In the mid-1990s, the number of cable failures at Salt River Project (SRP) was escalating at an unmanageable rate. There was no doubt that SRP, which serves the Phoenix, Arizona area, had many aging feeders and underground residential distribution (URD) cables. But faced with numerous cable replacement projects, SRP saw the rapidly increasing cost of this maintenance activity rising faster than its budget could handle.
Therefore, SRP tried a new approach: In addition to replacing failed cable, SRP decided to try a more capital-efficient cable rejuvenation program with cable injection technology. Cable rejuvenation is the injection of a fast-acting silicone fluid into strands of medium-voltage underground cable to repair and extend its life, and to reduce power outages.
EVALUATING CABLE FAILURES
SRP currently has 22 million feet of direct, buried URD cable, most of which is #2 XLPE insulated stranded cable. In the mid-1990s, SRP’s policy was to replace any cable that failed three times — a so-called “three strikes and you’re out” policy. The policy was applied to all electrical cable — both URD and feeder cable. Most of SRP’s failing cable was direct-buried cable that was installed between 1968 and 1993.
But most of the impact on reliability was due to feeder cable failures, not URD cable failures. Therefore, SRP’s replacement policy made greater economic sense for the replacement of feeder cables.
THE REJUVENATION APPROACH
While SRP continues to replace feeder and sub-feeder cable today, it uses rejuvenation on URD cable to improve reliability in this part of its distribution system to minimize future failures.
With rejuvenation, SRP breaks even at only five years of failure-free operation. In fact, the cost of cable replacement is as much as 10 times the current cost of cable rejuvenation.
In 1987, SRP tried an early version of cable rejuvenation injection at an apartment complex, but the results were not very successful. Therefore, cable rejuvenation wasn’t considered again for another 10 years. In 1998, SRP revisited cable rejuvenation, hoping that there were improvements in the technology, and has found ways to integrate it into the company’s cable asset management.
Over time, SRP determined it would be better to use cable rejuvenation before the cable reached a saturated point of failure. Even if SRP had unlimited funds, the company couldn’t replace all of its cable at one time due to the amount of labor it would require. SRP found that its current sweet spot is to replace about one million feet of cable per year. Unfortunately, SRP still has over 20 million feet of URD cable, which would require 20 years to replace. With rejuvenation, the company can better avoid failures in these aging cables. This proactive approach is working very well.
Since 1993, all new distribution cable has been installed using a conduit system. It’s more reliable and there’s no worry about cable being impacted by poorly screened native backfill or other settling issues.
SRP’s approach today is to rejuvenate the youngest cable first, while simultaneously replacing the oldest cable in its system until the two meet. In 1998, the company tried to inject the poorest-performing cable and didn’t find completely successful results.
SRP now replaces feeder cable because these failures involve an outage for the whole circuit, and have a greater reliability impact on customers. URD cable is fused so that when a failure occurs, it is isolated from the rest of the system and the main feeder lines.
The physical environment in Phoenix has a direct impact on electrical cables. On an average summer day, afternoon temperatures can peak at or above 110 degrees. The urban area is surrounded by concrete and asphalt that absorbs the heat and radiates throughout the evening. This puts a high load on cables around the clock.
Since adopting cable rejuvenation, SRP has received significant, positive feedback. The cable failure rate is improving and the process has improved the company’s bottom line. This makes all of SRP’s constituents happy.
SRP is rejuvenating the least-reliable URD cable using a hybrid approach of Improved Unsustained Pressure Rejuvenation (iUPR) and Sustained Pressure Rejuvenation (SPR) injection processes with Cablecure 732 injection fluid. This strategy allows SRP to delay replacement of faulty cable, while extending the cable life by hopefully decades. To date, SRP has used Novinium to rejuvenate 780,805 feet of cable.
Rejuvenated cable is restored to like-new condition and is backed by a 25-to-40-year warranty. Novinium’s cable rejuvenation is now an integral part of the SRP asset management plan. SRP has experienced a rejuvenated cable failure rate of less than one percent using Novinium’s hybrid approach.
When it comes right down to it, the cost savings and improved reliability achieved through injection are reasons to integrate this process into managing older cable assets.
PROVIDING RELIABLE AFFORDABLE SERVICE UNDER TIGHT BUDGETS
By Jon Engman, Novinium
Utilities face a complex challenge: They must balance tight budgets and maintain high safety standards, while providing customers with reliable service at affordable rates.
Our nation’s aging infrastructure cannot be replaced all at once. There is a need to develop capital-efficient strategies to maintain underground electrical reliability. Suppliers need to work with utilities to develop asset management programs to prioritize projects and optimize capital. A combination of cable replacement and injected cable rejuvenation is finally receiving widespread adoption, as these technologies have proven themselves to provide reliability, cost efficacy and sustainability.
One factor that will drive this adoption is favorable budget treatment of rejuvenation expenses. The Federal Energy Regulatory Commission has noted that a company may capitalize the cost of installing injection rehabilitation products, provided that the product is used by the company to extend the useful life of its segments of URD cables beyond their original estimated useful lives. This is one of several opportunities available to utilities when budgeting asset management. A growing number of utilities are sharing their experiences with colleagues to create asset management programs that work both short term and long term.
Electric utilities are always looking for ways to enhance their infrastructure’s reliability and performance, while controlling expenses. No electric utility ever wants their power to go off. At many utilities, management of aging infrastructure is centered around addressing faults and cable replacement. Cable rejuvenation is a viable, and often ideal, option for electric utilities to consider.