icc fall 2010 icc education session (1)

8/10/2019 ICC Fall 2010 ICC Education Session (1)

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Fall 2010 ICC Education Session

ICC Education Session

Cable Accessory Failure Analysis

F. Dean Williams

Fall 2010 Meeting


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Outline

Background

Overall Process for an Effective Forensic Program Primary Modes of Failure

Benefits of a Forensic Program

Summary


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Background Significance of Problem

OldMiddle AgedNew

80

70

60

50

40

30

20

10

0OldMiddle AgedNew

Accessories

Age Description

PercentageofServiceInteruptions(%

)CableCable accessories have a significant

Infant mortality rateNewly installed accessories account

for 20% of accessory related service

interruptions

Workmanship is the Number 1 cause

of failure representing nearly 50% ofthe total failures

The number of unknown cause of

failure is high (about 20%) showing the

need for more thorough forensic

evaluations

Manufacturing defects represent 15%

of the total failures


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Analysis of Collated Data Cable Accessories -Cause of Failure

Faul t Type

0

510

15

20

25

30

35

40

Poor

workm

anship

Manuf

actu

ringproblem

Corro

sion

Mecha

nical

Dam

ageEv

ent

Aging

Overloa

d

Unkn

own

Moist

ure

Othe

r

Dielectric

breakd

own

Contamina

tion

Overhe

at

Incorre

ctrecord

Mainten

ance

failu

re

%o

fTotalCases


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Analysis of Collated Data Failures by AccessoryVintage

Accessory Vintages - All Utilities

0

5

10

15

20

25

30

35

40

1970-1975

1975-19

80

1980-19

85

1985-19

90

1990-19

95

1995-20

00

2000-20

05

>2005

Vintage

%o

fTota

lFailures

Joints Terminations Junctions


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Analysis of Collated Data Cause of Failure

SummarybyFailureTypeAllUtilities

Overheat

4%

Dielectric

breakdown

10%

Aging

6%

Corrosion

4%

Moisture

4%

Event

3%

Manufacturing

problem

14%

Overload

2%

Maintenancefailure

2% Mechanical Damage

1%Contamination

1%

Poor

workmanship

49%


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Overall Process for an EffectiveForensic Program

Preservation of sample integrity

Importance of sister components

Collection of background information

Obtain installation instructions

Choose the right evaluation technique/document all findings Identify all installation errors/determine most probable root cause of

failure

Clearly and accurately report all findings/forward to the appropriate

personnel Track results of examinations


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Preservation of Sample Integrity

Remove sufficient cable length on either side of failedcomponent

Label sample to clearly identify location of failure

Seal cable ends and wrap component to protect from

environment

Keep associated components together

Store in a dry location prior to performing analysis


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Preservation of Sample Integrity

If you do not know what you are doing Do Not attempt

your own analysis


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Importance of Sister Components

Sister components are those installed at

the same time of the failed component,

likely by the same installer

Significant damage to failed component

may prevent determining most probable

root cause of failure

Sister components allow for easy

detection of installation/workmanship

errors if installed by the same personnel


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Sister Units

JacketCutback

Constant Force Spring

Ground Strap

Copper Tape

Shield

Jacket

Cutback


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Sister Units

Cut in Cable Insulation at

Jacket Cutback


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Sister Units

Cut in Tape Shield

at Jacket Cutback

Copper Tape

Shield intact


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Collection of Background Information

Events leading up to failure (weather, switching events,previous failures, etc.)

Circuit diagram

Number of re-closures on circuit after initial failure

Available fault current Typical loading conditions

Type of load being served

Any additional information that may be helpful indetermining the root cause of failure


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Obtain Installation Instructions

Obtain installation instructions for vintage of

component to be evaluated

A proper analysis of most failed components is the

exact reverse of the installation instructions

Check for function, not for detailed compliance

A perfectly installed accessory may fail by means

outside the installers control


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Outside the Installers Control

Termite

Damage

UV Aging


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Outside the Installers Control

12 Inches

Over inch

Total InsulationShrinkback


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Think before you cut

Document all findings/observations

through photographs

Preserve failure site, Do Not make

cuts directly through failure site

Cuts should be made at locations 90

degrees on either side of failure site

Cuts through failure site should only

be made, if necessary, and once a

detailed examination of the variousmating interfaces has been made

Choose the Right EvaluationTechnique

Failure Site

Cut through Failure

Site


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X-Ray


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Identify all Installation Errors/Determine

Most Probable Root Cause of Failure

Identification of all installation errors should be documented to

enhance training efforts

Multiple errors may have contributed to the failure

Determine most probable cause by process of elimination through a

detailed analysis of the available evidence

When you have eliminated the impossible, whatever remains, however

improbable, must be the truth

Sherlock Holmes In the Sign of the Four


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Clearly and Accurately Report allFindings

