This high voltage insulator coating FAQ answers the questions engineers and maintenance teams ask most about Si-COAT 570, made by CSL Silicones. It covers how the coating works, how to apply it, how long it lasts and where it fits. The data sheet and documents are on the product page.
High Voltage Insulator Coating: How It Works
What is Si-COAT 570 and what does it do?
Si-COAT 570 is a room temperature vulcanising (RTV) silicone high voltage insulator coating for insulators, bushings, busbars and switchgear. It keeps the insulator surface water repellent, so moisture cannot form a conductive film over the dirt. As a result, it prevents pollution flashover. According to CSL, it has more than 15 years of field service with zero failures.
How does a pollution flashover happen?
First, salt, industrial fallout or dust settles on the insulator. When it is dry, that layer does little harm. However, fog, dew or light rain dissolves the salts and turns the layer into a conductive film. Leakage current then flows, heats the surface unevenly and forms dry bands. Arcing starts across those bands, and in bad enough conditions it grows into a full flashover that trips the line or damages equipment.
What is hydrophobicity, and why does it matter?
A hydrophobic surface makes water bead and roll off instead of spreading. Because the water cannot form a continuous film, the dirt underneath stays dry and resistance stays high. Furthermore, silicone passes its water repellence into the dirt layer over time, as low molecular weight silicone migrates into it. That is why an RTV coating keeps working as pollution builds up. Our article on hydrophobicity explains this in more depth.
What is the difference between RTV and HTV silicone?
HTV silicone cures at high temperature, so it suits factory made composite insulators only. RTV silicone, by contrast, cures at ambient temperature and humidity. Therefore, it goes on in the field, over existing porcelain, glass or composite insulators.
How does an RTV coating compare with silicone grease?
Grease gives good water repellence at first, but it absorbs dirt as it ages. As a result, it needs regular reapplication, and the old grease has to come off each time. An RTV coating, on the other hand, cures to a solid rubber film that stays put in heat and wind. We supply both, including CSL 880 insulator grease, so we can help you choose.
How does it compare with insulator washing?
Washing removes the dirt for a while, but it does not change the surface. So contamination starts building up again straight away, and the washing programme never ends. A coated insulator, by contrast, stays water repellent between cleans, so washing becomes rare. Our article on insulator washing covers this in more detail.
Applying Si-COAT 570
What voltages and insulators does it suit?
CSL lists it for AC and DC systems at all voltage levels. It goes onto porcelain, toughened glass and composite insulators, including disc strings, post insulators, long rods, pin insulators and hollow core bushings. In addition, it suits busbars and switchgear surfaces.
Can it go on energised equipment?
CSL recommends applying it before energisation on new equipment, or during a planned outage on existing equipment. Any work near live equipment is the utility’s decision under its own safety rules.
How do you prepare the insulators?
First, wash them with high pressure water at 14 to 70 bar. Cement build up needs dry abrasive cleaning instead. If old grease is present, remove it completely, then wipe the surface with acetone followed by isopropyl alcohol.
How do you apply it?
Airless spray is the recommended method, although brush and dip also work. Aim for about 0.38 mm dry film (15 mil, 380 microns), and never less than 0.25 mm (10 mil). That works out to roughly half a litre per square metre, before losses. Also, cover the undersides of the sheds, where dirt and leakage current concentrate.
What conditions and cure times apply?
Do not apply below 5°C, and keep the surface at least 3°C above the dew point. At 25°C and 50% humidity, it skins in 20 to 25 minutes and is tack free in 30 to 40 minutes. Then it cures through in about 6 hours and reaches full properties in 7 days.
High Voltage Insulator Coating Performance
How long does it last?
As noted above, CSL reports more than 15 years of field service with zero failures. In service, the film handles minus 40°C to 250°C. Still, inspect it at normal maintenance intervals for mechanical damage.
What results has it given in the field?
In a CSL and GRUPO NTI case study from Chile, Si-COAT 570 went onto insulation, with Si-COAT 579CM on the transformer casings. For example, a 66 kV line at the Minera Algorta lithium mine near Antofagasta had suffered flashovers from saline contamination. Since 2019, it ran four years with no flashovers, and insulator cleaning dropped from monthly to once every four years. Similarly, Saesa near Osorno, on the southern coast, cut cleaning from monthly to once every three years, with no failures over three to four years. In addition, ENEL and TEN use it on 220 kV and 500 kV transformers in polluted areas.
