This image was created with artificial intelligence – marked under Art. 50 of the AI Act, Regulation (EU) 2024/1689. It is a placeholder until the company's photos arrive.High-voltage applications: which plastics are suitable?
Which plastics are suitable for high-voltage applications? Everything about properties and materials such as PI, PEEK, PTFE & silicone.
Materials play a central role in electrical engineering, particularly when it comes to high-voltage applications. Whether in transformers, insulators or switchgear – the right choice of material determines safety, efficiency and longevity. Unlike applications in the low-voltage range, the focus here is on extreme requirements. The electrical fields are significantly stronger, the thermal loads higher and the consequences of material failure more serious.
Since plastics must reconcile both electrical and mechanical properties, their selection is regarded as a key factor for the safe operation of modern energy networks and industrial high-voltage systems. In this article you will receive a comprehensive overview of suitable plastics, their specific properties, practical examples and future developments.
Requirements for plastics in high-voltage applications
The requirements for plastics in the high-voltage range are diverse and highly complex. One of the central properties is electrical dielectric strength, i.e. the ability of the material to withstand high electrical fields without electrical breakdown occurring. Equally decisive is tracking resistance, which determines how resistant a surface is to conductive deposits and moisture. Resistance to partial discharges is also of great importance, since these tiny discharges can damage the material over many years.
In addition, plastics must be thermally stable, since high continuous and peak temperatures frequently occur in high-voltage systems. Dimensional stability must not be impaired by heat or mechanical forces.
A further aspect is environmental resistance: many components are permanently exposed to moisture, dust, salt spray or aggressive chemicals. Finally, ageing resistance also matters – the materials must reliably retain their properties over decades. Mechanical strength and machinability should not be underestimated either, since many components are exposed to high vibrations and mechanical loads.
Suitable plastics and their properties
Polyimide (PI)
Polyimide is regarded as one of the most capable insulating materials in the high-voltage range. It is temperature-resistant up to over 300 °C, has a high dielectric strength and is also flame-retardant. Polyimide films are frequently used as insulating material in electric motors, generators and transformers.
PI is also used in printed circuit board laminates, since it reliably insulates high voltages and is at the same time chemically resistant. One advantage is its low moisture absorption, which means the electrical properties remain stable even at high humidity. Furthermore, PI is used in aerospace projects where the highest voltage and temperature resistance are required.
Epoxy resins (EP)
Epoxy resins are among the most important thermosetting plastics in high-voltage engineering. They are used both as casting resins for encapsulating coils and switching elements and as insulating material in transformers. Their high mechanical strength makes them ideal for components that must not only insulate but also stabilise.
Modern epoxy resins can be modified with fillers in order to increase tracking resistance or thermal conductivity. A typical field of application is medium- and high-voltage switchgear, where epoxy resins are used for cast-resin insulators. In combination with glass-fibre reinforcements, composite materials are created that are excellent under both electrical and mechanical load.
Silicones (SI)
Silicone elastomers are a standard material for outdoor high-voltage insulators owing to their excellent weather resistance. They withstand UV radiation, ozone and large temperature fluctuations without appreciable ageing. They also have good resilience, which makes them particularly suited to flexible insulation solutions. Silicones have a high tracking resistance and, through their hydrophobic surfaces, reduce susceptibility to contamination.
Typical applications are long-rod insulators, cable terminations and housing seals in high-voltage switchgear. Silicones are also used in high-voltage test equipment, where they provide safe insulation under changing ambient conditions.
Polyethylene terephthalate (PET) and polyethylene naphthalate (PEN)
PET and PEN are thermoplastic polymers that impress with their good electrical insulation, dimensional stability and chemical resistance. PET films are used in capacitors, while PEN, thanks to even higher temperature and voltage resistance, is also used in more demanding applications.
Cable insulation and layered insulation systems benefit from the low dielectric losses of these materials. PEN is increasingly used in power electronics, for example in DC-link capacitors of converters.
Polytetrafluoroethylene (PTFE)
PTFE, better known under the trade name Teflon, has outstanding electrical insulation properties, a very low dielectric constant and remains stable up to over 250 °C. Its extreme chemical resistance makes it suitable for environments with aggressive media.
Typical applications are high-voltage cables, connectors, sensor sheathing and seals. PTFE is also used in microwave and high-frequency technology, since it exhibits low losses at high frequencies. In high-voltage test laboratories, PTFE is frequently used as insulating material in measuring instruments.
Polyetheretherketone (PEEK)
PEEK is a high-performance polymer with outstanding mechanical strength, very good chemical resistance and excellent electrical insulation. It can be used up to about 250 °C and is particularly suitable for components that are subject to high electrical and mechanical loads. Examples are connectors, insulating sleeves and precision moulded parts in high-voltage systems.
