Ceramic vs. Polymer (NonCeramic) InsulatorsMarch 2002 Andrew Phillips EPRI
Polymers Historyl
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Late 1950s: Lightweight NCI considered necessary for 1,000 kV lines 1959: GE develops first NCI, but experiences problems with tracking & erosion of epoxy sheds Early 1960s: Europeans introduce first generation of modern Polymers (fiberglass rod covered with various types of polymer sheds & hardwareAJPOctBAC 99 p.-2
Advantage of polymers over ceramicsl l l l l l l l
90% weight reduction Reduced breakage Lower installation costs Aesthetically more pleasing Improved resistance to vandalism Improved handling of shock loads Improved power frequency insulation Improved contamination performance
AJPOctBAC 99 p.-3
Early ProblemsTracking and erosion flashover and line drops l Chalking and crazing incr. Contamination, arcing, and flashover l Bonding failures flashover Failure l Hardware separation, failures of fiberglass core line drops l Splitting of sheds, water penetration electrical failurelAJPOctBAC 99 p.-4
Resultl
Some manufacturers left the business Some focused on Transmission Polymers only Some focused on Distribution Polymers only Some developed second- and third-generation Polymers
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AJPOctBAC 99 p.-5
Polymers Applied As:Suspension insulators: carry tension loads in I-string, Vee-string, and dead-end applications l Post insulators: Carry tension, bending, or compression loads l Phase-to-phase insulators: Loaded in tension, torsion, bending, or compression to couple two phases together to control conductor spacing during gallopingl
AJPOctBAC 99 p.-6
Elements of Modern PolymersGrounded End Fitting
Energized metallic end fitting l Energized end grading ring* l Fiberglass reinforced plastic rod (FRP) l Polymeric weathershed system (weathersheds and sheath) l Grounded end grading ring* l Grounded metallic end fitting*l
Grounded End Grading Ring
Fiberglass Rod
Shed
Sheath
Energized End Grading Ring
*Not all applications
Energized End Fitting
AJPOctBAC 99 p.-7
Basic Make-up
End Fitting
Fiberglass rod Sheds Sheath
Sheds
End Fitting Sheath
Cross-section through a Distribution Class NCI(Basic makeup is identical to a transmission class NCI)
Photograph of Suspension NCI showing main components
AJPOctBAC 99 p.-8
Hydrophobicity (Appendix D TR 111- 566)l
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Surface wetting property of rubber materials Hydrophobic - resists wetting by forming beads of water Hydrophilic - Surface wets out, films of water Silicone Rubber Units Hydrophobic EP Rubber Units l Hydrophilic l Could be hydrophobic initiallyl
HC1
HC2
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HC3
HC4
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HC5
AJPOctBAC 99 p.-9
HC6
Grading rings
Energized End Grading Ring
Grounded End Grading Ring
AJPOctBAC 99 p.-10
Grading Ringsl
Reduce E-field magnitudes at live and ground end fittingsNo Grading Ring With Grading Ring
AJPOctBAC 99 p.-11
Why Grading Rings?l
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Prevent corona under dry conditions l Radio interference, audio noise Prevent internal discharge l Voids & defects in rubber Reduce wetting corona activity l Ages rubber & end fitting seal
AJPOctBAC 99 p.-12
Wetting Corona Activityl
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Result of: l Non-uniform wetting l High E-field Occurs mainly at live and ground ends Lower hydrophobicity makes discharge activity more likely
AJPOctBAC 99 p.-13
Wetting Corona Activityl
Is a function of: l Type & magnitude of wettingl l
Hydrophobic/hydrophilic Rain/mist/fog/condensation Grading ring dimension and position End fitting design Configuration and live end hardware
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Magnitude of surface E-fieldl l l
AJPOctBAC 99 p.-14
Wetting Corona Aging Mechanisml
Corona generates l UV light l Heat l Gaseous by-productsl
03 (Ozone), NO2
NO 2 + H 2O = HNO 3 (Nitric Acid)EPRI tests: Wetting on NCI lowers pH to 3.4 after 15 min. of wetting corona activityAJPOctBAC 99 p.-15
Failure ModesBrittle fracture l Failure of rod due to discharges l Flash-under l End fitting attachment l Contamination flashover l Mechanical failure of rodl
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Water Reaches Rod
AJPOctBAC 99 p.-16
Brittle Fracturel l
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Water reached rod Acids form l Discharge activity l Contaminants l Acid rain l Corrosion Fibers cut by stress corrosion cuttingAxial Delamination Fracture Plane
