IEEE T&D – Insulators 101 “ “ Insulators 101” Insulators 101” Section A – Introduction Section A – Introduction Presented by Andy Schwalm Presented by Andy Schwalm IEEE Chairman, Lightning and Insulator IEEE Chairman, Lightning and Insulator Subcommittee 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, 2010 April 20, 2010
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IEEE T&D – Insulators 101 Insulators 101 Section A – Introduction Presented by Andy Schwalm IEEE Chairman, Lightning and Insulator Subcommittee IEEE/PES.
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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.
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.
• 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!!!
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.
“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.
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
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
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
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..
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
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.