Tracking & Erosion in composite insulators

Understanding Electrical Tracking and Erosion in Polymeric Insulators

Electrical tracking and erosion are two major issues that can affect the performance and lifespan of polymeric insulators. These problems often arise when insulators are continuously exposed to moisture, pollution, and high electrical stress.

What is Electrical Tracking?

Electrical tracking occurs when conductive pathways form on the surface of an insulator, eventually leading to electrical failure. This typically happens due to the accumulation of contaminants like dust, dirt, salt, acid rain, or other conductive particles. When moisture or humidity is present, these contaminants can conduct small amounts of electricity, leading to leakage currents—unintended electrical flows across the surface of the insulator.

Over time, these leakage currents can generate localized heating, causing the material to degrade and form carbonized tracks. These tracks act as electrical conductors, increasing the risk of insulation failure and potential power outages.

What is Erosion?

Erosion occurs when the surface of the insulator physically degrades due to continuous exposure to electrical activity, particularly dry band arcing (DBA). DBA happens when moisture evaporates unevenly from the insulator’s surface, creating small dry zones that experience intense electrical discharge. These arcs gradually wear away the insulating material, leading to deep cracks, surface roughness, and eventually complete failure.

The Role of Hydrophobicity

Hydrophobicity—the ability of an insulator’s surface to repel water—is the first line of defense against tracking and erosion. A hydrophobic surface prevents water from forming continuous conductive layers, reducing the risk of leakage currents. However, if hydrophobicity is lost due to aging, contamination, or extreme weather conditions, the insulator becomes more vulnerable to electrical tracking and erosion. This can result in the formation of carbonized pathways that accelerate degradation.

By maintaining the hydrophobicity of polymeric insulators and minimizing contamination, utilities can extend the service life of insulators and reduce the risk of electrical failures.

Enhancing Insulator Performance with Inorganic Fillers

One effective way to improve the durability of polymeric insulators is by incorporating inorganic fillers into their housing material. These fillers help reduce the proportion of organic components in the insulator’s structure, particularly the base polymer matrix, making the material more resistant to tracking and erosion.

How Do Inorganic Fillers Help?

Inorganic fillers strengthen insulators in several ways:

 1. Improved Electrical Resistance – These fillers reduce the formation of conductive paths on the surface, lowering the risk of electrical tracking.

 2. Enhanced Mechanical Strength – The addition of fillers increases the overall toughness of the insulator, making it more resistant to physical wear and environmental stress.

 3. Better Thermal Stability – Inorganic particles help dissipate heat more effectively, preventing localized overheating that can lead to erosion.

 4. Increased Resistance to Environmental Factors – Fillers improve resistance to pollution, UV radiation, and moisture, all of which contribute to surface degradation.

By carefully choosing and incorporating the right combination of inorganic fillers, composite insulators can achieve superior erosion resistance, extend their service life, and reduce the likelihood of insulation failure. This makes them a more reliable and cost-effective choice for high-voltage applications in harsh environments.

Testing for Tracking and Erosion

To ensure that composite insulators can withstand harsh outdoor conditions, various tests are conducted to evaluate their resistance to tracking and erosion. These tests simulate real-world electrical and environmental stressors to determine how well the materials perform in high-voltage (HV) applications.

Inclined Plane Test (IPT)

Over the past few decades, the Inclined Plane Test (IPT) has become the most widely used method for classifying insulation materials based on their resistance to dry band arcing (DBA). This test follows international standards set by:

• IEC 60587 (International Electrotechnical Commission)

• ASTM D2303 (American Society for Testing and Materials)

Both standards provide guidelines for evaluating the relative tracking resistance of solid insulating materials.

Test Setup for IPT

The test involves five flat samples of insulating material, each measuring 5.0 cm × 12.0 cm with a thickness of 0.6 cm. The setup includes:

• Mounting the samples on a PTFE (Teflon) insulating support at an angle of 45° ± 2°

• Top and bottom electrodes placed 50 mm apart, with a reference line marked at the center

• The upper electrode connected to a high-voltage (HV) supply through a current-limiting resistor

• The lower electrode grounded via a resistance for measuring leakage current

Creating a Controlled Tracking Environment

• To simulate contamination, a conductive liquid is applied to the sample’s surface. The solution consists of:

• Distilled water

• 0.1% ammonium chloride (NH₄Cl) (to simulate pollution)

• 0.02% non-ionic wetting agent (to ensure even distribution)

The electrical conductivity of this solution is maintained at 3.95 ± 0.005 Ωm at 23 ± 1°C. Filter papers are placed beneath the upper electrode to ensure a steady flow of liquid onto the test sample.