Insulators in Electrical Engineering: How to Choose the Right Type for High Voltage, Temperature Resistance, and Long Service Life

Photo: American Public Power Association / Unsplash

In the electrical engineering industry, the selection of an insulator plays a key role in ensuring safety, efficiency, and the service life of equipment. Liquid insulators, such as mineral oils or synthetic esters, offer excellent cooling and dielectric strength but require regular maintenance. Solid insulators, such as epoxy resins or silicone rubbers, are characterized by mechanical resistance and stability; however, their processing can be more demanding. Gaseous insulators, such as sulfur hexafluoride (SF6), provide high dielectric strength at low pressure, but their environmental impact necessitates alternative solutions. The choice of insulator for a specific application depends on a combination of technical requirements, operating conditions, and economic factors.

Key types of insulating materials for high voltage

In electrical engineering, insulating materials play a key role in ensuring the safety and reliability of equipment, particularly in high-voltage applications. The most commonly used types include organic polymers (e.g., epoxy resins, polyethylene, polyamides), inorganic materials (mica, ceramics, glass), and composite systems combining the advantages of both groups. Organic polymers excel in processability and flexibility, but their temperature resistance is typically limited to 150–200 °C. In contrast, inorganic materials such as mica or ceramics can withstand temperatures up to 1000 °C but are brittle and more demanding to process.

When selecting an insulating material for high voltage, it is crucial to consider dielectric strength, which indicates the maximum electric field the material can withstand without breakdown. For example, epoxy resins achieve a dielectric strength of around 20–30 kV/mm, while mica can exceed 100 kV/mm. Another important factor is resistance to partial discharges, which gradually degrade insulating properties. For applications with extreme requirements, combinations of materials are often chosen, such as mica tapes impregnated with epoxy.

Temperature Resistance and Its Impact on Insulation Lifespan

The temperature resistance of insulating materials directly affects their lifespan and operational reliability. According to international classifications, insulating materials are divided into temperature classes (e.g., 130 °C, 155 °C, 180 °C), which determine the maximum operating temperature at which the material can endure without degradation for 20,000 hours. Exceeding this temperature leads to accelerated aging, loss of mechanical strength, and reduced dielectric properties. For example, polyimide films (class 220 °C) maintain stability even during long-term exposure to temperatures around 200 °C, whereas standard polyethylene degrades at just 90 °C.

For applications with cyclic temperature loading (e.g., electric motors, transformers), thermal stability and resistance to thermal shock are crucial. Materials such as silicone rubbers or ceramics exhibit minimal changes in properties even during rapid temperature fluctuations, whereas some polymers may crack or lose adhesion. Another important parameter is the coefficient of thermal expansion, which should be as close as possible to the values of the metallic parts of the equipment to avoid mechanical stress on the insulation.

Photo: American Public Power Association / Unsplash

Resistance to external factors: Moisture, chemicals, and mechanical stress

Insulators in electrical engineering are often exposed not only to electrical and thermal stress but also to environmental influences such as moisture, chemicals, or mechanical strain. Moisture is one of the most critical factors, as it penetrates the material and reduces its insulating properties. For example, polyamides absorb up to 8% water from the air, leading to a decrease in dielectric strength by tens of percent. For humid environments, hydrophobic materials such as silicones or fluoropolymers (e.g., PTFE) are therefore chosen, as they repel water and maintain their insulating properties even at high humidity.

Chemical resistance is crucial in industrial applications where insulating materials may come into contact with oils, solvents, or acids. Epoxy resins and polyurethanes are generally resistant to most chemicals, but some aggressive substances (e.g., strong acids or alkalis) can degrade them. For extreme conditions, fluorinated polymers or ceramics, which are practically inert, are used. Mechanical stress, such as vibrations or abrasion, requires materials with high strength and elasticity, such as glass fabrics impregnated with epoxy or polyimide composites.

