What does a composite insulator consist of?

Composition of Composite Insulators

Composite insulators (also known as synthetic insulators) are modern electrical insulation devices widely used in high-voltage transmission lines and substations. They combine the advantages of traditional porcelain and glass insulators while overcoming some of their limitations. A composite insulator primarily consists of the following components:

1. Core Rod 

• Material: Typically made from glass fiber-reinforced plastic (FRP, Fiber Reinforced Plastic), or sometimes epoxy resin or other high-strength composite materials.

• Function: The core rod serves as the mechanical support structure of the composite insulator, providing the necessary mechanical strength to withstand tensile, bending, and other mechanical stresses. It also offers excellent corrosion resistance and aging resistance, ensuring long-term stability in harsh environments.

2. Housing (Sheath)

• Material: Usually made from silicone rubber (SI) or ethylene propylene diene monomer (EPDM).

• Function: The housing encases the core rod and provides electrical insulation, preventing current leakage. It has excellent hydrophobic properties, effectively reducing surface flashover caused by contamination. Additionally, the housing is highly resistant to ultraviolet light, ozone, and chemical corrosion, maintaining good insulation performance under various climatic conditions.

3. Sheds (Skirts)

• Material: Made from the same material as the housing, typically silicone rubber or EPDM.

• Function: The sheds are the protruding parts on the housing, increasing the creepage distance, which is the path length along the insulator's surface that current must travel. This helps prevent surface flashover and arcing, especially in polluted or humid environments. The shed design is often stepped or wavy to increase the surface area and enhance insulation performance.

4. Metal End Fittings 

• Material: Usually made from aluminum alloy, stainless steel, or galvanized steel.

• Function: The metal end fittings connect the composite insulator to transmission towers or equipment. They not only provide mechanical connections but also ensure safe current transmission. To prevent corona discharge and electromagnetic interference, these fittings are often specially designed for good conductivity and electromagnetic compatibility.

5. Seals

• Material: Typically made from rubber or other elastic materials.

• Function: Seals are located between the core rod and the metal end fittings, ensuring that the internal core rod is isolated from the external environment. They prevent moisture, contaminants, and gases from entering the insulator, protecting the core rod from corrosion and aging. Good seal design is crucial for the long-term reliability of composite insulators.

6. Auxiliary Components

• Anti-flashover Coating: In some cases, a special anti-flashover coating may be applied to the surface of the composite insulator to further improve its pollution and flashover resistance.

• Monitoring Devices: Some composite insulators may be equipped with online monitoring devices to real-time monitor operational parameters such as temperature, humidity, and leakage current, allowing for timely detection of potential issues.

Advantages of Composite Insulators

• Lightweight: Compared to traditional porcelain and glass insulators, composite insulators are lighter, making them easier to transport and install.

• High Mechanical Strength: The core rod, made from high-strength composite materials, can withstand significant mechanical loads, making it suitable for long-span and high-wind areas in transmission lines.

• Excellent Electrical Performance: The materials used for the housing and sheds provide superior insulation and hydrophobic properties, effectively preventing flashover due to contamination and moisture.

• Strong Weather Resistance: Composite insulators are highly resistant to ultraviolet light, ozone, and chemical corrosion, ensuring stable performance in various harsh environments.

• Simple Maintenance: Due to their self-cleaning properties and aging resistance, composite insulators require less maintenance, reducing operational costs.

Application Areas

Composite insulators are widely used in high-voltage transmission lines, substations, power plants, and other power systems, particularly in regions with severe pollution, harsh climates, or complex terrain, where their advantages are most pronounced.