Gridtech 2015 CIGRE B2: Enhancing Grid Reliability with Gen-4 RTV Silicone Insulator Coatings in...

April 8th - 9th, 2015, Pragati Maidan, New Delhi, India

International Colloquium on Overhead Lines in association with CIGRE SC B2

by

ENHANCING GRID RELIABILITY

WITH

GEN-4 RTV SILICONE COATINGS

NEELESH ARORA

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EPSILON

[email protected]



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1. Contamination Flashovers vs. Grid Reliability

• Insulators are a fraction of the cost of Transmission Grids yet

heavily impact grid reliability.

• In some coastal locations, up to 32.5% of all outage faults are

attibuted to pollution

• Contamination flashovers are still a global problem

• Robustness of Insulators across varying service conditions needed

• Ultimate target: To bring insulator monitoring/maintenance to ‘near

zero’ levels in all service conditions



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2. Pollution Conditions

• Much research has gone into pollution

types, severities and the impact on AC

and DC insulators

• As per IEC60815:

– ESDD of 10μg/cm2 is considered ‘light’

– ESDD > 400μg/cm2 considered ‘very heavy’

• This presentation is concerned with

“Fourth Generation RTV Silicone

Rubber Insulator Coatings in medium

to very heavy level of contamination”

• This paper is valid for global conditions;

however, since colloquium venue is India,

most examples/references are local

400kV Switchyard, Udupi Power Corp. Ltd., Udupi, India



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3. Common Methods to Eliminate Pollution Flashovers

• Insulator Washing in Live-line and Offline state

• Silicone Greases

• Anti-fog insulators

• Contamination Source Reduction

• Use of Non-ceramic Insulators

• Insulator Modification: RTV Insulator Coatings



Washing: High risk; Recurring Silicone Grease: Short-term efficacy

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Anti-Fog Insulators: Nonceramic Insulators

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Multiple failures Reported

PSTCL, Ludhiana

• Generally Encouraging except:

• Arid/Semi-arid conditions

• Where mechnical strength is critical

• Coastal locations (Peru, Colombia, etc.)



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Composite Silicone Rubber Insulators (SRIs)

• Generally positive feedback

• Exceptions:

– Arid/Semi-arid Conditions: Long

rod Insulators with RTV Coating

preferred in most of the Middle

East

• In VH pollution conditions,

failures reported [*]

– Red de Energia del Perú S.A.

– ISA Colombia (Interconexión

Eléctrica S.A.

[*] INMR Q1/2011, Utility Practice and Experience”, ISA Colombia (Interconexión Eléctrica S.A. E.S.P and REP (Red de

Energia del Perú S.A.)



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Excerpts: INMR: “Utility Practice and Experience”[*]

SRI Experience, South America

“Prevailing wisdom is that SRIs offer the best performance when it comes to

reducing or even eliminating service problems triggered by pollution

flashovers.

Based on this premise, Colombia’s Interconexión Eléctrica and Red de

Energia del Perú began incorporating SRI Technology in the late 1990s

mainly for lines running near a desert coastal plain dominated by subtropical

climate, high humidity and low rainfall.

In both cases, results were not as had been expected and a considerable

number of failures occured.

This eventually forced both utilities to replace the composite insulators.





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Colombia’s ISA: Experience with SRIs[*]

Fault Rate of SRIs: up to 3 faults per 100 circuit km/year

2003: SRIs replaced with Porcelain in high-failure sections

No failures reported since

Other Challenges:

Ease of Access for Maintenance Personnel while inspecting conductors,

fittings & spacers. Typically, workers crawl out on SRIs which can deform or

break with a corresponding loss in insulation properties

SRIs are typically custom-designed therefore cost of spares is higher





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Peru RED: Experience with SRIs[*]

Experience: 12,000 SRIs (220kV) installed in coastal area up to 2009

Failures between 2004 – 2011: 17, all due to mechanical failure caused

by high pollution, high humidity and electrical stress

Average Insulator Life:

Ceramic Insulator: 30 years

Glass Insulator: 34 years

SRI: 6-7 years. Even less when close to the sea

“Future Installation of SRI’s thrown into doubt’





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SRI: Critical Maintenance Limitations

No established protocol for Live-Line Work (LLW) on SRIs unlike for ceramic

insulators

LLW by maintenance workers on SRIs is not encouraged

For critical lines, (system stability and revenue producing lines), this is a

major deterrent

Lines must be taken out of service for maintenance and this defeats the aim

of ‘uninterrupted performance’

Therefore, many utilities have banned the use of non-ceramic insulators on

critical lines



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4. What is an RTV Insulator Coating?

