Rehabilitation: The 3R’s
Glen J. Bertini and Richard K. Brinton
Novinium, Inc.
Abstract: There are over 2 billion feet of aging underground
power cable in North America. This large quantity of cable must
be rehabilitated for the circuits to continue to provide a reliable
electric supply. This paper provides a strategic paradigm for
optimal use of capital to tackle this problem. Re-evaluate,
Rejuvenate, and Replace are the 3R’s of an advanced tactical
rehabilitation program, which provides the optimum benefit-tocost ratio. An improved set of materials and processes are
introduced to rejuvenate cables with unsustained pressure for the
few cases where the more advanced sustained pressure
rejuvenation method is difficult to implement.
Re-evalulate
Replace
INTRODUCTION
Circuit owners recognize in [1] the daunting task of aging
circuit rehabilitation which requires attention and massive
financial resources over the next several decades:
Rejuvenate
“Engineering experts now believe the nation is entering a period
that could be marked by a dramatic increase in local power
outages unless considerably more is spent on addressing old and
deteriorated lines.
Many utilities feel a pressing need to spend more money on their
power-distribution systems. In a survey of 39 top utility
executives … distribution-system spending ranked as the No. 1
priority, ahead of generation and environmental compliance,
according to Jone-Lin Wang, senior director … Cambridge
Energy Research Associates.
Black & Veatch estimates the industry needs to spend an
additional $8 billion to $10 billion a year to tackle the problem
of obsolete … equipment.”
The reliability expectations of the electrical consumer and
electrical regulators continue to rise as more and more homebased businesses and telecommuters require uninterrupted
power. The imminent arrival of plug-in vehicles driven by the
rising cost of oil will provide another large increase in
electrical consumption and still higher reliability expectations.
Wholesale replacement of these two billion feet would likely
exceed 80 billion U.S. dollars or about 4 billion dollars per
year for the next two decades. Wholesale replacement is the
second worst option. The least favourable course is to allow
the cables to fail, since the total cost of failure will rise much
faster than inflation. This paper provides a road map for the
most capital efficient approach to this rehabilitation challenge.
3R’S
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. Figure 1
shows the relationship of these three R’s.
[email protected]; [email protected]
ICC SubA, October 28, 2008
Figure 1.
The 3R's of rehabilitation:
Rejuvenate, and Replace.
Re-evaluate,
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. As
shown in [2] for almost all conceivable circumstances, stateof-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 as documented in [3,4]. Because of its
inherent capital efficiency, rejuvenation is applied to the
majority of the identified population of at risk cables.
However, some portion of those cables may not be practically
treatable and hence some of the identified population must be
replaced. Because 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.
RE-EVALUATE AND THE 3D’S
Figure 2, shows the three kinds of inputs that need to be
considered in the process to re-evaluate the population of atrisk cables. The 3 inputs, or 3D’s are:
1. Database of failure statistics and cable “demographics”
2. Distribution hierarch of needs or the 5P’s
3. Diagnostics
Failure
Statistics
Preventati
ve
Proacti
ve
tic
D
is
t.
5P
s
ia
gn
os
Proble
matic
Postfailure
(reacti
ve)
s
Preemp
tive
D
t
os
gn
ia
ics
D
Distribution Hierarchy of Needs
Re-evaluate
No
Identify
splices &
corrosion
Figure 2. The 3D's (Database, Distribution hierarchy of
needs, and Diagnostics are input tools to perform
rehabilitation’s re-evaluation requirement.
As shown in [5] the database of failure statistics and the
“demographics” of the cable, while requiring some effort to
collect and verify, 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 concept of the 5P’s of
the distribution hierarchy of needs was introduced in [2]. The
5P’s focus attention and resources on the sub-population of
cables, which have the largest impact on circuit-owner-defined
reliability requirements. As of this writing the third “D”,
diagnostics, has only limited applicability. In [5] 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 reevaluation process. The balance of this paper will focus on
the integration of the two proven rehabilitation options once
the re-evaluation has been completed.
>0
splices &
corrosion
?
Yes
Rehab?
