Ageing rate of paper insulation used in power transformers Part 2: Oil/paper system with medium and high oxygen concentration

Aging rate of grade 3 presspaper insulation used in power transformers

“…The water content of Kraft and Grade 3 was measured during one aging test, at 100°C, high oxygen and 2.7% paper water content. A discussion on the comparison between Kraft paper, pressboard and the value provided by the Fessler equation was given in [2]. The measured water content of the pressboard, 2.6 %, was found to be very similar to its calculation, 2.7 %.…”

“…This was performed by adding oxygen if the level of this gas became too low, or by removing the paper and conditioning to return its water content back to the desired value. This technique is fully described in [1,2].…”

“…IN our previous work equations for modelling the aging of both Kraft and thermally upgraded paper were given [1,2]. The motivation for this work was to provide transformer users a tool to estimate the end of life of their assets.…”

“…(4) was used to model the fall in DP for both oxidation and hydrolysis reactions, based on a pseudo zero order kinetic equation. Emsley substituted equations (1) and (3) to form this equation [8], which was used to model the degradation of Kraft and thermally upgraded Kraft papers in [1,2]. (4) In order to apply equation (4) to a transformer using Grade 3 presspaper the A-values must be found, which was the goal of this research.…”

A Review of Condition Monitoring Assessment of Power Transformers Insulation

“…These diagnostic techniques include fault gas analysis, moisture analysis, dielectric monitoring, UHF sensors, acoustic sensors, off line or on line PD testing, dielectric response measurements, time response dielectric spectroscopy, dielectric discharge method and return voltage measurement, interpretation of measurements, transfer function analysis and expert system diagnostic software. The phenomenon of understanding the ageing of Kraft paper insulation shows that paper degradation is the cause of production of furan based aldehydes or hydrocarbon gases produced in mineral oil which results in change in DP (degree of polymerization) of cellulose in insulating paper or effect of various parameters using electrical, mechanical and chemical techniques is evaluated which are relevant to assess the state of both paper and oil insulation with identifying its effective life [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Thermal degradation of Kraft paper is caused due to increase in operating temperature so this insulating paper is thermally upgraded to neglect the aging by treating it with additional additives which result in formation of a new modified insulating paper such as amine modified Kraft paper, cyan ethylated paper, and carbamate modified paper by chemical modification for better performance and some other alternative oils are used as a substitute to mineral oil like alkyl-naphthalene oil, vegetable oil to increase the life of oil-paper insulation [21][22].…”