Report should indentify most

probable cause of failure and allinstallation errors observed

Share report with all parties to reduceor prevent future occurrences

Discuss product defects with

manufacturer to improve processes Discuss installation errors with

training personnel or installers toeliminate installation errors

If installation errors are the result of

unclear installation instructions reviseinstructions

As-Buil t of termination used in report


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Track Examination Results

Results of examinations should be tracked in a database

A database will help responsible personnel to observe and

take appropriate action when trends in installation errors

or manufacturing defects are evident


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Common Failure Modes

Workmanship

Manufacturing Defects

Design Issues


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Workmanship

Cut in CableInsulation


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Workmanship

Nicks in Conductor

StrandsCuts in Conductor

Strands


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Workmanship

Lower Cold Shrink Tube Incorrectly

Installed at Upper End of Termination

Black StressControl Tube

Electrical Activity off

Insulation Shield Cutback


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Workmanship

Incomplete Shrink Down of Dual

Layer Tube Leading to Failure

Puncture


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Workmanship

Discharge between Inner

Stress Control Tube and

Cable Insulation Caused by

Incomplete Shrink Down


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Workmanship

Discharge between Inner Stress ControlTube and Dual Layer Tube Caused by

Incomplete Shrink Down and Failure to

Keep Stress Control Tube Hot


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Workmanship

Corrosion

Deposits

Lack of Bond between

Mastic and Jacket

Water

Migrated

Past End

Seal

No Mastic between

Solder Blocks


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Workmanship

Discharge between

Stress Control

Tube and Insulation

Shield

Puncture at KnifeCut in Cable

Insulation


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Workmanship

Interface Tracking

from Surface

Contamination


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Workmanship

Water

Dirt Depositsand Lack of

Bond


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Workmanship

Contamination between InsulatingTube and Stress Control Tube


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Workmanship

Stress Relief Mastic Across

Entire Cable Interface


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WorkmanshipBrown Discoloration

of TRXLPE caused

by Overheating

CompressionConnector

No Wire Brush Marks on Conductor

in Area of Crimp Down


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WorkmanshipDeformation of

Insulation

Transition of Insulation Color

Away from Connector

Thermal

Damage to

Joint Body


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Workmanship

Brown Discoloration of

TRXLPE caused by

Overheating Compression

Connector

Thermal

Damage

Tool Cuts in

Conductor

Strands


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WorkmanshipAluminum

Oxides

Area of Crimpdown

in Connector Body

Arc Pit in

ConnectorBody


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Workmanship

Bent

Probe

Melting of Arc

Quenching

Probe


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Workmanship

Surface

Tracking

Surface

Contamination


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Workmanship

Corrosion

Deposits

Ground

Strap

Soldier Block Located over Dual

Layer Tube


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Workmanship

Cut in Cable

Insulation

Dielectric

Puncture

Start of Penciling on Cable Insulation

Thin Area of Insulation Wall In Line

With Failure


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Workmanship

Note that Cut Al igns with

Centerline of Puncture

Electrical

Treeing

Fault

Channel


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WorkmanshipFailure

Site

Open Neutrals Arcing

to Bracket

Bracket Cutting into

Cable


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Workmanship

Compression Lug

Vaporized


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Workmanship/Manufacturing

Knife Cuts Created During

removal of Joint Body

Sanding

Marks

Folds/Wrinkles in

Copper Tape

White

Bedding Tape


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Manufacturing Defect

Puncture Site

Area of

Discoloration

Puncture Site


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Manufacturing Defect

Insulation

Conductor

Shield

Puncture in

Conductor

Shield

Void in

Insulation


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Manufacturing DefectFault

Channel in

Joint

Insulation

Metal

Contaminant


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Design Issues

Surface Trackingon Cable

Insulation

Erosion of Stress

Control Tube


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Design Issues

Corrosion on

Conductor

Path of MoistureMoisture Entry

Point


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Design Issue

Dielectric

Puncture

Cable

Training


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Design IssueComplete Break in

Sheath

Stress Cracking

Failure Site


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Design Issue - UV AgingSurface Tracking and

Erosion

Stress

Cracking


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Benefits of a Failure Analysis Program

Improve Training

Reduce outages

Increase in revenue

Reduce need for expensive diagnostic testing


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Summary Surveys and data analysis show

cable accessory failures make up a

large percentage of in-serviceoutages

About 20% of accessory failures

have no known cause, indicating a

need for more detailed forensic

analysis About 15% of accessory failures

can be attributed to manufacturing

defects, indicating a need for

tighter control of manufacturing

processes Surveys and data analysis show

the need for improved training of

cable accessory installers

Unknown1.1%Terminations

5.6%

Splices37.1%

Cable56.2%

Utility Survey Showing System Failure Causes


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Summary

All evidence points to

improved TRAININGas the single most

cost effective

means of improvingsystem reliability

icc fall 2010 icc education session (1)

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