Download Novel Dielectrics and Advanced Electrical Insulation Technology

Novel Dielectrics and Advanced
Electrical Insulation Technology
Hulya Kirkici, Ph.D.
IEEE Conference Committee; TAB Representative
IEEE DEIS Past President (2009 & 2010)
Electrical and Computer Engineering,
Auburn University, Auburn, Alabama, 36830, USA
July 21, 2011, IEEE POCO, H. Kirkici
IEEE Regions and
Auburn University, AL, USA
• Enrollment: >25,000 (~5,000 postgraduate, >20,000 undergraduate)
• Offers degrees in 13 schools & colleges
• Chartered in 1856, Opened in 1859
http://en.wikipedia.org/wiki/Auburn_University
July 21, 2011, IEEE POCO, H. Kirkici
IEEE Dielectrics and Electrical
Insulation Society (DEIS)
• One of the technical Societies of IEEE
• Field of interest:
– the study and application of dielectrics from the molecular
level, through nano-structured materials, to insulation
systems in industrial, commercial, and power system
equipment, to emerging applications such as those at high
power levels and in biological and other small-scale
systems.
• DEIS supports the entire scope of this field:
– from advancing the basic science, to enhancing the ability
of practicing engineers to use emerging dielectric
materials, to the development of standards for the
prudent application of existing and new insulation systems.
• http://ewh.ieee.org/soc/deis/
July 21, 2011, IEEE POCO, H. Kirkici
July 21, 2011, IEEE POCO, H. Kirkici
Research Program
• Fundamental Research in Physical-Electronics
– Dielectrics; electrical insulation; high voltage-high frequency
dielectric breakdown applied to space and aerospace
vehicles.
– Surface Flashover Characteristics of nanodielectrics in
vacuum and sub-atmospheric pressures
– Pulsed Electric Field Studies of Bio-Dielectric Weed Seeds
– Repetitive Pulsed Power: cold cathode development –
carbon nano tube (CNT) fabrication
July 21, 2011, IEEE POCO, H. Kirkici
Electrical Insulation and Dielectrics
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Everything electrical has to be insulated to prevent electrical breakdown in circuits /
systems, thus the use of dielectric materials
Insulators (dielectric materials) can be solid, liquid, gaseous form, in which valance
electrons “strongly” attached to the atom under “normal” electrical stress (provide “high”
resistance to the passage of the “electrical current”)
“High Voltage” is defined as the voltage above which breakdown phenomena are likely to
occur (from a few volts in microelectronics devices to MV in utility power systems).
Anything that reduces weight is important particularly for airborne applications.
Electrical Insulation in space like environments usually have special requirements and
design techniques specific to airborne vehicle power systems, high-voltage parts,
components, and sub-systems.
A few 100 volts is “high-voltage” for systems operating in sub-atmospheric pressures.
Dielectric breakdown under high frequency applied voltage is lower than dc breakdown
under same conditions.
Vacuum and partial vacuum surface flashover and gaseous breakdown are more-likely to
occure than solid-dielectric breakdown.
July 21, 2011, IEEE POCO, H. Kirkici
Dielectrics and Factors Affecting
dielectric Strength
• Dielectric materials serve as
– Insulator in electrical components
– Working media (plasma switches)
– Support of electrical circuit while isolating the system from
outside environment
• They either intentionally breakdown (to perform a desired
task – vacuum or plasma switches) or they may breakdown
unintentionally (resulting a failure)..
