cellulose-based electrical insulation
TRANSCRIPT
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