Epsilon G4 RTV Coating

What is
an RTV HVIC?

Epsilon G4 is a one-part ultra-hydrophobic UV-resistant coating that enhances an insulator’s surface properties to prevent the formation of a conductive layer even in the most polluted of environments. The HVIC is designed to protect AC and DC T&D insulators and Air Core Reactors (ACRs) from pollution flashovers. Considering the silicone coating is in liquid form, it takes the shape of any substrate or insulator that it is applied upon and imparts the long-lasting hydrophobic surface properties of a polymer insulator while retaining the mechanical strength of a ceramic insulator.

Essentially, an RTV Coating prevents the onset of leakage current and the formation of an electrically conductive path across the insulator due to its sustained property of hydrophobicity. 

Intended use

Coastal, Industrial and other forms of pollution are a major cause for leakage current, corona, arcing and flashovers on insulators, Air Core Reactors and metallic equipment. The application of G4 is a proven and 100% effective method to mitigate the risks of pollution and eliminate leakage current flashovers – while reducing or even altogether eliminating the need for insulator washing.
  • Ceramic, Porcelain, Glass and Composite Insulators
  • Air Core Reactors
  • Metallic Substrates
Coatings at 1200 kV AC and 800 kV HVDC
Pollution Flashovers are a crippling factor for any power delivery system, irrespective of voltage. The Epsilon G4 coating has a 100% flashover-elimination record on thousands of pieces of equipment on EHV and UHV AC of 400 kV, 765kV, 1200 kV as well as 500kV HVDC insulators and Air Core Reactors (ACRs)

Why G4 the best RTV HVIC

You could use less coating than a GEN-3 coating with ATH (Alumina Trihydrate) filler, and it would still perform as well, if not better.

ATH (Al2O3.3H2O), principally used as a smoke retardant in some silicone polymer blends, irreversibly breaks down at around 180ºC-200ºC due the heat generated under electrical arcing conditions and releases water of hydration. Water serves to cool the coating surface, and this works pretty well – but ATH in a layer of coating just a few microns thick is limited and with every temperature spike, more ATH breakdowns occur and coating mass drops …

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Time-to track
Two key attributes of a good Insulator coating are to (a) remain hydrophobic for as long as possible and (b) delay the onset of leakage current as much as possible. Therefore, “Time to Track” is often a purposely concealed critical phenomenon but provides a true insight into how effective an RTV HVIC coating really is.
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Thinner layers work

Epsilon G4 RTV can be applied at 300µ and work better than any other coating – big savings!

Even with half-coated insulators (coating on the ‘pin-side’) with a 300-micron coating layer, pollution performance has been demonstrated to withstand artificial salt fog tests at 400kV at a staggering 224kg/cu.m saline density. It is very unlikely that an RTV coating would ever encounter such pollution levels in the field – but is built to withstand it all the same. In contrast, a composite rubber insulator must pass this same test at 160 kg/cu.m salt fog density.

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The Classic Success Story

CGPL, TATA Power has a long history of excellence and will often over-spec equipment in the name of safety and best-engineering-practices. This is why design creepage opted for was 33 mm/kV and 35 mm/kV which is well above what is recommended by IEC 60815. Mundra, located in the coastal desert region of Kutch in India is arguably one of the harshest service environments in the world and with massive power plants and cooling towers in the vicinity – it doesn’t get tougher for an insulator!

LINKS: (a) Downloadable PDF Case study; (b) Paper authored by TATA Power

Superior Coverage area

Coverage area depends on a range of factors from % solids, insulator geometry, ambient conditions, applicator skill and method of application.
Factors Influencing Coating Coverage Area

Coating quantity usage for an intended film thickness depends on various factors, as stated below:

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The “price per kg” Trap

Most GEN-3 coatings contain “more solvent and less solids” that naturally reduces the “unit rate per kg”. You think you’re paying less per kg of coating, but actually all you’re doing is “paying more for solvent”! …
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Hydrophobic

Retention of hydrophobicity (the ‘tendency to repel water’) is a key performance indictor of an RTV HVIC for assessing field performance and ascertaining coating life. Checking hydrophobicity on a new insulator is usually meaningless, but a very simple way to check is by means of “Hydrophobicity Recovery Test”. The silicone coating sample is exposed to 100 hours of corona to completely destroy hydrophobicity, and then retested for hydrophobicity after a 48-hour recovery period. Look for “HC2” as a result at the least.

