Ceramic vs. Polymer Insulators PDF

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Summary

Ceramic vs. Polymer (Non- Ceramic) Insulators March 2002 Andrew Phillips EPRI Polymers History l Late 1950s: Lightweight NCI considered necessary for 1,000 kV lines l 1959: GE develops first NCI, but experiences problems with tracking & erosion of epoxy sheds l Early 1960s: Europeans introduce f...

Description

Ceramic vs. Polymer (NonCeramic) Insulators March 2002 Andrew Phillips EPRI

Polymers History l

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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 & hardware AJPOctBAC 99 p.-2

Advantage of polymers over ceramics l 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 Problems Tracking 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 failure l

AJPOctBAC 99 p.-4

Result l

Some manufacturers left the business

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Some focused on Transmission Polymers only

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Some focused on Distribution Polymers only

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Some developed second- and third-generation Polymers

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 galloping l

AJPOctBAC 99 p.-6

Elements of Modern Polymers Grounded 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

Energized End Fitting

*Not all applications

AJPOctBAC 99 p.-7

Basic Make-up

End Fitting

Fiberglass rod Sheds

Sheds

Sheath

End Fitting Sheath

Cross-section through a Distribution Class NCI

Photograph of Suspension NCI showing main components

(Basic makeup is identical to a transmission class NCI)

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 initially

HC1

HC2

HC3

HC4

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HC5

HC6

AJPOctBAC 99 p.-9

Grading rings

Energized End Grading Ring

Grounded End Grading Ring

AJPOctBAC 99 p.-10

Grading Rings l

Reduce E-field magnitudes at live and ground end fittings No 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 Activity l

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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 Activity l

Is a function of: l Type & magnitude of wetting l l

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Hydrophobic/hydrophilic Rain/mist/fog/condensation

Magnitude of surface E-field l l l

Grading ring dimension and position End fitting design Configuration and live end hardware

AJPOctBAC 99 p.-14

Wetting Corona Aging Mechanism l

Corona generates l UV light l Heat l Gaseous by-products l

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 activity AJPOctBAC 99 p.-15

Failure Modes Brittle fracture l Failure of rod due to discharges l Flash-under l End fitting attachment l Contamination flashover l Mechanical failure of rod l

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Water Reaches Rod

AJPOctBAC 99 p.-16

Brittle Fracture l 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 cutting

Broomstick

Axial Delamination Fracture Plane AJPOctBAC 99 p.-17

Failure of Rod Due to Discharges Water ingress into rod l Discharge activity degrades rod l Chemically l Ionic wind l UV l Temperature l Rod fails under load l

AJPOctBAC 99 p.-18

Flash-under Water ingress l Conductive path l Through rod itself l On rod surface l NCI cannot hold voltage - flashover l Power arc bursts through rubber l

AJPOctBAC 99 p.-19

End-fitting Attachment Under crimping - pull out l Over Crimping l Cracked rod l May break with time l

AJPOctBAC 99 p.-20

Contamination Flashover Insulator becomes severely contaminated due to local environment l Flashover may occur under critical wetting conditions l

AJPOctBAC 99 p.-21

Mechanical Failure of Rod l

Rod may fail mechanically in service due to: l Poor rod manufacture l Mishandling during shipping or installation l l

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Severe torsion Severe bending

Mistreatment during manufacture Overloading

AJPOctBAC 99 p.-22

Issues with Polymers l

Aging of Polymer Materials

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Limited Experience

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Large Variation in designs, materials and manufacturing techniques

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Handling concerns l Storing, transporting and installing AJPOctBAC 99 p.-23

Ceramic Insulators Types

AJPOctBAC 99 p.-24

Porcelain Cap & Pin Insulators Basic Components l

Porcelain Shell

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Portland Cement

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Hardware

AJPOctBAC 99 p.-25

Issues with Ceramic Insulators Flashovers l Punctures l Cement Growth Cracking l Pin erosion l Long Term M&E Strength Reduction l Coupling Hardware Corrosion l

AJPOctBAC 99 p.-26

Ceramic vs. Polymers Ceramics l

Polymers

Made from Inorganic materials l Do not age

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>80 years of experience

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Flexibility in Length

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High Leakage Distance Profiles Can be coated & washed

Made from Organic Materials l Age > 30 years experience l

Latest designs < 10 years

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Lighter

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Less susceptible to vandalism

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Smaller Viewing Profile

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Good short term performance in polluted environments AJPOctBAC 99 p.-27

Polymers vs. Ceramic Weight Item

Type

Voltage (kV) Dist. 15 Dist. 15 Trans. 69

Insulator Arrester Post Insulator Suspension Trans. Insulator Intermediate Subs. Arrestor Station Subs. Arrester

Ceramic Weight (lbs) 9.5 6.0 82.5

Polymer Weight (lbs) 2.4 3.8 27.2

Weight Reduction (lbs) 74.7 36.7 67.0

138

119.0

8.0

93.2

69

124.0

28.0

77.4

138

280.0

98.9

64.7

AJPOctBAC 99 p.-28

Ceramic vs. Polymer Dry Arc Distance Dry Arc Distance = 72”

Dry Arc Distance = 63”

Dry Arc Distance = 58”

Connection Length = 69” AJPOctBAC 99 p.-29

Polymer vs. Ceramic Connection Length & Dry Arc Distance l

For the same connection Length Polymers have shorter Dry Arc Distances Example for 12 Bell Equivalent

Ceramic Polymer Reduction

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Voltage Level

Connection Length

Dry Arc

230 kV 230 kV 0%

69” 69” 0%

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%

Therefore: One needs to be careful when replacing a Ceramic with a Polymer!!

