
LineVue™ Inspection
LineVue™ is a non-destructive device used for measuring the remaining cross-sectional area of steel strands.  The device can also detect local breaks and deep pits in the steel strands.  LineVue™ can be deployed in the field, in energized and de-energized conditions.
 
For this case study, LineVue™ was installed on the damaged OPGW, and the device was run over the length of OPGW to inspect for signs of damage to the steel strands.  While the LineVue™ device was running over the OPGW, the optical circuit was being monitored using power meters.
 
Results
 
The results were recorded after completion of the LineVue™ trial in inspecting the damage to the OPGW caused during the Lightning Arc Test.
 
Lightning Arc Test (LAT)
The OPGW cable was subjected to a Class 3 LAT: a nominal current of 400 A was applied over 0.5 seconds, for a target charge transfer of 200 coulombs.  After each hit, the number of burnt, damaged or broken aluminum alloy (AA) and aluminum-clad steel (ACS) strands was recorded.
 
LineVue™ Inspection
A length of OPGW of approximately 15 m was installed in a tension test frame, with LAT Hits #1 and #2 located within the tensioned section.  The LineVue™ device was run over the length of OPGW for a total of four (4) passes (i.e. two cycles, with each cycle including a back and forth pass).  
 
The damage at Hit #2 from the burnt and broken aluminum-clad steel (ACS) strands was clearly identified in both the LF and LMA channels.  There did not appear to be significant damage to the steel strands at the location of Hit #1, and therefore this damage was not detected in the LF or LMA channels. 
 
The optical attenuation was monitored in the OPGW sample with the use of power meters.  A slight variation was noted as the LineVue™ ran over the length of the sample. However, there did not appear to be any permanent change in optical attenuation due to the LineVue™ passing over the OPGW.   
 
In summary, the LineVue™ successfully detected the damaged and broken steel strands at the location of simulated lightning arc strike Hit #2; and the LineVue™ inspection did not appear to interfere with the optical performance of the OPGW.  Additional testing would be required to determine the actual remaining tensile strength of the OPGW in these two (2) locations.
 
Client Benefits 
 
Using LineVue™ for non-destructive inspection of OPGW for lightning arc damage and corrosion in the field will enable clients to assess the tensile strength and extent of degradation of their OPGW lines.  Paired with an optical fiber maintenance program, a mechanical inspection program may significantly reduce the risk of safety incidents or costly unplanned fiber network outages.  The client can gather information during these inspections that will lead to more informed and confident decisions related to their assets.  These informed decisions can potentially facilitate substantial cost savings for the client by reducing unnecessary repairs or premature replacement of their ageing OPGW infrastructure.  

About This Case Study

Industry Sector

  • Transmission & Distribution

Nature of Service

  • Inspection
  • |
  • Testing - Field Services

Client Assets

  • Lines

Kinetrics Facilities

  • Mechanical Equipment Testing Facilities

Tags

  • OPGW
  • |
  • overhead lines
  • |
  • optical groundwire
  • |
  • tensile strength
  • |
  • Conductors