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Project planning and procedure documents are very good. Work completed with good quality and ensuring high safety standards and within timeline. Shutdown related work also completed within shortest communication time

Vasant PatelAdani Power Ltd. Mundra TPP, 2015

Our UPCL project was facing a major challenge of frequent pollution flashovers in the 220kV and 400kV switchyards, even though a higher design creepage was adopted.

Manoj PantSr. Vice President (EPC Engineering)

The deliveries and application were completed well within schedule and to the quality, workmanship and safety standards of our satisfaction

Ranjan K DasGeneral Manager

All procedures adopted by the vendor are well designed and project planning is good. Work carried out with full consideration of safety & within allocated time limit.
All expectations met

Vivek TidkeTATA POWER, 220kV, Trombay
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Why it’s better

You could use less coating than a GEN-3 coating with ATH (Alumina Trihydrate) filler, and it would still perform as well, if not better.

ATH (Al2O3.3H2O), principally used as a smoke retardant in some silicone polymer blends,irreversibly breaks down at around 180ºC-200ºC due the heat generated under electrical arcing conditions and releases water of hydration. Water serves to cool the coating surface, and this works pretty well – but ATH in a layer of coating just a few microns thick is limited and with every temperature spike, more ATH breakdowns occur and coating mass drops

Well, you could use more GEN-3 coating for a longer life – except that thicker coating layers hamper heat dissipation which is not a good sign.(Link: PDF: Dr. Suat Ilhan, Technical University of Istanbul paper)

A TGA(thermogravimetric analysis) will show ATH-filled coatings lose mass drastically starting at around 200ºC. GEN-4 coatings are not plagued with this “breakdown at 200ºC” problem and have almost a 2x better initial breakdown temperature. So, you could use 25% less thickness compared to a GEN-3 coating and still have nothing to worry about.

Interpreting the Graph

  • Irreversible breakdown of GEN-3 coatings with ATH starts at ~200 °C
  • Coating mass erodes
  • GEN-4 quartz-filled coatings lose mass only beyond 400 °C
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Time-to track

Two key attributes of a good Insulator coating are to (a) remain hydrophobic for as long as possible and (b) delay the onset of leakage current as much as possible. Therefore, “Time to Track” is often a purposely concealed critical phenomenon but provides a true insight into how effective an RTV HVIC coating really is.

When coated insulators are installed in a true vertical orientation, performance improvements of a GEN-4 quartz start out small and go all the way to being 800% better when in horizontal orientation!

A considerable number of insulator strings and switchyard insulators is installed at a slant.

  • Get the full paper as published in IEEE Explore here
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Thinner thickness

Our RTV Coatings can be applied over a wide range of With half-coated insulators (coating on the ‘pin-side’) with a 300-microns HVIC layer, pollution performance has been demonstrated to withstand artificial salt fog tests at 400kV at a staggering 224kg/m3 saline density. It is very unlikely that an RTV coating would ever encounter such pollution levels in the field – but is built to withstand it all the same.

