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IEEE T&D – Insulators 101

“Insulators 101”“Insulators 101”Section A Section A –– IntroductionIntroduction

Presented by Andy SchwalmPresented by Andy SchwalmIEEE Chairman, Lightning and Insulator SubcommitteeIEEE Chairman, Lightning and Insulator Subcommittee

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” mechanically

�Secondary function– electrical

�Air is the insulator

�Outer shells/surfaces are designed to increase leakage distance and strike distance


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

�Maintains an Air Gap�Separates 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 Stresses�system voltage/fields, overvoltages

�Resists Environmental Stresses�heat, cold, UV, contamination, etc.


Where Did Insulators Come From?Where Did Insulators Come 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 complex

�Ceramics (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, polymeric

�Dead end insulators – polymeric, porcelain, glass

�Spool insulators – porcelain, polymeric

�Strain insulators, polymeric, porcelain


Types of Insulators Types of Insulators –– DistributionDistribution



� 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 Types of Insulators –– TransmissionTransmission



� 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 Types of Insulators –– SubstationSubstation


Insulator Types Insulator Types -- ComparisonsComparisons

�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 Section B -- Design CriteriaDesign Criteria

Presented by Al BernstorfPresented by Al BernstorfIEEE Chairman, Insulator Working GroupIEEE Chairman, Insulator Working Group

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 Design Criteria -- MechanicalMechanical

�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 testing�Based 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 loads

�Available Vertical load as a function of Transverse loading

�Manufacturers 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

VE

RT

ICA

L L

OA

D,

LB

F

0 Longitudinal

500 Longitudinal

1000 Longitudinal

1500 Longitudinal

2000 Longitudinal

LINE POST APPLICATION CURVES9-12-05

Compr e ssion Ten sion


Design Criteria Design Criteria -- ElectricalElectrical

�An Insulator is a mechanical support!

�Air imparts Electrical Characteristics

�Strike 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

electrodesF.” 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)(l ine A/1.732)* 1.05

59.1 kV (peak)

e=(line B * 1.414)

1

H. INSULATOR LEAKAG E (MIN.)41.8 inches

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

J. PEAK IMPULSE WITHSTAND = (I(t) * R(f))+eI(t) = 20 kA (typical val ue = 50 kA)R(f) = 15 ohm (typi cal value = 10 - 20 ohm)

e = 59.1 (li ne C)

K. IMPULSE WITHSTAND = 359 kV

(typical val ues) (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 VO LTAGE

B. MAXIMUM SYSTEM LINE-TO-GROUND VOLTAGE

C. MAXIMUM PEAK LINE-TO-G ROUND VOLTAGE (e)

LEAKAGE DISTANCE REQUIREMENTS

SELECT INSULATO R BASED ON REQUIREMENTS:

(li ne B)*(inches/kV) =

Enter inches/kV -

PICKING A SUITABLE INSULATOR

ELECTRICAL PARAMETERS

SUGGESTED LEAKAGECONTAMINATION LEVEL

D. ZEROE. LIGHTF. MODERATE

POLYMER VALUES

NUMBER OF

PO RCELAIN BELLS

K. IMPULSE W ITHSTAND T. SELECT INSULATOR

41.8

125

359

SYSTEM

REQUIREMENT

VALUE FROM

PAGE 1

H. LEAKAGE DISTANCE

I. SWITCHING SURGE VOLTAGE


Design Criteria Design Criteria –– Leakage DistanceLeakage 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 Monitors

�Dummy Insulators

�Remove 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)

Le

ak (

"/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

Porc elain

New EPDM

Aged EPDM

New SR

Aged SR

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



�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 Selection

�Where 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)



�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)(l ine A/1.732)* 1.05

59.1 kV (peak)

e=(line B * 1.414)

1

H. INSULATOR LEAKAG E (MIN.)41.8 inches

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

J. PEAK IMPULSE WITHSTAND = (I(t) * R(f))+eI(t) = 20 kA (typical val ue = 50 kA)R(f) = 15 ohm (typi cal value = 10 - 20 ohm)

e = 59.1 (li ne C)

K. IMPULSE WITHSTAND = 359 kV

(typical val ues) (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 VO LTAGE

