Life Expectancy

Spring ICC 2017 A6D

Nigel Hampton, Josh Perkel, Thomas Parker

1

Bridging the gap

between Lab Tests

and estimates of

Service Performance

Life Expectancy

Spring ICC 2017 A6D

Feedback shows its important to

estimate / assure the longevity of

an installed cable system

Life Expectancy

Spring ICC 2017 A6D

Limited field data

but have accelerated tests

ACLT

Cores in water - tanks

??yr

AWTT

Cores in water - tubes

1yr

Life Expectancy

Spring ICC 2017 A6D

Details of accelerated tests

ACLT

Cores in water - tanks

??yr

Time to Failure metric

Continuum of un defined times

Moderate samples (#*l)

AWTT

Cores in water - tubes

1yr

Breakdown metric

Multiple defined times

Small samples (#*l)

Life Expectancy

Spring ICC 2017 A6D

Details of accelerated tests

ACLT

Cores in water - tanks

??yr

Time to Failure metric

Continuum of un defined times

Moderate samples (#*l)

AWTT

Cores in water - tubes

1yr

Breakdown metric

Multiple defined times

Small samples (#*l)

Time to Failure Data

seems like a good place

to start

Life Expectancy

Spring ICC 2017 A6D

Details of accelerated tests

ACLT

Cores in water - tanks

??yr

Time to Failure metric

Continuum of un defined times

Moderate samples (#*l)

AWTT

Cores in water - tubes

1yr

Breakdown metric

Multiple defined times

Small samples (#*l)

Time to Failure Data

seems like a good

place to start

Unfortunately when

you start looking

around there is not

much data out there &

available

Life Expectancy

Spring ICC 2017 A6D

Details of accelerated tests

ACLT

Cores in water - tanks

??yr

Time to Failure metric

Continuum of un defined times

Moderate samples (#*l)

AWTT

Cores in water - tubes

1yr

Breakdown metric

Multiple defined times

Small samples (#*l)

Time to Failure Data

seems like a good

place to start

Unfortunately when

you start looking

around there is not

much data out there &

available

Can anything be done

with Breakdown

Strengths at defined

times

Life Expectancy

Spring ICC 2017 A6D

What is there to work with?

8

=

Life Expectancy

Spring ICC 2017 A6D

Still some concerns

Are they representative only 3 numbers at each time

Are they sensible lengths 15ft is wet

How do we handle uncertainty

Are the failure modes translatable

Is acceleration reasonable

9

Life Expectancy

Spring ICC 2017 A6D

Meta Analysis

10

Are they representative YES

Are the failure modes translatable - YES

Life Expectancy

Spring ICC 2017 A6D

Approaching Service Length Weibull Scale

11

Sensible

lengths?

=

1 4

873

Life Expectancy

Spring ICC 2017 A6D

Length extension of Meta Analysis

12

Sensible

lengths?

=

1 4

873

Are they sensible lengths - YES

Life Expectancy

Spring ICC 2017 A6D

Uncertainty: Shape & Scale @ 300ft

13

=

n 3

How do we handle uncertainty YES, with confidence limits

Life Expectancy

Spring ICC 2017 A6D

B63 stress by which 63% of the population is expected to fail

B10 stress by which 10% of the population is expected to fail

B1 stress by which 1% of the population is expected to fail

Utility Risk Acceptance @ 300ft

14

Is acceleration reasonable

NOT UN REASONABLE

Life Expectancy

Spring ICC 2017 A6D

In Conclusion

Utilities remain interested in life expectancy

Need to use test data, but some steps are required

Are they representative

Are they sensible lengths

How do we handle uncertainty

Are the failure modes translatable

Is acceleration reasonable

There likely is some approximate translation between

test performance and service expectation

Life Expectancy

Spring ICC 2017 A6D

More Information

The New Weibull Handbook Bob Abernethy

IEEE Guide for the Statistical Analysis of Electrical

Breakdown Data Fothergill, Montanari, Hampton,

Ross, Stone

Statistical Treatment of Fatigue Experiments Leonard

Johnson

Water Treeing Fred Steenis

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