Effects of aging on the mechanical and dielectric properties of transformer grade Kraft paper

Hosier, I. L.; Lewin, P.L.; Pilgrim, James; Wilson, Gordon

doi:10.1109/eic47619.2020.9158661

Cited by 4 publications

(5 citation statements)

References 10 publications

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“…The break strain was higher in the cross-fiber (transverse) direction than in the fiber (longitudinal) direction as anticipated [8] and following aging, the break strain was reduced. Since examples of the raw data are provided elsewhere [23], for brevity, Fig. 3 shows the correlation [9] between break strain and measured DP which holds for both thermal aging and UVC exposure.…”

Section: A Initial Characterizationmentioning

confidence: 99%

“…To avoid such complications, the authors have elected to use a fan oven and our previous investigations [23] have shown that this methodology provides suitable samples exhibiting minimal oxidation. Oil flow testing [24], which to our knowledge has never been undertaken previously on Kraft paper, then showed that the surface texture of aged paper can be disrupted by high rates of oil flow; however, at the low oil temperatures and short exposure times, which are far from conditions in a working transformer, there was no detectable erosion.…”

Section: Introductionmentioning

confidence: 99%

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An Assessment of the Potential for Oil Flow Damage in Kraft Paper Under Normal Operation and Reclamation in a High-Voltage Transformer

Hosier

Lewin

Wilson

2022

IEEE Trans. Dielect. Electr. Insul.

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Thermal aging and UV irradiation are used as methods to prepare samples of Kraft paper spanning its full lifecycle within a high voltage transformer, from new to end of life. The mechanical break strain is correlated to the DP value, representing a progressive deterioration of mechanical properties during aging. Subsequent exposure to oil flow mimicking both normal plant operation and reclamation activities, shows that aged paper exposed to high rates of flow experiences noticeable surface roughening. Despite this, no measurable erosion occurs even after long term temperature/flow cycling in used mineral oil containing a notable particulate content. This indicates that Kraft paper is unlikely to be eroded by normal reclamation activities, even in a severely aged asset. This confirms the validity of using this approach to extend plant life.

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Section: A Initial Characterizationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

An Assessment of the Potential for Oil Flow Damage in Kraft Paper Under Normal Operation and Reclamation in a High-Voltage Transformer

Hosier

Lewin

Wilson

2022

IEEE Trans. Dielect. Electr. Insul.

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“…The papers were cut into 7 cm square pieces for dielectric analysis and into strips of 26 cm x 1.5 cm for tensile test. Due to paper anisotropy [9]- [11], the strips were cut with two different fiber direction angles (longitudinal and transverse) to measure mechanical properties (tensile strength, strain, energy per unit volumen...).…”

Section: A Samplesmentioning

confidence: 99%

Dielectric and mechanical assessment of cellulosic insulation during transformer manufacturing

Sanz

Sancibrian

Fernández

et al. 2021

2021 IEEE Electrical Insulation Conference (EIC)

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Due to the impact of cellulose of paper insulation on transformer life, it is imperatire to remove moisture from the oil and the solid insulation. Several techniques have been implemented during manufacturing of power transformers to reduce water content in transformers. These drying processes can involve different costs and time, and they can damage the insulation paper. In this work, a drying process has been implemented in the laboratory trying to simulate the most aggressive conditions that can be suffered by the paper in transformer manufacturing in a real industry. Then the effect of the drying process on paper was evaluated using the analysis of mechanical and dielectric properties and the degree of polymerization. Different commercial papers were studied to quantify the possible degradation induced by the drying process. The results of the mechanical strength study showed a reduction on the degree of polymerization from 1100 to 850 after 4 days of drying. The dielectric analysis of the samples showed different behavior in one of the solids evaluated and it was also found a decreased hygroscopic capacity of degraded samples in comparison with new samples.

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“…Even though this ageing cannot be avoided, its effect on the dielectric behaviour of the solid insulation is not clear. Some authors have tried to establish this relationship, [4]- [6]. Since these latter studies found different results when quantifying the effect of DP on the dielectric properties, it is not possible to drawn clear conclusions.…”

Section: Introductionmentioning

confidence: 99%

Numerical and experimental evaluation of dielectric properties of thermally aged insulating paper used in power transformers

Díaz

Méndez

Olmo

et al. 2022

2022 IEEE 4th International Conference on Dielectrics (ICD)

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Due to the relevant role of the cellulosic insulation in the dielectric system of a power transformer, it is necessary to know its dielectric properties and its evolution as insulating material. The dependence of the dielectric properties of solid insulation on the moisture content, temperature, or pressure is well-defined. However, it is not clear the effect of the paper degradation on its insulating capacity. To study the impact of ageing on the dielectric properties, samples of Kraft paper were subjected to an accelerated hygrothermal ageing. Degree of polymerization (DP) value was reduced from 1000 to 200, with intermediate study points. All samples were conditioned to the same moisture content in order to only evaluate the effect of the paper degradation. Different dielectric properties, such as loss factor (tan δ) and complex permittivity (ε) were measured using the dielectric spectroscopy technique. These experimental results were used to develop a numerical model with the finite elementbased tool Comsol Multiphysics. This model provided some extra information about the material properties, such as the electric field distribution. Results showed that the degradation of Kraft paper modifies its dielectric response.

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Effects of aging on the mechanical and dielectric properties of transformer grade Kraft paper

Cited by 4 publications

References 10 publications

An Assessment of the Potential for Oil Flow Damage in Kraft Paper Under Normal Operation and Reclamation in a High-Voltage Transformer

An Assessment of the Potential for Oil Flow Damage in Kraft Paper Under Normal Operation and Reclamation in a High-Voltage Transformer

Dielectric and mechanical assessment of cellulosic insulation during transformer manufacturing

Numerical and experimental evaluation of dielectric properties of thermally aged insulating paper used in power transformers

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