KTH ROYAL INSTITUTE OF TECHNOLOGY Cellulose-based electrical insulation A more efficient electrical energy generation and transmission will be increasingly vital to meet growing societal needs. The major failures in oil- filled high voltage transformers, a key component in power transmission networks (with paper and pressboard used as the solid insulation material), are related to the insulation material. The aim of this PhD-project is to use novel modification routes for wood-fibres, such as nano fibrillation and layer-by-layer (LbL) adsorption of modifying components to clarify the influence of chemistry and morphology on relevant electrical phenomena and improve the electrical insulating capability of wood-fibre based electrical insulation. REBECCA HOLLERTZ Supervised by Lars Wågberg and Claire Pitois Rebecca Hollertz PhD-Student KTH Royal Institute of Technology School of Chemistry Department of Fibre and Polymer Technology Teknikringen 56 10044 Stockholm IN COOPERATION WITH: Email: [email protected] Permittivity and dielectric loss are important dielectric properties which affect the loss of energy and the build- up of electric fields in the insulator, and at inter-faces. The dielectric strength is used to describe the maximum electric field a material can with-stand before flash-over or short- circuiting. Before experiencing break- 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 transformer failures. The ultimate goal of this PhD project is a better understanding of which paper properties are most critical, and should consequently be altered, to control the streamer inception and propagation. 3. Effect of composition and morphology on the dielectric response *** . a. Dielectric spectroscopy on paper samples 2. Silica nanoparticle modified papers to enhance dielectric properties ** Model surfaces of pure lignin and glucomannan Papers were prepared from fibres where silica nanoparticles had been pre-adsorbed onto the fibres using the layer-by-layer (LbL) technique. Setup for dielectric measurements in vacuum. 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. b. Spectroscopic ellipsometry on model surfaces 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. The setup constructed gives valuable information about streamer inception and propagation at the solid-liquid interface and will be used to characterize the influence of the solid material by testing different polymers and modified paper sheets. Some of the parameters investigated are porosity, surface roughness, polarizability and electron affinity. 1. Streamer inception and propagation * INTRODUCTION DIELECTRIC PROPERTIES RESULTS AND OUTLOOK * David Ariza, Marley Beccera, Rebecca Hollerz, Claire Pitois, , IEEE Conference on Electrical Insulation and Dielectric Phenomena, 2015 ** 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 Increasing voltage levels Integration of renewables Increased reliability Demand for improved electrical insulation materials Education: M.Sc. in Engineering 2008 Licentiate Thesis 2014 Ph.D. planned 2016 Research interest: Polymer Science Pulp and Paper Chemistry Dielectrics Nanotechnology ABOUT ME PAPER Streamer inception