Optical Ground Wire (OPGW) installed in the field experienced an optical failure event during the winter months. Preliminary testing by the client's field crews had revealed seveal broken optical fibers, with other fibers showing very high attenuation.
The client contracted Kinectrics to perform an analysis of a harvested OPGW sample in an attempt to determine the extent and cause of the damage. The harvested OPGW sample sent to Kinectrics was approximately 850 m in length and wound on a wooden reel.
Kinectrics' analysis included several tests chosen to locate and understand the extent and type of damage that had occurred, and to investigate potential causes for the fiber damage described above. The scope of testing was updated throughout the process to maximize the information obtained from the harvested sample.
Fault Finding using Optical Time Domain Reflectometer (OTDR): to identify the damaged or broken fibers along the length of the harvested sample.
Nitrogen Pressure Test: to verify whether the integrity of the aluminum tube had been compromised and verify its performance as a humidity barrier.
Dissection and Visual Inspection: to identify whether there were any areas of significant damage to the OPGW and its components; and look for clues to the possible causes of the failure.
Metallurgical Analysis: to inspect the profile of the weld (weld quality) and confirm the suspected failure mode.
The Fault Finding using OTDR found three (3) locations of fiber damage. The Nitrogen Pressure Test found another location where the aluminum tube was split. The Visual Inspection confirmed the four (4) locations where the aluminum tube was split, and where the buffer tube was damaged and / or broken. Additional areas of damage to the aluminum clad steel (ACS) wires were noted. The Metallurgical Analysis found a partial lack of fusion defect in the aluminum tube seam weld.
In summary, the laboratory testing found that the fiber outage appeared to be the result of several locations of damaged/pinched buffer tube. The damage to the aluminum tube was likely caused by a lack of fusion weld in the aluminum tube seam weld. The split aluminum tube may then have caused the damage to the buffer tubes, during handling, installation, stringing, in-service loading conditions, etc. It was acknowledged that although the testing found visible damage to the aluminum and buffer tubes, several unknown causes remained and additional steps were recommended to the client.
A comprehensive in-depth failure analysis of the harvested OPGW was delivered to the client in order to better understand the extent of damage and failure mode. A number of additional steps were recommended to assist in the development of practical tools to perform and expedite future OPGW failure investigations. Information gathered during the failure investigation may assist when making repair and maintenance decisions for ageing OPGW infrastructure.