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RehabilitateGround CablePinpoint SplicesChoose Rehabilitation OptionSPRUPR

Most people think that the 3R’s are “Reading, ‘Righting, and ‘Rithmitic.” The 3R’s of the distribution rehabilitation business are Re-evaluate, Rejuvenate, and Replace. The relationships of these three R’s is shown in the illustration nearby.

The 3R's of rehabilitation include: Re-evaluate, Rejuvenate,
and Replace. The 3D's (Database, Distribution hierarchy of
needs, and Diagnostics are input tools to perform the
re-evaluation step.

Continual re-evaluation of the population of at-risk cables surrounds the process. Those cables, which are most likely to fail and which have the greatest impact on reliability, are identified and segregated from the entire population. For almost all conceivable circumstances, state-of-the-art rejuvenation requires less than half of the capital required to replace cables. Modern rejuvenation extends reliable cable life to a par with the anticipated life of new replacement cable. Because of its inherent capital efficiency, rejuvenation is applied to the majority of the identified population of at risk cables. However, a small portion of those cables may not be practically treatable, and hence, some of the identified population must be replaced. Replacement is so much less capital efficient than rejuvenation, a tactical plan is required to minimize the added cost of the replacement portion of the rehabilitation plan.

The 3Ds drive the re-evaluation process, starting with the database of failure statistics including the "demographics" of the cable, while requiring some effort to collect and verify, these data are an inexpensive and reliable diagnostic. These statistics empower the circuit owner to thoughtfully assess the probability that a subset of cables is likely to fail, at what rate they are likely to fail, and most importantly, how fast that rate changes with time. The second "D" is the Distribution 5Ps. The concept of the 5P’s of the distribution hierarchy of needs is described in "Underground Distribution Reliability: The 5Ps". The 5P’s focus attention and resources on the sub-population of cables, which have the largest impact on circuit-owner-defined reliability requirements. The third "D", diagnostics, has only limited applicability. In "Diagnostics Testing of Stochastic Circuits" it was shown that currently available diagnostics generally fall outside either or both the economic test criterion and/or the thermodynamic test criterion. Advancements in diagnostics are likely to continue, and future tests may become integral parts of the re-evaluation process.

The integrated rehabilitation method maximizes capital efficiency and reliability.
The top portion down to the "Rehab?" diamond of the nearby flowchart, recaps the re-evaluation process. Cable’s that will not be rehabilitated in the current planning cycle are recycled back into the at-risk-population to be re-evaluated in the next cycle.
Those that will be rehabilitated move on to the "Identify splices and corrosion" process. This process involves visual inspection of the cable and its components and high resolution time-domain reflectometry to locate splices and neutral corrosion issues. Typically about half of the cables tested will have no splices or significant neutral corrosion. The next decision diamond divides the population of cables to be rehabilitated into two approximately equal sub-populations: Those with no splices or corrosion and those with 1 or more splice or corrosion issues.

Cables that fall in the first category are immediately treated with sustained pressure rejuvenation, which yields a cable likely to provide reliable service for 40 more years. Cables in the second group advance to a more complete analysis. The analysis identifies and pinpoints all buried splices or corrosion issues and is labeled, "Pinpoint splices or corrosion". Using a multi-antenna radio frequency (RF) locator, a signal is impressed upon the conductor and perturbations in the RF field near splices and neutral corrosion sites allow the pinpointing of splices or corrosion. On average, the population of pre-1985 vintage, North American bare-concentric neutral cables have less than a 2% incidence of significant neutral corrosion.

The tactic with greatest benefit-to-cost ratio (sustained pressure rejuvenation) is executed as often as possible. The second best tactic (unsustained pressure rejuvenation) is applied as often as possible to the leftovers. The residual is replaced as a last resort at the highest capital intensity.
Typically the lion’s share of the rehabilitation population can be treated with the most robust sustained pressure rejuvenation (SPR), a small amount is treated with unsustained pressure rejuvenation (UPR), and an even smaller residual is replaced.
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