Composite (polymeric) Insulators


With the development of the power industry, the continuous expansion of transmission capacity and the voltage levels of transmission lines and substations, the requirements for insulators in the power system are getting higher and higher. Porcelain or glass insulators that have been used for high-voltage transmission lines for more than 100 years have both advantages and disadvantages, such as bulky and fragile, low pollution resistance, and easy breakdown of internal insulation. Therefore, there is an urgent need for a type of insulator to replace the traditional porcelain insulator. At the same time, due to the rapid development of the chemical industry and the emergence of new composite materials, a new generation of insulators with organic materials as the main component has also emerged. .

In order to facilitate the installation of insulators, or to use in places with relatively high pollution levels, composite insulators are a very good choice.

Composite insulators are insulated by a composite structure composed of two or more organic materials. The composite insulators operating in the power grid are mainly rod-shaped suspension insulation, which accounts for more than 95% of the total number of various operating composite insulators in China.

The main structure of the insulator is shown in the figure below:

composite insulator structure

EFR core

The core rod is the abbreviation of the epoxy resin glass fiber drawing rod. It is the load-bearing part of the composite insulator's mechanical load and the main part of the internal insulation. It is required to have high mechanical strength, insulation performance and long-term stability. Now the core rod material generally adopts resin-reinforced unidirectional glass fiber drawing rod. It is the skeleton of the composite insulator, which plays multiple roles such as supporting the umbrella cover, inner insulation, connecting the two ends of the fittings, and bearing the mechanical load. It has a high tensile strength, generally up to 600Mpa or more, which is twice that of ordinary steel. 5 to 8 times that of porcelain materials, and has good dielectric properties and chemical resistance, as well as good resistance to bending fatigue, creep resistance and impact resistance.

Weather Sheds

Weather Sheds is the outer insulating part of the composite insulator, and its function is to make the composite insulator have sufficiently high external insulation performance against moisture flashover and pollution flashover to protect the core rod from atmospheric attack. Umbrella sheaths are exposed to the outdoors for a long time, and are subject to various severe weather conditions and industrial pollution, and may also be ablated by spark discharge or local arc during operation. Therefore, it is generally required that the umbrella skirt sheath must have excellent anti-fouling flashover, tracking resistance and electrical corrosion resistance, as well as resistance to atmospheric aging such as ozone and high temperature.

The adhesive layer is the interface between the core rod and the sheath. It penetrates between the two ends of the fittings and is another main part of the insulation in the composite insulator. If the bonding quality is not good, it will become a part of the composite insulator operation in the future. weakness.

End fittings

The fitting is the transmission component of the mechanical load of the composite insulator. It is assembled with the core rod to form the connector of the composite insulator, and is connected to the pole tower and the wire through the connector to transmit the mechanical load. The quality of the hardware and its connecting structure with the core rod directly affects the strength of the core rod and the mechanical properties of the composite insulator.


CIGRE 33204: Considerations on the design of composite suspension insulators based on experience from natural ageing testing and electric field calculations.

IEC 603832: Insulators for overhead lines with a nominal voltage above 1000 V  Part 2: Insulator strings and insulator sets for a.c. systems – Def, test methods and acceptance criteria.

IEC 60587: Electrical insulating materials used under severe ambient conditions  Test methods for evaluating resistance to tracking and erosion.

IEC 606951110: Fire hazard testing  Part 1110: Test flames  50 W horizontal and vertical flame test methods.

IEC 608151: Selection and dimensioning of highvoltage insulators intended for use in polluted conditions  Part 1: Definitions, information and general principles.

IEC 608153: Selection and dimensioning of highvoltage insulators intended for use in polluted conditions  Part 3: Polymer insulators for a.c. systems.

IEC 61109: Insulators for overhead lines  Composite suspension and tension insulators for a.c. systems with a nominal voltage greater than 1 000 V  Definitions, test methods and acceptance criteria.

IEC 61621: Dry, solid insulating materials  Resistance test to highvoltage, lowcurrent arc discharges.

IEC 61466 1: Composite string insulator units for overhead lines with a nominal voltage greater than 1000 V  Part 1: Standard strength classes and end fittings.

IEC 61466 2: Composite string insulator units for overhead lines with a nominal voltage greater than 1000 V  Part 2: Dimensional and electrical characteristics.

IEC 61952: Insulators for overhead lines  Composite line post insulators for A.C. systems with a nominal voltage greater than 1 000 V  Definitions, test methods and acceptance criteria

IEC 619521: Insulators for overhead lines – Composite line post insulators for AC systems with a nominal voltage greater than 1 000 V – Part 1: definitions, end fittings and designations

IEC 62631: Dielectric and resistive properties of solid insulating materials.


Mostly, the composite insulators are designed and tested according the standards IEC 61109 (only for string composite insulators) and IEC 61952 (only for line post composite insulators).

Tests for insulators are usually divided into four groups:

  1. Design tests
  2. Type tests
  3. Sample tests (Factory Acceptance Tests)
  4. Routine tests

brittle failure test

These tests are intended to verify the suitability of the design, materials and method of manufacture (technology). A composite suspension insulator design is defined by the following
– materials of the core, housing and their manufacturing method;
– material of the end fittings, their design and method of attachment (excluding the coupling);
– layer thickness of the housing over the core (including a sheath where used);
– diameter of the core.

The type tests are intended to verify the main characteristics of a composite insulator, which depend mainly on its shape and size. They also confirm the mechanical characteristics of the assembled core. They are made on insulators whose class has satisfied the design tests.

The sample tests are for the purpose of verifying other characteristics of composite insulators, including those which depend on the quality of manufacture and on the materials used. They are made on insulators taken at random from lots offered for acceptance.

The aim of these tests is to eliminate composite insulators with manufacturing defects. They are made on every composite insulator offered for acceptance.