MV Reliability Hampton & Perkel 110507

7/31/2019 MV Reliability Hampton & Perkel 110507

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1C26D Medium Voltage Underground Cable Reliability - Fall 2007 ICC Meeting Scottsdale, AZ

Selection:The most critical part of maintenance

N. Hampton & J. Perkel


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C26D 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 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.

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MV Reliability Hampton & Perkel 110507