Through glass-fibre or ceramic fillers, PEEK can additionally be reinforced and specifically adapted to particular requirements. Furthermore, PEEK is used in offshore wind farms and in the field of renewable energies, where extreme conditions prevail.
Other relevant plastics
In addition to the main materials mentioned, other high-performance plastics such as polyphenylene sulfide (PPS) and polybutylene terephthalate (PBT) are also used. PPS is distinguished by high temperature stability and chemical resistance, while PBT is particularly frequently used in insulating components for connectors.
Practical examples of the use of plastics in high-voltage applications
The applications can be divided into three groups:
- Indoor applications: transformers (epoxy resins as casting compounds), generators and motors (polyimide films for winding insulation), switchgear (epoxy resin modules for safe switching operations).
- Outdoor applications: overhead line construction (silicone insulators as a replacement for porcelain), offshore wind farms (PEEK and silicone against salt spray and moisture), outdoor high-voltage test equipment (PTFE for stable insulation).
- Special applications: power electronics (PEN in DC-link capacitors), high-frequency technology (PTFE for low losses), test engineering (PEEK or PTFE insulators for extremely high voltages).
Comparison table of the most important plastics
| Plastic | Temperature resistance | Electrical properties | Advantages | Disadvantages | Typical applications |
|---|---|---|---|---|---|
| Polyimide (PI) | up to over 300 °C | high dielectric strength, low moisture absorption | flame-retardant, chemically resistant | expensive, difficult to process | motors, generators, transformers |
| Epoxy resin (EP) | up to approx. 180 °C | good dielectric strength, modifiable with fillers | high mechanical strength, versatile | brittle, sensitive to cracks | switchgear, transformers, cast-resin insulators |
| Silicone (SI) | -60 to +200 °C | high tracking resistance | UV- and weather-resistant, flexible | lower mechanical strength | outdoor insulators, cable terminations |
| PET/PEN | up to approx. 150 °C | low dielectric losses | good dimensional stability, cost-efficient | limited temperature resistance | film capacitors, cable insulation |
| PTFE | up to approx. 250 °C | very low dielectric constant | extremely chemically resistant, low losses | difficult to machine, costly | high-voltage cables, connectors |
| PEEK | up to approx. 250 °C | very good insulation | mechanically high-strength, chemically resistant | high material price | connectors, offshore applications |
| PPS | up to approx. 200 °C | good insulation values | chemical-resistant, temperature-stable | brittle properties | insulating components, housing parts |
| PBT | up to approx. 130 °C | solid insulating properties | cost-efficient, easy to process | lower temperature resistance | connectors, components |
Future prospects
Material development in the high-voltage range is concentrating on even more capable and more sustainable solutions. Nanocomposites are regarded as promising: by incorporating nanoparticles, electrical and thermal properties can be significantly improved, for example tracking resistance or thermal conductivity. Bio-based and recyclable polymers are likewise gaining in importance in order to reduce environmental impact.
A further trend is the miniaturisation of components combined with increasing power density. This requires plastics that withstand extremely high electrical fields and are at the same time thermally conductive. Self-healing materials that can automatically repair damage caused by partial discharges are also the subject of intensive research. In addition, hybrid systems made of polymer materials and ceramic fillers are being developed that combine the advantages of both material worlds.
In summary
Plastics for high-voltage applications must fulfil a large number of demanding criteria – from electrical dielectric strength through thermal stability to resistance to environmental and ageing influences. Proven materials such as polyimide, epoxy resins, silicones, PTFE or PEEK form the basis of today's high-voltage insulation and have proven reliable over decades.
In practice this means: For outdoor use, silicones are the first choice, for high temperatures polyimide, for aggressive environments PTFE and for mechanically demanding applications PEEK.
With a view to the future, however, innovations are required that combine higher dielectric strength, improved sustainability and better machinability. Anyone who makes the right material choice in high-voltage engineering lays the foundation for safe, long-lasting and efficient systems.
FAQ
Which plastics are best suited to outdoor use at high voltage? Silicones in particular have proven themselves in overhead line construction, since they are UV- and weather-resistant and retain their insulating properties even under strong temperature fluctuations.
Why is polyimide so widespread in high-voltage applications? Polyimide is extremely temperature-resistant, chemically stable and offers high dielectric strength, which is why it is frequently used in motors, generators and transformers.
What is the difference between PTFE and PEEK in application? PTFE impresses with its very low dielectric constant and chemical resistance, while PEEK additionally offers high mechanical strength and is used in offshore or high-load applications.
Do sustainable materials already play a role in the high-voltage range? Yes, recyclable and bio-based plastics as well as nanocomposites are increasingly being researched in order to reduce environmental impact while at the same time increasing performance.
What risks arise from the wrong choice of material? Insufficient insulation can lead to partial discharges, breakdowns and in the worst case to the failure of entire systems. The right choice of plastics is therefore essential.