Practical Recommendations for Selecting and Applying Insulating Materials

When selecting an insulating material for high-voltage applications, several key factors must be considered. The first step is to analyze the operating conditions: maximum voltage, temperature range, humidity, chemical environment, and mechanical stress. Based on these parameters, a material with the appropriate properties can be chosen. For example, for transformers operating at 150 °C and high voltage, mica tapes with epoxy impregnation are often used, while fluoropolymers are suitable for cables in chemically aggressive environments.

Another important aspect is the processability of the material and its compatibility with other components. Some insulation systems require specific processing technologies, such as vacuum impregnation or hot pressing. During application, it is essential to follow technological procedures to avoid the formation of voids or inhomogeneities, which could lead to partial discharges. Regular maintenance and diagnostics of the insulation condition (e.g., measuring the loss factor or partial discharges) then extend the service life of the equipment and increase its reliability.

Photo: Andrew Hall / Unsplash

Impact of dielectric strength on the selection of insulators for high-voltage applications

Dielectric strength is one of the key parameters of insulating materials, especially in high-voltage environments. It indicates the maximum electric field intensity a material can withstand without breakdown and directly affects the safety and reliability of equipment. For high-voltage applications such as transformers, cables, or switchgear, insulators with dielectric strength in the range of tens to hundreds of kV/mm are required. For example, epoxy resins achieve values around 20–30 kV/mm, while special ceramic materials can exceed 100 kV/mm.

When selecting an insulator, it is necessary to consider not only the nominal value of dielectric strength but also its dependence on material thickness, temperature, and humidity. Thinner insulation layers exhibit higher strength but may be more susceptible to mechanical damage. Conversely, thicker layers reduce the risk of breakdown but increase weight and costs. It is also important to verify the material's behavior under long-term stress, where gradual degradation may occur due to partial discharges or thermal aging.

Optimization of Insulation Systems for Combined Stress

Under real-world conditions, insulating materials are exposed to simultaneous electrical, thermal, mechanical, and chemical stress. For example, in electric motors, insulation must withstand high temperatures, vibrations, and potential contact with lubricants or coolants. For such applications, different types of insulators are often combined to leverage their synergistic properties. A typical example is the use of glass fibers impregnated with silicone resin, where the fibers provide mechanical strength and the resin ensures electrical and thermal resistance.

When designing an insulation system, the compatibility of materials with each other must also be considered. Some combinations may lead to undesirable chemical reactions, such as between polyimides and certain solvents, or to degradation due to differing coefficients of thermal expansion. Standard test methods are used to verify resistance to delamination, crack formation, and changes in electrical properties under cyclic stress. High resistance to combined stress extends the service life of equipment and reduces maintenance costs.

Ecological and Economic Aspects of Insulation Material Selection

Modern industry places increasing emphasis on the sustainability and ecological safety of insulation materials. Traditional materials such as asbestos or certain chlorinated compounds have been replaced by safer alternatives due to health and environmental risks. For example, mineral oils in transformers are gradually being replaced by biodegradable esters, which have comparable insulating properties but lower toxicity and better recyclability. Similarly, halogen-free polymers for cable insulation are being developed to minimize emissions of toxic gases in the event of a fire.

The economic aspect of insulation selection includes not only the purchase price but also the costs of installation, maintenance, and disposal. More expensive materials with a longer service life, such as polyimides or ceramic insulators, may prove cost-effective in the long term due to lower replacement and downtime costs. Conversely, for short-term applications or less demanding conditions, more affordable options such as polyethylene or PVC may be suitable. It is also important to consider legislative requirements, such as the REACH regulation, which restricts the use of certain hazardous substances, and to ensure that the selected material complies with all applicable standards and certifications.

Need help choosing an insulator?

Every application requires an individual approach – GCG Group provides technical data sheets and safety data sheets (SDS) for all chemical raw materials and will advise you on selecting an insulator tailored to your requirements for voltage, temperature, and service life. Contact us – or browse our catalogue of over 1,300 products.