Performance Assessment of Cellulose Paper Impregnated in Nanofluid for Power Transformer Insulation Application: A Review

Abstract

Insulation cellulose paper is a basic measure for a power transformer’s remaining useful life, and its advantageous low cost, electrical, and mechanical properties have made it an extensive insulation system when impregnated in a dielectric liquid. Cellulose paper deteriorates as a result of ageing due to some chemical reactions like pyrolysis (heat), hydrolysis (moisture), and oxidation (oxygen) that affects its degree of polymerization. The condition analysis of cellulose paper has been a major concern since the collection of paper samples from an operational power transformer is almost impossible. However, some chemicals generated during cellulose paper deterioration, which were dissolved in dielectric liquid, have been used alternatively for this purpose as they show a direct correlation with the paper’s degree of polymerization. Furthermore, online and non-destructive measurement of the degree of polymerization by optical sensors has been proposed recently but is yet to be available in the market and is yet generally acceptable. In mitigating the magnitude of paper deterioration, some ageing assessments have been proposed. Furthermore, researchers have successfully enhanced the insulating performance of oil-impregnated insulation paper by the addition of various types of nanoparticles. This study reviews the ageing assessment of oil-paper composite insulation and the effect of nanoparticles on tensile strength and electrical properties of oil-impregnated paper insulation. It includes not only significant tutorial elements but also some analyses, which open the door for further research on the topic.

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

“…Analysis of the data collected was changed into descriptive data ranging from A “Excellent” to E “Critical” condition 112 , 113 . DP of cellulose paper 114 , 115 was used to estimate the remaining life of the transformer. An accurate estimate of DP to 2FAL was achieved by implementing an algorithm with a BPNN 116 , 117 .…”

Analyzing Transformer Insulation Paper Prognostics and Health Management: A Modeling Framework Perspective

“…Bleaching of the paper is circumvented to increase the content of lignin in the paper, which helps improve its thermal strength and integrity [20]. Figure 3 represents the molecular structure of cellulose [7], [21]. Typically, solid insulation comprises two types of cellulose, which are thermally upgraded paper (TUP) and Kraft paper [22].…”

“…Subsequently, the dried sample is introduced into the copper ethylenediamine solvent, and stirred until fully dissolved using a magnetic stirrer. The degree of polymerization is then determined by measuring the outflow time of the prepared solution with a Ubbelohde viscometer at a temperature of 20°C [7], [24]. The DP of new insulation paper is about 1000 -1200 where its lifespan is approximately 180 000 h while the insulation paper DP has its least value (200) at the hottest spot of the transformer, which is considered its end-of-useful life [4], [25].…”

“…The DPn is DP after the ageing period tn, DPn-1 is the paper DP at the end of the last interval, Ea in J/mol is the activation energy, R in Jmol -1 K -1 is the ideal gas constant, tn is time-period, and T is the temperature in Kelvin. The value for A is obtained from the oxygen level of the insulating liquid and the moisture content of the insulating paper as seen in [7].…”

“…Measuring the degree of polymerization directly from an insulating paper sample is a practicable approach. However, when it comes to a power transformer in active operation, adopting this practice involves undesirable disconnection and invasive handling of the unit [7]. Hence, several techniques discussed later in this study have been employed as an indirect measure due to the established correlations between degree of polymerization (DP) and these parameters.…”