SI-COAT 570 HVIC High Voltage Insulator Coating: Frequently Asked Questions
What is SI-COAT 570 HVIC and what does it do?
SI-COAT 570 HVIC is a room temperature vulcanising RTV silicone high voltage insulator coating manufactured by CSL Silicones. It prevents pollution induced flashover on high voltage insulators, transformer bushings, switchgear, busbars and substation equipment by maintaining a permanently hydrophobic surface that stops moisture from forming a conductive film over contamination deposits. Furthermore, it transfers hydrophobicity to accumulated contamination over time, meaning it continues to perform as pollution builds rather than being overwhelmed by it. One application before energisation or during a planned maintenance outage delivers more than 15 years of maintenance free flashover protection in the most contaminated environments in the world.
What is a pollution induced flashover and how does it occur?
A pollution induced flashover is an electrical discharge across the surface of a high voltage insulator caused by a conductive contamination layer on the insulator surface. The mechanism follows a predictable sequence that utility engineers recognise worldwide.
Contamination first accumulates on the insulator surface over time. Salt aerosol from coastal environments, industrial emissions, dust from mining and arid terrain, agricultural chemicals and cement dust all deposit as dry layers on porcelain, glass or composite insulator surfaces. In dry conditions this contamination layer is not conductive and presents no immediate risk.
The danger begins when moisture contacts the contaminated surface. Rain, fog, dew and condensation wet the contamination layer and dissolve the soluble salts and chemicals within it, forming an electrolytic solution across the insulator surface. This solution is conductive. Leakage current begins to flow across the surface from the energised conductor toward earth.
As leakage current flows, it heats the surface unevenly. Some areas dry faster than others, forming dry bands. The leakage current path concentrates across these dry bands, generating localised voltage stress. This produces dry band arcing, which is the characteristic crackling and sparking visible on heavily contaminated insulators under wet conditions.
Dry band arcing progressively tracks and erodes the insulator surface. As the arcing extends, the surface resistance falls further and leakage current increases. Under sufficient contamination and wetting, this process culminates in a full flashover, a complete electrical discharge across the insulator surface that trips the line or piece of equipment, can damage or destroy the insulator, and in severe cases damages associated equipment including transformers and circuit breakers.
What is hydrophobicity and why does it matter for insulator performance?
Hydrophobicity is the property of a surface that causes water to bead and run off rather than spreading into a continuous film. A hydrophobic insulator surface fundamentally changes the flashover mechanism because moisture cannot form the continuous conductive film that activates the contamination layer into an electrolytic solution.
On a hydrophobic surface, water droplets form discrete beads that roll off the insulator rather than spreading. Even when contamination is present on the surface, the moisture required to dissolve that contamination and create a conductive leakage pathway cannot spread uniformly. The electrical resistance of the surface remains high. Leakage current does not develop. Dry band arcing does not occur. Flashover cannot follow.
SI-COAT 570 HVIC provides permanent hydrophobicity to porcelain, glass and composite insulator surfaces through the silicone chemistry of the cured film. Silicone is hydrophobic at the molecular level. Furthermore, SI-COAT 570 HVIC transfers this hydrophobicity to contamination deposits that accumulate on the coated surface over time, through the migration of low molecular weight silicone components into the contamination layer. This hydrophobicity transfer property is unique to silicone chemistry and is what distinguishes RTV silicone coating performance from all other insulator protection methods.
What is the difference between RTV and HTV silicone for insulator coatings?
RTV stands for room temperature vulcanising. HTV stands for high temperature vulcanising. The difference relates to the curing mechanism of the silicone material.
HTV silicone requires elevated temperatures to cure, typically above 150 degrees Celsius, making it suitable for factory manufacture of composite insulators where the material is processed under controlled conditions. It cannot be applied in the field to existing insulators.
RTV silicone cures at ambient temperature and humidity, making it suitable for field application to existing porcelain, glass or composite insulators whether they are new, in service, or being maintained. SI-COAT 570 HVIC is an RTV silicone coating. This means it applies in the field, cures without any heat source, and delivers the same fundamental silicone hydrophobicity and contamination resistance as factory vulcanised HTV composite insulators.
What is the difference between RTV silicone coating and silicone grease for insulators?
Silicone grease has been used as an insulator protection method since the 1960s. It provides initial hydrophobicity by coating the insulator surface with a viscous silicone fluid. However, it carries fundamental performance limitations that RTV coating does not.