• Either case understanding of the breakdown characteristic
of materials is important to achieve the intended “task”
• Dielectric strength decreases with increase in thickness in
solid dielectrics
• It is function of pressure (gases and liquids)
• It decrease with increase frequency (both gases and solids)
Insulation and Gaseous Breakdown in Sub-atmospheric
Environments
Breakdown voltage of a gas in a uniform field is
constant if the product, pd, is held constant
Breakdown Voltage (Volts -rms)
10000
8000
6000
4000
Electrodes: Parallel Plates
Temperaure: 300 K (23 C)
Frequency: 400 Hz
2000
n(
go
Ar
1000
800
600
CO2
O2
400
el
ste
ctr
ele
es)
od
H2
Ne
Air
200
He
N2
100
0.2
0.5
1
Operates in
10e-6 to 10e-10 torr
(& crosses entire range)
m
nu
mi
Alu
(
g on
Ar
2
5
10
20
50
(Pressure)x(Spacing) (Torr-cm)
100
o de
ctr
ele
200
s)
500
20 to 30 km
(100 to 10 torr)
Crosses
entire range
July 21, 2011, IEEE POCO, H. Kirkici
July 21, 2011, IEEE POCO, H. Kirkici
High –Frequency Breakdown
• To reduce weight and increase efficiency, switched-mode power
supplies are favorable for space / aerospace power systems.
• Switching regulators are used as replacements for the linear regulators
when higher efficiency, smaller size or lighter weight are required.
• They are, however, more complicated, their switching currents can
cause electrical noise problems if not carefully suppressed
From: H. Kirkici, SEA International, Space power
Systems Conference
July 21, 2011, IEEE POCO, H. Kirkici
High Frequency Breakdown at atmospheric
pressures: Earlier Work
Breakdown at high frequency voltage in air;
Point-plane electrodes, inhomogeneous field
Breakdown at high frequency voltage in air;
Homogenous field
High frequency breakdown in air
[From: W. Pfeiffer, IEEE Trans. EI, April 1991]
kHz Frequency Breakdown in Partial Vacuum
Breakdown voltage versus pressure in Helium for
DC and 20 kHz (unipolar - sinusoidal) field.
K. Koppisetty & H. Kirkici., TDEI 2007
kHz Frequency Breakdown in Partial
Vacuum (square pulsed, unipolar)
DC
Breakdown voltage as a function of pressure
helium (top) and Nitrogen (bottom) for point
to point electrode geometry.
K. Koppisetty & H. Kirkici
TDEI August 2008
Emission Spectroscopy at Breakdown
DC and 1 ms integration time
N2_line 1 refers to (0,0) line and N2_line2 refers to
(0,1) line of First Negative system
100kHz 10 ms integration time
100 kHz, 1.2 torr, 1 ms integration time
Nanodielectrics [1]
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Mix two things and get a new thing that is more than the sum of its parts
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Nanodielectrics (nanocomposites): fabricated by combining synthetic polymers (like
polyethylene) and nanoscale particles (made from silica or other metal oxides)
leading to materials with dramatically better electrical properties.
Used in electrical insulating applications; have higher voltage endurance; enhanced
breakdown strength; improved erosion resistance; better electrochemical treeing
performance; extended high-temperature & cryogenic operation.
Enhanced breakdown strength: insulation can be used more effectively or larger
voltages can be used (i.e. reduced thickness of cables or a circuit boards)
Voltage endurance: an order of magnitude difference can be seen – that means, if it
base dielectric operates five years, theoretically the nanodielectrics expected to
operate ~ 50 years (can reduce the need for maintenance and extend the life of
equipment that uses insulating materials, such as the thermosetting resins used in
large electrical generators).
Tailoring of permittivity and losses (at frequencies where conduction and interfacial
effects are minimal)
One of the initial papers is by Prof. T.J. Lewis (now professor emeritus at the
University of Wales): a theoretical paper on the potential of nanodielectrics.
An early a previous patent in 1988 by: Johnston & Markovitz
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[1] J.K. Nelson & L. Schadler; Special Issue, IEEE Trans. on Dielect. and Elect. Insulation Vol. 15, No. 1; Feb. 2008
July 21, 2011, IEEE POCO, H. Kirkici
Nanodielectrics (cont.)