What about other RTV coatings in South Africa?
RTV silicone coatings in general have a strong local record. At Duinefontein substation in the Western Cape, about 600 m from the sea, a 132 kV yard received an RTV coating from another manufacturer in 2004. Afterwards, it recorded no flashovers for 18 years. That result is not Si-COAT 570, but it shows what the technology does on our coast, as our article on RTV insulator coating explains.
Does it need recoating?
In most cases, not for many years. When it does, clean the surface and apply a fresh coat over the old film, provided the old coating still adheres well.
Which standards apply?
Film thickness follows IEEE 1523, the IEEE guide for RTV silicone coatings on outdoor ceramic insulators. In addition, the data sheet reports testing to IEC 62073 for water repellency, IEC 60587 for tracking and erosion, and IEC 61109 for UV and salt fog. It also lists IEEE 957 water blast adhesion, ASTM D149 dielectric strength, and CEA tracking wheel and boiling water tests.
Where It Fits
Which environments benefit most?
Coastal sites suffer most, because sea salt forms a highly conductive layer. The KwaZulu-Natal and Western Cape coasts, coastal Namibia and Mozambique are typical. Industrial areas near mines, smelters, cement plants and power stations add sulphur dioxide, fly ash and dust. Meanwhile, the Northern Cape, Namibia and Botswana bring heavy dust that holds moisture once it gets wet. Where these combine, flashover risk is highest. For mining sites, see our article on insulator coating for mines.
Why is flashover such a problem in South Africa?
We have all of those conditions at once: salty coasts, heavy industrial pollution on the Highveld, and dusty interior corridors. In addition, much of the grid is old, while new lines for renewable energy run through some of the dirtiest corridors. Without protection, insulators there can start causing flashover problems early in their life. The steel towers on those lines also corrode, as our article on transmission tower corrosion shows.
Is it suitable for transformer bushings?
Yes. A bushing flashover can lead to a transformer fault or even a fire, so bushings carry high consequences. It goes onto porcelain and composite bushings. Ideally, apply it before energisation on new transformers or during a planned outage on existing ones. Our article on shunt reactor insulator protection covers a similar case.
What about switchgear and busbars?
Yes, it suits both. Dirt that gets into enclosures through vents and cable entries can track across internal insulation in humid weather. A coat of Si-COAT 570 keeps those surfaces water repellent and stops that tracking.
Can it protect renewable energy substations?
It can. Solar farms in the Northern Cape and Karoo face heavy dust, while coastal wind farms face salt. Coating insulators at commissioning removes most of that maintenance load. See our article on insulator coating for renewable energy.
How does it compare with switching to composite insulators?
Composite insulators have silicone housings, so they resist pollution well and suit new builds. However, replacing existing porcelain or glass strings means outages, new hardware and handling work on towers. Coating the existing insulators gives a similar water repellent surface at a fraction of that cost.
What does a flashover cost?
More than the repair. On top of damaged insulators or bushings, a fault can trip generation, trigger supply penalties and call out emergency crews. If it damages a transformer, the cost multiplies. Coating a substation’s insulators costs far less than one transformer failure.
Supply and Support
Where is it available?
Technical Solution Supplies distributes CSL Silicones products across Southern Africa, including the DRC and the Seychelles. We offer technical specifications, application guidance, samples, applicator training and site support.
Who do I contact?
For a high voltage insulator coating specification or quote, phone 031 002 7376, email sales@tssupplies.co.za or use our contact page.
Proud exclusive distributor of CSL Silicones in Southern Africa.
