IEEE T&D – Insulators 101 Insulators 101 Section A – Introduction Presented by Andy Schwalm IEEE...

IEEE T&D – Insulators 101

““Insulators 101”Insulators 101”Section A – IntroductionSection A – Introduction

Presented by Andy SchwalmPresented by Andy SchwalmIEEE Chairman, Lightning and Insulator IEEE Chairman, Lightning and Insulator

SubcommitteeSubcommittee

IEEE/PES 2010 Transmission and Distribution IEEE/PES 2010 Transmission and Distribution Conference and Exposition Conference and Exposition

New Orleans, Louisiana New Orleans, Louisiana April 20, 2010April 20, 2010


What Is an Insulator?What Is an Insulator?

An insulator is a “dam***” poor conductor!

And more, technically speaking!

An insulator is a mechanical support!Primary function - support the “line” mechanicallySecondary function– electrical

Air is the insulatorOuter shells/surfaces are designed to increase leakage distance and strike distance


What Does an Insulator Do?What Does an Insulator Do?

Maintains an Air GapSeparates Line from Ground

length of air gap depends primarily on system voltage, modified by desired safety margin, contamination, etc.

Resists Mechanical Stresses“everyday” loads, extreme loads

Resists Electrical Stressessystem voltage/fields, overvoltages

Resists Environmental Stressesheat, cold, UV, contamination, etc.


Where Did Insulators Come Where Did Insulators Come From?From?

Basically grew out of the needs of the telegraph industry – starting in the late 1700s, early 1800s

Early history centers around what today we would consider very low DC voltages

Gradually technical needs increased as AC voltages grew with the development of the electric power industry


HistoryHistory

Glass plates used to insulate telegraph line DC to Baltimore

Glass insulators became the ”norm” soon thereafter – typical collector’s items today

Many, many trials with different materials – wood – cement – porcelain - beeswax soaked rag wrapped around the wire, etc.

Ultimately porcelain and glass prevailed


HistoryHistory

Wet process porcelain developed for high voltage applications

Porcelain insulator industry started

Application voltages increased Insulator designs became larger, more complexCeramics (porcelain, glass) still only choices at high

voltages


HistoryHistory

US trials of first “NCIs” – cycloaliphatic based Not successful, but others soon became interested

and a new industry started up

Europeans develop “modern” style NCI – fiberglass rod with various polymeric sheds

Now considered “First generation”


HistoryHistory

NCI insulator industry really begins in US with field trials of insulators

Since that time - new manufacturers, new designs, new materials

NCIs at “generation X” – there have been so many improvements in materials, end fitting designs, etc.

Change in materials have meant changes in line design practices, maintenance practices, etc.

Ceramic manufacturers have not been idle either with development of higher strength porcelains, RG glazes, etc.


HistoryHistory

Domestic manufacturing of insulators decreases, shift to offshore (all types)

Engineers need to develop knowledge and skills necessary to evaluate and compare suppliers and products from many different countries

An understanding of the basics of insulator manufacturing, design and application is more essential than ever before


Insulator TypesInsulator Types

For simplicity will discuss in terms of three broad applications:

Distribution lines (thru 69 kV)

Transmission lines (69 kV and up)

Substations (all voltages)



Distribution lines

Pin type insulators -mainly porcelain, growing use of polymeric (HDPE – high density polyethylene), limited use of glass (in US at least)

Line post insulators – porcelain, polymericDead end insulators – polymeric, porcelain, glassSpool insulators – porcelain, polymericStrain insulators, polymeric, porcelain


Types of Insulators – DistributionTypes of Insulators – Distribution



Transmission lines

Suspension insulators - new installations mainly NCIs, porcelain and glass now used less frequently

Line post insulators – mainly NCIs for new lines and installations, porcelain much less frequent now


Types of Insulators – TransmissionTypes of Insulators – Transmission



Substations

Post insulators – porcelain primarily, NCIs growing in use at lower voltages (~161 kV and below)

