Download - Clean%2C High Performance Materials
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Challenge the future
DelftUniversity ofTechnology
Clean, high performance materials
Challenges and developments
Peter Morshuis
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Materials used in
Electrical Power Engineering
The building blocks of electrical power components
Metals (conductors, housing)
Dielectrics (electrical insulation, power electronics, support structures, cooling)
Gasses
Liquids
Solids
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Material challenges
(clean, high performance)
Environment friendly during entire life cycle
High efficiency/Low losses
Long life
Smart, self-healing
High energy density
Non-flammable
High operating temperature
In case of fire, low smoke production and non toxicity
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1.MetalsReduction of losses using superconducting materials
Reduction of losses using carbon nanotubes
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Carbon nanotubes
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3D model of three types of single-
walled carbon nanotubes. Source:
wikipedia
Length to diameter ratio > 107
Source: wikipedia
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Ballistic conduction
As the length of a conductor approaches zero, the conductance approaches a finite
value, and not infinity
This conductance is determined by the interface between conductor and contact
pads
If the length of the conductor is much smaller than the mean free path, all resistance
occurs at the interfaces
For a carbon nanotube: 6454 /tube
Closely packed parallel-connected tubes,
4 m long, 1.2 nm diameter: resistivity = 0.88 cm
Copper: resistivity = 1.67 cm
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Ultra low resistivity in practice
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Calculated resistivity of composites of
CNT and copper
8Source: O. Hjortstam,et al, Applied Physics A, Vol. 78, No. 8, 2004
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The importance of size
Take a sphere, with radius R
The surface/volume ratio increases with decreasing R
The effect?
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Ultracapacitors
Ultracapacitors can store only a fraction (5%) of the energy of an equivalent-size
lead-acid or lithium-ion battery.
The recipe for a better ultracapacitor is more surface area.
By using tightly bunched nanotubes, the surface area can be increased drastically.
MIT believes the storage capacity can be increased to between 25 and 50 percent
of a batterys energy. At that point, it becomes a compelling device for many
applications.
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A cross section of an electrode made
with carbon nanotubes. Source: MIT
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The ultracapacitor
increasing active surface area
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Plain Old Plates: In a typical capacitor,electrons are removed from one plate and
deposited on the other. Polarized molecules
in the dielectric concentrate the electric field.
One major factor determining capacitance is
the surface area of the plates.
Plated Packed with Ions: An ultracapacitor
can store more charge than a capacitor
can, because the activated carbon has a
pocked interior, much like a sponge. This
means that ions in the electrolyte can cling
to more surface area.
Enter the Nano-World: With finer
dimensions and more uniform distribution,
carbon nanotubes enable greater energy
storage in ultracapacitors than activated
carbon does.
Source: Joel Schindall, IEEE Spectrum Nov 2007
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2.Electrical insulationDevelopment of green and high performance alternatives
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Gases SF6
(sulphur hexafluoride)
SF6
is used world-wide in electric power industry for
Electrical insulation
Arc interruption
Cooling
Examples: Gas insulated systems, switchgear, transformers, capacitors, cables
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Gases - SF6
In spite of its advantages:
High dielectric strength
Thermal stability
SF6 has significant disadvantages:
Harmful for environment
Decomposes into toxic substances
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SF6
a greenhouse gas
According to the Intergovernmental Panel on Climate Change, SF6
is the most
potent greenhouse gas that it has evaluated, with a global warming potential of
22,200 times that of CO2
when compared over a 100 year period.
However, due to its high density relative to air, SF6
flows to the bottom of the
atmosphere which limits its ability to heat the atmosphere.
Its mixing ratio in the atmosphere is lower than that of CO2
about 6.5 parts per
trillion (1012) in 2008 versus 380 ppm (106) of carbon dioxide, but has steadily
increased (from a figure of 4.0 parts per trillion in the late 1990s). Its atmospheric
lifetime is 3200 years.
