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Selection:The most critical part of maintenance
N. Hampton & J. Perkel
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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 recommendationsexpressed in this material are those of the author(s) and donot necessarily reflect the views of the Department ofEnergy.
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Outline Motivation
SAGE
Selection
Choice of when to start
Choice of location
Choice of action
Choice of diagnostic
Impact of Selection on Benefits / Value
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SAGE
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A Useful Way to Visualize thisSAGE
Selection of circuits Actions that might be taken
Generation of data including Diagnostics
Evaluation of the outcome
The name of the herb Sage comes fromthe Latin salvere or salvation meaning 'to
be in good health, to cure, to save.'
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Expectations
No.ofF
ailures
Failures Increasing
Failures Decreasing
Selection
Action
Generation
Evaluation
Failures increasingas time passes since test
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Selection
Choice of when to start
Choice of location
Choice of actionChoice of diagnostic
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When to start?
How to spot the trend
How late can you leave it before it is too late
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Falling Reliability
Year
Failur
es
2015201320112009200720052003
800
700
600
500
400
300
200
100
0
Whenshould we
start aprogram?
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Bathtub Curve for Failures
0
2
4
6
8
10
12
14
16
18
20
0 50 100 150 200 250 300
Time
Tot
alNum
berofFailur
es
Early FailuresWeibull Shape 1TBF decreases
Time Between Failures
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Too Soon
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Too Late
Aging
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Just Right...
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Location
The failure rate is not the same everywhere
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Selecting from the Whole Population
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Local Failure Rates
Port ion of t he Syst em
LocalFailureRate-relto
overalla
verage(%
)
250
200
150
100
50
0
100
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Local Failure Rates - Importance
Importance
RelativeFailureRate
(%
ofaverage)
HighMediumLow
200
150
100
50
0
100
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Action
How the circuits fail will determine how they are fixed
Age and Type will also determine actions
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Failures by Equipment Type
Perce
ntage
ofserv
icefailures(%
)
AccessoriesUnknown SourceCable
100
80
60
40
20
0
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Length adjusted MV system
InstalledCapacity(%)
UNKNOWNTRXLPEEPRXLPEHMWPEPILC
100
90
80
70
60
50
40
30
20
10
0
25
50
75
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Diagnostic
What diagnostic to use for which actions andequipment
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Selection of Diagnostic
Diagnostic technologies are available that provide eitherlocalized or global assessments of circuits.
These techniques should fit with the actions that will betaken.
Diagnostic should be sensitive to the prevalent failuremechanism.
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Failure by Equipment Type
Perce
ntage
ofserv
icefailures(%
)
AccessoriesUnknown SourceCable
100
80
60
40
20
0
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Economic Benefit
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Data for Economics Calculations
Different data are needed before one can begin tocompute the economics for diagnostic programs
System Diagnostic
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Consequence
Diagnostic Program CostsCost [$]
Selection
Diagnostic
Maintenance Total DiagnosticProgram Cost
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System Data
Failure Rate
Global
Local Maintenance/Replacement costs
repair
rejuvenation replacement
Cost of Poor Reliability
Reliability indices Customer, regulator, or media intervention
Emergency restoration cost
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Diagnostic Data
Selection
Testing
Diagnostic vender or equipment Switching crew
Pilot Study data from testing in other areas
Percent of tested population requiring each level ofmaintenance (i.e. percent of segments that needed to bereplaced according to diagnostic)
Percent of tested segments failing on test Accuracy (i.e. how often do segments perform as
diagnosed?)
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Consequence
Diagnostic Program CostsCost [$]
Selection
Diagnostic
Maintenance Total DiagnosticProgram Cost
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Program Savings
b
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Population Composition
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Summary
Selecting the right segments to test is key to achievinggood performance from the diagnostic program
Selection should focus on failure rates and importance ofcircuits.
System cannot be either too good or too bad.
Chosen diagnostic technique should match the systemcharacteristics (i.e. failure mechanism) and possible
maintenance actions
A diagnostic program requires substantial planning to beeffective.