Suspension insulators –NCIs (primarily), ceramic

Cap and Pin insulators – “legacy” type


Types of Insulators – SubstationTypes of Insulators – Substation


Insulator Types - ComparisonsInsulator Types - Comparisons

Ceramic• Porcelain or toughened glass • Metal components fixed with

cement• ANSI Standards C29.1

through C29.10

Non Ceramic• Typically fiberglass rod with

rubber (EPDM or Silicone) sheath and weather sheds

• HDPE line insulator applications

• Cycloaliphatic (epoxies) station applications, some line applications

• Metal components normally crimped

• ANSI Standards C29.11 – C29.19



Ceramic• Materials very resistant to

UV, contaminant degradation, electric field degradation

• Materials strong in compression, weaker in tension

• High modulus of elasticity - stiff

• Brittle, require more careful handling

• Heavier than NCIs

Non Ceramic• Hydrophobic materials

improve contamination performance

• Strong in tension, weaker in compression

• Deflection under load can be an issue

• Lighter – easier to handle• Electric field stresses must

be considered



Ceramic• Generally designs are

“mature”• Limited flexibility of

dimensions• Process limitations on sizes

and shapes• Applications/handling

methods generally well understood

Non Ceramic• “Material properties have

been improved – UV resistance much improved for example

• Standardized product lines now exist

• Balancing act - leakage distance/field stress – take advantage of hydrophobicity

• Application parameters still being developed

• Line design implications (lighter weight, improved shock resistance)


““Insulators 101”Insulators 101”Section B - Design CriteriaSection B - Design Criteria

Presented by Al BernstorfPresented by Al BernstorfIEEE Chairman, Insulator Working IEEE Chairman, Insulator Working

GroupGroup

IEEE/PES 2010 Transmission and Distribution IEEE/PES 2010 Transmission and Distribution Conference and Exposition Conference and Exposition

New Orleans, Louisiana New Orleans, Louisiana April 20, 2010April 20, 2010


Design Criteria - MechanicalDesign Criteria - Mechanical

An insulator is a mechanical support!

• Its primary function is to support the line mechanically

• Electrical Characteristics are an afterthought.

• Will the insulator support your line?

• Determine The Maximum Load the Insulator Will Ever See Including NESC Overload Factors.



Suspension Insulators

• Porcelain- M&E (Mechanical & Electrical) Rating

Represents a mechanical test of the unit while energized.When the porcelain begins to crack, it electrically punctures.Average ultimate strength will exceed the M&E Rating when new.

- Never Exceed 50% of the M&E Rating

• NCIs (Polymer Insulators)- S.M.L. – Specified Mechanical Load

Guaranteed minimum ultimate strength when new.R.T.L. – Routine Test Load – Proof test applied to each NCI.

- Never Load beyond the R.T.L.



Line Post insulators

• Porcelain- Cantilever Rating

Represents the Average Ultimate Strength in Cantilever – when new.Minimum Ultimate Cantilever of a single unit may be as low as 85%.

- Never Exceed 40% of the Cantilever Rating – Proof Test Load

• NCIs (Polymer Insulators)- S.C.L. (Specified Cantilever Load)

Not based upon lot testingBased upon manufacturer testing

- R.C.L. (Rated Cantilever Load) or MDC or MDCL (Maximum Design Cantilever Load) or MCWL or WCL (Working Cantilever Load)

- Never Exceed RCL or MDC or MDCL or MCWL or WCL- S.T.L. (Specified Tensile Load) - Tensile Proof Test=(STL/2)



Other Considerations

• Suspensions and Deadends – Only apply tension loads

• Line Posts – - Cantilever is only one load

- Transverse (tension or compression) on line post – loading transverse to the direction of the line.

- Longitudinal – in the direction of travel of the line

- Combined Loading Curve – Contour curves representing various Longitudinal loadsAvailable Vertical load as a function of Transverse loadingManufacturers have different safety factors!!!



69 kV Post - 2.5" Rod

0

500

1000

1500

2000

2500

-3000 -2000 -1000 0 1000 2000 3000

TRANSVERSE LOAD, LBF

VERT

ICAL

LOAD

, LBF

0 Longitudinal

500 Longitudinal

1000 Longitudinal

1500 Longitudinal

2000 Longitudinal

LINE POST APPLICATION CURVES9-12-05

Compression Tension


Design Criteria - ElectricalDesign Criteria - Electrical

An Insulator is a mechanical support!Air imparts Electrical CharacteristicsStrike Distance (Dry Arcing Distance) is the

principal constituent to electrical values. • Dry 60 Hz F/O and Impulse F/O – based on strike distance.• Wet 60 Hz F/O

- Some would argue leakage distance as a principal factor.- At the extremes that argument fails – although it does play a role.- Leakage distance helps to maintain the surface resistance of the strike distance.

