In 2004, a 132kV substation situated 600 metres from the South African coastline received a single application of RTV silicone insulator coating. Before that application, the substation experienced flashovers on an annual basis. In February 1999, it had survived a catastrophic Type B instantaneous pollution event — the kind of event that takes substations offline, damages equipment, and costs utilities far more than any planned maintenance programme. After the 2004 coating application, the substation recorded zero flashovers over the next 18 years. That included surviving another catastrophic coastal pollution event in February 2006.
Duinefontein is not a laboratory result. It is not a manufacturer’s claim. It is a documented Southern African proof point for RTV insulator coating Southern Africa’s utilities can build specifications around. This article explains what happened at Duinefontein, why it happened, and what it means for every substation and transmission line operating in Southern Africa’s contaminated environments today.
Why Southern Africa’s Insulators Face a Unique Threat
No two pollution environments in Southern Africa are identical, but every one of them presents a serious and ongoing threat to unprotected high voltage insulators. Understanding the specific threat in each corridor is the starting point for any credible insulator maintenance strategy.
The KwaZulu-Natal coastline exposes insulators to constant marine salt aerosol. Salt deposits are highly conductive and accumulate rapidly on insulator surfaces, particularly during offshore wind events. The Western Cape marine zone presents similar conditions, with the added challenge of significant seasonal fog that activates surface contamination without visible rainfall. Duinefontein sits in precisely this environment — coastal salt, fog events, and high humidity creating the conditions for rapid leakage current development on unprotected surfaces.
Inland, the Highveld industrial corridor from Mpumalanga through Gauteng exposes insulators to decades of accumulated airborne pollution from coal-fired generation, heavy industry, and vehicle emissions. The Northern Cape combines extreme UV radiation with high dust loading from arid terrain and mining operations. Limpopo and the North West province add further mining-related fallout to the contamination picture.
Beyond South Africa’s borders, the threat is equally serious. Zambia and the DRC’s Copperbelt corridor exposes transmission infrastructure to mining dust and industrial chemical fallout. Tanzania’s coastal industrial zones mirror the KwaZulu-Natal marine environment. Namibia’s coastal Benguela current zone generates persistent fog and salt aerosol along the entire Atlantic seaboard. In every one of these environments, the failure pathway for unprotected insulators is identical — contamination accumulates, moisture activates it, leakage current flows, dry band arcing develops, and flashover follows.
What RTV Silicone Coating Actually Does
The reason Duinefontein has recorded zero flashovers since 2004 is not complicated. It comes down to a single surface property: hydrophobicity.
An uncoated porcelain or glass insulator is hydrophilic. When moisture contacts it — whether from rain, fog, dew or condensation — that moisture spreads across the surface as a continuous film. If contamination is present, that film dissolves soluble salts and becomes electrically conductive. Leakage current flows across the surface. The current dries sections unevenly, creating dry bands. Arcing occurs across those dry bands. In severe contamination events, that arcing escalates into full flashover.
RTV silicone coating changes the surface fundamentally. A correctly applied silicone coating causes water to bead and run off rather than spreading as a film. Contamination on a hydrophobic surface cannot dissolve into a continuous conductive layer. Consequently, the leakage current pathway is broken before it begins. Dry band arcing cannot develop. Flashover cannot occur.
Furthermore, silicone chemistry has a property that no other coating technology offers: hydrophobicity transfer. Low molecular weight silicone components migrate from the cured coating into contamination deposits that accumulate on the surface over time. The contamination layer itself becomes hydrophobic. This means the coating continues to protect even as pollution builds — rather than being overcome by it as contamination levels rise.
In light rainfall, this hydrophobic surface acts as a self-cleaning mechanism. Loose contamination is carried away by water running off the surface in discrete droplets. This reduces the rate of contamination accumulation and, in many environments, significantly extends the interval between any required maintenance interventions.
The Koeberg Test Station Data
Duinefontein is the field proof. Koeberg provides the independent laboratory confirmation.
Testing at the Koeberg Insulator Pollution Test Station — one of Southern Africa’s most credible independent insulator testing facilities — produced results that engineers can cite directly in maintenance specifications and procurement documents. RTV silicone coated porcelain produced only 27% of the leakage current recorded on uncoated porcelain, and 56% of that recorded on silicone rubber composite insulators.
