Insulators101PanelFinalA.ppt

IEEE T&D – Insulators 101
“Insulators 101”
Section A – Introduction
Presented by Andy Schwalm
IEEE Chairman, Lightning and Insulator Subcommittee
IEEE/PES 2010 Transmission and Distribution
Conference and Exposition
New Orleans, Louisiana
April 20, 2010

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?
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?
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

History
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

History
 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

History
 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”

History
 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.

History
 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 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)

Insulator 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, polymeric
Dead end insulators – polymeric, porcelain, glass
Spool insulators – porcelain, polymeric
Strain insulators, polymeric, porcelain

Types of Insulators – Distribution

Insulator 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

Types of Insulators – Transmission

Insulator 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

Types of Insulators – Substation

Insulator 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)

Section B - Design Criteria
Presented by Al Bernstorf
IEEE Chairman, Insulator Working Group
April 20, 2010

Design 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 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
TRANSVERSELOAD, LBF
VERTICAL
LOAD,
LBF
0 Longitudinal
500 Longitudinal
1000 Longitudinal
1500 Longitudinal
2000 Longitudinal
LINEPOSTAPPLICATION
CURVES
9-12-05
Compression Tension

Design Criteria - Electrical
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
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))+e
I(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 - 1.25
1.50 - 1.75
2.00 - 2.50
G. 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 LEAKAGE
CONTAMINATION LEVEL
D. ZERO
E. LIGHT
F. MODERATE
POLYMER VALUES
NUMBER 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 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 Severity
Leakage 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)
Leak
("/kV
l-g)
IEEE V
IEEE I
IEC
Poly. (IEC)
Poly. (IEEE V)
Poly. (IEEE I)

Improved Contamination Performance
Flashover Vs ESDD
0
50
100
150
200
250
300
0.01 0.1
ESDD (mg/cm^2)
Flashover
Voltage
Porcelain
New EPDM
Aged EPDM
New SR
Aged SR
CEA 280 T 621
SR units - leakage equal to porcelain
EPDM 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 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)

Insulator 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))+e
I(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 - 1.25
1.50 - 1.75
2.00 - 2.50
G. 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 LEAKAGE
CONTAMINATION LEVEL
D. ZERO
E. LIGHT
F. MODERATE
POLYMER VALUES
NUMBER 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 Selection
Porcelain – 5-3/4 X 10” bells X 4 units
Characteristic Required Available
Leakage
Distance
42” 46”
Wet Switching
Surge W/S
125 kV 240 kV
Impulse W/S 359 kV 374 kV
M & E 12,000 lbs 15,000 lbs

Grading 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 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?

Insulators 101
Section C - Standards
Presented by Tony Baker
IEEE Task Force Chairman, Insulator Loading
April 20, 2010

American 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 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 Standards
Applies to new insulators
Definitions
Materials
Dimensions & 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 Ratings
Electrical & Mechanical Ratings
How are they assigned?
How is conformance demonstrated?
What are application limits?

Electrical 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° 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 Distance
Shortest distance through the surrounding medium between terminal
electrodes , or the sum of distances between intermediate electrodes ,
whichever is shortest, with the insulator mounted for dry flashover test.

Electrical 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 Ratings
Dry 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)
Flashover
(kV)
Station Post and Line Post
Suspension Insulator

Electrical Ratings
ANSI C2 Insulation Level Requirements
ANSI C2-2007, Table 273-1
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 - 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 Ratings
Sample & Routine Mechanical Tests
are based on the primary in-service loading conditions
STD. 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 Cantilever
Torsion
Tension
Tension
C29.9 “ Station Post Cantilever
Tension
Tension, Cantilever or
Bending Moment
C29.12 Composite Suspension SML Tension
C29.13 “ Deadend SML Tension
C29.17 “ Line Post Cantilever
Tension
Tension
C29.18 “ Dist. Line Post Cantilever Tension

Mechanical Ratings
M&E Test
Ceramic Suspensions
Bending Tests
Composite Posts
Hubbell Power Systems
Kinectrics

ANSI C29 High Voltage Insulator Standards
Std.
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 – 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 C29.2
Possible low strengths for ceramic suspension
units in a lot minimally acceptable according
to ANSI C29.2
Coefficient
of variation, vR
Strength value
at -3σ
5% 90% of M&E rating

Lot Acceptance Criteria – CSA C411.1
Possible low strengths for ceramic suspension
units in a lot minimally acceptable according to
CSA C411.1
Requirements
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 C29
Possible low strengths for ceramic units in a lot
minimally acceptable according to
ANSI C29.7, C29.8 & C29.9
Cantilever rating ≤ X3 & no xi< 85% of rating
Coefficient
of variation, vR
Strength value
at -3 σ
5% 85% of Cantilever rating

Lot Acceptance Criteria
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 Limits
NESC ANSI C Table 277-1
Allowed 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 Post4
40%
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 ----------

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.

Composite Post Insulators – Combined Loading

Recent Developments for Application Limits
Component strength cumulative distribution function FR and
probability density function of maximum loads fQ.

Component 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 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

Section D – Achieving ‘Quality’
Presented by Tom Grisham
IEEE Task Force Chairman, “Insulators 101”
IEEE/PES – T&D Conference and Exposition
New Orleans, LA
April 20, 2010

Objectives 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 – 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?
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?
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

Handling of Ceramics – NEMA HV2-1984
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’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 Failures
Your objective is to find the problem, quickly!

Inspection 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 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

Non-Ceramic (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?
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’ 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 Presentation
http://ewh.ieee.org/soc/pes/iwg/

Insulators101PanelFinalA.ppt

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