Silicone grease absorbs contamination into the grease layer rather than encapsulating it as hydrophobic particles. Over time, as the grease becomes saturated with contamination, its effectiveness deteriorates. Grease typically requires reapplication every six to twelve months in contaminated environments, generating repeated maintenance cycles with their associated access costs, outage requirements and labour costs.
RTV silicone coating cures to a solid elastomeric film on the insulator surface. This film encapsulates contamination particles and transfers hydrophobicity to them through low molecular weight silicone migration, rather than absorbing the contamination into a sacrificial layer. The result is a coating that maintains its hydrophobicity and flashover protection performance for 15 or more years rather than six to twelve months. Furthermore, the solid cured film does not slump, run or migrate off the insulator surface under the influence of gravity or wind, as liquid grease can in hot conditions.
What is the difference between RTV silicone insulator coating and live line washing?
Live line washing uses high pressure water to remove contamination from energised insulators and is widely used by utilities as a short term flashover prevention measure. It is effective at removing accumulated contamination in the immediate term but carries significant limitations as a long term strategy.
Washing requires specialised equipment, trained personnel, and strict safety protocols. There is an inherent risk of flashover during the washing process itself if the water stream creates a conductive bridge across an insufficiently contaminated insulator. Furthermore, washing removes contamination temporarily but does not change the hydrophilic nature of the insulator surface. Contamination begins reaccumulating immediately after washing. Washing programmes therefore become an ongoing operational cost with no end point.
RTV silicone coating changes the fundamental surface property of the insulator, making it permanently hydrophobic. A coated insulator does not need to be washed because the hydrophobic surface prevents moisture from activating contamination deposits into conductive pathways in the first place. One application eliminates the need for repeated washing cycles for 15 or more years, replacing an ongoing operational cost with a single capital maintenance investment.
What voltage levels is SI-COAT 570 HVIC suitable for?
SI-COAT 570 HVIC is suitable for all voltage levels used in transmission and distribution systems. Applications range from medium voltage distribution at 11kV through to extra high voltage transmission at 400kV and 765kV. It applies to all insulator types at all voltage levels including pin insulators, disc suspension strings, post insulators, hollow core bushings, long rod insulators, and composite insulator strings. The silicone chemistry of the coating provides electrical insulation performance that does not compromise the dielectric properties of the underlying insulator at any voltage level within the normal operating range of transmission and distribution systems.
What insulator types can SI-COAT 570 HVIC be applied to?
SI-COAT 570 HVIC applies to porcelain insulators, toughened glass insulators and composite polymer insulators. It is suitable for all standard insulator profiles and geometries used in transmission and distribution systems including disc suspension strings, station post insulators, line post insulators, hollow core bushings on transformers and circuit breakers, long rod insulators, and pin type insulators. It also applies to busbars, switchgear components and other high voltage equipment surfaces requiring contamination protection.
Can SI-COAT 570 HVIC be applied to energised equipment without taking it out of service?
Yes. SI-COAT 570 HVIC can be applied to energised high voltage equipment by trained live-line applicators using approved live-line work methods. This eliminates the need for planned outages during application, which is a significant operational and commercial advantage for utilities where outage scheduling is constrained by network loading, customer supply requirements or regulatory obligations.
For new substation projects, application before energisation is recommended as the most straightforward and cost effective approach. For existing substations and transmission infrastructure where outage scheduling is difficult, live-line application allows the full insulator population to be coated without any interruption to network operation.
How is SI-COAT 570 HVIC applied?
SI-COAT 570 HVIC applies by brush or spray to clean, dry insulator surfaces. The application process involves cleaning the insulator surface to remove existing contamination, loose material and any previous grease treatments, then applying the coating to achieve the specified dry film thickness across the full insulator profile including shed undersides and shed roots where contamination and leakage current concentrate.
The coating cures at ambient temperature and humidity without any requirement for elevated temperature or forced curing. Cure to a tack free surface occurs within approximately two hours under ambient conditions. Full cure develops within 24 hours. Application can proceed at any ambient temperature above approximately 5 degrees Celsius provided the insulator surface is dry and free from condensation.
How long does SI-COAT 570 HVIC last?
Under field conditions in contaminated environments including coastal, industrial, desert and mining environments, SI-COAT 570 HVIC provides a service life exceeding 15 years without recoating. Field performance data from utilities worldwide, including applications in the UAE, Italy, South Africa, and across Sub-Saharan Africa, confirm 15 year plus performance in environments ranging from severe coastal salt contamination to extreme desert dust loading.
