Introduction
In recent years, the field of electrical insulation for power transformers has witnessed significant advancements, particularly with the introduction of hybrid materials. A notable study, "Analysis of Polarization and Depolarization Currents of Samples of NOMEX®910 Cellulose–Aramid Insulation Impregnated with Mineral Oil," delves into the properties and performance of NOMEX®910 insulation. This research was aimed at evaluating how this advanced material behaves under various conditions, especially when subjected to thermal degradation and moisture.
Research Objectives and Methodology
The primary goal of the research was to analyze the polarization and depolarization currents (PDC) in NOMEX®910 insulation samples, which are impregnated with Nynas Nytro 10× inhibited insulating mineral oil. By simulating the aging process and controlling the moisture content, the researchers aimed to understand the activation energy and dominant time constants of the insulation's relaxation processes. These parameters are crucial for diagnosing the technical wear and effectiveness of insulation in power transformers.
Experimental Setup
The study utilized a high-resistance meter, the MIC-15k1 from Sonel®, to measure polarization and depolarization currents. This meter ensured a stable UC charging voltage of 500V and allowed for precise adjustments in polarization and depolarization times, with data communicated wirelessly via Bluetooth.
Key Findings
Temperature Effects
The research revealed that the temperature significantly influences the polarization and depolarization currents of the insulation. As the temperature increased from 20°C to 60°C, the depolarization current also increased proportionally. This phenomenon is attributed to the declining resistivity of both the mineral oil and cellulose at higher temperatures. Interestingly, the presence of aramid fibers did not significantly alter the characteristics of the polarization and depolarization currents, confirming the validity of the measurements.
Moisture Impact
Moisture content was another critical factor examined in the study. Higher moisture levels in the insulation samples led to a noticeable increase in the polarization current at the initial measurement stage. This effect diminished over time, highlighting the importance of moisture control in maintaining insulation effectiveness. The research indicated that water primarily resides in the cellulose layer, with temperature increases facilitating water migration to the mineral oil.
Activation Energy and Time Constants
The study's analysis of activation energy and time constants provided insights into the material's relaxation processes. It was found that temperature and moisture significantly impacted these parameters. Higher temperatures and moisture levels resulted in predictable changes in activation energy and time constants, which are vital for diagnosing insulation wear using the PDC method.
Conclusions
The research confirmed that NOMEX®910 cellulose–aramid electro-technical paper is a robust material suitable for long-term use in power transformer insulation systems. The hybrid nature of this material, combining cellulose with a thin layer of aramid, enhances its durability without significantly altering its electrical properties. The study also highlighted the potential of the PDC method in diagnosing moisture levels in such hybrid insulation systems, providing a promising tool for future maintenance and diagnostics.
Future Prospects
Despite the promising results, the research acknowledged the need for further studies to refine diagnostic methods for hybrid insulation materials. The challenge lies in adapting traditional diagnostic techniques, used for classic cellulose–oil insulation, to newer synthetic and semi-synthetic materials like NOMEX®910. Continued research is essential to develop reliable, cost-effective diagnostics for the evolving landscape of power transformer insulation systems.
Credits
This blog post is based on the research article "Analysis of Polarization and Depolarization Currents of Samples of NOMEX®910 Cellulose–Aramid Insulation Impregnated with Mineral Oil," which provides detailed insights into the experimental procedures and findings.
Understanding and leveraging such cutting-edge research helps in advancing the reliability and efficiency of electrical insulation systems, ensuring robust performance of power transformers in the future.