Impact of the Use of Vegetable Oil on the Mechanical Failure of the Cellulosic Insulation of Continuously Transposed Conductors in Power Transformers

Abstract

Natural esters have become of interest for the industry in recent years as dielectric liquids for power transformers, and many studies are focused on their dielectric and chemical properties, and on their influence in the degradation of the solid insulation due to ageing. However, very little is known about their impact on the evolution of the mechanical properties of the paper insulation, which are acknowledged to have a considerable influence in their overall performance and reliability during the operating life of power transformers. This work studies the effects of thermal ageing with vegetable oil in some commercial components which are commonly used in power transformers, such as an insulated continuously transposed conductor (CTC) and samples of thermally upgraded crepe insulation. The changes in the properties of the crepe paper insulation are characterised through the degree of polymerisation and tensile testing. Failure initiation and propagation in the insulation of the CTC is analysed macroscopically. The results are compared with those obtained when using mineral oil, showing that the use of vegetable oil has a protective effect over mechanical properties of the studied types of paper insulation.

Study on the degradation of the compression strength of spacers made of high-density pressboard used in power transformers under the influence of thermal ageing

“…Besides, it can be inferred that a reduction in the formation of acids, which could be achieved by changing some operating conditions or using other dielectric liquids, would better preserve the compressive properties of high-density cellulosic components in power transformers in operation. In the future, it would be interesting to study the compressive mechanical response of high-density pressboard when using other dielectric liquids, as it has been reported that the use of vegetable oil better preserves the tensile mechanical properties of thin paper during ageing, see Oria et al (2022), but there is no information about the effects of using this oil on compressive properties of pressboard.…”

Application of back propagation neural network in complex diagnostics and forecasting loss of life of cellulose paper insulation in oil-immersed transformers

“… Refs. Years Proposed technique Contribution 42 2021 Regression modeling The study estimated DP utilizing the furfural marker at different oil-to-pressboard ratios and oil change statuses 43 2022 Artificial Neural Network (ANN) The study estimated furans by analyzing temperature, carbon dioxide, carbon monoxide, and moisture to estimate DP 44 2022 Empirical modeling The study estimated DP utilizing methanol concentrations obtained at low temperatures. The relative error was 7% 45 2023 ANFIS, Roger’s ratio approach A hybrid Rogers ratio technique-based ANFIS was proposed to detect transformer faults.…”

Understanding the Ageing Performance of Alternative Dielectric Fluids

“…Numerical simulations carried out have shown that the temperatures reached in a transformer using esters could be similar, or even lower, to those reached with mineral oils in adapted winding designs [12], [13], [14] Some manufacturers apply special treatments to improve the viscosity or the oxidation stability of these alternative liquids [15]. The effect of the fluid used on the degradation of the solid insulation, measured by the control of the chemical [16], mechanical [17] or light techniques [18] after a thermal [19] or electrical [20] ageing process, have also been afforded. Researchers have demonstrated that the degradation suffered by the cellulosic materials is lower when the cooling fluid is a natural ester, derived from sunflower, rapeseed, soy or palm, instead of a mineral oil at similar conditions [16], [17], [19], [21], [22], [23].…”

“…The effect of the fluid used on the degradation of the solid insulation, measured by the control of the chemical [16], mechanical [17] or light techniques [18] after a thermal [19] or electrical [20] ageing process, have also been afforded. Researchers have demonstrated that the degradation suffered by the cellulosic materials is lower when the cooling fluid is a natural ester, derived from sunflower, rapeseed, soy or palm, instead of a mineral oil at similar conditions [16], [17], [19], [21], [22], [23]. The levels of degradation depended on the specific oil and the conditions of the study, not all the natural esters protected the insulation from degradation in the same degree [19], [24], and other natural esters of different origin (corn, peanut, coconut or mustard) showed worst performance [25], [26], [27], [28] The results with synthetic esters reflects slightly lower degradation than with the mineral oils [19], [29].…”

“…Additionally, the conditions of the ageing usually vary. Only respecting the researches here cited, there are examples of thermal ageing carried out at 80 [29], 100 [29], 110 [16], 120 [16], [21], [24], [29], [32], [35], 130 [16], [19], 140 [32], [35], 150 [17], [22], [25], [33], 151 [23], 160 [23], [32], [33], 165 [22], 168,5 [23], 170 [33], [36], 180 [22], 200, 400 and 800 • C [37]. This dispersion is worsened if the moisture initial content is considered.…”