A leading global insulator major jointly conducted various Artificial Pollution Performance Tests (IEC 60507) on their porcelain disc insulators after coating with Epsilon G4 coating to see whether performance could exceed the required 160 kg/m3 level for polymer insulators and uncoated insulators. The tests all passed at the highest pollution class, whether the discs were coated partially or fully, or at 300µ or 500µ DFT

  • • 120 kN discs 300µ DFT: salt density 224kg/m3
  • • 120 kN discs 500µ DFT: salt density 224kg/m3
  • • 160 kN discs 300µ DFT: salt density 224kg/m3
  • • 160 kN discs 500µ DFT: salt density 224kg/m3

This is 40% better pollution performance, and 40% less coating thickness

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Factors Influencing Coating Coverage Area

Coating quantity usage for an intended film thickness depends on various factors, as stated below:

Factors Uncontrollable during Outdoor RTV
Coating		Factors Controllable during Outdoor RTV
Coating
Voltage class
Design creepage
Equipment shape/geometry
Weather/wind conditions
Coating formulation
Viscosity
% solids
Type of filler(s)
ATH nozzle blockage
Skill/experience of the applicator(s)
Waste minimization procedures
Optimizing coating start/stops
Type of spray equipment used

Coating quantity usage for an intended film thickness depends on various factors, as stated below:

  • ATH filler is incompatible with the molecular structure of liquid silicone rubber and is not held in suspension in the one-part RTV liquid coating
  • Therefore, like silt in water, ATH rapidly settles at the bottom of the container
  • Large ATH particle sizes (>10 microns) settle more rapidly
  • Sedimentation of ATH particles results in inconsistency in the coating applied
  • ATH filler concentration at the bottom of the container causes clogging of spray nozzles

Therefore, 13µ ATH-filled RTV Coatings are more prone to wastage and a have a lower coverage area compared to Quartz filled HVICs

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The “price per kg” Trap

Most Gen-3 coatings sold in price-sensitive tender-driven markets are of the lowest grade from the suppliers’ product range that are tactically overfilled with solvent and with reduced silicone and solid %. This reduces the “unit rate per kg” having the buyer believe he is paying less per kg of coating whereas he is merely “paying more for solvent”! The solvent evaporates and the ‘coating coverage area comes down considerably’

Most Gen-3 RTV coatings sold in price-sensitive and tender-driven markets are of the lowest grade from the supplier’s product range that are overloaded with solvent that cost a fraction of what silicone does. However, the solvent evaporates in seconds and the ‘coating coverage area comes down considerably’ To put things in perspective, a 5-US gallon drum of regular GEN-3 coating overfilled with solvent weighs 21 kg. The same brand GEN-3 coating with higher solids (HS) % [upper price/performance range GEN-3 product sold in more quality-conscious markets] weighs 24 kg! An Epsilon Gen-4 HVIC 5-gallon pail weighs 24.25 kg (average weight)

Epsilon Gen-4 RTV coating has a significantly higher solid % and requires significantly less quantity than what would be required to complete the same job using a GEN-3 coating – even the high solid % one due to far less nozzle blockages and wastage.

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Hydrophobicity Simplicity

Retention of hydrophobicity (the ‘tendency to repel water’) is a key performance indictor of an RTV HVIC for assessing field performance and ascertaining coating life. Checking hydrophobicity on a new insulator is usually meaningless, but a very simple way to check is by means of “Hydrophobicity Recovery Test”. The silicone coating sample is exposed to 100 hours of corona to completely destroy hydrophobicity, and then retested for hydrophobicity after a 48-hour recovery period. Look for “HC2” as a result at the least.

Transmission grade equipment is meant to last long. Really long. And therefore, the coating on the Insulators needs to remain alive, hydrophobic and resistant to damaging UV rays for decades as well. Epsilon G4 RTV HVIC has a 20+ life in most outdoor service environments. Moreover, as recent joint testing with a global insulator major demonstrates, with coating just on the underside of the insulator works to stave off pollution flashovers. The underside of an insulator (pin side) is always will be better protected from UV because of the natural shade provided by the insulator profile/shed – this will further enhance the life of the G4 coating.

  • • Sterlite
  • • CGPL
  • • Adani
  • • GMR
  • • Trench

This is 40% better pollution performance, and 40% less coating thickness