Leakage Requirements do play a role!!!



Dry Arcing Distance – (Strike Distance) – “The shortest distance through the surrounding medium between terminal electrodes….” 1

1 – IEEE Std 100 - 1992



Define peak l-g kV

Determine Leakage Distance Required

Switching Over-voltage Requirements

Impulse Over-voltage

Chart Courtesy of Ohio Brass/HPS – EU1429-H

69 kV (rms)

41.8 kV (rms)(line A/1.732)*1.05

59.1 kV (peak)e=(line B * 1.414)

1

H. INSULATOR LEAKAGE (MIN.)41.8 inches

I. SSV = (line B) * 3.0 125 kV (peak)

J. PEAK IMPULSE WITHSTAND = (I(t) * R(f))+eI(t) = 20 kA (typical value = 50 kA)R(f) = 15 ohm (typical value = 10 - 20 ohm)e = 59.1 (line C)

K. IMPULSE WITHSTAND = 359 kV

(typical values) (inches/(kV line-to-ground))

SWITCHING OVERVOLTAGE REQUIREMENTS

IMPULSE OVERVOLTAGE REQUIREMENTS

1.00 - 1.251.50 - 1.752.00 - 2.50G. HEAVY

UP TO 1.00

A. NOMINAL SYSTEM LINE-TO-LINE VOLTAGE

B. MAXIMUM SYSTEM LINE-TO-GROUND VOLTAGE

C. MAXIMUM PEAK LINE-TO-GROUND VOLTAGE (e)

LEAKAGE DISTANCE REQUIREMENTS

SELECT INSULATOR BASED ON REQUIREMENTS:

(line B)*(inches/kV) =

Enter inches/kV -

PICKING A SUITABLE INSULATOR

ELECTRICAL PARAMETERS

SUGGESTED LEAKAGECONTAMINATION LEVEL

D. ZEROE. LIGHTF. MODERATE

POLYMER VALUESNUMBER OF

PORCELAIN BELLS

K. IMPULSE WITHSTAND T. SELECT

INSULATOR

41.8

125

359

SYSTEM REQUIREMENT

VALUE FROM PAGE 1

H. LEAKAGE DISTANCE

I. SWITCHING SURGE VOLTAGE


Design Criteria – Leakage DistanceDesign Criteria – Leakage Distance

What is Leakage Distance?

“The sum of the shortest distances measured along the insulating surfaces between the conductive parts, as arranged for dry flashover test.” 1

1 – IEEE Std 100 - 1992



What’s an appropriate Leakage Distance?

• Empirical Determination- What’s been used successfully?

- If Flashovers occur – add more leak?

• ESDD (Equivalent Salt Deposit Density) Determination- Measure ESDD

Pollution MonitorsDummy InsulatorsRemove in-service insulators

- Evaluate ESDD and select appropriate Leakage Distance



“Application Guide for Insulators in a Contaminated Environment” by K. C. Holte et al – F77 639-8

ESDD (mg/cm2) Site Severity

Leakage Distance

I-string/V-string

(“/kV l-g)

0 – 0.03 Very Light 0.94/0.8

0.03 – 0.06 Light 1.18/0.97

0.06 – 0.1 Moderate 1.34/1.05

>0.1 Heavy 1.59/1.19



IEC 60815 Standards

ESDD (mg/cm2) Site SeverityLeakage Distance

(“/kV l-g)

<0.01 Very Light 0.87

0.01 – 0.04 Light 1.09

0.04 – 0.15 Medium 1.37

0.15 – 0.40 Heavy 1.70

>0.40 Very Heavy 2.11



Leakage Distance Recommendations

0

0.5

1

1.5

2

2.5

0 0.1 0.2 0.3 0.4 0.5

ESDD (mg/cm^2)

Lea

k ("

/kV

l-g

)

IEEE V

IEEE I

IEC

Poly. (IEC)

Poly. (IEEE V)

Poly. (IEEE I)


Improved Contamination PerformanceImproved Contamination Performance

Flashover Vs ESDD

0

50

100

150

200

250

300

0.01 0.1

ESDD (mg/cm^2)

Fla

sh

ov

er

Vo

lta

ge

Porcelain

New EPDM

Aged EPDM

New SR

Aged SR

CEA 280 T 621SR units - leakage equal to porcelainEPDM Units - leakage 1.3 X Porcelain



Polymer insulators offer better contamination flashover performance than porcelain?

