Thermal stress and moisture absorption can cause a synergetic negative impact on kraft paper. Among various approaches for improving the dielectric properties of kraft paper, nanotechnology has had promising results. However, the hydrophilicity of most metal oxide nanoparticles renders nanomodified kraft paper more vulnerable to thermal stress and moisture, thereby inducing degradation. In nanomodified kraft paper research, the use of TiO2 nanoparticles has yielded the most promising results. The major shortfall, however, is the hydrophilicity of TiO2. This work investigated surface modifications of rutile-TiO2 nanoparticles (NPs) for improved hydrophobicity and thermal stability. Rutile-TiO2 NPs is a nontoxic metal oxide that can withstand high temperature and is stable in chemical reactions. Two cases of surfactants were used—alkyl ketene dimer (AKD) and alkenyl succinic anhydride (ASA). The intention was to increase heat resistance and reduce the surface free energy of the rutile-TiO2 NPs. The impacts of the surface modifiers on the rutile-TiO2 NPs were characterised using FT-IR, muffle furnace, analytical weight balance, and TGA. It was discovered that new functional groups were formed on the modified NPs examined through FT-IR spectra. This indicates new chemical bonds, introduced through the surface modification. The unmodified rutile-TiO2 NPs absorbed moisture, increasing their mass by 3.88%, compared with the modified nanoparticles, which released moisture instead. TGA analysis revealed that AKD- and ASA-modified rutile-TiO2 needed higher temperatures than the unmodified rutile-TiO2 to markedly decompose. AKD, however, gave better performance than ASA in that regard. As an example, those modified with 5% AKD sustained a 45% higher temperature than the pure TiO2 nanoparticles. Furthermore, in both cases of the surfactants, the higher the percent of surfactant content was, the more thermally stable the nanoparticles became. This work demonstrates the possibility of fabricating rutile-TiO2 NPs to give improved hydrophobicity and thermal stability for possible dielectric applications such as in kraft paper for power transformer insulation.

Improving Thermal Stability and Hydrophobicity of Rutile-TiO2 Nanoparticles for Oil-Impregnated Paper Application

The fuzzy method is proposed for ageing analysis of transformer. The fuzzy controller is used for various input and one output, strictly depends on the number of membership function and there rule base and the type of the defuzzification method. The ageing of transformers is influenced by short term and long term over loads, number and intensity of short circuits, incidence of lightning, and internal faults. The recent development of various techniques for detecting the incipient fault conditions have been improved to some extent; the life expectancy of transformers by resorting to corrective actions in time. The ageing behavior is likely to be different for different types of transformers. The life span of the transformer, thus depends initially on the design and quality of manufacture and later on service conditions and maintenance standard, these factors vary considerably and affect the useful span of service life which therefore needs to be taken into account for residual life assessment. During the natural ageing of transformers, the insulation of winding deteriorates. Cellulose insulation degrades due to heating or electrical breakdown which is dissolved in oil. Hence, the chemical analysis of the Transformer oil gives evidence of changes that are taking place in the winding insulation during operation. Deterioration in transformer cellulose decreases both its electrical and mechanical strength. In this paper a novel fuzzy based algorithm has been implemented on three samples of power transformer oil.

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Intelligent Diagnostic Method for Ageing Analysis of Transformer

Dielectric response measurement based on polarization and depolarization current are being used these days as a tool for non-destructive testing of transformer insulation. Linear insulation models derived from such measurements are being used by researchers to analyze results and draw inference about insulation condition there from. However, dielectric response of a complex insulation structure such as in a transformer is believed to be non-linear in nature with respect to test conditions. These present contribution reports results of a series of experiments is an attempt to identify such non-linear insulation behavior with respect to excitation voltage.

An attempt to identify voltage related non-linearities of transformer insulation from dielectric response measurements

The main focus of this article is to investigate the relation between recovery voltage peaks and moisture content in oil-paper insulation system in power transformers. It investigates the causes of non-standard recovery voltage peaks and uses an algorithm to simulate different oil-paper moisture conditions. Two different transformers have been studied and an attempt has been made to correlate the shifting of recovery voltage peaks in the response to variations in oil and paper moisture contents. A brief discussion on the appearance of subdominant peaks has also been given to relate their presence with interfacial polarization processes.

Analysis of variations in measured recovery voltage peaks due to presence of moisture in insulation of power transformers

Dielectric properties of oil-paper insulation transformer are influenced intensively by moisture; therefore, it is imperative to assess integral condition of oil-paper insulation for assuring normal operation of power transformers. As a non-destructive diagnostic technique, return voltage measurements have been introduced for the assessment of water content in transformer pressboard. This paper further investigates the possibilities of assessing moisture contents of power transformer by return voltage method. Field test results performed on several transformers and its interpretation are given. The derived integral moisture and ageing assessment procedures using the return voltage method are discussed. Moreover, the influence of on-the-spot factors on the test result are also detailed and analyzed in this paper, and the approaches to eliminating them were given accordingly. Finally, reliability of the method was assessed by comparing derived moisture contents based on return voltage measurements with dielectric loss. The test results show that this method is reliable and practical.

Jin-ding Cai

Papers

Moisture content assessment of transformer solid insulation using return voltage spectrum