B. MAXIMUM SYSTEM LINE-TO-GROUND VOLTAGE

C. MAXIMUM PEAK LINE-TO-G ROUND VOLTAGE (e)

LEAKAGE DISTANCE REQUIREMENTS

SELECT INSULATO R BASED ON REQUIREMENTS:

(li ne B)*(inches/kV) =

Enter inches/kV -

PICKING A SUITABLE INSULATOR

ELECTRICAL PARAMETERS

SUGGESTED LEAKAGECONTAMINATION LEVEL

D. ZEROE. LIGHTF. MODERATE

POLYMER VALUES

NUMBER OF

PO RCELAIN BELLS

K. IMPULSE W ITHSTAND T. SELECT INSULATOR

41.8

125

359

SYSTEM

REQUIREMENT

VALUE FROM

PAGE 1

H. LEAKAGE DISTANCE

I. SWITCHING SURGE VOLTAGE



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

Characteristic Required Available

Leakage

Distance42” 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 & TVI

�Porcelain 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 Section C -- StandardsStandards

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 Standards�Consensus 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 appealBy 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 insulators

�Definitions

�Materials

�Dimensions & Marking (interchangeability)

�Tests1. 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 RatingsANSI C 29 Insulator Standard Ratings

Electrical & Mechanical Ratings

How are they assigned?

How is conformance demonstrated?

What are application limits?


Electrical RatingsElectrical Ratings�Average flashover values

�Low-frequency Dry & Wet

�Critical 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°°°° CCCC

- 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±±±±27ΩΩΩΩm, m, m, m, 10 sec. ws


Dry Arcing DistanceDry Arcing DistanceShortest distance through the surrounding medium between terminal Shortest distance through the surrounding medium between terminal electrodes , or the sum of distances between intermediate electrodes , electrodes , or the sum of distances between intermediate electrodes ,

whichever is shortest, with the insulator mounted for dry flashover test. whichever is shortest, with the 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≥ ≥ ≥ ≥ YesYesYesYes

where = 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

over

(kV

)

Station Post and Line Post

Suspension Insulator


Electrical RatingsElectrical RatingsANSI C2 Insulation Level RequirementsANSI C2 Insulation Level Requirements

ANSI C2ANSI C2--2007, Table 2732007, Table 273--11

0

200

400

600

800

1000

1200

1400

0 100 200 300 400 500 600 700 800 900

Rated Dry

FOV, kV

Nominal Phase-to-Phase Voltage, kV

Higher insulation levels required in areas where severe lightning, high

atmospheric contamination, or other unfavorable conditions exist


Electrical Ratings Electrical Ratings -- ApplicationApplication

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 ≥ T ≥ T ≥ T ≥ RRRR

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 StandardsANSI C29 High Voltage Insulator StandardsStd.

No.

Insulator

Type

Ult. Strength

QC Test

Lot Acceptance

Criteria

Routine

Test

C29.2 Ceramic

Suspension

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 Type

Cantilever & tension strengths

of 3 units each

X3≥ R

no one xi ≮ .85 R

Tension

at 50% of R

or

4 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 Lot Acceptance Criteria –– ANSI C29.2ANSI 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 ≤ X≤ X≤ X≤ X10101010 ----1.2S1.2S1.2S1.2SHHHH

&

s10 ≤1.72S≤1.72S≤1.72S≤1.72SHHHH

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

Possible low strengths for ceramic suspension Possible low strengths for ceramic suspension units in a lot minimally acceptable according units in a lot minimally acceptable according

to ANSI C29.2to ANSI C29.2

Coefficient

of variation, vR

Strength value

at -3σσσσ

5% 90% of M&E rating





Lot Acceptance Criteria Lot Acceptance Criteria –– CSA C411.1 CSA C411.1 Possible low strengths for ceramic suspension Possible low strengths for ceramic suspension

units in a lot minimally acceptable according to units in a lot minimally acceptable according to CSA C411.1CSA C411.1

�Requirements

Rating≤ X≤ X≤ X≤ XSSSS –––– 3s3s3s3s

&&&&

XXXXiiii ≥ R≥ R≥ R≥ 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.IEEE T&D – Insulators 101