Yes
Pinpoint
splices
and/or
corrosion
Yes
Excavate
criteria
met?
No
Sustained
Pressure
Rejuvenation
(SPR)
Unsustained
Pressure
Rejuvenation
(UPR)
Replace
No
Air test
Flowable
?
Yes
No
Figure 3. Integrated rehabilitation method maximizes
capital efficiency and reliability.
INTEGRATED REHABILITATION
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. In about half of the cables tested, there will
be 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.
Figure 3 provides an overview of the tactical implementation
of the 3R’s processes. For the first time the benefits of all
available rehabilitation methods are integrated into a unified
strategy. This fully integrated approach is only available from
the authors’ firm, because critical aspects of the process enjoy
patent protection as listed in [6]. The patent protection
includes both granted and pending patent applications.
The top portion of Figure 3 down to the “Rehab?” diamond,
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.
Cables that fall in the first category are immediately treated
with sustained pressure rejuvenation (SPR), which yields a
cable likely to provide reliable service for 40 more years.
Cables in the second group advance to a more complete
2
analysis. The analysis identifies and pinpoints all buried
splices or corrosion issues and is labeled, “Pinpoint splices or
corrosion” on Figure 3.
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 as shown in
[7]. A typical splice distribution is shown in Figure 4 for the
same population.
100%
90%
Failure Distribution
80%
2.
3.
30%
8
5
18
12
9
22
3
17
6
10
20
1
2
11
24
19
15
7
13
23
4
14
16
Utility #
Figure 5. Surveyed failure experience of NEETRAC
member companies. On average 55% of the failures in the
population are perceived as cable failures, 39% are
perceived as accessory failures, and 6% are unknown.
Some circuit owners are reluctant to excavate splices in almost
any circumstance. For some insight on why this may be,
Figure 5 from [13] shows a wide disparity in perceived failure
experience among prominent circuit owners. The overall
cause of URD circuit failure, where the failure was caused by
the cable failing, ranges from 5% to 97%. For accessories
including splices, the range is from 3% to 80%. It will come
as little surprise that circuit owners that experience 97% of
their faults in cables and only 3% in splices are reluctant to
remove a splice, which is perceived to be “perfectly good.”
Such sentiment is understandable, but a careful analysis of the
economics and risks should be considered before ruling out
aggressive splice replacement. In addition to the three
aforementioned problems and the costs associated with
flowing through legacy splices, the circuit owner should
consider carefully the lament of the stockbroker, “Past
performance is not a guarantee of future results.” Just because
splices have not been a reliability issue, they none-the-less are
approaching, or have already passed, their design lives and
will likely experience accelerating wear-out failures.
1
2
3
Historically the application rate of the unsustained pressure
rejuvenation (UPR) paradigm ranges from 50% to 90% and
averages about 75%. Thus about 25% of the cables in which
unsustained pressure rejuvenation is attempted are not treated.
About half of the cables to be rejuvenated are splice-free and
consequently, easy to treat. While actual results vary
significantly between circuit owners, on average about half of
the splices on which injection is attempted will support flow.
As a consequence non-aggressive splice replacement and the
unsustained pressure approach leave about one-quarter of the
cables untreated. This 25% must be replaced for reliable
service. In fact, as demonstrated in [2], the cables with the
most splices are likely the least reliable.
4
12.5%
40%
21
0
6.3%
50%
0%
Accordingly, for typical circuit owners about 40% of the atrisk cable population will fulfill the “Excavate criteria met?”
test. The splices are excavated, the cables injected with the
sustained pressure paradigm, and the aged splices are replaced
with new state-of-art components.
1.6%
60%
10%
The splice may be many decades old and its ability to
provide reliable service for additional decades is less
than certain.
The process of flowing through splices sometimes
causes them to fail as discussed in [8].
The unsustained pressure paradigm utilized to flow
through splices is inherently less robust than the
sustained pressure injection approach as shown in [3],
[4], [9], [10], [11], and [12]. The supplier-guaranteed
lifetime on the former is 20 years and 40 years on the
later.
