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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
IEEE T&D – Insulators 101
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
IEEE T&D – Insulators 101
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.
IEEE T&D – Insulators 101
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
IEEE T&D – Insulators 101
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
IEEE T&D – Insulators 101
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
IEEE T&D – Insulators 101
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”
IEEE T&D – Insulators 101
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.
IEEE T&D – Insulators 101
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
IEEE T&D – Insulators 101
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)
IEEE T&D – Insulators 101
Insulator TypesInsulator Types
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
IEEE T&D – Insulators 101
Types of Insulators – DistributionTypes of Insulators – Distribution
IEEE T&D – Insulators 101
Insulator TypesInsulator Types
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
IEEE T&D – Insulators 101
Types of Insulators – TransmissionTypes of Insulators – Transmission
IEEE T&D – Insulators 101
Insulator TypesInsulator Types
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
IEEE T&D – Insulators 101
Types of Insulators – SubstationTypes of Insulators – Substation
IEEE T&D – Insulators 101
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
IEEE T&D – Insulators 101
Insulator Types - ComparisonsInsulator Types - Comparisons
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
IEEE T&D – Insulators 101
Insulator Types - ComparisonsInsulator Types - Comparisons
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)
IEEE T&D – Insulators 101
““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
IEEE T&D – Insulators 101
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.
IEEE T&D – Insulators 101
Design Criteria - MechanicalDesign Criteria - Mechanical
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.
IEEE T&D – Insulators 101
Design Criteria - MechanicalDesign Criteria - Mechanical
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)
IEEE T&D – Insulators 101
Design Criteria - MechanicalDesign Criteria - Mechanical
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!!!
IEEE T&D – Insulators 101
Design Criteria - MechanicalDesign Criteria - Mechanical
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
IEEE T&D – Insulators 101
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!!!
IEEE T&D – Insulators 101
Design Criteria - ElectricalDesign Criteria - Electrical
Dry Arcing Distance – (Strike Distance) – “The shortest distance through the surrounding medium between terminal electrodes….” 1
1 – IEEE Std 100 - 1992
IEEE T&D – Insulators 101
Design Criteria - ElectricalDesign Criteria - Electrical
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
IEEE T&D – Insulators 101
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
IEEE T&D – Insulators 101
Design Criteria - ElectricalDesign Criteria - Electrical
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
IEEE T&D – Insulators 101
Design Criteria - ElectricalDesign Criteria - Electrical
“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
IEEE T&D – Insulators 101
Design Criteria - ElectricalDesign Criteria - Electrical
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
IEEE T&D – Insulators 101
Design Criteria - ElectricalDesign Criteria - Electrical
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)
IEEE T&D – Insulators 101
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
IEEE T&D – Insulators 101
Improved Contamination PerformanceImproved Contamination Performance
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
IEEE T&D – Insulators 101
Improved Contamination PerformanceImproved Contamination Performance
“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”
IEEE T&D – Insulators 101
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)
IEEE T&D – Insulators 101
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
IEEE T&D – Insulators 101
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
IEEE T&D – Insulators 101
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
IEEE T&D – Insulators 101
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.
IEEE T&D – Insulators 101
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
IEEE T&D – Insulators 101
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
IEEE T&D – Insulators 101IEEE T&D – Insulators 101
American Standards Committee
on Insulators for Electric Power Lines
ASC C-29
EL&P Group
IEEE
NEMA
Independents
IEEE T&D – Insulators 101IEEE T&D – Insulators 101
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)
IEEE T&D – Insulators 101IEEE T&D – Insulators 101
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.
IEEE T&D – Insulators 101IEEE T&D – Insulators 101
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?
IEEE T&D – Insulators 101
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
IEEE T&D – Insulators 101
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.
IEEE T&D – Insulators 101
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
IEEE T&D – Insulators 101IEEE T&D – Insulators 101
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
IEEE T&D – Insulators 101
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
IEEE T&D – Insulators 101
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.
IEEE T&D – Insulators 101
IEEE T&D – Insulators 101
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
IEEE T&D – Insulators 101
Mechanical RatingsMechanical Ratings
M&E Test
Ceramic Suspensions
Bending Tests
Composite Posts
IEEE T&D – Insulators 101
Hubbell Power SystemsKinectrics
IEEE T&D – Insulators 101
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
IEEE T&D – Insulators 101
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.
IEEE T&D – Insulators 101
IEEE T&D – Insulators 101
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
IEEE T&D – Insulators 101
IEEE T&D – Insulators 101
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.
IEEE T&D – Insulators 101
IEEE T&D – Insulators 101
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
IEEE T&D – Insulators 101
IEEE T&D – Insulators 101
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.
IEEE T&D – Insulators 101
IEEE T&D – Insulators 101
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 ----------
IEEE T&D – Insulators 101
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.
IEEE T&D – Insulators 101
IEEE T&D – Insulators 101
Mechanical Ratings – Application LimitsMechanical Ratings – Application LimitsComposite Post Insulators – Combined LoadingComposite Post Insulators – Combined Loading
IEEE T&D – Insulators 101
IEEE T&D – Insulators 101
Mechanical Ratings – Application LimitsMechanical Ratings – Application LimitsComposite Post Insulators – Combined LoadingComposite Post Insulators – Combined Loading
IEEE T&D – Insulators 101
IEEE T&D – Insulators 101
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..
IEEE T&D – Insulators 101
IEEE T&D – Insulators 101
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.
IEEE T&D – Insulators 101
IEEE T&D – Insulators 101
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
IEEE T&D – Insulators 101
““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
IEEE T&D – Insulators 101
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
IEEE T&D – Insulators 101
‘‘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.
IEEE T&D – Insulators 101
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
IEEE T&D – Insulators 101
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
IEEE T&D – Insulators 101
‘‘Proven’ Installation ProceduresProven’ Installation Procedures
IEEE T&D – Insulators 101
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…..
IEEE T&D – Insulators 101
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…”
IEEE T&D – Insulators 101
Line outage FailuresLine outage FailuresYour objective is to find the problem, quickly!
IEEE T&D – Insulators 101
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
IEEE T&D – Insulators 101
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
IEEE T&D – Insulators 101
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!
IEEE T&D – Insulators 101
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?
IEEE T&D – Insulators 101
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.
IEEE T&D – Insulators 101
Source of PresentationSource of Presentation
http://ewh.ieee.org/soc/pes/iwg/