Lot Acceptance Criteria Lot Acceptance Criteria –– ANSI C29ANSI C29Possible low strengths for ceramic units in a lot Possible low strengths for ceramic units in a lot

minimally acceptable according to 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 σσσσ

5% 85% of Cantilever rating





Lot Acceptance CriteriaLot Acceptance CriteriaANSI C29 ANSI C29 ––Composite InsulatorsComposite 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 Mechanical Ratings –– Application LimitsApplication LimitsNESC ANSI C Table 277NESC ANSI C Table 277--1 1

Allowed percentages of strength ratingsAllowed percentages of strength ratings

Insulator Type % Strength Rating Ref. ANSI Std.

Ceramic

Suspension 50%

Combined

mechanical & electrical strength (M&E) C29.2-1992

Line Post 40%

50%

Cantilever strength

Tension/compression strength

C29.7-1996

Station Post440%

50%

Cantilever strength

Tension/compression/torsion strength C29.9-1983

Station

Cap & Pin

40%

50%

Cantilever strength

Tension/compression/torsion strength C29.8-1985

Composite

Suspension 50% Specified mechanical load (SML)

C29.12-1997

C29.13-2000

Line Post 50%

Specified cantilever load (SCL) or

specified tension load (STL)

C29.17-2002

C29.18-2003

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


Mechanical Ratings Mechanical Ratings –– Application LimitsApplication 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 Mechanical Ratings –– Application LimitsApplication LimitsComposite Post Insulators Composite Post Insulators –– Combined LoadingCombined Loading



Recent Developments for Application LimitsRecent Developments for Application Limits

Component strength cumulative distribution function FComponent strength cumulative distribution function FRR and and

probability density function of maximum loads probability density function of maximum loads ffQQ..



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

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

IEEE/PES IEEE/PES –– T&D Conference and ExpositionT&D Conference and ExpositionNew Orleans, LANew Orleans, LA

April 20, 2010April 20, 2010


Objectives of ‘Quality” PresentationObjectives of ‘Quality” Presentation

�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’ Defined‘Quality’ 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 Plan?What Is Needed in a Quality Plan?

�Identifying critical design parameters

�Qualifying ‘new’ suppliers

�Evaluating current suppliers

�Establishing internal specifications

�Monitoring standards compliance (audits)

�Understanding installation requirements

�Establishing end-of-life criteria

�Ensuring safety of line workers

�Communicating and training

�All aspects defined by the company plan


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

�Catalog specifications and changes

�Supplier audit records and lot certification

�Qualification 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 Procedures‘Proven’ Installation Procedures


Handling of Ceramics Handling of Ceramics –– NEMA HV2NEMA HV2--19841984

�Insulators should not be dropped or thrownF..

�Insulators strings should not be bentF..

�Insulator strings are not laddersF..

�Insulators with chips or cracks should be discarded and

companion units should be carefully inspectedF..

�Cotter keys should be individually inspected for twisting,

flattening or indentations. If found, replace keys and

retest the insulatorF..

�The maximum combined load, including safety requirements of NESC, must not exceed the ratingF..

�Normal operating temperature range for ceramics is

defined as –40 to 150 Degrees FF..


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

products. It will likely includeFFFFFFFF

• “Insulators should not be dropped, thrown, or bentT”

• “Insulators should not be used as laddersT”

• “Cotter keys for ball sockets should be inspected identically to the instructions for ceramic insulatorsT”

• “The maximum combined loads should not exceed the RTLT”

• Normal operating temperature is –40 to 150 Degrees FT”• “Insulators should not be used as rope supportsG”

• “Units with damaged housings that expose the core rod should

be replaced and discardedG”

• “Units with cut or torn weathersheds should be inspected by

the manufacturerG”

• “Bending, twisting and cantilever loading should be avoided

during construction and maintenanceG”


Line outage FailuresLine outage Failures

�Your 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 Failures

�Failures 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 new

�Should the insulators be replaced?

• Establish internal criteria by location


NonNon--Ceramic (NCI) FailuresCeramic (NCI) Failures�Cause 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 Failure?What To Do for an Insulator 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’ PresentationSummary of ‘Quality’ Presentation�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/