Compiled from a From: J. K. Nelson,
Nordic Insulation Symposium
Tampere, Finland, June 2010
July 21, 2011, IEEE POCO, H. Kirkici
Nanodielectrics (cont.)
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Typically about 10 nm in radial dimension
Represents a physical region whose properties differ from the bulk polymer
Rich in surface radicals and charge trapping sites
Provides the basis for permitting a measure of selfassembly, and tailoring through
preferential coupling
From: J. K. Nelson; Nordic
Insulation Symposium
Tampere, Finland, June 2010
July 21, 2011, IEEE POCO, H. Kirkici
High Voltage / High Frequency Surface
Breakdown of Nano-dielectrics
• Surface flashover phenomenon (breakdown) in vacuum is due to
field emission of electrons at the cathode ‘triple-junction’
(electrode/insulator/vacuum interface) when the applied field
exceeds a certain threshold value [Latham,1995; Kirkici, 1997].
• Surface flashover initiation mechanism in sub-atmospheric
pressure is similar to the vacuum surface flashover with an
influence of avalanche process
• Other contributing factors
– the type of dielectric material: Polymer, Nano-dielectric (filled epoxy), Nanoparticulates on silicon, oil impregnated paper, etc.,
– its surface condition: smooth polished, mechanically roughened, corona/plasma
etched surfaces
– the type of electrode material and its corresponding surface condition
– selected environments: vacuum, atmospheric pressure, partial vacuum, ionosphere
(plasma), contamination
– the applied field DC field, AC – 50/60 Hz, AC-rf (kHz and MHz), Pulsed (single or
repetitive – kHz), Uniform / non-uniform fields
July 21, 2011, IEEE POCO, H. Kirkici
High Voltage / High Frequency
Breakdown of Nano-dielectrics (cont.)
Nano-particle
exposed on the
surface of
dielectric polymer
Breakdown comparison
under different operation
conditions
Breakdown characteristics of nano-dielectrics
(fabricated from nano particles in polymer
materials).
dc & ac
applied fields
Surface breakdown of nanodielectrics
and plasma formation
From: K. Koppisetty, M. Serkan, and H. Kirkici, Image Analysis: A Tool for Optical-Emission
Characterization of Partial-Vacuum Breakdown, IEEE Transactions on Plasma Science, Vol.: 37, pp
153-8, 2009
July 21, 2011, IEEE POCO, H. Kirkici
High Voltage / High Frequency Surface
Breakdown of Nano-dielectrics (cont.)
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Partial vacuum (sub-atmospheric) condition in Breakdown voltage, current and
Helium and Nitrogen
light emission waveforms for 2%
DC and 20kHz AC (with DC off-set)
filled nano-dielectric sample under
Non-uniform field (curved electrodes)
pulsed electric field
Copper electrodes with 1 cm electrode gap
Non-filled and filled Epoxy (prepared in-house):
Mostly micron size particles cast into epoxy to
prepare filled dielectric material
Smooth and plasma etched surfaces of the
dielectric material
Optical Spectra of the Emission
From: Li and Kirkici, IEEE IPMHVC, 2010]
Three different
sample
surface
flashover
characteristics
comparison
July 21, 2011, IEEE POCO, H. Kirkici
Single and Polycrystalline
Diamond Surface
Flashover in Vacuum (1)
Electrode gap = 1 mm
July 21, 2011, IEEE POCO, H. Kirkici
Single and Polycrystalline Diamond Surface
Flashover in Vacuum (2)
From: H. Kirkici, IEEE-Trans on Dielectrics and Electrical Insulation, 1997
July 21, 2011, IEEE POCO, H. Kirkici
Diamond-Like Carbon Thin
Films Surface Flashover in
Vacuum
[H. Kirkici, TDEI 1997]
July 21, 2011, IEEE POCO, H. Kirkici
Bio-dielectrics Research and
Applications
• From an electrical viewpoint, the lipid bilayer portion of the cell membrane is a
good insulator (with averaged membrane resistivity of more than 109 W-cm for
the plasma membrane) – thus “biodielectrics”
• Living biological cells contain many membranes, first at the outer boundary
(the plasma membrane), and then further in, at the boundary of the nucleus,
mitochondria, endoplasmic reticulum and many other subcellular structures.