The Duinefontein Substation in the Western Cape of South Africa provides a particularly well documented example. Prior to RTV silicone coating application, the substation experienced annual flashovers despite regular maintenance. Following coating application in 2004, no flashovers occurred across 18 subsequent years including during a severe pollution event in 2006 that caused flashovers on uncoated insulators at nearby facilities.
What environments is SI-COAT 570 HVIC most effective in?
SI-COAT 570 HVIC delivers its greatest performance advantage in contaminated environments where unprotected insulators face the highest flashover risk.
Coastal environments are among the most demanding for insulator performance globally. Salt aerosol deposits from the sea create highly conductive contamination layers on insulator surfaces. The KwaZulu-Natal coastline, Western Cape, coastal Namibia and Mozambique all present severe coastal contamination conditions for transmission and distribution infrastructure.
Industrial environments around mining operations, chemical plants, smelters and power stations generate airborne pollutants including sulphur dioxide, cement dust, fly ash and chemical aerosols that deposit on insulator surfaces and create conductive contamination at accelerated rates compared to rural environments.
Desert and arid environments in the Northern Cape, Namibia, Botswana and across the Sahel generate dust storms that deposit heavy non-soluble contamination on insulator surfaces. While dust alone is less immediately conductive than salt, it creates a surface that holds moisture more effectively when wetting occurs, accelerating the flashover mechanism significantly.
Mixed pollution environments where coastal, industrial and dust contamination combine present the most severe conditions for insulator performance and generate the highest flashover frequency on uncoated insulators.
What is the cost of a flashover event on a substation or transmission line?
The direct and indirect costs of a flashover event on transmission infrastructure are substantial and extend well beyond the immediate repair cost.
Direct costs include the replacement or repair of damaged insulators, which can range from a few thousand rand for individual disc insulators to several hundred thousand rand for bushings on large power transformers. If the flashover causes a transformer fault, transformer repair or replacement costs can reach tens of millions of rand per unit.
Indirect costs include the cost of unplanned generation disconnection from the grid if the flashover trips a substation servicing a wind farm or solar plant. Load shedding penalties or supply interruption compensation where applicable under licence conditions. Emergency maintenance mobilisation at premium rates. The reputational and regulatory consequences of supply interruptions on major industrial customers.
The cost of applying SI-COAT 570 HVIC to the full insulator population of a substation is a fraction of the cost of a single transformer replacement. Against the background of South Africa’s R26 billion transmission expansion programme, protecting every new substation insulator population from day one with RTV silicone coating is not a discretionary maintenance decision. It is a commissioning requirement for reliable operation.
Why is insulator flashover a particular problem in South Africa and Sub-Saharan Africa?
South Africa and Sub-Saharan Africa present a combination of contamination conditions that make pollution induced flashover a more frequent and more severe problem than in many other parts of the world.
The coastal zones of KwaZulu-Natal, the Western Cape, coastal Namibia and Mozambique combine high salt aerosol deposition with high UV radiation and high humidity, all of which accelerate contamination accumulation and insulator surface degradation.
The industrial Highveld corridor in Gauteng, Mpumalanga and Limpopo carries decades of accumulated industrial pollution from coal fired power generation, mining and heavy industry, creating airborne contamination levels that approach the most severe industrial pollution categories in the international classification system.
The arid interior of the Northern Cape, Botswana, Namibia and the Sahel generates extreme dust loading on insulator surfaces in transmission corridors serving new renewable energy developments.
Furthermore, South Africa’s transmission grid is ageing, and the new transmission infrastructure being built to connect renewable energy capacity is going into some of the most contaminated corridors in the country. Left unprotected, the insulator populations on this new infrastructure will begin generating flashover related outages within years of commissioning in the most contaminated zones.
How does SI-COAT 570 HVIC compare to replacing insulators with composite polymer insulators?
Composite polymer insulators have inherently hydrophobic silicone rubber housing material that provides the same fundamental contamination resistance as RTV coated porcelain or glass insulators. In new build applications where the design specifies composite insulators from the outset, they provide an effective solution.
However, replacing existing porcelain or glass insulator populations with composite insulators is a significantly more expensive and operationally disruptive option than applying RTV silicone coating to the existing insulator population. Full insulator replacement requires energised line work or outages, mechanical handling of the existing insulator strings, procurement of replacement units, and the associated civil and structural work on towers and substation structures.