Technical Articles:
- Shunt Reactor Insulator Protection: Preventing Flashover on Transmission Equipment
Shunt reactors keep South Africa’s transmission network stable. Consequently, they absorb excess reactive power on long, lightly loaded high-voltage lines. However, a shunt reactor insulator faces the same contamination risks as any outdoor high-voltage component. Over time, dust, coastal salt, and industrial pollution settle on the surface and form a conductive film. As a result, flashover threatens reactor bushings just as it threatens substation insulators and transmission tower hardware. What Shunt Reactors Do on the Grid Long transmission lines generate reactive power naturally, especially at night when demand drops. Engineers call this the Ferranti effect. As a result, voltage rises… Read more: Shunt Reactor Insulator Protection: Preventing Flashover on Transmission Equipment - High Voltage Insulator Coating South Africa: Everything You Need to Know About SI-COAT 570 HVICHigh voltage insulator coating is one of the most critical and most overlooked maintenance interventions in South Africa’s electrical infrastructure. Flashover events on contaminated insulators trip substations, shut down transmission lines, and plunge communities and industries into unplanned outages — often with no warning and at enormous cost. Yet the solution has been available for decades, proven at major South African substations, and grid operators, mining operations, and renewable energy developers across the continent are now applying it as they take insulator protection seriously for the first time. This article answers every key question about high voltage insulator coating in… Read more: High Voltage Insulator Coating South Africa: Everything You Need to Know About SI-COAT 570 HVIC
- Insulator Coating for Mines: Preventing Flashover on Africa’s Mine-Owned Power InfrastructureMining operations across Africa are no longer simply consumers of grid electricity. Persistent load shedding, ageing national grids, and the sheer scale of power demand at modern mining operations have pushed the sector toward generating and distributing its own electricity. Mines are building private substations, transmission infrastructure, and renewable generation facilities at a scale that rivals national utility projects, with single mining-sector substations now designed to handle gigawatt-scale capacity. This shift brings a new operational reality. Mines that once relied on a national utility to manage flashover risk, insulator maintenance, and contamination control now carry that responsibility themselves. An insulator… Read more: Insulator Coating for Mines: Preventing Flashover on Africa’s Mine-Owned Power Infrastructure
- RTV Insulator Coating Southern Africa: 18 Years of Proof at DuinefonteinIn 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… Read more: RTV Insulator Coating Southern Africa: 18 Years of Proof at Duinefontein
- South Africa’s New Transmission Grid: Why Every New Substation Needs High Voltage Insulator Coating From Day OneHigh Voltage Insulator Coating South Africa: Protecting the Transmission Grid from Day One South Africa is building transmission infrastructure at a scale not seen in a generation. Insulator coating decisions made on new substations today will determine whether that infrastructure performs reliably for decades or begins failing within years. Eskom has approved R26 billion in capital investment for transmission infrastructure, with 47 projects in development that will unlock 37 000MW of grid connection capacity between 2025 and 2033. New substations are rising across the Northern Cape, Western Cape, Eastern Cape and beyond. Every project engineer and asset owner must answer… Read more: South Africa’s New Transmission Grid: Why Every New Substation Needs High Voltage Insulator Coating From Day One
- Insulator Washing: Why Scheduled Maintenance Alone Is Not Enough to Prevent FlashoverSouth Africa recently passed 200 consecutive days without load shedding. Eskom credited disciplined planned maintenance as the primary driver of that milestone. Scheduled insulator washing is a core part of that maintenance discipline. In KwaZulu-Natal and Gauteng, utilities wash insulators during planned winter outages to remove contamination before the wet season. However, insulator washing alone does not change the surface behaviour of the insulator. Once contamination returns, the electrical risk returns with it. What Insulator Washing Actually Achieves Insulator washing removes accumulated contamination from porcelain, glass and composite insulator surfaces during a planned maintenance outage. In South Africa, this typically… Read more: Insulator Washing: Why Scheduled Maintenance Alone Is Not Enough to Prevent Flashover
- Transmission Tower Corrosion: Why Africa’s Power Grid Is One Rust Patch Away from CollapseOne of the 132 kV transmission towers that collapsed in January 2026. (Photo: Facebook / Nelson Mandela Bay Municipality) Transmission tower corrosion is one of the most underrated threats to electricity supply in Southern Africa. It builds up over years, gives plenty of warning, and is largely preventable. Yet when maintenance slips, the warning signs go unheeded until a tower comes down. Nelson Mandela Bay shows exactly how that plays out. What Transmission Tower Corrosion Does Most lattice towers have a hot dip galvanised coating. The zinc corrodes slowly in place of the steel and protects it for years. However,… Read more: Transmission Tower Corrosion: Why Africa’s Power Grid Is One Rust Patch Away from Collapse
- High-Voltage Silicone Coating for Power Plants – Stop Dust & FlashoverThe Challenge Inside Power Plants Coal-fired and thermal power stations are harsh environments for electrical equipment. Insulators and bushings are constantly exposed to dust, fly ash, coal soot, steam, and chemical contaminants. These pollutants settle on surfaces, creating conductive paths. Add moisture or condensation, and you have the perfect conditions for tracking, dry-band arcing, and flashover—leading to outages, costly repairs, and safety risks. Why Silicone Coating Is the Solution SI-COAT 570 HVIC is engineered to protect high-voltage components in the toughest conditions. Unlike traditional cleaning cycles or grease applications, silicone coatings provide long-term hydrophobic protection and resist contamination. Key Technical… Read more: High-Voltage Silicone Coating for Power Plants – Stop Dust & Flashover
- Hydrophobicity in High Voltage Insulator Coatings.Hydrophobicity in High‑Voltage Insulator Coatings: Why Si‑Coat 570 HVIC Matters Moisture and surface contamination are persistent risk factors for outdoor insulation. When a continuous water film forms on an insulator, it can create conductive paths, elevate leakage current, and increase the likelihood of surface tracking and flashover—especially under polluted or coastal conditions. A hydrophobic, silicone‑based high‑voltage insulator coating (HVIC) changes that surface physics: water beads and rolls off instead of wetting, and contaminants are far less able to dissolve into conductive electrolyte layers. What engineers mean by “hydrophobicity” Hydrophobicity quantifies water repellency. At the surface, the contact angle between a… Read more: Hydrophobicity in High Voltage Insulator Coatings.
