Presented at Fall 2007 PES-ICC Meeting.This material is based upon work supported by the Department of Energy under Award No DE-FC02-04CH1237 and CDFI

Hampton, Nigel

Perkel, Josh

English

Scholarly Materials And Research @ Georgia Tech

1C26D Medium Voltage Underground Cable Reliability - Fall 2007 ICC Meeting – Scottsdale, AZ Selection:The most critical part of maintenanceN. Hampton & J. Perkel2C26D Medium Voltage Underground Cable Reliability - Fall 2007 ICC Meeting – Scottsdale, AZ Acknowledgements• This material is based upon work supported by the Department of Energy under Award No DE-FC02-04CH1237 and CDFI.• Any opinions, findings, conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the Department of Energy.3C26D Medium Voltage Underground Cable Reliability - Fall 2007 ICC Meeting – Scottsdale, AZ Outline• Motivation• SAGE• Selection– Choice of when to start– Choice of location– Choice of action– Choice of diagnostic• Impact of Selection on Benefits / Value4C26D Medium Voltage Underground Cable Reliability - Fall 2007 ICC Meeting – Scottsdale, AZ Motivation• The goal of proactive maintenance is to prevent future service failures– Wholesale Replacement– Targeted Maintenance• A Targeted Maintenance program uses diagnostic test(s) to identify the “weak” circuits.• Program carries upfront costs that must be offset by program benefits.• The economics of diagnostics are difficult to model and even more difficult to quantify. Must be used to quantify the benefits.5C26D Medium Voltage Underground Cable Reliability - Fall 2007 ICC Meeting – Scottsdale, AZ SAGE6C26D Medium Voltage Underground Cable Reliability - Fall 2007 ICC Meeting – Scottsdale, AZ A Useful Way to Visualize this SAGE• Selection of circuits• Actions that might be taken• Generation of data – including Diagnostics• Evaluation of the outcomeThe name of the herb Sage comes from the Latin salvere or salvation meaning 'to be in good health, to cure, to save.' 7C26D Medium Voltage Underground Cable Reliability - Fall 2007 ICC Meeting – Scottsdale, AZ ExpectationsNo. of FailuresFailures IncreasingFailures DecreasingSelectionActionGenerationEvaluationFailures increasingas time passes since test8C26D Medium Voltage Underground Cable Reliability - Fall 2007 ICC Meeting – Scottsdale, AZ SelectionChoice of when to startChoice of locationChoice of actionChoice of diagnostic9C26D Medium Voltage Underground Cable Reliability - Fall 2007 ICC Meeting – Scottsdale, AZ When to start?How to spot the trendHow late can you leave it before it is too late10C26D Medium Voltage Underground Cable Reliability - Fall 2007 ICC Meeting – Scottsdale, AZ Falling ReliabilityYearFailures20152013201120092007200520038007006005004003002001000When should we start a program?11C26D Medium Voltage Underground Cable Reliability - Fall 2007 ICC Meeting – Scottsdale, AZ Bathtub Curve for Failures024681012141618200 50 100 150 200 250 300TimeTotal Number of Failures Early FailuresWeibull Shape <1TBF increasesReliable OperationWeibull Shape =1TBF stableAgeingWeibull Shape >1TBF decreasesTime Between Failures12C26D Medium Voltage Underground Cable Reliability - Fall 2007 ICC Meeting – Scottsdale, AZ Too Soon13C26D Medium Voltage Underground Cable Reliability - Fall 2007 ICC Meeting – Scottsdale, AZ Too LateAging14C26D Medium Voltage Underground Cable Reliability - Fall 2007 ICC Meeting – Scottsdale, AZ Just Right...15C26D Medium Voltage Underground Cable Reliability - Fall 2007 ICC Meeting – Scottsdale, AZ Sample Circuit PopulationTime to First Failure (Days)Percent200010005002001005020999080706050403020105321Shape 1.419Scale 748.016C26D Medium Voltage Underground Cable Reliability - Fall 2007 ICC Meeting – Scottsdale, AZ Bathtub Curve024681012141618200 50 100 150 200 250 300TimeTotal Number of Failures Early FailuresReliable OperationAgeingSample Circuits17C26D Medium Voltage Underground Cable Reliability - Fall 2007 ICC Meeting – Scottsdale, AZ LocationThe failure rate is not the same everywhere18C26D Medium Voltage Underground Cable Reliability - Fall 2007 ICC Meeting – Scottsdale, AZ Selecting from the Whole Population19C26D Medium Voltage Underground Cable