Preparation of Composite Insulating Paper With Decreased Permittivity, Good Mechanical and Thermal Properties by Kevlar/Nano Cellulose Fibrils/Softwood Pulp Hybrid

Yang Mo,Tiantian Zou,Lijun Yang,Ruijin Liao,Wei Hou

doi:10.1109/access.2019.2930981

Yang Mo, Tiantian Zou + Show 3 more

Open Access

https://doi.org/10.1109/access.2019.2930981

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Abstract

Kevlar pulp treated with low-temperature plasma and nano cellulose fibrils (NCFs) have been introduced as reinforcements in the preparation for composite insulating paper with low relative permittivity, dielectric loss, good mechanical properties, and thermal stability. More polar groups of Kevlar fibers could be exposed after plasma treatment. Results showed that the relative permittivity of the composite paper containing 20% Kevlar pulp, 10% NCF, and 70% softwood pulp is decreased by 29.6% and the dielectric loss is decreased by 43.2% at 50 Hz, 25°, compared with the conventional paper formed by pure softwood pulp. The change was due to the introduction of Kevlar pulp with intrinsic low dielectric constant and loss, which decreases the whole polarizability of the paper. The mechanical properties of the composite paper became worse after introducing 20% Kevlar pulp. About 10% NCF can work as a mechanical reinforcement to compensate for the tensile and Yang's modulus loss. Scanning electron microscopy results showed that NCF could fill the void defects and improve the interface bonding of the fibers to enhance the paper mechanical properties. The composite paper also had better insulating and thermal properties than the conventional paper. It has been concluded that the Kevlar pulp/NCF/softwood pulp composite paper has the potential to replace the pure softwood paper for the application of high-voltage ac transformer insulation.

Highlights

Lignocellulose material, together with insulating oil, is widely applied in the power transformers due to its low cost, renewability and relatively good insulating performances [1]
This study aims to prepare a kind of composite insulating paper with low permittivity, low dielectric loss and good mechanical properties suitable for insulation of ultra-high voltage transformers, by blending Kevlar pulp, nano cellulose fibrils (NCFs), and lignocellulose pulp
In this study, Kevlar pulp treated with low temperature plasma, NCF and softwood pulp were applied to prepare a novel composite insulating paper with low relative permittivity, low dielectric loss, and good mechanical and thermal properties

Summary

Introduction

Lignocellulose material, together with insulating oil, is widely applied in the power transformers due to its low cost, renewability and relatively good insulating performances [1]. The main insulation structure in transformer is mainly formed by oil ducts, pressboards and paper barriers [2]. The oil-impregnated lignocellulosic insulating paper has a permittivity around 4.1–4.8, which is over twice that of insulating oil [3]. The electrical field strength in the oil ducts is more than two times that in paperboards under AC electrical stress. The electrical strength of the oil is far less than that of insulating paper. Insulating oil is easy to initiate discharge and becomes the weakness of the insulation. Reducing the permittivity of the insulating paper

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Conclusion