For more than 60 years, polyethylene (PE) and ethylene-propylene rubber (EPR) underground cables have powered communities, industries, and progress. The hope was these cables could last decades before needing to be replaced, but due to water treeing—microscopic moisture-induced formations that degrade insulation and threaten reliability, they’re aging more rapidly than expected. With traditional replacement being costly and labor-intensive, it was time for a new solution.
In the 1980s, engineers discovered that injecting a silicone dielectric fluid into aging cables could restore their strength from the inside out and extend their lifespan for many decades. Southwire embraced this innovation, refining the process into a service that’s now a cornerstone of its utility offerings.
COMMENTARY
Breaking Down the Process
Cable rejuvenation is a simple but powerful process. Dielectric fluid, or siloxane fluid, is injected into the conductor strands of the cable. The fluid then migrates (diffuses) through the conductor shield and permeates the insulation (PE or EPR), displacing moisture and repairing the chemical structure. As a result, the cable’s dielectric strength increases, extending the reliable life of the cable and postponing the need for replacement by many decades. The process is fast, efficient, and minimally invasive, often completed in under 90 minutes per segment. Overall, cable rejuvenation can extend the life of a cable by up to 40+ years and restore it to a better-than-new condition at roughly one-third the cost of cable replacement.
Test Then Inject—The Cable Rejuvenation Methodology
Estimates from the California Public Utilities Commission suggest that about half of the U.S. distribution grid will require either strategic undergrounding or underground rehabilitation by 2040. Underground cable makes up 20% of the 10.1 million kilometers of lines in the U.S. distribution network. Replacing these cables is projected to cost more than $1 trillion, factoring in inflation, urban constraints, materials, labor, and permitting costs. The Test and Inject methodology provides a reliable and scalable approach, combining the revolutionary cable rejuvenation technology with partial discharge (PD) testing.
PD testing is a diagnostic test that identifies cable defects while the cable is in service, helping prevent unplanned outages. This helps determine whether issues can be mitigated before rejuvenation or if a full replacement may be necessary. For example, a PD test could lead to the discovery that the original underground cable has a jagged cut at a termination or joint. By identifying this defect beforehand, the utility company can mitigate the existing cable and then follow through with the cable rejuvenation process, reducing the chances of cable failure while simultaneously extending the life of the cable.
From there, the rejuvenation process starts by isolating and grounding the cable. Once the cable is safe to work with, a Time Domain Reflectometer (TDR) is used to determine the length of the cable, locate the joints, and assess the condition of the neutrals. The terminations are then changed to injection terminations, and airflow is introduced to confirm that a clear path exists from one end of the cable to the other. Once confirmed, a special tank and hose are attached to the injection termination to inject the Dielectric fluid into the cable until it is fully treated. Finally, the tanks are removed, and the cable is put back into service. Typically, a crew can rejuvenate three to six cables in a single day– significantly faster and safer than a cable replacement program.
The Impact of Cable Rejuvenation
Cable rejuvenation has many other benefits outside of generally extending the life of a cable. It reduces carbon emissions, landscape disruption, and waste. For instance, rejuvenating a 350-foot 1/0 175b mil aluminum conductor cable is roughly the equivalent of driving a typical car 5.9 miles, compared to more than 3,200 miles for a full replacement, as well as mitigating 660K metric tons of CO2.
Over the past 30+ years, Southwire has rejuvenated over 165 million feet of underground cable, achieving a 99% success rate. This has saved utilities billions of dollars, reduced outages, and improved grid reliability for millions of customers. One utility’s case study revealed dramatic results: rejuvenating 12 million feet of URD cable, reducing outages by 1,300 annually, and deferring replacement by many years, saving $800 million for rate payers.
In the end, total cable replacement is costly, labor-intensive, and may be environmentally disruptive. While cable replacements have a time and place, cable rejuvenation is a more sustainable, cost-effective alternative as utilities continue to face the pressures of grid modernization and electrification. Combined with the Test and Inject methodology, cable rejuvenation can help utilities stay ahead of failures, saving them time and money. At the end of the day, cable rejuvenation is more than a cable system stability strategy; it’s a commitment to reliability, sustainability, and innovation.
—Wayne J. Chatterton, PhD, is Services Solutions Sales Vice President at Southwire.