These are not marginal improvements. Reducing leakage current to 27% of the uncoated baseline means that the conditions required for dry band arcing and flashover are dramatically harder to achieve on a coated insulator. Combined with the Duinefontein field data, the Koeberg results give Southern African utilities two independent, locally generated data sets to support RTV insulator coating specifications.
The 30-Year Cost Case
The Duinefontein proof point settles the performance question. The 30-year cost comparison settles the financial one.
RTV coating is the most competitive long-term solution, significantly lowering total maintenance costs compared to washing or greasing. Because it can be applied under de-energised conditions, power shutdown costs can be excluded from the annual maintenance cost computation. Over a 30-year asset lifecycle, greasing costs are approximately eight times that of silicone rubber coating.
The cost drivers behind this gap are straightforward. Washing requires repeated planned outages, maintenance teams, specialised equipment, and water at pressure. It must be repeated annually or more frequently in high-contamination environments. Each wash cycle resets the contamination level but does nothing to change the hydrophilic surface behaviour that makes the insulator vulnerable in the first place. Greasing requires similar outage frequency, is labour-intensive to apply correctly, degrades over time, and accumulates contamination within the grease layer itself — creating its own maintenance problems.
A single application of RTV silicone coating during a planned outage delivers more than 15 years of continuous hydrophobic protection. One outage. One application. Fifteen or more years before recoating is required. For utilities managing large insulator populations across substations and transmission lines in Southern Africa, that difference in maintenance frequency translates directly into fewer planned outages, lower labour costs, reduced safety exposure for maintenance teams, and a significantly lower total cost of ownership over the asset lifecycle.
SI-COAT 570hs: What Separates It From Competitive HVICs
Not all RTV insulator coatings are equal. SI-COAT 570hs from CSL Silicones is the product that coated Duinefontein, and it is technically differentiated from competitive products in ways that directly affect long-term field performance.
The foundation of SI-COAT 570hs is its patented alumina trihydrate (ATH) particle technology. ATH is essential in HVIC formulations because it protects the coating from tracking — the progressive surface degradation caused by electrical activity along the coating surface. However, the performance of ATH is critically dependent on particle size. CSL Silicones’ patent is built on the discovery that a 13-micron ATH particle size is optimum for both tracking resistance and long-term hydrophobicity maintenance. Competitive products use sub-micron ATH particles that are far from this optimum, compromising long-term performance.
SI-COAT 570hs is supplied ready to use — no thinning, no excessive mixing, and no additional preparation before application. This is a practical advantage in the field, where product consistency directly affects coating quality and therefore service life. It applies to glass, porcelain, HTV silicone, LSR silicone and EPDM insulators without primer, across AC and DC systems at all voltage levels from distribution through to very high voltage transmission.
Independent performance testing confirms what Duinefontein demonstrated in the field. SI-COAT 570hs has passed 5,000 hours of UV and salt fog accelerated weathering with no degradation, the Inclined Plane Tracking and Erosion Test to IEC 60587, and the CEA 100-hour boiling water adhesion test. Its service life exceeds 15 years under Sub-Saharan African field conditions.
SI-COAT 570hs is available across Sub-Saharan Africa exclusively through Technical Solutions Supplies. For full technical specifications, visit the SI-COAT 570hs product page or the SI-COAT 570hs FAQ.
Frequently Asked Questions About RTV Insulator Coating in Southern Africa
What causes insulator flashover in polluted environments?
Insulator flashover in polluted environments results from a sequence of conditions that begin with contamination accumulation on the insulator surface. When moisture — from rain, fog, dew or condensation — contacts a contaminated insulator surface, soluble salts dissolve into a conductive electrolytic film. Leakage current flows across that film. The current generates heat and dries sections of the surface unevenly, creating dry bands. Arcing occurs across those dry bands, and in severe contamination events that arcing escalates into full flashover. Southern Africa’s coastal, industrial, mining and arid environments all accelerate the contamination accumulation that drives this process.
What is the difference between washing, greasing and RTV coating insulators?
Washing removes contamination temporarily but does not change the hydrophilic surface behaviour of porcelain and glass insulators. Contamination reaccumulates after every wash and the risk cycle repeats. Greasing applies a hydrophobic layer that provides temporary protection, but grease degrades over time and must be reapplied frequently — at a 30-year lifecycle cost approximately eight times that of RTV coating. RTV silicone coating creates a permanent hydrophobic surface that lasts 15 or more years from a single application. It also transfers hydrophobicity to accumulating contamination layers, maintaining protection as pollution builds rather than being overcome by it.
