Composite insulators play a vital role in power transmission by supporting and insulating high-voltage power lines. Compared to ceramic or glass types, they’re lighter, more pollution-resistant, and ideal for harsh environments such as coastal or industrial zones.

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But behind these advantages lie hidden risks. Internal defects, such as debonding of the sheath and core rod, air holes inside the sheath, faults, and poor bonding, together with ageing and contamination, can lead to partial discharges, interface breakdown, and even flashovers, threatening the safety of the network.

This article covers the structure, working principles, types, and key benefits of composite type insulators, while also revealing the potential issues engineers must not overlook.

1. What is a Composite Insulator?

1.1 Definition

Maybe many people don’t know what is a composite insulator. It is made by combining two or more materials, like a steel core, polymers, and other composites. Its main job is to separate electrical conductors from the ground in power systems, stopping dangerous current leaks while keeping power lines stable. Unlike old-style ceramic or glass insulators, these are lighter, tougher, and better at handling harsh weather or physical impacts. That’s why they’re now a go-to choice for modern power grids!

1.2 Structure of composite insulators

Composite insulators are engineered to balance electrical insulation, mechanical strength, and long-term durability. A typical unit consists of the following elements:

• Core Rod (Load-bearing member)
  High-quality epoxy resin E-glass FRP rod specifically formulated for electrical and mechanical duty. It provides the primary tensile strength and is the backbone of the assembly.

• Housing (Sheath & Sheds)
  One-piece HTV (high-temperature vulcanized) injection-molded silicone rubber housing that is chemically bonded to the core rod to block moisture ingress at the interface. The hydrophobic silicone surface limits water-film formation, reducing leakage current, RI/TVI, and washing frequency in service. 
  Engineering note: larger “umbrella” sheds increase creepage distance for contamination performance; GOTO transmission units reach creepage distances up to 6,121 mm in 230 kV class.

• Field Grading & Discharge Hardware (instead of “lightning protection layer”)
  Where required, corona/grading rings and arcing hardware are applied to smooth the electric-field distribution and improve impulse behavior. Catalog values require correction factors if rings are omitted, so selection should follow the ring configuration used.

• End Fittings (Connection to line/tower)
  Available in DU clevis-tongue, ball-and-socket, eye, y-clevis and other configurations; drawings show iron-swaged terminations and galvanized steel pins with cotter keys for secure attachment. Different fitting combinations correspond to specified mechanical ratings. 
  Typical ratings: distribution pin-type insulators carry SML 70–90 kN with 62 N·m torsion test value; transmission suspension series are offered in 100 kN and 160 kN classes.

• Performance & Standards (Quality foundation)
  The silicone housing’s hydrophobicity lowers leakage current and maintenance; benefits include improved power quality (lower RIV) and life-cycle cost versus porcelain. Products comply with IEC , ANSI C29.13, CSA C411.5 under an ISO QMS. Representative RIV at 1 MHz is below 1–3 μV on distribution types.

Tip: Unlike legacy porcelain/glass, a composite insulator’s reliability hinges on the bonded FRP–silicone interface and field-grading hardware choice. Always specify the ring configuration used for the published electrical ratings and verify creepage against the site’s pollution level.

To ensure the reliability and safety of composite insulators in high-voltage applications, manufacturers adhere to international and national standards. In the United States, the American National Standard for Insulators—Composite Suspension Type (ANSI/NEMA C29.12- ) provides comprehensive guidelines on design, testing, and performance requirements for these insulators.

1.3 Working principle of composite insulators

They might look simple, but they play a vital role in power systems. By combining smart designs with advanced materials, they safely isolate electricity and support heavy power lines. Here’s how they work in four key ways:

Blocking Electricity Leaks: The outer layer of a composite insulator is made of special polymer materials that act like a shield. These materials stop electricity from flowing between power lines and the metal towers holding them up. Even under high voltage, the insulator’s surface won’t let electricity pass through, keeping the system safe.

Staying Strong in Tough Conditions: Inside every insulator is a tough core rod, usually made of fiberglass. This rod gives the insulator its strength. Whether facing strong winds, heavy ice, or extreme temperatures, the core rod keeps power lines steady and prevents collapses.

Stopping Dangerous Sparks (Flashovers): High voltage can cause sparks to jump along an insulator’s surface. To prevent this, they have umbrella-like “sheds” that create a longer path for electricity to travel. The sheds are coated with silicone rubber, which repels water and stops conductive films from forming. Some insulators also have metal rings (called grading rings) attached to spread out the electric field evenly, reducing spark risks.

Fighting Water and Dirt: The silicone rubber coating on the sheds doesn’t just block sparks—it also resists water, dust, and grease. In wet or polluted areas, this keeps the insulator’s surface clean and dry, preventing short circuits or power failures.

Why It All Matters

When power flows through lines, composite insulators do two critical jobs:

Their insulating materials keep electricity moving only through the cables, never leaking into the towers.

Their strong core rods hold up heavy cables, even in harsh weather.

By balancing electrical safety and physical strength, these insulators keep power grids running smoothly and reliably.

2. Types of Composite Insulators

They come in different types, each designed for specific jobs and environments. Here are the most common ones:

Composite Line Post Insulators: Often called High Voltage Composite Insulators, these are used on upright posts in high-voltage power lines. They handle extreme electrical stress while keeping power lines securely attached to structures like steel towers.