Smaller core and weathershed diameter increase

leakage current density.

Higher leakage current density means more Ohmic Heating.

Ohmic Heating helps to dry the contaminant layer and reduce leakage currents.

In addition, hydrophobicity helps to minimize filming



“the contamination performance of composite insulators exceeds that of their porcelain counterparts”

“the contamination flashover performance of silicone insulators exceeds that of EPDM units”

“the V50 of polymer insulators increases in proportion to the leakage distance”

CEA 280 T 621, “Leakage Distance Requirements for Composite Insulators Designed for Transmission Lines”


Insulator SelectionInsulator SelectionWhere do I get these values?

Leakage Distance or Creepage Distance• Manufacturer’s Catalog

Switching Surge• Wet W/S• ((Wet Switching Surge W/S)/√2) ≥ 60 Hz Wet Flashover (r.m.s.)• Peak Wet 60 Hz value will be lower than Switching Surge Wet W/S

Impulse Withstand• Take Positive or Negative Polarity, whichever is lower• If only Critical Impulse Flashover is available – assume 90%

(safe estimate for withstand)


Insulator SelectionInsulator Selection

Select the 69 kV Insulator shown at right.

I-string – Mechanical• Worst Case – 6,000 lbs• Suspension: ≥ 12k min

ultimate

Leakage Distance ≥ 42”

Switching Surge ≥ 125 kV

Impulse Withstand ≥359 kV

69 kV (rms)

41.8 kV (rms)(line A/1.732)*1.05

59.1 kV (peak)e=(line B * 1.414)

1

H. INSULATOR LEAKAGE (MIN.)41.8 inches

I. SSV = (line B) * 3.0 125 kV (peak)

J. PEAK IMPULSE WITHSTAND = (I(t) * R(f))+eI(t) = 20 kA (typical value = 50 kA)R(f) = 15 ohm (typical value = 10 - 20 ohm)e = 59.1 (line C)

K. IMPULSE WITHSTAND = 359 kV

(typical values) (inches/(kV line-to-ground))

SWITCHING OVERVOLTAGE REQUIREMENTS

IMPULSE OVERVOLTAGE REQUIREMENTS

1.00 - 1.251.50 - 1.752.00 - 2.50G. HEAVY

UP TO 1.00

A. NOMINAL SYSTEM LINE-TO-LINE VOLTAGE

B. MAXIMUM SYSTEM LINE-TO-GROUND VOLTAGE

C. MAXIMUM PEAK LINE-TO-GROUND VOLTAGE (e)

LEAKAGE DISTANCE REQUIREMENTS

SELECT INSULATOR BASED ON REQUIREMENTS:

(line B)*(inches/kV) =

Enter inches/kV -

PICKING A SUITABLE INSULATOR

ELECTRICAL PARAMETERS

SUGGESTED LEAKAGECONTAMINATION LEVEL

D. ZEROE. LIGHTF. MODERATE

POLYMER VALUESNUMBER OF

PORCELAIN BELLS

K. IMPULSE WITHSTAND T. SELECT

INSULATOR

41.8

125

359

SYSTEM REQUIREMENT

VALUE FROM PAGE 1

H. LEAKAGE DISTANCE

I. SWITCHING SURGE VOLTAGE


Insulator SelectionInsulator Selection

Porcelain – 5-3/4 X 10” bells X 4 units

Characteristic Required Available

Leakage Distance

42” 46”

Wet Switching

Surge W/S125 kV 240 kV

Impulse W/S 359 kV 374 kV

M & E 12,000 lbs 15,000 lbs


Grading RingsGrading Rings

Simulate a larger, more spherical object

Reduce the gradients associated with the shielded object

Reduction in gradients helps to minimize RIV & TVIPorcelain or Glass –

• Inorganic – breaks down very slowly

NCIs• Polymers are more susceptible to scissioning due to corona• UV – short wavelength range – attacks polymer bonds. • Most short wavelength UV is filtered by the environment• UV due to corona is not filtered


NCIs and RingsNCIs and Rings

Grading (Corona) Rings

• Due to “corona cutting” and water droplet corona – NCIs may require the application of rings to grade the field on the polymer material of the weathershed housing.

• Rings must be:- Properly positioned relative to the end fitting on which they are mounted.

- Oriented to provide grading to the polymer material.

• Consult the manufacturer for appropriate instructions.