Applying SI-COAT 570 HVIC to existing porcelain or glass insulators delivers the equivalent surface hydrophobicity to composite insulators at a fraction of the replacement cost, extends the service life of existing infrastructure without the capital expenditure of full replacement, and can be executed live-line without outages on existing in service equipment.
Does SI-COAT 570 HVIC require recoating after the initial application?
In most applications, recoating is not required for 15 or more years following correct initial application. The silicone chemistry of the cured film does not degrade under UV radiation, does not wash off in rain, does not slump in heat, and continues to transfer hydrophobicity to accumulated contamination deposits throughout the service life. Visual inspection at regular maintenance intervals confirms the coating condition and identifies any areas where mechanical damage may have compromised the film integrity.
In the event that recoating is required after the initial service life, the process involves cleaning the insulator surface and applying a fresh coat of SI-COAT 570 HVIC over the aged existing coating, without the need for removal of the original coating provided it retains adequate adhesion to the insulator surface.
What standards does SI-COAT 570 HVIC meet?
SI-COAT 570 HVIC meets the requirements of IEEE 1523, the IEEE Guide for the Application, Maintenance and Evaluation of Room Temperature Vulcanised RTV Silicone Rubber Coatings for Outdoor Ceramic Insulators. It also meets the performance requirements of IEC standards for RTV silicone coatings on outdoor high voltage insulators, and the relevant DL/T 627 standard for room temperature vulcanised silicone rubber anti-pollution flashover coatings. These standards cover hydrophobicity performance, tracking and erosion resistance, UV stability, adhesion, dielectric properties and long term field performance requirements.
Is SI-COAT 570 HVIC suitable for transformer bushings?
Yes. Transformer bushings are among the highest consequence insulation components in a substation because a bushing flashover can result in transformer fault, transformer fire or transformer destruction. In contaminated environments, bushing flashover is a well documented failure mode. SI-COAT 570 HVIC applies to porcelain and composite transformer bushings and provides the same permanently hydrophobic flashover protection that it delivers on line insulators and station post insulators. Application before energisation on new transformers or during planned maintenance outages on existing transformers is the recommended approach.
Is SI-COAT 570 HVIC suitable for switchgear and busbars?
Yes. SI-COAT 570 HVIC applies to the insulated surfaces of switchgear and to busbars in both indoor and outdoor substation environments. In substations where contamination penetrates into switchgear enclosures through ventilation and cable entry points, internal insulation surfaces can accumulate contamination that generates leakage current and tracking under humid conditions. SI-COAT 570 HVIC provides a protective hydrophobic coating on these surfaces that prevents the moisture activation of internal contamination deposits and eliminates the tracking and arcing failure mode.
Can SI-COAT 570 HVIC be applied to insulators on renewable energy infrastructure?
Yes. Solar photovoltaic farms, wind farms and their associated substation and transmission infrastructure present specific insulator contamination challenges. Solar farms in the Northern Cape and Karoo operate in high dust environments where soiling of both PV panels and insulator surfaces is a significant maintenance challenge. Wind farms in coastal zones face salt aerosol contamination on insulator surfaces throughout the generation equipment and substation. SI-COAT 570 HVIC applied to insulator populations on renewable energy substations from commissioning eliminates flashover risk and removes the insulator maintenance burden from operational budgets for the full expected service life of the renewable energy facility.
Where is SI-COAT 570 HVIC available?
SI-COAT 570 HVIC is manufactured by CSL Silicones and distributed exclusively across Sub-Saharan Africa by Technical Solutions Supplies. We supply throughout South Africa, Namibia, Botswana, Zimbabwe, Zambia, Mozambique, Tanzania, Kenya, Uganda, Rwanda, Angola, the Democratic Republic of Congo, Malawi, Madagascar, Mauritius, Eswatini and Lesotho.
We cover the full Sub-Saharan transmission and distribution network, from Eskom’s national grid and the SAPP regional interconnection through to rural electrification projects across Eastern and Southern Africa. We provide technical specifications, application guidance, product samples, applicator training and on site technical support for insulator coating projects of all sizes across the continent.
Who should I contact for a technical specification or project quote?
Contact Technical Solutions Supplies directly for project specific technical guidance, coating system specification and pricing.
Phone: 031 002 7376 Email: sales@tssupplies.co.za
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