Cutting-Edge Scientific News: Research Reveals Degradation Mechanisms of Silicone Rubber under Electrical Tracking

Background: Motivation and Challenges

With the rapid development of power transmission and distribution systems, polymer composite insulators have gradually replaced traditional glass and ceramic insulators as the preferred materials for outdoor high-voltage transmission. Among these, silicone rubber-based composite insulators have gained widespread attention in engineering due to their lightweight properties, high heat resistance, chemical stability, and excellent hydrophobic performance. They not only offer high cost-effectiveness during production and installation but also demonstrate exceptional anti-aging properties during long-term operation. However, under real operational conditions, these insulating materials are gradually degraded due to electrical and environmental stresses (e.g., high voltage, variable weather conditions, salt fog corrosion), which can eventually lead to equipment failure or even grid outages. Therefore, understanding the degradation mechanisms of silicone rubber materials and investigating the significant structural changes during this process hold great scientific and practical value.

To address this issue, this study focuses on real-world silicone rubber samples from substation equipment. By simulating the surface structural changes caused by environmental and electrical stresses using an electrical tracking test (tracking wheel test), advanced spectroscopic techniques such as Attenuated Total Reflection Fourier Transform Infrared Spectroscopy (ATR FT-IR) and Two-Dimensional Correlation Spectroscopy (2D-COS) were employed to explore the molecular structural changes during the degradation process. This research aims to reveal the dynamic changes in silicone rubber materials from macroscopic to microscopic structures under stress, ultimately providing scientific insights for predicting insulator lifetimes and optimizing manufacturing processes.

Authors and Source Information

The study was authored by Harpreet Kaur, Kavin Bhuvan, Rajkumar Padmawar, and Dennis K. Hore, affiliated with the Department of Chemistry, University of Victoria; ASASoft Canada Inc.; and the Department of Computer Science, University of Victoria, Canada. The research was published in Applied Spectroscopy, Special Issue on “Two-Dimensional Correlation Spectroscopy (2D-COS),” Volume 79, Issue 1, 2025, article pages 199–205.

Detailed Research Overview

Experimental Design and Key Methods

This research explores the molecular and surface-level degradation of silicone rubber composite insulators subjected to electrical tracking. The key experimental designs are as follows:

1. Sample Preparation and Experimental Process:

   • Five 15 kV composite silicone rubber insulators were selected, cleaned, and subjected to tracking wheel tests. The tracking wheel test simulated dynamic running conditions involving high salt (1.4 g/L NaCl solution) and high voltage (12.5 kV) environments. The experimental design involved alternating wet cycles (40 seconds of immersion in solution) and dry cycles (simulating electrical cooling stages). The total tracking cycles ranged incrementally from 20,000 to 30,000 cycles.

2. Spectroscopic Characterization and Contact Angle Measurements:

   • ATR FT-IR spectroscopy was employed to investigate the characteristic absorption frequencies of the material between 500 cm⁻¹ and 3700 cm⁻¹, analyzing changes in the absorption intensities of different functional groups on the surface. Additionally, 2D-COS was utilized to study the sequential changes in these functional groups under synchronous and asynchronous conditions.
   • Static contact angles were measured to evaluate changes in the hydrophobicity of the material. Measurements were conducted using five droplets of deionized water, and the average value was recorded.

3. Data Analysis Methodology:

   • Pareto scaling was applied to amplify the details of cross-peaks in the 2D correlation spectra, enabling the analysis of smaller molecular changes.
   • Using Noda’s rules, the molecular sequence of changes in response to external stresses was determined by analyzing the signs of synchronous and asynchronous cross-peaks.

Results and Discussion

1. ATR FT-IR Results:

   • Electrical tracking caused a significant decrease in the infrared absorption peaks corresponding to various functional groups. Specifically, the Si–O–Si backbone (1010 cm⁻¹), Al–O and hydroxyl peaks in ATH filler (555, 663, 733 cm⁻¹, and 3200-3700 cm⁻¹), and methyl side chains (789, 1262, and 2965 cm⁻¹) showed a continuous decline.
   • This indicates degradation mechanisms such as backbone cleavage, filler decomposition (producing alumina crystals), and surface hardening.

2. Contact Angle Measurements and Hydrophobic Recovery:

   • The contact angle increased from 91° in pristine samples to 99° after 30,000 tracking cycles, demonstrating enhanced surface hydrophobicity under high salt and electrical stress conditions. This change was attributed to increased microscale surface roughness (the so-called lotus effect).

3. 2D-COS Molecular Change Sequence:

   • The sequence of changes in low-frequency functional groups was: Al–O and hydroxyl in ATH > Si–O–Si backbone > methyl side chains.
   • In the high-frequency region, changes in hydroxyl peaks (3520 cm⁻¹ altered before 3620 cm⁻¹) followed a particular order. Peaks at 3370 and 3440 cm⁻¹ were altered simultaneously.
   • Cross-referencing low- and high-frequency regions revealed that ATH filler degraded first, followed by changes in the silicone backbone and finally in the surface methyl functional groups.

Conclusion and Scientific Implications

This study systematically investigated the molecular and surface structural changes of silicone rubber composite insulators subjected to electrical tracking and salt exposure. The findings highlighted degradation mechanisms involving filler decomposition, backbone oxidation, and surface hardening during prolonged high-voltage operation. The study’s conclusions have multiple implications:

• Scientific Value: It provides a deep understanding of the degradation mechanisms in extreme environments, offering foundational theoretical support for optimizing silicone rubber insulators’ design and performance.
• Practical Value: It provides a physical model for predicting the lifetimes of insulating materials in power systems, helping reduce unplanned failures and maintenance costs.

Highlights and Significance

1. Innovation in Methods: By leveraging 2D-COS techniques, the study for the first time comprehensively analyzed the sequential molecular changes during degradation, highlighting the breakdown processes of filler and matrix interactions.
2. Real-World Problem Solving: The research answered critical questions about the stability and functional degradation dynamics of electrical insulating materials under complex operational environments.

Future Extensions

This study can be extended to explore a broader range of environmental variables, such as extreme UV exposure and acid rain. Coupled with AI-based predictive algorithms, these investigations can provide more precise tools for forecasting the lifecycle of polymer insulators and formulating optimized material compositions.