• As a general rule – rings should be over the polymer – brackets should be on the hardware.


Questions? Questions?

IEEE T&D – Insulators 101IEEE T&D – Insulators 101

Insulators 101Insulators 101Section C - StandardsSection C - Standards

Presented by Tony Baker

IEEE Task Force Chairman, Insulator Loading

IEEE/PES 2010 Transmission and Distribution

Conference and Exposition

New Orleans, Louisiana

April 20, 2010


American National StandardsAmerican National StandardsConsensus standards

Standards writing bodies must include representatives from materially affected and interested parties.

Public review

Anybody may comment. Comments must be evaluated, responded to, and if found to be

appropriate, included in the standard .

Right to appeal By anyone believing due process lacking.

Objective is to ensure that ANS Standards are developed in an environment that is equitable, accessible, and responsive to the requirements of various stakeholders*.

* The American National Standards Process, ANSI March 24, 2005


American Standards Committee

on Insulators for Electric Power Lines

ASC C-29

EL&P Group

IEEE

NEMA

Independents


C29 ANSI C29 Insulator Standards (available on-line at nema.org)

.1 Insulator Test Methods

.2 Wet-process Porcelain & Toughened Glass - Suspensions

.3 Wet-process Porcelain Insulators - Spool Type

.4 “ - Strain Type

.5 “ - Low & Medium Voltage Pin Type

.6 “ - High Voltage Pin Type

.7 “ - High Voltage Line Post Type

.8 “ - Apparatus, Cap & Pin Type

.9 “ - Apparatus, Post Type

.10 “ - Indoor Apparatus Type

.11 Composite Insulators – Test Methods

.12 “ - Suspension Type

.13 “ - Distribution Deadend Type

.17 “ - Line Post Type

.18 “ - Distribution Line Post Type

.19 “ - Station Post Type (under development)


ANSI C29 Insulator StandardsANSI C29 Insulator Standards

Applies to new insulatorsDefinitionsMaterialsDimensions & Marking (interchangeability)Tests

1. Prototype & Design, usually performed once for a given design. (design, materials, manufacturing process, and technology).

2. Sample, performed on random samples from lot offered for acceptance.

3. Routine, performed on each insulator to eliminate defects from lot.


ANSI C 29 Insulator Standard ANSI C 29 Insulator Standard RatingsRatings

Electrical & Mechanical Ratings

How are they assigned?

How is conformance demonstrated?

What are application limits?


Electrical RatingsElectrical RatingsAverage flashover values

Low-frequency Dry & WetCritical impulse, positive & negative

Impulse withstand Radio-influence voltage

Applies to all the types of high voltage insulators Rated values are single-phase line-to-ground voltages.Dry FOV values are function of dry arc distance and test configuration.Wet FOV values function of dry arc distance and insulator shape,

leakage distance, material and test configuration. Tests are conducted in accordance with IEEE STD 4-1995 except

test values are corrected to standard conditions in ANSI C29.1.

-Temperature 25° C - Barometric Pressure 29.92 ins. of Hg

- Vapor Pressure 0.6085 ins. of Hg

- For wet tests: rate 5±0.5 mm/min, resistivity 178±27Ωm, 10 sec. ws


Dry Arcing DistanceDry Arcing DistanceShortest distance through the surrounding medium between Shortest distance through the surrounding medium between terminal electrodes , or the sum of distances between terminal electrodes , or the sum of distances between intermediate electrodes , whichever is shortest, with the intermediate electrodes , whichever is shortest, with the insulator mounted for dry flashover test. insulator mounted for dry flashover test.


Electrical RatingsElectrical Ratings Product is designed to have a specified average flashover.

• This is the manufacturer’s rated value, R.

Samples are electrically tested in accordance with standard• This is the tested value, T.

Due to uncontrollable elements during the test such as atmospheric fluctuations, minor differences in test configuration, water spray fluctuations, etc. the test value can be less than the rated value.

Does T satisfy the requirements for the rating R?