Broomstick
AJPOctBAC 99 p.-17
Failure of Rod Due to DischargesWater ingress into rod l Discharge activity degrades rod l Chemically l Ionic wind l UV l Temperature l Rod fails under loadlAJPOctBAC 99 p.-18
Flash-underWater ingress l Conductive path l Through rod itself l On rod surface l NCI cannot hold voltage - flashover l Power arc bursts through rubberl
AJPOctBAC 99 p.-19
End-fitting AttachmentUnder crimping - pull out l Over Crimping l Cracked rod l May break with timel
AJPOctBAC 99 p.-20
Contamination FlashoverInsulator becomes severely contaminated due to local environment l Flashover may occur under critical wetting conditionsl
AJPOctBAC 99 p.-21
Mechanical Failure of Rodl
Rod may fail mechanically in service due to: l Poor rod manufacture l Mishandling during shipping or installationl l
Severe torsion Severe bending
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Mistreatment during manufacture Overloading
AJPOctBAC 99 p.-22
Issues with Polymersl
Aging of Polymer Materials Limited Experience Large Variation in designs, materials and manufacturing techniques Handling concerns l Storing, transporting and installingAJPOctBAC 99 p.-23
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Ceramic Insulators Types
AJPOctBAC 99 p.-24
Porcelain Cap & Pin Insulators Basic Componentsl
Porcelain Shell Portland Cement Hardware
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AJPOctBAC 99 p.-25
Issues with Ceramic InsulatorsFlashovers l Punctures l Cement Growth Cracking l Pin erosion l Long Term M&E Strength Reduction l Coupling Hardware Corrosionl
AJPOctBAC 99 p.-26
Ceramic vs. PolymersCeramicsl
Polymersl
Made from Inorganic materials l Do not age >80 years of experience Flexibility in Length High Leakage Distance Profiles Can be coated & washed
Made from Organic Materials l Age > 30 years experiencel
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Latest designs < 10 years
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Lighter Less susceptible to vandalism Smaller Viewing Profile Good short term performance in polluted environmentsAJPOctBAC 99 p.-27
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Polymers vs. Ceramic WeightItem Voltage (kV) Dist. 15 Dist. 15 Trans. 69 138 69 138 Type Ceramic Weight (lbs) 9.5 6.0 82.5 119.0 124.0 280.0 Polymer Weight (lbs) 2.4 3.8 27.2 8.0 28.0 98.9 Weight Reduction (lbs) 74.7 36.7 67.0 93.2 77.4 64.7
Insulator Arrester Post Insulator Suspension Trans. Insulator Intermediate Subs. Arrestor Station Subs. Arrester
AJPOctBAC 99 p.-28
Ceramic vs. Polymer Dry Arc DistanceDry Arc Distance = 72
Dry Arc Distance = 63
Dry Arc Distance = 58
Connection Length = 69AJPOctBAC 99 p.-29
Polymer vs. CeramicConnection Length & Dry Arc Distancel
For the same connection Length Polymers have shorter Dry Arc DistancesExample for 12 Bell EquivalentVoltage Level Connection Length 69 69 0% Dry Arc 72 58.4 -19% AC flashover Dry 690kV 585kV -15% Wet 490kV 510 kV +4% Critical Impulse +ve 1105kV 945kV -15% -ve 1105 kV 970kV -12%
Ceramic Polymer Reduction
230 kV 230 kV 0%
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Therefore: One needs to be careful when replacing a Ceramic with a Polymer!!AJPOctBAC 99 p.-30
*Note: Example for one specific polymer manufacturer and 5 Bells
Electrical designVoltage Level 138 kV 60 Hz Low Freq. Dry 390kV (NESC) Connect Length 42.5 46.0 51.7 Requirements for 138 kV 60 Hz Low Impulse Contamination Freq. Wet +ve -ve Level 741 kV 722 kV Low Specific Leakage Distance 16 mm/kV
CeramicNo of Bells 7 bells 8 bells 9 bells 60 Hz Low Freq. Dry 435 kV 485 kV 540 kV 60 Hz Low Freq. Wet 295 kV 335 kV 375 kV Impulse +ve -ve 695 kV 780 kV 860 kV 670 kV 760kV 845 kV Leakage Distance 2.04 m 2.34 m 2.63 m Specific Leakage Distance 15 mm/kV 17 mm/kV 19 mm/kV
Polymer
Connect Length 47.4 49.5 53.9 58.2
P1 P2 P3 P4
60 Hz Low Freq. Dry 390 kV 410 kV 450 kV 490 KV
60 Hz Low Freq. Wet 320 kV 340 kV 380 kV 415 kV
Polymer
Impulse +ve -ve 635 kV 670kV 735 kV 805 kV
Leakage Distance 2.53 m 2.68 m 2.99 m 3.30m
605 kV 640 kV 710 kV 780 kV
Specific Leakage Distance 18 mm/kV 19 mm/kV 22 mm/kV 24 mm/kVAJPOctBAC 99 p.-31
Polymer vs. CeramicStrike Distance
Vertical Strike Distance
Connection Length
Dry Arc Distance
Horizontal Strike Distance Vertical Strike Distance Horizontal Position of Conductor Vertical Bundle Position
Vertical Position of Conductor
Horizontal Strike Distance
One needs to be careful when replacing a Ceramic with a Polymer!!
