Age Is A Poor Proxy

Why relying on age-based replacement is imprudent

Presented by Dan O’Neill

to the

EUCI Aging T&D Infrastructure Workshop

February 21, 2001

2

Number of states with new electric reliability rules

Source: Article by Navigant Consulting Inc.’s Dan O’Neill, Public Utilities Fortnightly, March 1999, updated

As public concern for reliability increases...

3

...Public cries to replace aging infrastructure increase

July 15, 1999, Thursday

Metropolitan Desk

And yesterday, Mr. Giuliani

continued his attacks on Con

Edison's response as too

passive. ''What Con Edison

should be saying is here are the

things that have to be done to

make it virtually impossible for

blackouts to take place,'' he

said. ''We need more power.

We need to purchase more

power. We need more

alternatives. We need a more

modern infrastructure,

meaning we have to improve

the feeder cables so we have

better material. We need to

insulate them better.''

(emphasis added)

4

But if the public knew the facts about age & reliability They would say that relying on age-based replacement is imprudent

Not cost-effective Replacing infrastructure components based

on age is one of the least cost-effective ways

of improving service

Not method-efficient There are better indicators of deterioration

than age, e.g., specific failure history, test

results, defective types

Not best practice

Other industries have learned not to rely

on age for reliability management, e.g.,

aerospace, automotive, even natural gas

pipelines and LDC’s

Relying on age-based replacement for reliability is

5

Customer

interruptions

Customer

minutes

Restoration

time

Device

outages

Customers per

device Vegetation

Animal

Lightning

Equipment

Trim, remove,

mow & spray

Guards, BIL

Arresters, BIL

shield, ground

Inspect,

repair/replace

Other Planning,

upgrades

SAIDI / SAIFI

Worst circuits

Satisfaction

Remediation Root cause

Effectiveness

$

Sectionalizing

Deployment

Asset management is key in the distribution business model

Accurate estimates

Know what you

spend by program Don’t spend money

on the wrong problem

Don’t just assume

75% reduction

Minimize the impact

of outages that remain

Make sure you

are right-sized

Customers really

want to know

Measure the

right things

6

Replacement is only one of the asset management strategies

And there are usually much better ways to improve customer service

Asset Management Strategies

- Improved standards for new construction

- Preventive maintenance

- Remediation of failure-prone conditions

- Replacement of failure-prone components

- Re-design for redundancy

- Reinforce for capacity

- Inspection and condition monitoring

- Mitigation of effects on customer satisfaction

- Rapid repair and restoration

And it is not

usually the

most cost-

effective...

…except when

combined with

inspection and

monitoring to

replace only

just-in-time

7

0

100

200

300

400

500

600

191

4

192

0

192

4

192

9

193

4

193

9

194

3

194

7

195

1

195

5

195

9

196

3

196

7

197

1

197

5

197

9

198

3

198

7

199

1

199

5

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

Cumulative Line Miles Line Miles Added

Cab

le M

iles A

dd

ed

by Y

ea

r Cum

ula

tive L

ine

Mile

s

‘Age’ is not the same as ‘vintage’ if the real issue is defects Manufacturing problems in certain ‘vintages’ are not really ‘age-based’

Certain early

vintages of

solid cable are

known to be

failure-prone

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Cable Failure

Improper

Installation

Mechanical

Damage Mark-

outs

Enforce

Penalties

Temperature

of cable

Manufacturer

Defect

Insulation

Breakdown

Dig In

Treeing

Rocky Soil

Enforce

Trench

Standards Improper

Training

Insulation

Thickness/Type

Cable

Injection Cable

Replacement

Lightning

One

Call

Upgrade to

MOV

Arresters

around open

New

Construction

Jacket/casing

missing/broke

Moisture in

cable/joint

Rock

Bruising

Corrosion

Strength

Steam

(Ducted)

Loading Ventilation

(Ducted)

Add

Capacity

Maintain

Manholes

Capacity

Planning

Thumping

Cathodic

Protection

Maintain

Cath Prot

Street

Crossing

In root cause analysis, age is often a proxy for ‘cycles’

