4 BackgroundAPS began installing direct buried underground primary distribution cable in the 1950’s and continued until the mid 1980’s.The majority of direct buried underground primary cable in the APS distribution system is a mil XLPE, non-jacketed type cable.PILC – Paper insulated lead sheathed cable
5 Cable FailuresIn the mid-1980’s, we started to experience a steady increase in direct buried underground cable failures.There were 0.3 failures for every circuit mile of underground cable, accounting for 24% of the Company’s overall SAIFI rating.System Average Interruption Frequency Index (SAIFI), it’s used as a reliability indicator by electric power utilities.IEEE Standard the median value for North American utilities is approximately 1.10 interruptions per customer
6 Cause of the FailuresThe direct buried XLPE primary cable had reached the end of its useful life. Although manufacturer’s projected a 30-year life expectancy; we were realizing 16 years.Contributing factors to cable failures were installation practices, mechanical failures, water trees, accessory failures, manufacturing defects, corrosion, or system overload.As a result, APS began to install 220 mil, TRXLPE, Jacketed UG cable in conduit in 1986 and fully transitioned to full conduit primary and secondary system in 1988.A series of tiny hollow voids or channels can develop under electrical stress. These hollow channels are filled with water or materials carried in by water at an earlier time in the cable’s history. Voltage stress over time will cause the small voids to grow. The void will form a small carbon track being burned through the insulation from the phase conductor to the concentric neutral.
8 Cable Replacement Project The Underground Distribution Cable Replacement Project began in 1992 with the goal of replacing all direct buried underground cable in the APS System.It has continued since then with the same objective, yet with changing funding levels and business drivers to achieve that goal.
9 Cable Replacement Plan Business Drivers The Business Drivers used to determine which cable runs to replace:Customer SatisfactionCritical Customers and Key AccountsOperating Demands and PrioritiesNumber of Faults per RunReliability (SAIFI)Cost ContainmentThe ‘Z” team came up with a Master Plan
10 Cable SAIFI (System Average Interruption Frequency Index) Cable SAIFI measures the number of outages customers see each year from cable faults:SAIFI - System Average Interruption Frequency Index1.1 North America Avg
11 Replacement Approaches Utilize a combination of quick response and planned tactics:Accelerated Replacement (AR) 1-1/0AQuick Hitters (QH) 3-1/0A750A and 1/0A Planned Replacement WorkCorroded Neutral Planned Replacement WorkLocate and RepairsService/Secondary Replacement
12 Quick Response Cable Replacement – AR’s and QH’s Three Phase 3-1/0A CableSingle Phase 1/0A Cable<= 500’Not in major streetNot in private easementUse blanket permit with municipalitiesContract out all excavation and conduit installationAPS crews install and terminate wireTypically a 7 working day turnaround on jobs with guards
13 Planned Feeder Cable Replacement - 750A 750kCmil Feeder CableJobs are scoped, designed, routed and permits acquiredBudget status determines when job is released for constructionA limited number of jobs are on the shelf so that we can react quicklyContract all excavation and conduit installationAPS crews install and terminate wire
14 Planned Cable Replacement – Corroded Neutral Cable 1/0A or 3-1/0 in Northern RegionsConcentric Neutral on DB cable has sacrificed itself due to corrosive soil conditionsJobs to replace multiple runs prioritized by DistrictsJobs are scoped, designed, routed and permits acquiredBudget status determines when job is released for constructionA limited number of jobs are on the shelf so that we can react quicklyContract all excavation and conduit installationAPS crews install and terminate wire
15 Locate & Repair Single Phase or Three Phase Circuits >500’ In major streetIn private easementNeeds a permit to replaceOther complications such as limited access
16 Service/Secondary Cable Replacement Includes both service and secondary direct buried low voltage (<600 volts) cable runsAdded emphasis in 2011 to replace rather than repair service/secondary faultsTypically, no guards since we can put a service kit on the houseAll work is completed by a contractor. They excavate, install conduit and conductor, and re-landscape
18 Replace Vs. Repair Primary Cable Philosophy is a balanced approach between Replace and RepairMean time between faults accelerates with each failure2nd Time Fault Recurrence – 3.58 years3rd Time Fault Recurrence – 2.13 years4th Time Fault Recurrence – 1.21 years5th Time Fault Recurrence – 1.40 years6th Time Fault Recurrence – 0.56 years
19 Replace Vs. Repair Primary Cable Average cost for Repairs (2011)$3,800 for 1/0A$5,800 for 750AAverage Replacement Cost (2011) per work order$10,190 for 1/0A$60,108 for 750ACan replace 1/0A for less than the cost to repair it three times.
21 How Much Direct Buried Cable Was Installed? It was estimated that we installed about 5,000 trench miles of direct buried underground primary cableWe have replaced approximately 2,300 trench miles through July 2012Mid 1960’s through mid 1980
22 Cable Replacement Year to Date Metro Primary Cable Replacement SummaryProject YearTrench Miles ReplacedTotal Expenditures88 thru 91289.571992117.92$22,922,8391993121.26$27,888,1191994180.78$27,568,8441995138.33$23,578,4621996127.70$19,597,1701997148.50$19,662,9761998155.59$18,866,0001999132.83$16,815,1722000130.76$17,857,8852001127.79$18,476,3402002114.71$16,507,908200375.91$8,014,052200466.16$10,448,000200564.18$11,068,871200655.68$12,345,972200754.36$13,940,602200844.12$15,031,960200930.83$14,601,760201047.23$13,120,202201149.21$16,316,439201225.65$11,563,707Total2,299.07$356,193,280* 2012 = Jan - JulMuch has taken place since my involvement in mid 2008
23 Estimated Direct Buried Cable Remaining Trench Miles (Aug 2012) Division1-1/0A3-1/0A3-750ATotalMetro1444133551632NE2881113402NW360544418SE9325121SW1351421512320337672724
25 Going Forward The Cable Replacement Program will focus on: Replacing all of the direct buried 750A feeder cable in the next 4-5 yearsReplacing all identified corroded neutral primary cable (estimated 67 trench miles) in next 7-8 yearsContinue with AR and QH programMid 1960’s through mid 1980
26 Going ForwardContinue the balanced approach to replace and repair both primary and secondary/serviceAdvocate funding cable replacement at the same levels as 2012Primary - $22MSvc/Sec - $3.5MMid 1960’s through mid 1980