3%
70%
20%
The pinpointing of splice and corrosion sites allows the
economics of excavation to be estimated. When it is
economical to excavate, it is generally prudent to do so.
While attempting to flow through a legacy splice is
seductively attractive from a short-term perspective, there are
3 reasons to minimize this approach as the long-term costs and
reliability will be compromised.
1.
Cable
Unknown
Accessories
Failure sources
5
Splices
51.6%
25.0%
Figure 4. Typical distribution of splices in pre-1985
vintage North American URD cable.
3
Rejuvenate
(sustained)
50-90%
Rehabilitate
Rejuvenate
(unsustained)
Figure 7. Incremental fluid supplied during typical soak
cycles for cables with No.2 and 1/0 conductors and 175
mils of XLPE insulation. Fluid is 95% phenylmethyldimethoxysilane, 4.8% acetophenone, and 0.2% titanium(IV) isopropoxide catalyst.
5-35%
Replace
2-8%
Figure 7 shows the results of an experiment to measure the
additional fluid delivered with a 60-day soak period. The
experiment included No.2 and 1/0 cables with 175 mils of
polyethylene (XLPE) insulation. Over the course of the 60day soak period 30% to 45% of the supplied fluid is delivered
to the strands. As shown by [11], one of the major causes for
the undersupply of fluid with the chemistry utilized in this
experiment is a mismatch of the diffusion rate of the
condensation catalyst and the monomers. The monomers
require the catalyst to form larger oligomers, which will not
exude quickly from the cable.
Figure 6. 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.
In addition to long-term reliability and life-cycle costs, there
are non-economic reasons to maximize the use of the
sustained pressure rejuvenation method together with
aggressive splice replacement and to minimize the use of the
unsustained pressure method. These reasons are described in
detail in [14] and include the risks associated with multimonth injection periods on energized cables. The next section
of this paper introduces an improvement in the unsustained
pressure injection paradigm. This improved approach is used
in the “Unsustained pressure rejuvenation” process of Figure
3. It is applied to spliced cables that support flow, but that do
not meet the economic criteria required to apply the more
robust sustained pressure rejuvenation method. Depending
upon the propensity of the circuit owner to support aggressive
splice replacement, this approach is typically executed in 535% of the rehabilitation population. This leaves the least
capital efficient process, replacement, for the residual 2-8% of
typical rehabilitation populations. Figure 6 illustrates the
typical distribution of the two rejuvenation paradigms and
replacement.
In [11], a new second generation catalyst system was
introduced. The new catalyst system reduces the 39%
exudation inefficiency suffered by the titanium catalyzed
approach about 20-fold to only a 2% exudation inefficiency.
This single improvement increases the amount of fluid
available for long term rejuvenation by about 37% – roughly
the same as the amount of fluid supplied in a typical soak
period.
This catalyst improvement, along with other
advancements detailed in [10], now provide 20-year life
extension without the need for a soak period.
When utilized, the soak period involves numerous safety and
reliability compromises, as detailed in [14]. Of particular
importance is the presence of potentially energized unshielded
components in otherwise dead-front devices. Figure 8,
excerpted from [16], shows a typical arrangement of soak
bottles left connected to elbows for 60 or more days. Tags
warn the circuit operating personnel that all of the equipment
must be treated as live-front and that the equipment may be
energized when the permanent shielded cap is not in place.
IMPROVED UNSUSTAINED PRESSURE
For over two decades the unsustained pressure injection
process has been executed with few changes. In [9] and [15] it
was demonstrated that the unsustained pressure method does
not allow a sufficient quantity of first generation rejuvenation
fluid to be injected in most URD cables. A soak period has
generally been employed to partially address the undersupply
of fluid.
A second safety issue associated with the unsustained
injection approach is described in [17] and [18]. In short, the
direct access injection port, shown in cross section in Figure 9,
provides for direct access from the conductor to the outside
and ground potential.
4
Second generation unsustained pressure injection can be
applied to cables with splices that support flow at low pressure
and can be utilized in the following cases:
1. In all live-front systems whether or not the cable is
energized.
