Solid Insulation Of Transformer Research Articles

Experimental investigation and evaluation of drying methods for solid insulation in transformers: A comparative analysis

Drying of transformer winding insulation has a direct impact on the dependability and durability of the transformer. The extraction of moisture from paper insulation is a crucial need in the manufacturing process of transformers. Insulation efficiency in transformers can be reduced over time due to the detrimental effects of temperature, moisture, and air, often known as aging. Heat, oxygen, and residual moisture increase the deterioration of cellulose in transformer solid insulation. This might potentially result in premature failure of the transformer. The factory's insulation drying process should ensure that the residual moisture content of bulk solid insulation remains below 0.5 %. The primary aim is to maintain a high degree of polymerization, often ranging from 1000 to 800. This article investigates the factors contributing to the degradation of cellulose insulation and analyzes various techniques that are used in manufacturing plants in Kazakhstan. In addition, this study experimentally investigates the impact of vacuum on the process of moisture evaporation and partial discharge (PD) in analysis with other methods of drying transformers.

Electrostatic Charging Tendency Analysis Concerning Retrofilling Power Transformers with Envirotemp FR3 Natural Ester

Natural and synthetic esters are liquids characterized by insulating properties, high flash point, and biodegradability. For this reason, they are more and more often used as an alternative to conventional mineral oils. Esters are used to fill new or operating transformers previously filled with mineral oil (retrofilling). It is technically unfeasible to completely remove mineral oil from a transformer. Its small residues create with esters a mixture with features significantly different from those of the base liquids. This article presents electrostatic charging tendency (ECT) tests for mixtures of fresh and aged Trafo EN mineral oil with Envirotemp FR3 natural ester from the retrofilling point of view. Under unfavorable conditions, the flow electrification phenomenon can damage the solid insulation in transformers with forced oil circulation. The ECT of the insulating liquids has been specified using the volume density of the qw charge. This parameter has been determined using the Abedian–Sonin model on the basis of the electrification current measured in the flow system, as well as selected physicochemical properties of the liquids. It was shown that ECT is strongly dependent on the type of insulating liquid and pipe material, as well as the composition of the mixtures. The most important finding from the research is that a small amount (up to 10%) of fresh and aged mineral oil is effective in reducing the ECT of Envirotemp FR3 natural ester.

Measurement of transformer solid insulation degradation using dilatometry and X-ray diffraction analysis

Physical degradation assessment of solid insulation in transformers is a challenge to the condition monitoring engineers. Solid insulation degradation in transformer is accessed indirectly by characterizing insulation oil. The present article describes application of dilatometry and X-ray diffraction (XRD) analysis as direct methods to characterize the degradation of transformer solid insulation. Experimental aging on oil/paper insulation has been simulated in laboratory conditions at elevated temperatures. Thermal expansion and shrinkage behavior of cellulose pressboards aged in mineral oil, synthetic ester, and mixed oil have been reported using dilatometry analysis. Measurement of change in cellulose crystal size and relative crystallinity of cellulose kraft papers have been reported using XRD analysis. The detailed procedure and interpretation of the dilatometry and diffractograph signatures for accessing the degradation of solid insulation are explicitly discussed. It is inferred that, dilatometry and XRD analysis provide a direct physical degradation assessment of transformer solid insulation.

Diffusion coefficient in transformer pressboard insulation part 2: mineral oil impregnated

Moisture is one of the most influencing parameters which accelerates solid insulation degradation process in transformers. Correct estimation of the moisture within solid insulation of transformer is still a challenge due to temperature driven complex moisture dynamics between oil and paper insulation. Although some authors have proposed coefficients for Kraft paper as well as for non-impregnated pressboard much less work has been done on oil-impregnated pressboard insulations. In this paper, the determination of the diffusion coefficient of moisture in transformer pressboard impregnated with mineral oil is tackled. Studies were carried out on different samples thickness of pressboard which are typical in power transformer. The experimental conditions were simulated using a mathematical model based on the Fick?s second law and an expression for the diffusion coefficient is proposed and validated experimentally.

Significance of cellulose power transformer condition assessment

Power transformers are designed to withstand system abnormalities such as over voltages and external short-circuits. Transformer monitoring and diagnostics are the effective techniques in preventing the eventual failures and contribute to ensure the plant's reliability. Transformer life mainly depends on the integrity of its solid insulation (cellulose). The solid insulation in transformers degrades with time at rates which depend on the temperature and the amount of moisture, oxygen and acids in the insulation system. Moisture and oxygen cause the paper insulation to decay much faster than normal. Moisture in a transformer accelerates the aging process and causes severe deterioration in the mechanical and electrical properties of insulation system. The aging of paper insulation is irreversible. The degree of polymerization value is a main relation between insulation deterioration and formation of aging products. To predict a failure or an unusual behavior, an accurate interpretation of monitoring, diagnostics and maintenance data is required. The monitoring of insulation system and verification of core and winding mechanical integrity allow optimization of the lifecycle management of an asset. This paper presents an investigation and condition assessment of 152 MVA, 512 kV, 1-phase, 2-winding generator step-up transformer having a history of combustible gases.