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
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
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
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.