- Silicone Insulator Coating Flashover Prevention – Why It WorksSilicone Insulator Coating Flashover Prevention – Why It Works Power utilities across Southern Africa face a growing challenge: silicone insulator coating flashover prevention is becoming essential to stop outages caused by contamination, moisture, and harsh environmental conditions. In coastal regions, salt spray accelerates leakage currents. In desert zones like Namibia, abrasive sand and dust create conductive paths. Traditional methods like washing or applying silicone grease offer temporary relief—but they require frequent maintenance and downtime, increasing operational costs. Why Silicone Insulator Coating Flashover Prevention Matters Flashovers can lead to outages, equipment damage, and safety risks. Silicone insulator coatings provide a long-term… Read more: Silicone Insulator Coating Flashover Prevention – Why It Works
- Infrared Electrical Imaging: Detecting Risks Before They Become Failures – How SI-COAT 570 HVIC Enhances ReliabilityThe Role of Infrared Electrical Imaging Infrared electrical imaging, or thermography, is a critical inspection tool for utilities and industrial operators. It uses thermal cameras to detect heat generated by electrical resistance. This helps spot hot spots on high-voltage equipment before they cause failures. The method requires no contact. As a result, technicians can scan live, energised equipment without shutting down a line or substation. This makes infrared electrical imaging one of the few inspection methods utilities can run on a routine schedule. It does not disrupt supply. Engineers commonly use temperature difference, or Delta T, to judge how urgent… Read more: Infrared Electrical Imaging: Detecting Risks Before They Become Failures – How SI-COAT 570 HVIC Enhances Reliability
- Protecting High-Voltage Equipment in Renewable Energy Projects with SI-COAT 570HSRenewable Energy Growth in South Africa South Africa is rapidly expanding its renewable energy infrastructure, including solar farms and wind power installations. However, these projects face unique challenges such as high-voltage equipment exposure to harsh weather, pollution, and coastal salt spray. Therefore, reliable insulation protection is critical for long-term performance. Why SI-COAT 570HS is Essential SI-COAT 570HS is a high-solids silicone insulator coating engineered for extreme environments. It provides superior electrical insulation, excellent hydrophobicity, and outstanding arc resistance, ensuring that power lines and substation equipment remain operational even under severe conditions. In addition, its UV stability and weatherproof properties make… Read more: Protecting High-Voltage Equipment in Renewable Energy Projects with SI-COAT 570HS
- Protect High Voltage Infrastructure with SI-COAT 570HSHigh-Voltage Insulating Coating for Arcing and Flashover Protection SI-COAT 570HS is a high-voltage insulating silicone coating designed to protect electrical infrastructure from arcing, tracking, and flashover. In high-voltage environments, contaminants like dust, moisture, and pollution can create conductive paths across insulators, leading to dangerous electrical discharge. This phenomenon — known as surface tracking — can escalate into flashover, causing equipment failure, fire risk, and costly downtime. 570HS forms a hydrophobic, non-conductive barrier that resists moisture and surface contamination. Its arc-resistant properties help prevent electrical discharge even under extreme conditions, making it ideal for substations, switchgear, transformers, and other exposed components.… Read more: Protect High Voltage Infrastructure with SI-COAT 570HS
