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ABSTRACT: The main objective of the present paper is to shed more light on
the multiple effects of the incorporation of certain additives into LDPE
(low density polyethylene) on some of the properties of the doped
material relevant to its use as an insulating material for HVDC cables.
In the present work, the effects of two additives on DC insulation
resistivity, DC breakdown strength, space charge accumulation under DC
conditions, polymer structure and morphology were investigated using
different techniques. Results of a multitude of experiments are
presented and discussed. It is concluded that, although the
incorporation of the additives may lead to certain beneficial effects
such as the reduction of space charge density in the polymer and the
improvement of the dependence of the DC insulation resistivity on
temperature and electric field, yet the DC breakdown strength as well as
the DC insulation resistivity itself may be reduced. It is also shown
that the incorporation of the additives have a significant effect on the
morphology of the doped material
Electrical Insulation, 2000. Conference Record of the 2000 IEEE International Symposium on; 02/2000
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ABSTRACT: The present work aims at determining the dependence of the DC
insulation resistivity on temperature and electric field for a
super-clean low density polyethylene (LDPE) used in manufacturing modern
high voltage AC cables. Resistivity measurements were made using
relatively thick (~2 mm) samples at different temperatures and DC
electric fields. Based on the present experimental data, a mathematical
model for the relationship between the insulation resistivity of the
polymer, temperature and electric field was determined using: (i)
computer curve fitting techniques, and (ii) artificial neural networks
(ANN) method. Comparison between the present results and previous
measurements, using less clean grades of LDPE, indicates that the
inherent dependence of the DC insulation resistivity of LDPE on
temperature and electric field has not been appreciably improved by
using an ultra-clean polymer. It is concluded that the successful
utilization of LDPE for HVDC cables will require the modification of
such dependence
IEEE Transactions on Power Delivery 08/1999; · 1.35 Impact Factor
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ABSTRACT: One of the reasons which has hampered the use of polyethylene (PE)
as an insulating material for HVDC cables is the inherent dependence of
its dc insulation resistivity ρ<sub>ν</sub> on temperature T and
electric field E. The objectives of the present work are: (i) to
investigate the possibility of modifying the dependence of the
insulation resistivity ρ<sub>ν</sub> of LDPE on temperature and
electric field by doping LDPE with an inorganic additive, and (ii) to
find a mathematical model representing that dependence. Measurements of
de resistivity were made using relatively thick samples (~2 mm) of
undoped and doped LDPE at different electric fields ranging from 17
kV/mm to 33 kV/mm for temperatures from 50°C to 80°C. Results
indicate that the use of the additive has a significant effect on the
rate of decay of the insulation resistivity with temperature in the
doped material. Based on these measurements, the dependence
ρ<sub>ν</sub>=f(E,T) was found to conform to the law
ρ<sub>ν</sub>=ρ<sub>o</sub>e<sup>-[α*(E)T+β*(E)]
</sup>. Nonlinear curve fitting was used to determine the coefficients
α*(E) and β*(E). It is concluded that use of additives to
LDPE can be a promising method for manufacturing insulating materials
for HVDC cables
Electrical Insulation and Dielectric Phenomena, 1998. Annual Report. Conference on; 11/1998
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ABSTRACT: Recently, the development of HVDC cables with polymeric insulation
has received a renewed attention. The present work aims at determining
the dependence of the dc insulation resistivity on temperature and
electric field for low-density polyethylene (LDPE) which is used for
manufacturing modern high voltage ac cables. Using a highly precise
technique, resistivity measurements were made using thick (~2 mm) disc
samples at different dc electric fields ranging from 17 kV/mm to 33
kV/mm for a temperature range from 50°C to 80°C. Results
indicate that the dc insulation resistivity of the investigated LDPE
(ρ) is a rapidly decreasing function of both temperature (T) and
electric field (E). This relationship conforms generally to the law
ρ=ρ<sub>0</sub> e<sup>-</sup>(αT+βE). The values of
ρ<sub>0</sub>, α and β were determined using computer
curve fitting techniques. Comparison between the present results and
similar previously reported measurements made on less clean grades of
LDPE indicates that the inherent dependence of the dc insulation
resistivity of LDPE on temperature and electric field has not been
appreciably improved by using a ultra-clean polymer. It is concluded
that the successful utilization of LDPE for HVDC cables will require the
modification of such dependence