Composite Pin-Type Insulators: Also known as Composite Pin Insulators, these are mostly used in power transmission lines and substations, especially for high or ultra-high voltage systems. They’re designed to hold single power lines at suspension points, keeping electricity isolated from support structures like poles or towers.

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Cross-Arm Insulators: These insulators are mounted on the horizontal cross-arms of power towers. Their job is to support power lines while blocking electricity from leaking between the cables and the tower. By safely holding the cables, they keep the grid stable and reduce the risk of outages.

Composite Post Insulators: Sometimes called Line Post Insulators, these are installed on vertical posts in high-voltage transmission systems. They’re popular for their strong electrical insulation, durability in tough weather, and lightweight design, which makes them easier to transport and install.

3. Advantages of Composite Insulator

High Strength: Composite insulators are very strong. They can handle heavy forces like strong winds, ice build-up, or vibrations without breaking. They can hold between 40 and 210 kN (around 9,000 to 47,000 pounds), so they’re great for storms and extreme weather. (Learn how composite insulators outperform porcelain types in mechanical strength in our comprehensive comparison here.).

Lightweight Design: They’re much lighter than ceramic or glass insulators. This makes them easier to carry, install, and maintain, especially in hard-to-reach areas like mountain power lines.

Rust and Corrosion Resistance: The materials used (like fiberglass and silicone rubber) don’t rust or corrode easily. This makes them perfect for coastal areas, humid climates, or places with heavy air pollution.

Survives Heat and Harsh Weather: The polymer parts can handle extreme heat and cold without cracking or aging. They stay strong through years of sun, rain, or snow.

Stays Clean in Dirty Conditions: Their smooth, slippery surface (often silicone rubber) stops dirt, dust, or salt from sticking. Even if they get dirty, rain usually washes them clean, preventing power leaks.

Saves Money Over Time: While they might cost about the same as traditional insulators upfront, they last longer and need less maintenance. Fewer replacements mean lower costs in the long run.

Works Almost Anywhere: You’ll find composite insulators in power lines (even ultra-high-voltage ones), substations, and city grids. They adapt well to deserts, forests, coasts, or industrial zones.

Quantified advantages: MV pin-type SML 70–90 kN, EHV suspension 100–160 kN, RIV @1 MHz <3 μV, creepage up to 6,121 mm for harsh-pollution duty.

4. Applications of Composite Insulator

• Pollution class → creepage: match required creepage distance to site pollution severity; use the ranges above (e.g., MV pin-type 384– mm, EHV suspension – mm) as a quick reference when screening models.

• Corona/Grading rings: confirm whether corona rings are included; if not, apply the correction factors noted in the catalog to electrical ratings.

In short, these versatile insulators work everywhere from giant power grids to wind turbines and train tracks. Their combination of strength, safety, and weather resistance makes them the go-to choice for keeping our modern world powered up.

Conclusion

Composite insulators are a crucial component in modern electrical systems. They provide mechanical support and electrical insulation for high-voltage power lines. Thanks to their lightweight design, durability, and ability to resist environmental factors, they have an edge over traditional porcelain or glass insulators.

Composite Insulator

What is Composite Insulator?

A composite insulator is a special insulation control component that plays an important role in overhead transmission lines. There are many types of polymer insulators.

What is Composite Insulator Made of?

Composite insulator is also called synthetic insulator, non-ceramic insulator, polymer insulator, rubber insulator, etc. The main structure is generally composed of umbrella skirt, FRP core bar and end fittings. The umbrella skirt is generally made of organic synthetic materials, such as ethylene propylene rubber, high temperature vulcanized silicone rubber, etc.; the FRP core bar is generally reinforced with glass fiber and based on oxidized resin; the end fittings are usually carbon steel or carbon structural steel coated with hot zinc aluminum.

Types of Composite Insulator (Types of Insulators And Their Applications)

Composite insulator can be divided into: composite suspension insulator, line post composite insulator, pin type composite insulator, post composite insulator, composite railway insulator, composite hollow insulator.

Advantages of Composite Insulator

• Composite insulator is small in size, light in weight, light in structure, easy to transport, easy to install and easy to maintain.

• The composite insulator has good fouling resistance and strong fouling flash voltage resistance. Its wet withstand voltage and fouling resistance voltage are 2 to 2.5 times of that of porcelain insulator with the same creepage distance. No need for cleaning and safe operation in heavily polluted areas.

• Polymer insulators have superior electrical properties and high mechanical strength. Polymer insulators have good tensile and flexural strength, 2 times higher than ordinary steel and 8-10 times higher than high-strength porcelain materials, which effectively improves the reliability of safe operation. 

• It has good waterproof performance. Its overall structure prevents internal insulation from moisture. It does not require preventive insulation monitoring tests or cleaning, thus reducing the workload of daily maintenance.

• Polymer insulators have good sealing performance and high resistance to electrical corrosion.

• Polymer insulators have high impact and shock resistance, good resistance to brittleness and creep.

• Polymer insulators have high bending strength, high torsional strength. It enables them to withstand internal pressure. And can be used in combination with porcelain insulators and glass insulators.

Applications of Composite Insulators