A chat about cables with SRP
We talk with Rick Hudson, PE, Engineering Supervisor, Distribution Improvements, with Salt River Project about the cables in their system and the rejuvenation process.
Tell us about SRP. How many customers you serve, location, physical environment, etc?
As one of the nation's largest public power utilities, SRP provides reliable, reasonably priced electricity and water to more than 2 million people in Central Arizona.
The Salt River Project is a utility of historic importance having been established in the early 1900s by President Theodore Roosevelt whose initial objective was to provide water to the farmers of the Phoenix area. SRP today, provides electricity to most of the southern part of Phoenix. We have 1 million electrical customers of which 900,000 are residential customers.
SRP is the oldest multipurpose federal reclamation project in the United States. We have been serving central Arizona since 1903, nearly 10 years before Arizona became the 48th state. Today the SRP power district is one of the nation's largest public power utilities. We provide electricity to approximately 1 million retail customers in a 2,900-square-mile service area that spans three Arizona counties, including most of the metropolitan Phoenix area (known as the Valley). We are an integrated utility, providing generation, transmission and distribution services, as well as metering and billing services.
Can you tell us about the age and type of the majority of the electrical cables in your system?
Our utility has 22 million feet of direct buried URD cable most of which is # 2 XLPE insulated stranded cable. In the mid-1990s, our policy was to replace any cable that failed 3 times—we called it the ‘3-strikes and your out’ policy. Unfortunately, we were applying this policy to all our electrical cable—both URD and feeder cable. But most of the reliability impact was the result of feeder cable failure not the URD cable failures. Once we distinguished between the two cable types, we were able to focus more clearly on the feeder cable and realize that our replacement policy made economic sense for the feeder cable but NOT for the URD cable. Most of our failing cable is direct buried cable that was originally installed between 1968 and 1993.
How did you learn about electrical cable rejuvenation?
I have been working SRP since 1987, standards group. At that time, we became aware of an early version of cable rejuvenation injection and even went as far as to trial the process . Unfortunately we tried apartment complex with too many splices and the results were not successful so consider again until almost 10 years later.
In 1998 we revisited the option of cable rejuvenation again, knowing that there were new improvements in the technology, but more importantly knowing that there were different ways of integrating this technology into the overall cable asset management our system.
Over time, we determined it would be better to use cable rejuvenation on cable before the cable reaches a saturated point of failure. We needed to change our criteria and not think of cable rejuvenation as the solution for our cables with the most failures as those cables tend to be the more troublesome segments. Rather, use the cable rejuvenation as a way to have a greater reach across our larger system.
What made you want to pursue electrical cable rejuvenation? Was cable replacement also considered? What are the cost differences?
We decided to look at rejuvenation specifically for our URD cable because that cable was more cost prohibitive to replace because of failure. We decided to put a proactive plan in place to evaluate all URD cable system-wide and rejuvenate that cable to improve reliability and stem the tide of future failures. We now focus on replacing primarily feeder and sub-feeder cable while using rejuvenation on URD cable to create the biggest impact on our overall reliability of service to customers.
Cable rejuvenation is the best way for us to manage the funds we have available for cable asset management. The cost to replace our cable is 10 times the current cost of injection. What we have determined is that for every cable that is successfully injected, we break even on the expense of replacement at only five years of failure-free operation from injection. So every year beyond 5 years, we are actually saving money by making interest on the money that would have otherwise been spent to replace the cable.
Tell us about the process of injecting. What did it involve in your case? How does the climate or terrain affect the process? Any special considerations/ techniques?
Our approach for cable rejuvenation today, is to rejuvenate the youngest cable first while simultaneously replacing the oldest cable in our system until eventually the two meet. In 1998, our approach was to try to inject the worse performing cable and we found we weren’t getting the outcomes we wanted.
We are focusing on the replacement of our feeder cable because these failures are circuit wide and have more of an impact on our customers. URD cable is fused so when a failure occurs, it is isolated from the rest of the system and the main feeder lines.
Our physical environment here in Phoenix has a direct impact on our electrical cables. On an average summer day, our afternoon temperatures during the day typically peak around 110 degrees. We live in an urban area surrounded by concrete and asphalt which absorbs the heat and radiates throughout the evening which continues to put a high load on the cables throughout all 24 hours.
We have learned that not all electrical cable rejuvenation has the same results. Our efforts are customized to a certain extent, based on various factors related to specific locations and type of cable being treated. We are currently using a hybrid approach to our treatment, in which we use iUPS and SPR specifically with a CableCure 732 fluid which has been extremely successful in our environment.
Can you tell us why you chose to pursue cable rejuvenation?
In the mid-1990s there was a public outcry because of the number of failures occurring in the system. As a result we were spending all of our resources on cable replacement activity (replacing direct buried cable with cable pulled through conduit) but not having the reach we knew we needed for our system.
Even if we had unlimited funds, we couldn’t replace all our cable at one time, as we would be limited by labor. We have found our sweet spot is to replace 1 million feet of cable per year. Unfortunately, we still have over 20 million feet of URD cable. Which means 20 years to replace this remaining cable. As a result, we are finding that by using cable injection/rejuvenation, we are able to have a much greater reach within our system to avoid failures in the other cables. It’s a proactive approach we find is working very well.
Since 1993, all new distribution cable is installed in a conduit system. It’s more reliable and we do not have to worry about cable being affected by native backfill or settling issues.
What benefits have you seen from this project? What advice would you give other utilities looking to replace a lot of old cable?
Since we adopted cable rejuvenation into the revised management of our cables, we have nothing but positive feedback. Our failure rate is improving and the process has significantly improved our bottom line. This makes all of our constituents happy. I would encourage utilities to talk to other utilities that have implemented injection to rejuvenate their cables. Find out how the process has worked for them and why. When it comes right down to it, the cost savings and improved reliability are the drivers to integrate this process into a completely proactive approach to managing older cable assets.
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