Cable Accessory Failure Analysis F. Dean Williams Fall 2010 Meeting - - PowerPoint PPT Presentation

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Cable Accessory Failure Analysis F. Dean Williams Fall 2010 Meeting - - PowerPoint PPT Presentation

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ICC Education Session Cable Accessory Failure Analysis F. Dean Williams Fall 2010 Meeting 1 Fall 2010 ICC Education Session Outline Background Overall Process for an Effective Forensic Program Primary Modes of Failure

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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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Fall 2010 ICC Education Session

Outline

  • Background
  • Overall Process for an Effective Forensic Program
  • Primary Modes of Failure
  • Benefits of a Forensic Program
  • Summary
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Fall 2010 ICC Education Session

Background – Significance of Problem

Old Middle Aged New 80 70 60 50 40 30 20 10 Old Middle Aged New Accessories Age Description Percentage of Service Interuptions (% ) Cable

  • Cable accessories have a significant

Infant mortality rate

  • Newly installed accessories account

for 20% of accessory related service interruptions

  • Workmanship is the Number 1 cause
  • f failure representing nearly 50% of

the 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%
  • f the total failures
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Fall 2010 ICC Education Session

Analysis of Collated Data – Cable Accessories - Cause of Failure

Fault Type

5 10 15 20 25 30 35 40 P

  • r

w

  • r

k m a n s h i p M a n u f a c t u r i n g p r

  • b

l e m C

  • r

r

  • s

i

  • n

M e c h a n i c a l D a m a g e E v e n t A g i n g O v e r l

  • a

d U n k n

  • w

n M

  • i

s t u r e O t h e r D i e l e c t r i c b r e a k d

  • w

n C

  • n

t a m i n a t i

  • n

O v e r h e a t I n c

  • r

r e c t r e c

  • r

d M a i n t e n a n c e f a i l u r e % of Total Cases

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Fall 2010 ICC Education Session

Analysis of Collated Data – Failures by Accessory Vintage

Accessory Vintages - All Utilities

5 10 15 20 25 30 35 40 1 9 7

  • 1

9 7 5 1 9 7 5

  • 1

9 8 1 9 8

  • 1

9 8 5 1 9 8 5

  • 1

9 9 1 9 9

  • 1

9 9 5 1 9 9 5

  • 2

2

  • 2

5 > 2 5

Vintage % of Total Failures

Joints Terminations Junctions

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Fall 2010 ICC Education Session

Analysis of Collated Data – Cause of Failure

Summary by Failure Type ‐ All Utilities

Overheat 4%

Dielectric breakdown 10%

Aging 6% Corrosion 4% Moisture 4% Event 3%

Manufacturing problem 14%

Overload 2% Maintenance failure 2% Mechanical Damage 1% Contamination 1%

Poor workmanship 49%

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Overall Process for an Effective Forensic 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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Fall 2010 ICC Education Session

Preservation of Sample Integrity

  • Remove sufficient cable length on either side of failed

component

  • 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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Fall 2010 ICC Education Session

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

Jacket Cutback Constant Force Spring Ground Strap Copper Tape Shield Jacket Cutback

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Fall 2010 ICC Education Session

Sister Units

Cut in Cable Insulation at Jacket Cutback

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Fall 2010 ICC Education Session

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 in

determining the root cause of failure

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Fall 2010 ICC Education Session

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
  • utside 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 ¾ inch Total Insulation Shrinkback

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Fall 2010 ICC Education Session

  • 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 various mating interfaces has been made

Choose the Right Evaluation Technique

Failure Site Cut through Failure Site

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X-Ray

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Fall 2010 ICC Education Session

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 all Findings

  • Report should indentify most

probable cause of failure and all installation errors observed

  • Share report with all parties to reduce
  • r prevent future occurrences
  • Discuss product defects with

manufacturer to improve processes

  • Discuss installation errors with

training personnel or installers to eliminate installation errors

  • If installation errors are the result of

unclear installation instructions revise instructions

As-Built of termination used in report

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Fall 2010 ICC Education Session

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

  • r manufacturing defects are evident
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Common Failure Modes

  • Workmanship
  • Manufacturing Defects
  • Design Issues
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Workmanship

Cut in Cable Insulation

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Workmanship

Nicks in Conductor Strands

Cuts in Conductor Strands

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Workmanship

Lower Cold Shrink Tube Incorrectly Installed at Upper End of Termination Black Stress Control 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 Control Tube 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 Knife Cut in Cable Insulation

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Workmanship

Interface Tracking from Surface Contamination

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Workmanship

Water Dirt Deposits and Lack of Bond

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Workmanship

Contamination between Insulating Tube and Stress Control Tube

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Fall 2010 ICC Education Session

Workmanship

Stress Relief Mastic Across Entire Cable Interface

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Fall 2010 ICC Education Session

Workmanship

Brown Discoloration

  • f TRXLPE caused

by Overheating Compression Connector No Wire Brush Marks on Conductor in Area of Crimp Down

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Fall 2010 ICC Education Session

Workmanship

Deformation of Insulation Transition of Insulation Color Away from Connector Thermal Damage to Joint Body

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Fall 2010 ICC Education Session

Workmanship

No Wire Brush Marks on Conductor Wire Brush Marks on Conductor

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Fall 2010 ICC Education Session

Workmanship

Brown Discoloration of TRXLPE caused by Overheating Compression Connector Thermal Damage Tool Cuts in Conductor Strands

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Fall 2010 ICC Education Session

Workmanship

Aluminum Oxides Area of Crimpdown in Connector Body Arc Pit in Connector Body

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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 Aligns with Centerline of Puncture Electrical Treeing Fault Channel

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Workmanship

Failure 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 Defect

Fault Channel in Joint Insulation Metal Contaminant

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Design Issues

Surface Tracking

  • n Cable

Insulation Erosion of Stress Control Tube

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Design Issues

Corrosion on Conductor Path of Moisture Moisture Entry Point

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Design Issue

Dielectric Puncture Cable Training

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Design Issue

Complete Break in Sheath Stress Cracking Failure Site

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Design Issue - UV Aging

Surface 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-service

  • utages
  • 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

Unknown 1.1% Terminations 5.6% Splices 37.1% Cable 56.2%

Utility Survey Showing System Failure Causes

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Summary All evidence points to improved TRAINING as the single most cost effective means of improving system reliability