2. On all dead-front systems that accept Cooper Power
Systems 15-35kV injection elbows or components. The
cable may be energized during injection and does not
need to be deenergized to disconnect the fluid supply or
vacuum components.
3. On all dead-front systems that accept Elastimold 15-35kV
injection components. The cable may be energized
during injection and does not need to be deenergized to
disconnect the fluid supply or vacuum components.
Figure 11 presents an application overview showing how low
pressure dry gas is used to pressurize a fluid delivery bottle.
The bottle in turn, typically pressurized to between 10 and 30
psig, delivers fluid to the access interface, into an injection
elbow, and into the strand interstices. Figure 12 demonstrates
how fluid flows around the compression connector in typical
molded splices. On the other end of the cable a vacuum draws
the fluid into a receiving vessel.
Figure 8. Typical arrangement of soak tanks and injection
caps in direct access elbows from [16] creates multi-month
hazards in the unsustained pressure injection approach
when utilizing first generation fluid injection technology.
This direct access must be exposed to swap permanent,
shielded caps or plugs and non-permanent injection caps or
plugs. Figure 9 shows a cut-away of a typical direct access
elbow. The proprietary reticular flash preventer (RFP) is a
recent innovation. The flash-over problem is so acute when an
RFP is not present on 35 kV systems that the caps or plugs
may not be removed when the system is energized. While deenergizing the cable eliminates the potential for electrical
flashover, there is a cost and customer service penalty that
must be borne by the circuit owner for this time consuming
approach. The RFP device is designed to hold dielectric fluid
in place against the pull of gravity using capillary action,
while at the same time not impeding the flow of fluid into or
out of the cable when an access port interface is attached to
facilitate unsustained pressure injection.
Figure 10 is a photograph of an access interface (AI) used to
safely deliver fluid to and from the cable strands with
conventional direct access elbows for unsustained pressure
injection.
RFP
Figure 10. Access Interface (AI) used on dead-front
elbows allows unsustained pressure injection on URD
systems.
Figure 9.
Direct access injection elbow used for
unsustained pressure injection.
The reticular flash
preventer (RFP) is absent from older injection methods.
5
Figure 12. Fluid flows from the strand interstices around
a compression connector and back into the strand
interstices at a typical molded splice at pressures between
10 and 30 psig.
REFERENCES
1. Smith, “Aged Equipment Sends Jolt through Strained
Power Industry”, Wall Street Journal, August 18, 2006, p.A1.
2. Brinton, “Underground Distribution Reliability: The 5•Ps”,
Electric Energy, Issue 1, 2007.
3. Bertini, “Accelerated Aging of Rejuvenated Cables – Part
I”, ICC, Sub. A, April 19, 2005.
4. Bertini, “Accelerated Aging of Rejuvenated Cables – Part
II”, ICC, Sub. A, November 1, 2005.
5. Bertini, “Diagnostic Testing of Stochastic Circuits”, ICC,
Sub. C, November 6, 2007.
6. See www.novinium.com/patents.
7. Gurniak, “Neutral Corrosion Problem Overstated Recent
study suggests problem may not be as serious as once
thought”, Transmission & Distribution World, Aug 1, 1996.
8. Bertini, “Improving Post-treatment Reliability: Eliminating
Fluid-Component compatibility Issues”, ICC DG C26D, Nov.
1, 2005.
9. Bertini, “New Developments in Solid Dielectric Life
Extension Technology”, IEEE ISEI, Sept. 2004.
10. Bertini & Vincent, “Cable Rejuvenation Mechanisms”,
ICC, Sub. A, March 14, 2006.
11. Bertini & Vincent, “Rejuvenation Reformulated”, ICC
SubA, May 8, 2007.
12. Bertini & Vincent, “Advances in Chemical Rejuvenation:
Extending medium voltage cable life 40 years”, Jicable 2007 –
International Conference on Insulated Power Cables, 2007.
13. Begovic, Perkel, Hampton, Hartlein, “Validating cable
“diagnostic tests”, B.6.6 presentation (CD), Jicable 2007 –
International Conference on Insulated Power Cables, 2007.