15Source: Wikipedia, Earth System Research Laboratory
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Time development CO2
and SF6
concentration in air(http://www.esrl.noaa.gov/gmd/ccgg/iadv/)
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Note the difference in y-axis scales: picomol/mol (left) versus micromol/mol (right)
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Alternatives for SF6
SF6-N
2mixtures (5% ... 20% SF
6), high pressure air insulation, vacuum insulation
Solid dielectric insulation
Fluid insulation (for instance esters, seed-based fluids)
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Liquids
Insulation systems consisting of a solid and a liquid are the most frequently used
systems in high voltage apparatus, where components have to be insulated and
loss heat has to be dissipated.
The requirements on the liquid part of the insulating system are not only the electric
and dielectric performance but also the performance regarding requirements
concerning the environment and low flammability.
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Liquids mineral oil
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Mineral oil is used world-wide in electric power industry for
Electrical insulation
Cooling
Examples: Transformers, cables
W4
W2
W4
W2
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Oil-impregnated insulation
Submarine cable links
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Liquids mineral oil
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In spite of its advantages:
High dielectric strength in combination with solids
High thermal conductivity
Proven technology
mineral oil has significant disadvantages:
Harmful for environment
Toxic
Low fire point
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Liquids alternatives for mineral oil
Use ester liquids (vegetable oils) instead of mineral oil
Esters are a class of chemical compounds and functional groups.
Examples: rapeseed oil, sunflower oil, biodiesel (natural); synthetic esters
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A carboxylic acid ester. R and R' denote any
alkyl or aryl group. Source: Wikipedia
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Ester liquid vs mineral oil
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Ester liquid vs mineral oil
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nanofluids
Thermal and electrical properties of liquids can be further improved
by adding small fractions (1%) of nanoparticles
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Solids
Oil-impregnated paper is used world-wide as insulation in
Transformers
High voltage cables
Capacitors
Epoxy resin is used in
Insulators
Cable accessories
Switchgear
Polyethylene is used in high voltage cables
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Solids - challenges
Design clean solid insulation materials to
-partly- replace oil insulated systems
Allow the construction of compact, light-weight insulation systems
Increase efficiency
Create self-healing properties
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Solids polymer insulation
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In spite of its advantages:
High dielectric strength
Low losses
clean
polymer insulation has significant disadvantages:
Bad heat conductivity
Susceptive to electrical degradation
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Solids designing new/better
properties
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We can add fillers to existing materials to affect properties
but we have reached the limits of what can be achieved
on microscopic to macroscopic level
Move to nano
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Nano dielectrics
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When we shrink the dimensions of a material we notice a change in materialproperties
In dielectric systems in which one of the length scales is below 200 nm, i.e.nanodielectrics, the surfacesand interfacesbetween dielectric elements become
increasingly important.
Take a spherical particle with radius R:
Surface = 4R2
Volume = 4/3R3
Carbon nano tubes
surface/volume-ratio increases
with decreasing R
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Importance of the interfacial zone
31*from: Lewis, Transactions on DEI, October 2004
In one cubic meter of a material containing 10volume % of 10 nm spheres, the total interfacearea is approximately 60 km2
Material properties may change drastically withinthe interfacial zonewhich may even becomemore important than the bulk dielectrics.
S f f i t
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Surface area; from micro to nano
(same volume fraction)
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Nanocomposites
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Nanocomposites consist of a dielectric matrix (host) and a disperse phase (nano-scalefiller)
Small size, 1 nm 100 nm small distance between neighbouring filler particles (forthe same volume fraction)
Very large surface area much more interactionbetween filler and host
New mesoscopic properties (between atomic and macroscopic scale)
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New/improved properties
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Higher mechanical strength
Better thermal properties
Higher electrical breakdown strength
Decreased flammability, gas-tight
Better adhesion Anisotropic character of certain nanomaterials provides new opportunities for
design: smart behavior
As yet, very few explanations for the behavior ofnanocomposites
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3.DevelopmentsBuilding macroscopic structures with nanosized bricks
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Developments
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4.SummaryTheres plenty of room at the bottom1959, Richard Feynman
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Summary
Conductors
Prospect of lower losses using carbon nanotubes
Ultra capacitors using large surface areas
Insulating systems Alternatives for greenhouse gases such as SF6
Alternatives for mineral oil
Prospects of creating clean, high performance materials using polymeric insulation and
nanotechnology
Sensors and smart materials
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