• The function of the cell membranes is to isolate regions of different materials,
but also to facilitate the flow of selected types of ions and molecules from one
region to the other.
• With a relative dielectric constant of approximately 5, the cell membrane
capacitance per unit area is on the order of 10–6 F/cm2.
• Depending on the type of membrane, and in turn the lipid composition, and
the number and types of channels, the average, effective membrane resistivity
varies tremendously
July 21, 2011, IEEE POCO, H. Kirkici
Equivalent Circuit of a Cell in
Suspension
From: K.H.
Schoenbach
et.al., IEEE TPS,
1997
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Capacitive and resistive properties of the suspension:
http://www.odu.edu/
engr/bioelectrics/rese
arch.html
– Capacitance Cs and resistance Rsp (parallel to the cell); Resistance Rss (in series to the cell)
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Capacitive and resistive properties of the cell immersed in the suspension:
– Capacitance Cc of the cell membrane, in series with the resistance of the cell interior Rc.
(Typical capacitances per unit area for the cell membranes are 1 micro-F/cm)
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The cell interior has a resistivity ρc on the order of 100 ohm-cm (model does not take the
effects of the structures inside the cell into account).
The membrane consists of a lipid bilayer with proteins embedded into the bilayer. Some
of the proteins act as voltage-gated channels that provide a pathway for the flux of ions.
– This effect is modeled by voltage-dependent conductances gi in series with driving voltage
sources Vi (Nernst potential) for each ion species
July 21, 2011, IEEE POCO, H. Kirkici
Pulsed Electric Field Effects on
Biological Matter
• Understanding of the electric properties of biological cell membranes and
bioengineering applications of electrical membrane effects.
• Measurements of electrical properties of natural and artificial lipid bilayer
membranes, Studies on electrical conduction and breakdown of
biomembranes, applications of stimulated electrical membrane effects, such
as electroporation and intracellular electromanipulation in bioengineering
are some of the current research in this field.
• Application of large electric fields to cells over times large compared to the
charging time of the membranes (~1 microsecond for the plasma membrane
of mammalian cells) results in charge redistribution, and the build-up of a
transmembrane voltage in addition to the resting voltage.
• Once the transmembrane voltage exceeds a few hundred mV, structural
rearrangements begins, and the membrane rapidly acquires some type of
new electrical conduction pathways.
• A large research Group at Old Dominion University, University of Southern
California, Japan, Germany,
July 21, 2011, IEEE POCO, H. Kirkici
Pulsed Electric-field effect on
biodielectric weed-seeds
Published in: International Journal of Vegetable Science, 2007
July 21, 2011, IEEE POCO, H. Kirkici
Abstract: Dielectrics have been fundamental building blocks of electrical
insulation for centuries and they have been studied in every aspect of
science and technology from chemistry, physics, utility power, and
advance electric power systems. This talk will review the state
of-the-art dielectric materials with an emphasis on biodielectric,
nanodielectrics and other novel dielectric materials and applications.
Pulsed electric field effects on biodilectrics and nanodielectrics uses
in power are presented. Space and aerospace vehicles require light
weight electrical power systems with efficient power conversion in order
to full fill desired high power levels onboard. With the advances in
power electronics devices this is now possible and the state-of-the art
aerospace power systems are designed utilizing kHz switching frequencies
and operated at higher voltages than the traditional 28V, distribution
power levels. This talk will also review the advances in electrical
insulation technology of high frequency, high altitude aerospace power
system and high voltage breakdown phenomena in partial pressure
environment.
July 21, 2011, IEEE POCO, H. Kirkici
Questions?
July 21, 2011, IEEE POCO, H. Kirkici