14. Bertini, “Injection Hazard Analysis”, updated August 13,
2001. Downloaded from www.utilx.com on December 30,
2002.
15. Bertini, "Injection Supersaturation in Underground
Electrical Cables", U.S. Patent 6,162,491.
16. Riley & Sheil, "Solid Dielectric Cable Rejuvenation
Technology", EDIST Conference, Jan 22, 2003.
17. Bertini & Stagi, “Method and Apparatus of Blocking
Pathways Between a Power Cable and the Environment”, U.S.
Patent 6,517,366.
18. Bertini & Stagi, “Method and Apparatus of Blocking
Pathways Between a Power Cable and the Environment”, U.S.
Patent 6,929,492.
Figure 11. Gas is supplied from the cylinder in the
foreground at 10-30 psig of pressure to push fluid from the
feed tank to the access interface (AI) on the elbow in the
transformer. The cable is typically energized during this
process and fluid generally flows overnight along a 100
meter (328 foot) length to a vacuum receiver on the other
cable end.
SUMMARY
A complete integrated package of strategic decision support
and tactical implementation tools is provided for the first time.
The toolset provides the highest possible system reliability at
the lowest possible capital cost. This integrated program
includes 3●R’s: Continual Re-evaluation, two flavors of
Rejuvenation, and Replacement. The program utilizes all of
the available tools, each playing to their individual strength.
Rejuvenation technology is almost always the most capital
effective rehabilitation tactic. Each tool is applied in order of
its benefit-to-capital ratio whittling away at the population of
at risk cables. Sustained pressure rejuvenation (SPR) has the
highest benefit-to-capital ratio and is applied at the greatest
possible rate to minimize the use of the tools with lower
benefit-to-capital ratios. The circuit owner should choose an
aggressive splice replacement regime to minimize capital cost
and provide the highest level of reliability. An improved
version of unsustained pressure rejuvenation (UPR) is applied
to that small population of cables, which cannot be injected
with the more robust (40 years of reliable life extension),
sustained pressure approach. The improved unsustained
pressure rejuvenation process eliminates the soak period,
eliminates the risk of injection port flashover, and provides
life extension of 20 years. While 20 years is half of the more
robust injection approach, the benefit-to-cost ratio is still
superior to replacement. The number of cables rejuvenated is
maximized, so that the most capital intensive rehabilitation
option, replacement, can be minimized. Together, these
elements provide the maximum reliability benefit with the
lowest capital and lowest capital overhead expenditures.
6
AUTHORS
Glen J. Bertini is the President,
CEO, and Chairman of Novinium,
Inc. He has spent the last two
decades working with cable
rejuvenation technology beginning
with its development at Dow
Corning in 1985 and continuing
through its commercialization and
growth to over 80 million feet of
cable rejuvenated so far. Mr. Bertini was employed by Dow
Corning, a silicon chemical manufacturer, where he was part
of a small team that developed and commercialized the first
cable rejuvenation products. Mr. Bertini has over 35 articles
published and holds a total of 17 patents on cable rejuvenation
and related technologies and has 7 more pending. In 1992, he
was co-recipient of the prestigious R&D 100 award for cable
rejuvenation.
Mr. Bertini holds a B.S. in Chemical
Engineering from Michigan Technological University, is a
Senior Member of the IEEE, a voting member of the ICC, and
is a licensed professional engineer.
Richard K. Brinton is the Vice
President of Business Development
of Novinium.
He has been
responsible for introducing cable
rejuvenation to utilities around the
world. Brinton has over 30 years
experience
in
business
development in the Americas,
Europe, Asia, and Australia. He
has focused his career on the
worldwide introduction of new
technologies and has gained
worldwide experience in industrial
processes, machine tools, robotics,
and construction.
Mr. Brinton
holds a B.S. in Industrial Engineering and a B.A. Liberal Arts
from the Pennsylvania State University, is a Senior Member of
the IEEE, a voting member of the ICC, and is a licensed
professional engineer.
7