Reliability - Fall 2007 ICC Meeting – Scottsdale, AZ Local Failure RatesPortion of the SystemLocal Failure Rate - rel to overall average (%)χηαϕνεβγδιµκφλ25020015010050010020C26D Medium Voltage Underground Cable Reliability - Fall 2007 ICC Meeting – Scottsdale, AZ Local Failure Rates - ImportanceImportanceRelative Failure Rate (% of average)HighMediumLow200150100500100νµλκϕιηγφεδχβα21C26D Medium Voltage Underground Cable Reliability - Fall 2007 ICC Meeting – Scottsdale, AZ ActionHow the circuits fail will determine how they are fixedAge and Type will also determine actions22C26D Medium Voltage Underground Cable Reliability - Fall 2007 ICC Meeting – Scottsdale, AZ Failures by Equipment TypePercentage  of service failures (%)AccessoriesUnknown SourceCable10080604020023C26D Medium Voltage Underground Cable Reliability - Fall 2007 ICC Meeting – Scottsdale, AZ Length adjusted MV systemInstalled Capacity (%) UNKNOWNTRXLPEEPRXLPEHMWPEPILC100908070605040302010025507524C26D Medium Voltage Underground Cable Reliability - Fall 2007 ICC Meeting – Scottsdale, AZ DiagnosticWhat diagnostic to use for which actions and equipment25C26D Medium Voltage Underground Cable Reliability - Fall 2007 ICC Meeting – Scottsdale, AZ Selection of Diagnostic• Diagnostic technologies are available that provide either localized or global assessments of circuits.• These techniques should fit with the actions that will be taken.• Diagnostic should be sensitive to the prevalent failure mechanism.26C26D Medium Voltage Underground Cable Reliability - Fall 2007 ICC Meeting – Scottsdale, AZ Failure by Equipment TypePercentage  of service failures (%)AccessoriesUnknown SourceCable10080604020027C26D Medium Voltage Underground Cable Reliability - Fall 2007 ICC Meeting – Scottsdale, AZ Economic Benefit28C26D Medium Voltage Underground Cable Reliability - Fall 2007 ICC Meeting – Scottsdale, AZ Data for Economics CalculationsDifferent data are needed before one can begin to compute the economics for diagnostic programsSystem Diagnostic29C26D Medium Voltage Underground Cable Reliability - Fall 2007 ICC Meeting – Scottsdale, AZ ConsequenceDiagnostic Program Costs Cost [$]SelectionDiagnosticMaintenance Total Diagnostic Program Cost30C26D Medium Voltage Underground Cable Reliability - Fall 2007 ICC Meeting – Scottsdale, AZ System Data• Failure Rate– Global– Local• Maintenance/Replacement costs – repair– rejuvenation– replacement • Cost of Poor Reliability– Reliability indices– Customer, regulator, or media intervention– Emergency restoration cost31C26D Medium Voltage Underground Cable Reliability - Fall 2007 ICC Meeting – Scottsdale, AZ Diagnostic Data• Selection• Testing– Diagnostic vender or equipment– Switching crew• Pilot Study data from testing in other areas– Percent of tested population requiring each level of maintenance (i.e. percent of segments that needed to be replaced according to diagnostic)• Percent of tested segments failing on test• Accuracy (i.e. how often do segments perform as diagnosed?)32C26D Medium Voltage Underground Cable Reliability - Fall 2007 ICC Meeting – Scottsdale, AZ ConsequenceDiagnostic Program Costs Cost [$]SelectionDiagnosticMaintenance Total Diagnostic Program Cost33C26D Medium Voltage Underground Cable Reliability - Fall 2007 ICC Meeting – Scottsdale, AZ Program Savingsb34C26D Medium Voltage Underground Cable Reliability - Fall 2007 ICC Meeting – Scottsdale, AZ Population Composition35C26D Medium Voltage Underground Cable Reliability - Fall 2007 ICC Meeting – Scottsdale, AZ Summary• Selecting the right segments to test is key to achieving good performance from the diagnostic program• Selection should focus on failure rates and importance of circuits. – System cannot be either “too good” or “too bad”.• Chosen diagnostic technique should match the system characteristics (i.e. failure mechanism) and possible maintenance actions• A diagnostic program requires substantial planning to be effective.

Selection: The Most Critical Part of Maintenance

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Selection: The Most Critical Part of Maintenance

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