• If T/R≥ 𝝃 Yes where 𝝃 = 0.95 for Low-frequency Dry flashover tests = 0.90 for Low-frequency Wet flashover

tests

= 0.92 for Impulse flashover tests


Electrical RatingsElectrical RatingsDry 60 Hz Flashover Data

0

200

400

600

800

1000

1200

1400

0 20 40 60 80 100 120 140 160

Dry Arcing Distance (inches)

Fla

sh

ov

er (

kV

)

Station Post and Line Post

Suspension Insulator


Electrical RatingsElectrical RatingsANSI C2 Insulation Level RequirementsANSI C2 Insulation Level Requirements

ANSI C2-2007, Table 273-1ANSI C2-2007, Table 273-1

Higher insulation levels required in areas where severe lightning, high atmospheric contamination, or other unfavorable conditions exist


Electrical Ratings - ApplicationElectrical Ratings - Application

Customer determines needs and specifies electrical requirements:

- 60 Hz Dry & wet flashover

- Impulse flashover and/or withstand

- Leakage distance

Does offered product meet customer’s specification S?

If R ≥ S and T ≥ 𝝃R yes, otherwise no.



Mechanical RatingsMechanical RatingsSample & Routine Mechanical Tests

are based on the primary in-service loading conditionsSTD. No. Insulator Type Sample test Routine test

C 29.2 Ceramic Suspension M&E Tension

C29.6 “ Pin Type Cantilever -----

C29.7 “ Line Post Cantilever 4 quad. cantilever

C29.8 “ Cap & Pin CantileverTorsionTension

Tension

C29.9 “ Station Post CantileverTension

Tension, Cantilever orBending Moment

C29.12 Composite Suspension SML Tension

C29.13 “ Deadend SML Tension

C29.17 “ Line Post CantileverTension

Tension

C29.18 “ Dist. Line Post Cantilever Tension


Mechanical RatingsMechanical Ratings

M&E Test

Ceramic Suspensions

Bending Tests

Composite Posts


Hubbell Power SystemsKinectrics


ANSI C29 High Voltage Insulator ANSI C29 High Voltage Insulator StandardsStandardsStd.

No.Insulator

TypeUlt. Strength

QC Test Lot Acceptance

Criteria Routine

Test

C29.2 CeramicSuspension

Combined M&E strength of 10 units

Ave. Std. dev. = S

X10 ≥ R +1.2 S

s10 ≤ 1.72 S

3 sec. tension at 50% of R

C29.7 Ceramic Line post

Cantilever strength of 3 units

X3≥ R

no one xi ≮ .85 R

4 quad. bending at 40% of R

C29.8 Ceramic Apparatus Cap & Pin

Cantilever, tension, & torsion strength of 3 units each

X3≥ R

no one xi ≮ .85 R

3 sec. tension at specified value

C29.9 Ceramic Apparatus

Post TypeCantilever & tension strengths

of 3 units each X3≥ R

no one xi ≮ .85 R

Tension at 50% of R

or4 quad. bending

at 40% of R

C29.12 Composite Suspension

Specified Mech. Load (SML) test of 3 units

xi ≥ .R 10 sec. tension at 50% of R

C29.13 Composite Distribution Deadend

SML test of 3 units xi ≥ .SML rating

10 sec. tension at 50% of R

C29.17 Composite Line Post

Cantilever strength of 1 unit Tension test of 1 unit

Strength ≥ R 10 sec. tension at 50% of R

C29.18 Composite Distribution Line Post

Cantilever strength of 1 unit Strength ≥ R 10 sec. tension at 50% of R


Lot Acceptance Criteria – ANSI C29.2Lot Acceptance Criteria – ANSI C29.2

Lot acceptance according to ANSI C 29.2.Select ten random units from lot and subject to M&E test.Requirements are:

M&E rating ≤ X10 -1.2SH &

s10 ≤1.72SH s10 is std. dev. of the 10 units

SH is historical std. dev.

If s10= SH then for minimally acceptable lot, ~ 11.5% of units in lot could have strengths below the rated value.



Lot Acceptance Criteria – ANSI C29.2Lot Acceptance Criteria – ANSI C29.2

Possible low strengths for ceramic Possible low strengths for ceramic suspension units in a lot minimally suspension units in a lot minimally acceptable according to ANSI C29.2acceptable according to ANSI C29.2

Coefficient

of variation, vR

Strength value at -3σ

5% 90% of M&E rating10% 79% of M&E rating15% 67% of M&E rating



Lot Acceptance Criteria – CSA C411.1 Lot Acceptance Criteria – CSA C411.1 Possible low strengths for ceramic Possible low strengths for ceramic suspension units in a lot minimally suspension units in a lot minimally

acceptable according to acceptable according to CSA C411.1CSA C411.1Requirements

Rating≤ XS – 3s&Xi ≥ R On a -3 sigma basis , minimum strength that could be expected in a lot is the rated value regardless of the coefficient of variation for the manufacturing process that produced the lot.