Electrical Insulation and Dielectric Phenomena, 1997. IEEE 1997 Annual Report., Conference on; 11/1997
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ABSTRACT: The effects of 5% wt BaTiO<sub>3</sub> additive and of electrode
material on space charge formation and electric field distribution in
low density polyethylene (LDPE) were investigated using a thermal step
technique. Space charge was formed at an average dc field of ~28 kV/mm
and at 50°C. Results indicate that the addition of BaTiO<sub>3</sub>
to LDPE has considerably reduced the remanent space charge and electric
field and changed their distribution patterns in the doped material when
compared with the plain material. It is also shown that the remanent
space charge and electric field in plain LDPE are strongly dependent on
the type of electrode material
IEEE Transactions on Dielectrics and Electrical Insulation 01/1997; · 1.09 Impact Factor
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M.S. Khalil
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ABSTRACT: The merits of HVDC power cables with polymeric insulation are well
recognized. However, the development of such cables is still hampered
due to problems resulting from the complicated dependence of the
electrical conductivity of the polymer on the temperature and the DC
electric field and the effects of space charge accumulation in this
material. Different methods have been suggested to solve these problems
yet none of these methods seem to give a conclusive solution. The
present report provides a critical review of the previous works reported
in the literature concerning the development of HVDC power cables with
polymeric insulation. Different aspects of those works are examined and
discussed. An account is given on an investigation using low density
polyethylene (LDPE) doped with an inorganic additive as a candidate
insulating material for HVDC power cables. Preliminary results from
measurements of DC breakdown strength and insulation resistivity of both
the undoped and the doped materials are presented. It is shown that the
incorporation of an inorganic additive into LDPE has improved the
performance of the doped material under polarity reversal DC conditions
at room temperature. Moreover, the dependency of the insulation
resistivity on temperature for the doped material appears to be
beneficially modified
Electrical Insulation, 1996., Conference Record of the 1996 IEEE International Symposium on; 07/1996
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ABSTRACT: A thermal step method was used to investigate the effects of
polarizing temperature and additive content on space charge formation
and electric field distribution in relatively thick samples (~2 mm) of
plain low density polyethylene (LDPE) and LDPE doped with 5 wt% barium
titanate (BaTiO<sub>3</sub>). Space charge was formed using dc field of
about 26 kV/mm at two different polarizing temperatures: 25°C and
50°C. Results indicate that for plain LDPE the remanent space charge
density and electric field increase with increasing the polarizing
temperature from 25°C to 50° C. The addition of 5 wt%
BaTiO<sub>3</sub> to plain LDPE appears to have remarkably reduced the
amounts of the remanent space charge and electric field and changed
their distribution patterns when compared with the corresponding values
for the plain material. The maximum values of the remanent electric
field reached in plain LDPE and doped LDPE are about 85% and 15% of the
external applied field respectively. Moreover, the distribution patterns
of the remanent space charge and electric field for the doped material
appear to be more sensitive to variations of polarizing temperature than
those for the plain material. Whereas in plain LDPE, the observed
distribution patterns of the remanent space charge exhibit a homocharge
at the cathode and a heterocharge at the anode for both polarizing
temperatures, for the doped material, the rise of the polarizing
temperature from 25°C to 50°C appears to have a considerable
effect on the distribution pattern of the remanent space charge in this
case: at 25°C, the remanent space charge distribution exhibits a
heterocharge at the anode and homocharge at the cathode while at
50°C the remanent space charge distribution pattern is reversed
showing a homocharge at the anode and a heterocharge at the
cathode
Conduction and Breakdown in Solid Dielectrics, 1995. ICSD'95., Proceedings of the 1995 IEEE 5th International Conference on; 08/1995
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ABSTRACT: The influence of the polarizing electrode material on the storage
of space charge in low density polyethylene (LDPE) was studied using the
thermal step technique. Test samples were discs of 1.9 mm thickness
provided with different types of electrodes: vacuum deposited gold and
aluminium, plasma enhanced chemical vapour deposited silicon carbide
(SiC), and pressed aluminium disc electrodes. Space charge was formed
using 50 kV de voltage for 72 hours at two different temperatures
25°C and 50°C. Results indicate that the distribution of space
charge density through the sample is dependent on the type of the