• Room temperature Vulcanizing (RTV) Insulator Coatings are one-

part hydrophobic, UV-resistant coatings

• Use: Enhancement of an insulator's surface properties to prevent

the formation of a conductive layer in all service conditions

• RTV Insulator coatings also be referred to as:

– “High Voltage Insulator Coatings (HVICs), or

– “Anti-Tracking Coatings”

– RTV Silicone Insulator Rubber (SIR) Coatings

• For AC and DC systems

• For equipment up to 1200kV class



5. About RTV Insulator Coatings

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• Usually Spray Coated in the

field, or pre-coated in

factories

• Eliminates flashovers in

pollution conditions without

compromising physical

integrity of equipment

• Maintenance-Free

• Tried, tested and evolved

technology



6. Advancement in RTV Coatings:

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RTV Core Characteristics

Gen-1 • Used in the early 1970s with Trichloroethane as a solvent

Gen-2 • Contain Alumina Trihydrate (ATH). • Focus on Inclined Plane Tracking and Erosion Tests as opposed to

Hydrophobicity

Gen-3 • Use variations of ATH in different sizes. • Solvent changed from Trichloroethane to Naphtha

Gen-4 • Primarily silica-based• Display improved thermal characteristics. • Silica extends thermal resistance of the coating to above 350°C • Display better Hydrophobicity Recovery Characteristics• Unlike older coatings, are not prone to acid depolymerization• Not Prone to Peeling like some GEN-3 Coatings



6a. Gen-4 RTV: Improved Hydrophobicity Recovery

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Gen-3 RTV Coating: Recovery

“Between HC2 & HC3” [1]

• HC3 Spec:

– 20° < θr <80° for majority of droplets

– Usually droplets are no longer

round at HC3

Gen-4 RTV Coating: Recovery

“to HC2” [1]

• HC2 Spec:

– 50° <θr < 80° for the majority of

droplets

– Droplets are Round

[1] Hydrophobicity Recovery Tests REC 76/2206 as

conducted by the Central Power Research Institute, India



6b. Dr. Cherney: The Argument for Gen-4 Coatings

Dr. Edward Cherney

Chairman, IEEE DEIS Outdoor Service Environment Committee

Contributing Participant, IEEE 1523-2002 Standard entitled “Guide for the Application,

Maintenance, and Evaluation of RTV Silicone Rubber Coatings for Outdoor Ceramic Insulators”

Co-Editor-in-Chief of the IEEE Electrical Insulation Magazine

Professor of High Voltage Studies at the University of Waterloo, Canada

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“ATH is very sensitive to moisture uptake and this causes problems in the manufacture of a coating as a ‘wet ATH’

leads to gels in the coating.

Secondly, there is no physical or chemical mechanism for bonding of ATH particles to the silicone rubber backbone,

and this leads to porosity, a bad thing for a coating as moisture uptake can lead to:

(1) Hydrolysis of a coating

(2) Higher dissipation factor or dielectric loss, and

(3) Higher relative permittivity

On the other hand, silica is not sensitive to moisture uptake, so none of the mentioned problems occur. In addition,

because of the chemically similar structure, silica actually forms chemical bonds with the host matrix thereby

improving strength, reduces porosity, and further improves adhesion to substrates.



7. Gen-4 RTV HVIC: 100% Success in Switchyards

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• 40+ Projects in just India alone

• 100% Flashover Elimination

• Only RTV coating with 0% Peeling and

Failure Rate

• TATA Power 4,000 MW UMPP (CGPL)

authored paper about success

• NTPC Kawas Gas Plant presented a

paper on their successful experience

with Gen-4 RTV Coating at “NTPC

Technogalaxy 2015”



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Success in Extreme Pollution

Environments

Pollution Source

Insulator yard



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8a. Case Overview: Tata Power CGPL 4,000 MW TPP

• 400kV Yard in Mundra,

coastal India

• 33mm/kV Creepage design

• 31 discs per 400kV string

• Multiple Flashovers Annually

• Existing Methods to Eliminate

Flashovers Unsuccessful

• Daily Live-line Washing cycle

through the year



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8b. Tata Power CGPL 4,000 MW TPP, Mundra

Tata Power Authored Paper for CPRI

Conference: Excerpts:

• All Flashovers Eliminated

• “The Gen-4 RTV Silicone coated

insulators are completely maintenance

free.”

• Additional advantages like reduction in

leakage current, saving due to reduction

in maintenance cost, etc. can be

considered as an additional gain”

Tata Power CGPL paper “Experiences with Gen-4 RTV Coating” can be provided upon request. Please contact the speaker at +91.98715.16222 or [email protected]

mailto:[email protected]



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9. Transmission Lines: Field testing in India

Year Location Details

2008 Delhi Transco,Mandola 220kV

Fully Flashed-over strings, coated with Gen-4 RTV HVIC and installed on Flashover Prone part of Line

2009 PGCIL, 400kV Hisasar-Bawana line

Fully Flashed-over string, coated and installed on flashover prone part of line, near brick kilns

2010 Punjab Transco, 220kV & 66kV

Coating on failed anti-fog insulators in highly flashover-prone area near dye factories

2010 PGCIL WRTS-2/Kawas Haldarwa220kV

500 Field Aged insulators (15 years old) coated and installed in flashover-prone Kawas-Haldarwa CKT-1.

2011 Indian Railways, 132kV: Pilot Project

4,500 discs on highly flashover prone line in North India

All field trials have been successful.