*Note: Example for one specific polymer manufacturer and 5 ¾“ Bells AJPOctBAC 99 p.-30

Electrical design Voltage Level 138 kV

Requirements for 138 kV 60 Hz Low Impulse Contamination Freq. Wet +ve -ve Level 741 kV 722 kV Low

60 Hz Low Freq. Dry 390kV (NESC)

Specific Leakage Distance 16 mm/kV

Ceramic No of Bells

Connect Length

7 bells 8 bells 9 bells

42.5 “ 46.0” 51.7”

Polymer

Connect Length

P1 P2 P3 P4

47.4 “ 49.5” 53.9” 58.2”

60 Hz Low Freq. Dry 435 kV 485 kV 540 kV

60 Hz Low Freq. Dry 390 kV 410 kV 450 kV 490 KV

60 Hz Low Freq. Wet 295 kV 335 kV 375 kV

Impulse +ve -ve 695 kV 780 kV 860 kV

Leakage Distance

670 kV 760kV 845 kV

2.04 m 2.34 m 2.63 m

Polymer

60 Hz Low Freq. Wet 320 kV 340 kV 380 kV 415 kV

Impulse +ve -ve

605 kV 640 kV 710 kV 780 kV

Leakage Distance

635 kV 670kV 735 kV 805 kV

2.53 m 2.68 m 2.99 m 3.30m

Specific Leakage Distance 15 mm/kV 17 mm/kV 19 mm/kV

Specific Leakage Distance 18 mm/kV 19 mm/kV 22 mm/kV 24 mm/kV AJPOctBAC 99 p.-31

Polymer vs. Ceramic

Vertical Position of Conductor

Dry Arc Distance

Connection Length

Vertical Strike Distance

Strike Distance

Horizontal Strike Distance

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Horizontal Bundle Position

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One needs to be careful when replacing a Ceramic with a Polymer!!

Dr y Ar Co c nn Di sta ec tio nc n e Le ng th

Horizontal Position of Conductor

Vertical Bundle Position

Vertical Strike Distance

Horizontal Strike Distance

AJPOctBAC 99 p.-32

Polymer vs. Ceramic Aging of Polymers l

Polymers made from Organic Materials l

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Materials age with exposure to environment l

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UV, rain, contamination, mist, E-fields

Different polymers age differently l l l

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Rubber & Fiberglass

Different manufacturers Different material types Environment

Experience with new Polymers & Processes is limited l

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Designs used today are from the early to late 90’s Less than 12 years experience AJPOctBAC 99 p.-33

Polymer vs. Ceramic Performance under contaminated conditions l

EPDM Polymers appear to perform similarly ceramic insulators in flashover tests

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SIR Polymers appear to perform better than ceramic insulators (in flashover tests) l

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Material properties (SIR – hydrophobicity)

In some cases Polymers have been found in to perform better than ceramic l Short term – SIR definitely l Long term – jury still out AJPOctBAC 99 p.-34

Polymer vs. Ceramic Performance under contaminated conditions EPDM l

Aged EPDM perform similarly or worse than to ceramic in flashover tests l

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Aging of rubber material

Rubber material can become aged & degraded - continual discharge activity l Dry Band Arcing l Leakage Currents Results in l Flashovers l Material degradation l

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cracking, rod exposure, tracking

Line Droppings AJPOctBAC 99 p.-35

Polymer vs. Ceramic Performance under contaminated conditions SIR l

Aged SIR can perform better than ceramic (in flashover 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 - Suspension Ceramic Insulators l

Mechanical & Electrical Rating (M&E) Mechanical Load at which the Insulator Bell stops functioning either: lMechanically

or

lElectrically l l

Every unit tested to a load of 50% of M&E rating for 10 secs. Every unit electrically tested (after or simultaneously with the mechanical test)

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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- Suspension l

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 loads AJPOctBAC 99 p.-38

Porcelain vs. Glass vs. Polymer Type Polymers

Pros Lightweight & Easier to Han dle

Cons Reduced Dry Arc Distance

Issues Susceptible to aging

“Reduced Installed Cost”

Susceptible to arcing damage due to flashovers

Prone to handling damage

Lack of standard dimensions

Contamination performance changes with time

Relatively “limited” experience

Brittle Fracture

Improved contamination performance Smaller profile

Grading rings

Difficult to inspect Damaged by Corona Activity, etc, Porcelain

Inert surface

Heavy and cumbersome

Pin corrosion

Performance well quantified

Hidden defects

Cement growth

Puncture of a single unit does not take out a string

Fun to shoot

Post cascade failures

Performance well quantified

Heavy and cumbersome

Surface defects – failure

Long history of use

Real Fun to shoot

Long history of use Damaged units easier to identify Flexible in Length (# of units) Glass

Easy to identify damaged unit Flexible in Length (# of units)

AJPOctBAC 99 p.-39

EPRI Related Research l

Aging of Polymer Insulators l 500 kV Full Scale Aging Test l

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Report Prod ID# 100719

230 kV Full Scale Aging Test

AJPOctBAC 99 p.-40

Insulator Related Guides Application 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 Guide l

AJPOctBAC 99 p.-41

Other Research Reports E-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 1006293 l

AJPOctBAC 99 p.-42

Ongoing research l 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...