Lot Acceptance Criteria – ANSI C29Lot Acceptance Criteria – ANSI C29Possible low strengths for ceramic units Possible low strengths for ceramic units

in a lot minimally acceptable according to in a lot minimally acceptable according to ANSI C29.7, C29.8 & C29.9ANSI C29.7, C29.8 & C29.9

Cantilever rating ≤ XCantilever rating ≤ X33 & no x & no xii< 85% of rating< 85% of rating

Coefficient

of variation, vR

Strength value at -3 σ

5% 85% of Cantilever rating10% 70% of Cantilever rating15% 55% of Cantilever rating



Lot Acceptance CriteriaLot Acceptance Criteria ANSI C29 –Composite Insulators ANSI C29 –Composite Insulators

Random samples selected from an offered lot.

Ultimate strength tests on samples.

Requirement is:

xi ≥ Rating

The rated value is assigned by the manufacturer based on ultimate strength tests during design.

However for a lot minimally acceptable according to the standard, statistical inference for the strength distribution for entire lot not possible.

Composite Insulators have a well defined damage limit providing good application direction.



Mechanical Ratings – Application LimitsMechanical Ratings – Application LimitsNESC ANSI C Table 277-1 NESC ANSI C Table 277-1

Allowed percentages of strength ratingsAllowed percentages of strength ratings

Insulator Type % Strength Rating Ref. ANSI Std.

CeramicSuspension

50%Combined

mechanical & electrical strength (M&E)

C29.2-1992

Line Post 40%50%

Cantilever strengthTension/compression strength

C29.7-1996

Station Post4

40%50%

Cantilever strengthTension/compression/torsion strength C29.9-1983

Station Cap & Pin

40%50%

Cantilever strengthTension/compression/torsion strength C29.8-1985

Composite Suspension

50% Specified mechanical load (SML)C29.12-1997C29.13-2000

Line Post 50%Specified cantilever load (SCL) or

specified tension load (STL)C29.17-2002C29.18-2003

Station Post 50% All strength ratings ----------


Mechanical Ratings – Application LimitsMechanical Ratings – Application Limits

Worst loading case load ≤ (% Table 277-1)(Insulator Rating)

In most cases , % from Table 277-1 is equal to the routine proof -test load.

Bending tests on a production basis are not practicable in some cases, (large stacking posts, cap & pins , and polymer posts) and tension proof-load tests are specified.



Mechanical Ratings – Application LimitsMechanical Ratings – Application LimitsComposite Post Insulators – Combined LoadingComposite Post Insulators – Combined Loading



Recent Developments for Application LimitsRecent Developments for Application Limits

Component strength cumulative distribution function FComponent strength cumulative distribution function FRR

and probability density function of maximum loads fand probability density function of maximum loads fQQ..



Component Damage LimitComponent Damage Limit DAMAGE LIMIT

Strength of a component below ultimate corresponding to a defined limit of permanent damage or deformation.

For composites the damage limit is fairly well understood.



Component Damage LimitComponent Damage Limit Defining Damage Limit for ceramics more difficult to define as shown by comparing stress-strain curves for

brittle and ductile materials.

L&I WG on Insulators is addressing this problem now


““Insulators 101Insulators 101””

Section D – Achieving Section D – Achieving ‘Quality’‘Quality’

Presented by Tom GrishamPresented by Tom GrishamIEEE Task Force Chairman, “Insulators 101”IEEE Task Force Chairman, “Insulators 101”

IEEE/PES – T&D Conference and ExpositionIEEE/PES – T&D Conference and ExpositionNew Orleans, LANew Orleans, LAApril 20, 2010April 20, 2010


Objectives of ‘Quality” Objectives of ‘Quality” PresentationPresentation

Present ideas to verify the supplier qualification, purchasing requirements, manufacturer inspections of lots, shipment approval, material handling, and training information for personnel

Routine inspection of the installation

Identify steps to analyze field complaints

To stimulate “Quality” improvement


‘‘Quality’ DefinedQuality’ Defined

QUALITY – An inherent, basic or distinguishing characteristic; an essential property or nature.

QUALITY CONTROL – A system of ensuring the proper maintenance of written standards; especially by the random inspection of manufactured goods.