9a. Field Trials on Field-Aged & Flashed Over Insulators

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PGCIL: Field Tests on Flashed Over and Aged Insulators Delhi Transco: Field Tests on Flashed Insulators



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10. Comparing Corona on Uncoated & Gen-4 Coated Insulators (UV Cam)

View Video Online

https://www.youtube.com/watch?v=NLZRZ6mYd2M



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11. Northern Grid Collapse: Jan 2010

Incident Description:

• Line tripping during dense winter fog (DEC-FEB) is a common feature in Northern region

• Northern Grid partially collapsed in 2007 due to pollution flashover

• On 02 JAN 2010, Northern Region (NR) experienced a grid disturbance in which power supply in

Punjab, North Haryana, HP, J&K & Chandigarh sub-system was affected.

• The incident was initiated to fog related tripping/ flashovers. [2]

If Gen-4 RTV Coatings had been Deployed…

• Considering no known failures of GEN-4 RTV Coating have been reported despite widespread

global deployment even in coastal conditions where weekly flashovers reported pre-coating, it is

near-certain that even dense fog would not result in pollution flashovers.

• NORTHERN GRID would not have collapsed had Gen-4 RTV Coating been applied

[2] CEA Report Of The Inquiry Committee On Grid Disturbance In Northern Region On 2nd January 2010, published June 2010



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11 a. Northern Grid Collapse: CEA Recommendations [3]

Recommended Remedial Measure Impact of Gen-4 RTV Coating

Replacement of Insulators Not Required

Routine Cleaning of Insulators Not Required

Shutdown of lines in order to facilitate insulators replacing/cleaning Not Required

Effective and experienced personnel should be made available particularly at important stations during foggy nights

Unrealistic, not required

Real-time Monitoring of Humidity & Temperature of Different Locations Not Required

Deployment of Additional manpower during night shifts Not Required

Classification of Pollution Levels Not Required, RTV Robust enough to handle extreme pollution

Banning brick kilns, industrial units or biomass/diesel based power plant with < 30 meter chimney to be set up within 0.5 km of the 220 kV + line

Method would further complicate ROW challenges. Not Required

Ensure availability of O&M and senior officers at all strategic locations if forecasted RH > 85-90% and temperature likely to fall below 15-17°C

Unrealistic, not required

[3] The Central Electricity Authority vide order no. CEA/5-41 (07)/Secy-2009 dated 08-01-2010 (Annexure-1/III) constituted a Committee to inquireinto the grid incident and ascertain the cause of grid disturbance and suggest remedial measures to avoid recurrence of such incidents.Recommendations u/s 9.4 were stated as are listed above



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12. RTV on HVDC: Operational Experience

• “Application of RTV hydrophobic coatings has contributed to the

achievement of the low pollution flashover rate.

• Insulation strength, after application of coatings has improved”

800KVDC: EXTERNAL INSULATION, INSULATION COORDINATION, TEST Levels, D. Wu, U. Åström, V. F Lescale, ABB

Power Systems, HVDC Ludvika, Sweden as presented at IEC/CIGRE UHV Symposium Beijing 2007-07-23

• In Italy, more than 2,000 RTV pre-coated toughened glass insulators have

been installed on HVDC lines after more than 4 years showing satisfying

performance

• Refurbishment of existing DC lines and future upcoming DC interties could

rely on RTV pre-coating technology

• RTV pre-coating could be the right answer to very polluted environments

DC-toughened glass insulators pre-coated with RTV silicone rubber – field returns from aged samples installed on HVDC lines;

M. Marzinotto, G. Lavecchia, M.R. Guarniere, A. Posati, M. Rebolini, Terna Rete Italia – TERNA Group, J-M. George, S. Prat,

SEDIVER



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13. RTV Coatings on Air Core Reactors

• A combination of light pollution and

moisture causes:

– Discharges between the windings/coils

– Tracking of the fibreglass support structure

short circuiting the windings

– inductance to be ineffective

• Under polluted operating environments

– Tracking could occur on the surface of an AC

stressed reactor winding

– Anti-tracking coating is applied on the winding

surface

– TRENCH, Installation & Maintenance Manual for Dry-Type Reactors

• “Reactors shall be finished with a uniform

RTV coating on its exposed surfaces”: – ESKOM Specification for Air Core Reactors



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14. Long Term Performance of RTV Coatings

UV Resistant therefore long outdoor life

Proven record with Pacific Gas & Electric, USA having 25+ years of

using RTV coating on 500kV bushings and insulators.

(These bushings were in a highly polluted area that previously

required routine washing)

Expected life: At least 20 years in most service conditions



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15. Silicones for Corrosion Prevention



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15. Silicones for Corrosion Prevention



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16. Conclusion

• RTV Coatings are tried and tested in switchyards with a 100%

performance record, even in H-VH pollution levels

• Considering line outages are not required for maintenance of RTV

Coated insulators unlike for SRIs, true uptime and TCO is more

favorable for RTV Coated insulators vis-à-vis SRIs

• RTV Coating is therefore a realistic and viable option for insulators

all Overhead Lines, up to 1200kV

• Methods for in-situ application (off line) on up to 400kV lines are

being developed which could further reduce downtime

Gridtech 2015 CIGRE B2: Enhancing Grid Reliability with Gen-4 RTV Silicone Insulator Coatings in...

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