Life Cycle Analysis: A Comparison of Cable Rejuvenation & Cable Replacement

By James Steele, Director of Engineering

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?“Reduce, Reuse and Recycle”. That phrase was coined after the passage of the Resource Conservation and Recovery Act of 1976 and then immortalized in songs during the 1980’s, which influenced children and helped shape our present values on conservation and environmental stewardship.? While recycling has become an established practice for many electric utilities with cables that can be pulled from conduit, rehabilitation options also exist that embody the other two R’s.? Southwire’s 360° Capital Rehabilitation? services enable electric utilities to reduce their overall carbon footprint by reducing the frequency of cable replacement and its associated carbon dioxide emissions through assessment tests and re-use of the existing cable found to be near the end of reliable service, enhanced through a chemical process known as cable rejuvenation.? This service extends the life of an aged underground cable by an additional 40-years while reducing global warming potential by 99.9% compared to replacement.? As one recent case study has demonstrated, the decreased carbon footprint through rejuvenation is comparable to removing more than 1,800 vehicles from the road for a year.?

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The problem with aging cable

The dielectric strength of underground cables decreases with age leaving them more susceptible to damage from transient voltages like switching events and lightning strikes that can transform localized defects into failures.? While modern cable insulations perform much better than earlier generations, cables insulated with tree-retardant compounds may still lose nearly half of their dielectric strength within their first 25 years (Figure 1).?? A recent study found that roughly 75% of the more than 8 million miles of underground cable installed in the United States is over 25 years old and either at or approaching the end of its reliable life.? With many utilities pledging carbon reduction initiatives including significant investments in renewable energy, fleet electrification, and smart metering, utilities should also consider the environmental impacts of their strategy to maintain their aging cable infrastructure.?

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Cable Rejuvenation

Cable rejuvenation offers dielectric strength recovery, allowing cables to be re-used by providing additional lifespan (Figure 2).? Cable rejuvenation has been used by more than 350 utilities worldwide to address more than 165 million feet of cable.? In its 37-years of practice, less than 1% of rejuvenated cables have failed during their service lifetime.?

Southwire’s cable rejuvenation process starts with a cable assessment to verify the integrity of the cable’s neutral system and its ability to carry fault current.? Tests like partial discharge or tan delta may be performed to prioritize at-risk circuits or defer treatment. At the beginning of the cable injection process, new craftwork is performed, and new accessories are installed, preparing the cable for another 40-plus years of reliability. Then, Cablecure? 732 fluid is injected into the conductor strands of the cable.? The fluid radially diffuses into the surrounding insulation, filling the water-tree voids and providing long-term protection against failure.?

VIDEO: https://bit.ly/3NG8gTY

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Life Cycle Analysis

A rigorous study of the environmental inputs and outputs for a particular product is called a life cycle analysis (LCA). It provides the scientific basis for evaluating the impacts of a product’s life including emissions, as well as the consumption of energy and material resources. Considerations are given for the 5 stages of a product's life including manufacturing, transportation, installation, operation/maintenance, and end of life. ?

While a typical LCA looks at various impacts including acidification, eutrophication, petroleum extraction, and water consumption; global warming potential (GWP) measured in kg-CO2 equivalent is a particularly important metric for utilities looking to meet their emission-reduction targets.? ?Considering a 40-year life of cable following the decision to either rejuvenate or replace, the study found GWP reductions for URD and feeder cable of 99.87% and 99.94% respectively.? For a 500 ft segment of URD cable, the GWP savings with rejuvenation is equivalent to the 2,701 miles driven between Seattle to New York City (Figure 3).?

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Case Study

At a time when key reliability indices were on the rise, this utility serving more over 1 million customers across a territory of 742 square miles, began their cable rejuvenation program in 2013 (Figure 4).? In a region known for harsh winters, they justified action out of concern for the more than 600 outages occurring per year on their pre-1990 vintage URD cable population and their climbing average duration of interruption that had grown by 19% over a 4-year period.??

Initially drawn to the increased capital reach enabled by cable rejuvenation, this utility saw other benefits including reduction in global-warming potential (GWP) which aligned with their net-zero greenhouse gas emissions target by year 2050.?

Since the initiation of the program, this utility has rejuvenated more than 3.4 million ft of cable that has effectively reduced their global warming potential by 8.4 million kg CO2-equivalent (Table 1).? In practical terms, their program has had the combined effect of reducing traffic driven by 21 million fewer miles or removing 1,830 cars from local roads for a year.?

Now, 11 years into the program, this utility has seen steady improvement to their reliability indices by taking a targeted approach to address their pre-1990 vintage URD.? In the utility’s words, “the [cable rejuvenation] process avoids significant costs and service disruptions, while minimizing the impacts on the environment.”

More information on cable rejuvenation can be found at https://bit.ly/4e3ZSIM

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