What Is Needed in a Quality What Is Needed in a Quality Plan?Plan?

Identifying critical design parametersQualifying ‘new’ suppliersEvaluating current suppliersEstablishing internal specificationsMonitoring standards compliance (audits)Understanding installation requirementsEstablishing end-of-life criteriaEnsuring safety of line workers Communicating and training All aspects defined by the company plan


What Documents Should Be What Documents Should Be Included?Included?

Catalog specifications and changesSupplier audit records and lot certificationQualification testing of the design

• Utility-specific testing• Additional supplier testing for insulators (vibration,

temperature, long-term performance, etc)• ANSI or equivalent design reports

Storage methods• Installation records (where, by whom, why?) • Interchangeability with other suppliers product

Handling methods (consult manufacturer)Installation requirements and techniques


‘‘Proven’ Installation ProceduresProven’ Installation Procedures


Handling of Ceramics – NEMA HV2-Handling of Ceramics – NEMA HV2-19841984

Insulators should not be dropped or thrown…..Insulators strings should not be bent…..Insulator strings are not ladders…..Insulators with chips or cracks should be discarded and

companion units should be carefully inspected…..Cotter keys should be individually inspected for twisting,

flattening or indentations. If found, replace keys and retest the insulator…..

The maximum combined load, including safety requirements of NESC, must not exceed the rating…..

Normal operating temperature range for ceramics is defined as –40 to 150 Degrees F…..


Handling of NCI’sHandling of NCI’s NEMA is working on a ‘new’ application guide for NCI

products. It will likely include……………………

• “Insulators should not be dropped, thrown, or bent…”• “Insulators should not be used as ladders…”• “Cotter keys for ball sockets should be inspected identically to the

instructions for ceramic insulators…”• “The maximum combined loads should not exceed the RTL…”• Normal operating temperature is –40 to 150 Degrees F…”• “Insulators should not be used as rope supports…”• “Units with damaged housings that expose the core rod should

be replaced and discarded…”• “Units with cut or torn weathersheds should be inspected by

the manufacturer…”• “Bending, twisting and cantilever loading should be avoided

during construction and maintenance…”


Line outage FailuresLine outage FailuresYour objective is to find the problem, quickly!


Inspection TechniquesInspection Techniques

Subjective: What you already know• Outage related• Visual methods from the ground• Previous problem• Thermal camera (NCI – live line)

Objective: Answer is not obvious• Leakage current measurements• Daycor camera for live line inspections (live)• Mechanical and electrical evaluations


Porcelain and Glass FailuresPorcelain and Glass FailuresFailures are ‘typically’ visible or have a new ‘history’ or upgrade on the site?

New products may not be your Grandfather’s Oldsmobile, however!

Have the insulators deteriorated? • Perform thermal-mechanical test before failing load and compare to ultimate failing load

• Determine current ultimate strength versus newShould the insulators be replaced?

• Establish internal criteria by location


Non-Ceramic (NCI) FailuresNon-Ceramic (NCI) FailuresCause of failures may NOT be visible!

• More ‘subjective’ methods used for live line replacement• Some external deterioration may NOT be harmful• Visual examples of critical issues are available to you

Imperative to involve the supplier!• Evaluate your expertise to define ‘root’ cause condition• Verify an ‘effective’ corrective action is in place• Utilize other sources in the utility industry

Establish ‘subjective’ baselines for new installations as future reference! Porcelain and glass, also!


What To Do for an Insulator What To Do for an Insulator Failure?Failure?

Inspection of Failure

• What happened?

• Extraordinary factors?

• Save every piece of the unit!

• Take lots of pictures!

• Inspect other insulators!

Supplier Involvement

• Verification of production date?

• Available production records?

• Determination of ‘root’ cause?

• Recommended action?

• Safety requirements?


Summary of ‘Quality’ Summary of ‘Quality’ PresentationPresentation

In today’s environment, this presentation suggests that the use of a well documented ‘quality’ program improves long term performance and reduces outages.

Application information that is communicated in the organization will help to minimize installation issues and reduce costs.

Actively and accurately defining the condition, or determining the root cause of a failure, will assist in determining end-of-life decisions.


Source of PresentationSource of Presentation

http://ewh.ieee.org/soc/pes/iwg/

IEEE T&D – Insulators 101 Insulators 101 Section A – Introduction Presented by Andy Schwalm IEEE...

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