How long does RTV silicone insulator coating last?
SI-COAT 570hs delivers more than 15 years of hydrophobic surface protection under Sub-Saharan African field conditions. The Duinefontein 132kV Substation, coated in 2004, recorded zero flashovers over 18 years following application — including surviving a catastrophic coastal pollution event in 2006. Independent accelerated weathering testing confirms no degradation after 5,000 hours of combined UV and salt fog exposure.
Is RTV coating better than silicone grease for insulators?
For long-term insulator protection, RTV silicone coating significantly outperforms silicone grease on both performance and cost grounds. Grease must be reapplied frequently, accumulates contamination within the grease layer over time, and costs approximately eight times more than RTV coating over a 30-year asset lifecycle. RTV coating creates a permanent bonded hydrophobic surface that does not degrade, does not require frequent reapplication, and transfers hydrophobicity to contamination deposits rather than trapping them. For utilities managing large insulator populations across Southern Africa, the cost and performance case for RTV coating over greasing is unambiguous.
What is hydrophobicity transfer and why does it matter?
Hydrophobicity transfer is a property unique to silicone chemistry. Low molecular weight silicone components migrate from the cured RTV coating into contamination deposits that accumulate on the insulator surface over time. This makes the contamination layer itself hydrophobic — meaning moisture cannot dissolve the contamination into a conductive film even as pollution builds. No other insulator coating technology offers this property. It is the reason RTV silicone coated insulators continue to perform in heavily polluted environments where other coating technologies would be overwhelmed by accumulating contamination.
Can RTV insulator coating be applied to glass and porcelain insulators?
Yes. SI-COAT 570hs applies directly to glass, porcelain, HTV silicone, LSR silicone and EPDM insulators without requiring a primer. It is suitable for both new insulators before energisation and existing insulators during planned maintenance outages or live-line application by trained applicators. It can also be applied as a refresh coat over old silicone HVICs, provided the existing coating is thoroughly cleaned and still demonstrates strong adhesion to the insulator surface.
What pollution environments is RTV insulator coating suitable for in Southern Africa?
SI-COAT 570hs is designed for use across the full range of Southern Africa’s pollution environments. These include coastal marine salt zones along KwaZulu-Natal, the Western Cape and Namibia’s Atlantic seaboard, industrial pollution corridors on the Highveld and in Mpumalanga, mining fallout environments in the Northern Cape, Limpopo, Zambia and the DRC Copperbelt, arid dust environments in the Northern Cape and Namibia, and cement dust and agricultural chemical environments across the broader region. It is also suitable for desert sand environments and performs across AC and DC systems at all voltage levels. For an overview of how Southern Africa’s transmission infrastructure challenges relate to insulator protection, see our article on new substation commissioning.
How much does insulator flashover cost utilities?
The direct costs of an insulator flashover event include equipment damage — potentially including transformer failure — emergency repair and replacement costs, loss of generation capacity during the outage, and the knock-on consequences of unplanned grid disruption. In Southern Africa’s transmission environment, where substations are unlocking thousands of megawatts of renewable generation capacity, the indirect costs of a single flashover on a critical substation can far exceed the direct equipment damage. The cost of applying SI-COAT 570hs to every insulator on a substation is a fraction of the cost of a single transformer replacement — and a smaller fraction still of the generation revenue lost during an unplanned outage. For detailed guidance on corrosion and coating protection for transmission infrastructure, see our related article on anti-corrosion coating for structural steel.
Protect Your Insulators With Southern Africa’s Proven RTV Coating
Duinefontein proved it in 2004. Koeberg confirmed it in independent testing. Eighteen years of zero flashovers on a substation 600 metres from the ocean is the most compelling RTV silicone insulator coating case study Southern Africa has produced.
SI-COAT 570hs from CSL Silicones is a high solids RTV silicone HVIC built on the same proven silicone chemistry — engineered specifically for Southern Africa’s coastal, industrial, mining and arid pollution environments. It is available across Sub-Saharan Africa exclusively through Technical Solutions Supplies. Whether you are commissioning new transmission infrastructure, planning a scheduled maintenance outage, or managing a high-risk insulator population in a coastal or industrial environment, our team can advise on the right application approach for your project.
Contact TSS today to discuss your insulator protection requirements.