Horizontal Bundle PositionB ra ce
D
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to
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Dr y Ar Co c nn Di sta ec tio nc n e Le ng th
AJPOctBAC 99 p.-32
Polymer vs. CeramicAging of Polymersl
Polymers made from Organic Materialsl
Rubber & Fiberglass UV, rain, contamination, mist, E-fields Different manufacturers Different material types Environment
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Materials age with exposure to environmentl
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Different polymers age differentlyl l l
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Experience with new Polymers & Processes is limitedl
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Designs used today are from the early to late 90s Less than 12 years experienceAJPOctBAC 99 p.-33
Polymer vs. CeramicPerformance under contaminated conditionsl
EPDM Polymers appear to perform similarly ceramic insulators in flashover tests SIR Polymers appear to perform better than ceramic insulators (in flashover tests)l
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Material properties (SIR hydrophobicity)
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In some cases Polymers have been found in to perform better than ceramic l Short term SIR definitely l Long term jury still outAJPOctBAC 99 p.-34
Polymer vs. CeramicPerformance under contaminated conditions EPDMl
Aged EPDM perform similarly or worse than to ceramic in flashover testsl
Aging of rubber material
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Rubber material can become aged & degraded - continual discharge activity l Dry Band Arcing l Leakage Currents Results in l Flashovers l Material degradationl
cracking, rod exposure, tracking
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Line DroppingsAJPOctBAC 99 p.-35
Polymer vs. CeramicPerformance under contaminated conditions SIRl
Aged SIR can perform better than ceramic (inflashover tests)l
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Material can become overwhelmed l Lower Hydrophobicity l Flashovers Short-term definite improvements Degradation Long-term can be a problem l Tracking both good & bad experiences l Rod Exposure
AJPOctBAC 99 p.-36
Polymer vs. NCI Mechanical Ratings - SuspensionCeramic Insulatorsl
Mechanical & Electrical Rating (M&E) Mechanical Load at which the Insulator Bell stops functioning either:lMechanically lElectrically
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Every unit tested to a load of 50% of M&E rating for 10 secs. Every unit electrically tested (after or simultaneously with themechanical test)
Units applied l < 20% of M&E rating for everyday load l < 50% of M&E rating for maximum loads
AJPOctBAC 99 p.-37
Polymer vs. NCI Mechanical Ratings- Suspensionl
Polymer Insulators Specific Mechanical load (SML)Mechanical Load that a Polymer can hold for 60 seconds without failing
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Every unit tested @ 50% of SML for 60-90 secs l Routine Test Load (RTL) l No electrical stress applied Units applied l < 20% of SML rating for everyday load l < 50% of SML rating for maximum loadsAJPOctBAC 99 p.-38
Porcelain vs. Glass vs. PolymerType Polymers Pros Lightweight & Easier to Han dle Reduced Installed Cost Improved contamination performance Smaller profile Cons Reduced Dry Arc Distance Susceptible to arcing damage due to flashovers Lack of standard dimensions Relatively limited experience Difficult to inspect Damaged by Corona Activity, etc, Porcelain Inert surface Performance well quantified Puncture of a single unit does not take out a string Long history of use Damaged units easier to identify Flexible in Length (# of units) Glass Performance well quantified Long history of use Easy to identify damaged unit Flexible in Length (# of units) Heavy and cumbersome Real Fun to shoot Surface defects failure Heavy and cumbersome Hidden defects Fun to shoot Pin corrosion Cement growth Post cascade failures Issues Susceptible to aging Prone to handling damage Grading rings Contamination performance changes with time Brittle Fracture
AJPOctBAC 99 p.-39
EPRI Related Researchl
Aging of Polymer Insulators l 500 kV Full Scale Aging Testl
Report Prod ID# 100719
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230 kV Full Scale Aging Test
AJPOctBAC 99 p.-40
Insulator Related GuidesApplication Guide for Transmission Line NCI TR 111-566 l Guide to Visual Inspection of NCI 10000998 l Guide to Corona & Arcing Inspection of OHT Lines 1001910 l Educational Video Storing, Transporting & Installing Polymer Insulators 1006353 l Storing, Transporting & Installing Polymer Insulators: An Practical GuidelAJPOctBAC 99 p.-41
Other Research ReportsE-field Modeling of NCI and Grading Ring Design & Application TR 113-977 l Effect of High Temperature Operation on NCI Product Id# 1000033 l Electrical & Mechanical Performance of Ceramic Insulators 1000505 l Fracture Analysis of Polymer Insulators 1006293l
AJPOctBAC 99 p.-42
Ongoing researchl l l l
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End fitting Performance and Design Evaluation of In-service Insulators Development of In-service Inspection Tools Industry Survey on experience with Polymers 71 utilities Failure Database 3 years in the making If you have had any failures @ voltages > 69 kV please send a note to [email protected]
AJPOctBAC 99 p.-43
