Transcript Title should be like this A P Robinson1, P L Lewin1, S

Smart Materials as Intelligent Insulation
A. F. Holt, A. C. Topley, R. C. D. Brown, P. L. Lewin, A. S. Vaughan, P.
University of Southampton, Southampton, UK
*EDF Energy Networks Ltd.
Introduction
*
Lang
Current Approaches
What are smart dielectrics?
Directly-doped pyrene blends
Smart dielectrics are materials which contain a functional chemical group
which produces a measurable response dependant on environmental changes.
Pyrene was dissolved into a solution of polystyrene,
owing to the good solubility of pyrene; precipitation of the
pyrene-polystyrene mixture was not possible. Samples
were instead oven dried for 3 hours at 40 oC
Electric field sensitive fluorophores can be designed and introduced into the
dielectric such that changes in fluorescent properties are indicative of the local
electrical environment or dielectric degradation.
Such materials can be tailored to the desired application.
Serial dilutions of a stock pyrene solution allowed for
concentrations of pyrene as low as 0.0001 %wt.
All samples showed strong fluorescence under a UV
lamp (254 nm).
Benefits and potential applications
Fig. 3. Chemcial
structure of pyrene
Smart dielectrics provide a means of continual condition assessment which
is non invasive, easily interpreted and inexpensive to maintain. One such
application would be the use of smart dielectrics to remotely monitor the
presence of charge on gas insulated switchgear (GIS) spacers.
Other uses in outdoor insulation systems to detect the presence of an
electric field or as a means of dielectric condition assessment can be
envisaged
Considerations
Requirements of material
Responsive to local electrical environment changes
Clear output which can be readily interpreted (e.g. colour change/
fluorescence).
Introduction of smart moiety must have minimal effect on electrical
properties of bulk material
Smart moiety functional group would ideally be cheap to synthesize and
easy to introduce into the bulk polymer.
Fig. 4. Comparison between polystyrene
doped with pyrene (5 %wt.) and unmodified
polystyrene (right)
Table 2. Summary of
breakdown data
Pyrene
Beta Eta
concentration
0%
16
161
5%
20
161
0.05%
20
156
0.0001%
16
162
Fig. 5. 0.0001 %wt. pyrene blend shows
weaker fluorescence of a more purple
colour compared to the 5 %wt. blend (right)
AC Breakdown results
Surprising lack of clear trends between the
different concentrations
Having studied the breakdown sites under
a microscope there was no visible reason
(such as areas of crystalline pyrene) as to
why a lower average breakdown strength
was observed for the 0.05 wt % blend
compared to the other pyrene blends.
Dendrimers
Polymeric macromolecules composed of
multiple
perfectly-branched
monomers
radially emanating from a central core.
Previous Approaches
Solid-supported pyrene as a filler
Pyrene was attached to small crosslinked polystyrene beads. These were
mixed with polystyrene using solution blending techniques.
Could be used to encapsulate the
fluorescent core, offering protection from
bulk polymer environment.
Head groups of dendrimer could be
modified to mimic surrounding polymer,
allowing for easier blending.
Fig. 6. Schematic representation
of a dendrimer
Fig. 1. fluorescent insoluble filler
Fluorescence spectra were
obtained, as shown in figure 2.
In the case of the 5.75 % and 1
% blends attenuators were
required to prevent saturation of
the spectrometer.
Fig. 2. Fluorescence spectra for 5.75 %, 1 % and 0 % filler blends
During sample manufacture it was
noted that in the 5.75 % blend the filler
was visually well dispersed. Conversely,
filler dispersion was poor in the 1 %
blend as shown by a microscope
photograph in figure 3, which shows an
example of the localized clusters of filler Fig. 3. A cluster of filler beads as observed in the 1%
filler blend viewed in reflection mode.
beads observed throughout the sample.
Breakdown Testing
.Table 1: Summary of
For AC electrical breakdown testing, a
breakdown data
Grazeby Specac press was used to press air
Beta
Eta Value
0C to a
Sample
and
defect
free
samples
at
180
Value
(kV/mm)
thickness of 100 µm..
Virgin PS
45
154
0% Control
16
172
1% Filler
11
165
5.75% Filler
23.
157
The test cell used two 6.3 mm ball bearing
electrodes submerged in silicone oil.
Calibration ensured that each sample was
subject to the same linear AC ramp rate of 50
V/s. A two-parameter Weibull distribution with
maximum likelihood confidence bounds was
used to analyze the data.
Conclusions
It was found that a fluorophore such as pyrene could be introduced into bulk
PS with only minimal effect on the AC electrical breakdown strength of the
material. Clear fluorescence spectra were observed for all blends although the
directly doped pyrene blends were visibly more fluorescent.
Good dispersion of the fluorophore throughout the polymer is essential in
order to obtain reliable experimental results, therefore, soluble fluorescent
fillers are preferable due to better dispersion when blending.
Further Work
Monitor the fluorescence spectra of the materials in real time whilst under
electrical stress.
Blending of a more polar fluorophore to determine what effect such a
modification will have one the sensing and electrical/ dielectric properties of
the material.
Comparison of electroluminescent and fluorescent properties of blended
materials will offer an insight into the most suitable systems for remote
monitoring of dielectric materials.
Explore the use of fluorescence modified dendritic molecules which are
soluble in blending solvents to produce a uniform dispersion of fluorophores
amongst the bulk material and protect the active core.
Contact Details
[email protected]
University of Southampton, Highfield, Southampton, SO17 1BJ, UK