360° Capital Rehabilitation Program: Improve Reliability in Less Time and with Fewer Resources than Traditional Approaches

The Challenge:?? Today’s electric utilities face unprecedented challenges as they try to maintain or improve the reliability of an aging grid in the face of significantly constrained Operations and Maintenance (O&M) and capital budgets.? Because they are being asked to “do more with less,” electric utilities must adopt new approaches to optimize the amount of reliability improvement per dollar spent by focusing the investment on the most critical assets.

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The Solution:???? Southwire’s 360° Capital Rehabilitation Program is a novel approach to asset management of aged underground medium voltage cable that combines Digital Grid Resiliency Assessments, Field Assessment of cable, Cable Rejuvenation, and Cable Replacement to drive significant improvement in reliability metrics for a comparatively modest capital investment.

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Implementation Process:

-??????? A Digital Grid Resiliency Assessment (DGRA) is performed using an electric utility’s Outage Management System (OMS), Geographic Information System (GIS), and Advanced Metering Infrastructure (AMI) data.? This is a one-way data transfer and does not require 3rd party access to sensitive information systems.? The GIS and OMS data are used to create a ranking of regions, circuits, and assets by criticality and probability where focused investment will yield significant improvement in reliability metrics.

-??????? Once the DGRA has identified potential areas for investment, the next step is Field Assessment.? For aged medium voltage cable, this includes a variety of tests including Time Domain Reflectometry (TDR), Tan Delta, and Partial Discharge (PD).? These tests evaluate the health of cable with respect to both global issues and latent point defects that can lead to premature failure.? Based on several weighting factors determined in conjunction with the electric utility, an Asset Health Score is calculated for each cable segment to reflect the likelihood of failure. Combining the likelihood of failure as determined by testing with a measure of the consequence of failure as determined by the DGRA, the overall risk is determined, and a true data-driven asset management strategy is recommended. In terms of medium voltage cable, a recommendation is made for each cable segment as to whether it should be left alone, rejuvenated, or replaced. ?

-??????? Cable Rejuvenation is a 30+ year old technology whereby a specialized fluid is injected into the interstitial area of the copper or aluminum strands which then diffuses into the insulation system restoring the deteriorated dielectric strength of the cable back to new or better than new levels.? Cable Rejuvenation is the most capitally efficient method of improving the reliability of aged medium voltage cables.? Cable Rejuvenation takes less time, fewer resources, causes less customer impact/interruption, and is typically less than half the cost of cable replacement.? Cable Rejuvenation can extend the life of a cable system by 40+ years.

-??????? In some cases, cable segments will be identified as high risk due to the combination of their likelihood and consequence of failure, but cable rejuvenation will not be an option.? In those cases, the cable will be recommended for replacement.? As can be seen from the case study below, replacement is typically only recommended for 5% or less of the population of worst performing circuits.

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Case Study:? A Midwest IOU identified 550 miles of their worst performing circuits and developed an asset management strategy based on the techniques described within this paper.? The below graph shows the results of testing of the first 2,000 cable segments in the population.? Whereas the electric utility anticipated that they would need to replace approximately 15% of the cable segments evaluated, the initial screening showed that 35% of the cable segments failed the initial screening.? By further refining the asset health model using the results of multiple tests, the segments that failed the initial screening could be categorized as either low risk, medium risk, or high risk.? Finally, a rehabilitation strategy was recommended based on the results of the testing.? The final recommended rehabilitation plan only required the replacement of 4% of the cables evaluated while 29% of the cable segments were recommended for rejuvenation.? This plan can be executed at a cost reduction of approximately 70% relative to a replacement-only strategy with considerably better near-term reliability improvements.

Conclusion:? Maintaining and improving the reliability of the aging grid is a difficult task, but it is nearly impossible in an environment with increasingly constrained budgets.? To be successful in the face of these challenges, electric utilities must be willing to adopt new approaches to maximize the reliability improvement achieved per dollar spent.? By combining DGRA, Field Assessment, Cable Rejuvenation, and limited cable replacement, electric utilities can create an optimized asset management strategy while deferring capital spend and minimizing O&M spend.

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