. Cellulose-based electrical insulation REBECCA HOLLERTZ Supervised by Lars Wågberg and Claire Pitois

DIELECTRIC INTRODUCTION

PROPERTIES The aim of this PhD-project is to use novel A more efficient electrical energy generation and modification routes for wood-fibres, such as nano Increasing voltage levels transmission will be increasingly vital to meet Demand for fibrillation and layer-by-layer (LbL) adsorption of Permittivity and dielectric growing societal needs. The major failures in oil- improved electrical loss are important dielectric filled high voltage transformers, a key component modifying components to clarify the influence of Integration of renewables insulation properties which affect the in power transmission networks (with paper and chemistry and morphology on relevant electrical materials loss of energy and the build- pressboard used as the solid insulation material), phenomena and improve the electrical insulating Increased reliability up of electric fields in the are related to the insulation material. capability of wood-fibre based electrical insulation. insulator, and at inter-faces. The dielectric strength is used to describe the RESULTS AND OUTLOOK maximum electric field a material can with-stand * before flash-over or short- 1. Streamer inception and propagation circuiting. Before experiencing break- Streamer inception down, the insulating material is often subjected to deteriorating discharges and streamers which can also be triggered and analysed in the laboratory. Streamers, conducting gaseous channels which can travel in high speed, at oil- pressboard inter-faces have been identified as a signi- ficant cause responsible for PAPER transformer failures. The ultimate goal of this PhD project is a better The setup constructed gives valuable information about streamer inception and propagation at the solid-liquid interface and understanding of which will be used to characterize the influence of the solid material by testing different polymers and modified paper sheets. paper properties are most critical, and should  Some of the parameters investigated are porosity, surface roughness, polarizability and electron affinity. consequently be altered, to control the streamer inception and propagation. 2. Silica nanoparticle modified papers to enhance dielectric properties ** ABOUT ME This study showed that the layer-by-layer technique provides an efficient method to tailor the dielectric and mechanical properties of wood-fibre-based electrical insulation materials with the aid of polyelectrolytes and inorganic nanoparticles.

Papers were prepared from fibres where silica nanoparticles had been pre-adsorbed onto the fibres using the layer-by-layer (LbL) technique. Education: M.Sc. in Engineering 2008 Licentiate Thesis 2014 Ph.D. planned 2016 *** 3. Effect of composition and morphology on the dielectric response Research interest: Polymer Science a. Dielectric spectroscopy on paper samples b. Spectroscopic ellipsometry on model surfaces Pulp and Paper Chemistry Dielectrics

Nanotechnology Model surfaces of pure lignin and glucomannan

Setup for dielectric measurements in vacuum. IN COOPERATION WITH:

The dielectric response is highly dependent on density since paper is the high-permittivity and high-loss component in the oil- paper system. The morphology of the paper does not affect the dielectric response Lignin contributes to increased charge transport and polarizability for the investigated materials in studied frequency ranges.

KTH ROYAL INSTITUTE OF TECHNOLOGY Rebecca Hollertz KTH Royal Institute of Technology Email: [email protected] PhD-Student School of Chemistry Department of Fibre and Polymer Technology Teknikringen 56 * David Ariza, Marley Beccera, Rebecca Hollerz, Claire Pitois, , IEEE Conference on Electrical Insulation and Dielectric Phenomena, 2015 10044 Stockholm ** Rebecca Hollertz, David Ariza, Claire Pitois, Lars Wågberg, IEEE Conference on Electrical Insulation and Dielectric Phenomena, 2015 *** a. Rebecca Hollertz, Claire Pitois, Lars Wågberg , IEEE Transactions on Dielectrics and Electrical Insulation, 22, p 2239-2248, August 2015 and b. Rebecca Hollertz, Hans Arwin, Bertrand Faure, Yujia Zhang, Lennart Bergström, Lars Wågberg, Cellulose, 20, p. 639-1648, August 2013