Thermal

Instability

Wet Manhole

9

Exponential density function

Mean = 15

0%

1%

2%

3%

4%

5%

6%

7%

0 5 10 15 20 25 30 35 40 45 50

Cycles to failure

Pro

bab

ilit

y o

f fa

ilu

re

Many components’ failures fit the exponential process model Which means they are ‘memory-less’ and independent of ‘age’ or ‘cycles’

So, for an

exponential

process,

preventive

replacement

will not work

at all, e.g.,

light bulbs

For the exponential curve,

the slope at the origin

points to the mean

At any point on the curve,

the mean ‘cycles to failure’

is the same

10

This is

typical for

devices

like circuit

breakers,

where the

‘cycles’ are

fault

operations

The Weibull curve assumes ‘wearout’ caused by cycles

With a failure rate that increases with ‘age’ or ‘cycles’

Weibull conditional failure rate

mean = 15

0%

10%

20%

30%

40%

50%

60%

70%

80%

0 5 10 15 20 25 30 35 40 45 50

Cycles at failure

Fa

ilu

re r

ate

(fa

ilu

res

/ su

rviv

ors

)

shape = 2.5

shape = 1.0

11

But for such components, overhaul often resets the ‘clock’ Older devices may simply require fewer cycles between overhauls

Weibull conditional failure rate

shape = 2.5

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

0 5 10 15 20 25 30 35

Cycles since last overhaul

Fa

ilu

re r

ate

(fa

ilu

res

/ su

rviv

ors

)

Older

Newer

Usually, the

real reason

to replace

old devices

is due to

economics,

not for

reliability

An older device of this type

can be maintained to have

the same rate of failure

12

Minutes per

outage

Growth rate

of outages

Past outages

per mile

Cost per

mile

The key to optimal replacement is high failure rate

Future minutes

per year avoided

Dollars

spent

Future minutes

avoided per year

Future outages

avoided per year

Future outages

avoided per year

Past outages

per year

Bang per

buck

Past outages

per year

Miles of line

to be replaced

1

$90,000 1.25 4500

1 min.

$2.00

Miles of line

to be replaced

Dollars

spent

8 x x x =

Where:

• $90,000 per mile = 5280 feet/mile x $17 per foot to replace

• 8 outages/mile/year = 13 spans/mile x (3 outages per 400ft span in past 5 years)

• 25% growth rate = 3 outages in past 5 years becomes 3 outages in next 4 years

• 4500 minutes per outage = 50 customers per outage x 90 minutes per outage

The higher the failure rate... …the higher the bang per buck

13

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0 5 10 15 20 25 30 35 40 45 50

Age of cable (years)

Ca

ble

fa

ilu

res

pe

r m

ile

Typically, age-based failure rates are still low (~ 50% above average) So age-based programs must replace a lot of good stuff to get the bad

Although a

failure rate

difference

of 3x is

significant,s

ome

conditions

provide 10x,

e.g., 250’

cable

sections

that have

failed 3

times in the

last 5 years

fail at 6.0

per mile

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Refocus on satisfaction Understand what aspects of reliability truly affect customer satisfaction, so

that you can do the right thing and not just do things right

Re-design the system Look for ways to cost-effectively re-design the system to build in

redundancy and to mitigate effects through sectionalizing and auto-restore

Research root causes Find other conditions that are cost-effectively monitorable, and develop the

predictive relationships that would allow more targeted action

Design solutions Find the best ways, including new ways, to remedy the root causes and to

mitigate the effects, including faster restoration and informing customers

Prioritize the work Compute the ‘bang per buck’ for each type of remediation, replacement,

redesign, etc., then optimize and prioritize accordingly

Monitor the results Monitor the effectiveness of the programs to see what is really working

and to discover any new insights that come only ‘after the smoke clears’

Here is a road map up to the ‘next level’

There is a better way than aged-based replacement

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Taking reliability programs to the ‘next level’

Questions and answers

DANIEL E. O’NEILL

Director, T&D Reliability

& Operations Practice

Main: (781) 270-0101

Home Office: (404) 816-5647

Mobile: (404) 307-3661

Fax: (404) 841-9460

DONeill@navigantconsulting.com

200 Wheeler Road, Suite 400

Burlington, MA 01803

1043 Lenox Crest NE

Atlanta, GA 30324