Technical review of the types of insulators used in polluted areas

Technical Evaluation of Various Insulators Used in Polluted Areas

The presence of reliable, integrated, and interconnected transmission lines in every country is among the prerequisites for the development of the electricity industry. In fact, having power plants without suitable transmission lines is meaningless. In this regard, the Ministry of Energy is committed to responding to demands and meeting the increasing needs of electricity consumers, which has led to the continuous development of reliable networks with minimal service interruptions in the power industry.

High-voltage insulators are essential components of transmission and distribution lines, serving as intermediaries between towers and energized conductors. These insulators, while bearing the weight and mechanical forces imposed on the conductors, prevent current from flowing towards the ground through necessary isolation.

The reliability of power networks is greatly influenced by high-voltage insulators. Errors occurring in these insulators can lead to disruptions in high-voltage power and lower voltage networks, resulting in energy loss and negatively impacting the overall balance of the high-voltage network.

4-1- Mechanical Properties:

Insulators must be able to withstand all incoming forces, including:

Tensile forces
Compressive forces
Bending forces
Torsional forces
The intensity of each force applied to the insulator depends on its specific application. For instance, in tension insulators, stronger tensile forces and greater mechanical effects are exerted on the insulator, while in support insulators, compressive and torsional forces have a more significant mechanical impact. In phase spacers, the main force is bending force.

Note: The individual impact of each force does not necessarily overlap with the effects of other forces. During design, the effect of each of the four applied forces should be thoroughly examined.

4-2- Electrical Properties:

Insulators isolate the main conductors from the ground in two primary directions:

External Insulation: This is influenced by the air gap created by the insulator, known as the arcing distance. The strength of external insulation is determined through tests such as Lightning Impulse Withstand Voltage at voltages above 400 kilovolts and Switching Impulse Withstand Voltage.
Internal Insulation: This internal insulation defines the insulator’s strength against network voltage and required insulating strength due to the existing insulation. The insulation’s power frequency withstand voltage is measured using tests.
The choice of insulation material for insulators is based on the region’s weather conditions, network voltage level, and it must have the necessary endurance against:

Network frequency voltage, which is approximately twice the phase voltage.
Spark-over voltage with a 50 microsecond wavefront, determined by the air gap and environmental conditions.
Voltage induced by network switching, which impacts the insulation through an impulse.
Note: Environmental factors, especially pollution, have a significant impact on the electrical characteristics of insulators, which will be discussed further.

The effects of environmental conditions and existing pollutants, including marine and industrial pollution and their deposits on ceramic and glass insulator surfaces, have led to significant developments in the field of high-voltage insulators. In fact, the insulation endurance of older generation insulators decreases after pollution settlement in humid conditions, leading to the formation of pathways for current conduction from high-voltage to the ground and ultimately causing electrical discharge and insulator failure.