electrode material, the nature of electrode/polymer interface and
temperature of space charge formation
Electrets, 1994. (ISE 8), 8th International Symposium on; 10/1994
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ABSTRACT: The effect of 5% Wt BaTiO<sub>3</sub> additive and electrode
material on space charge formation and electric field distribution in
low-density polyethylene (LDPE) was investigated using the thermal step
technique. Space charge was formed under high-voltage direct-current
(HVDC) conditions at an average field of about 28 kV/mm and a
temperature of 50°C. Results indicate that the addition of
BaTiO<sub>3</sub> to LDPE considerably reduced the remanent space charge
and electric field, and changed their distribution patterns in the doped
material compared with the plain material. It is also shown that the
remanent space charge and electric field in plain LDPE are dependent on
the type of electrode material. The density of the remanent space charge
in the sample with gold electrodes is much higher and its distribution
is different, than the sample with aluminum electrodes. The remanent
field distributions in the two cases are also different
Electrical Insulation and Dielectric Phenomena, 1993. Annual Report., Conference on; 11/1993
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M.S. Khalil
[show abstract]
[hide abstract]
ABSTRACT: A thermal step method was used to investigate space charge
formation in low-density polyethylene (LDPE) and LDPE doped with an
inorganic additive. Space charge was formed at a field of about 3.3
× 10<sup>5</sup> Vcm<sup>-1</sup> and at two different
temperatures, 40°C and 70°C. Results indicate that the addition
of such an additive considerably reduced the density of the remnant
space charge in the doped material and appreciably changed its
distribution pattern. It is also shown that the remnant space charge in
the doped material is sensitive to the forming temperature, while in the
plain material the space charge appears to be insensitive to the change
of temperature within the temperature range used
Electrical Insulation and Dielectric Phenomena, 1993. Annual Report., Conference on; 11/1993
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ABSTRACT: The effect of temperature cycling between 40°C and 80°C
during combined temperature and electric field conditioning on the DC
conductivity of LDPE (low-density polyethylene) has been studied and
compared with DC conductivity results using a constant temperature of
80°C and an identical sample under the same experimental conditions.
Results indicate that the drop in the current level at 80°C after
ten days of conditioning is lower in the thermally cycled sample than in
the sample subjected to constant temperature. The difference is
attributed to different morphological changes in each sample due to
different thermal treatment
Conduction and Breakdown in Solid Dielectrics, 1992., Proceedings of the 4th International Conference on; 07/1992
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Electrical Insulation and Dielectric Phenomena, 1991. CEIDP. 1991 Annual Report. Conference on; 02/1991
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ABSTRACT: Measurements of the flowing current under the effect of DC fields
were conducted using relatively thick samples (1.8 mm) of three
different materials: plain low density polyethylene (LDPE), crosslinked
polyethylene (XLPE), and 1-wt% TiO<sub>2</sub> doped LDPE. The
measurements were performed over a range of temperatures from 40°C
to 80°C and at electric fields as high as 3×10<sup>5</sup>
V/cm. Results indicate that the observed DC conductive characteristics
are different for the three materials. Those differences are attributed
to the differences of the chemical and morphological structures of the
materials used. Scanning electron micrographs seem to support this
finding
Electrical Insulation and Dielectric Phenomena, 1990. Annual Report., Conference on; 11/1990
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ABSTRACT: The effect of the addition of 1% by weight of titanium dioxide
fine particles to low-density polyethylene (LDPE) on the short-term DC
breakdown strength of the LDPE was investigated using direct and reverse
polarity voltages. The samples used were cylinders of both plain and
doped materials, with hemispherically tipped cylindrical electrodes
completely embedded in the material, with a minimum gap length between
the electrode tips of 0.25 mm. All tests were conducted at room
temperature. Results indicate that, although the addition of TiO<sub>2
</sub> reduces the DC breakdown strength of the doped material if
compared to the plain material, it significantly improves its DC reverse
polarity characteristics. The doped material seems to be insensitive to
the DC polarity reversals. The observed beneficial effect of the
addition of TiO<sub>2</sub> on the DC reverse polarity characteristics
is attributed to the role of this additive in modifying the trapping
levels in the polymer, and the consequent change in the space charge
pattern in the doped material
Electrical Insulation, 1990., Conference Record of the 1990 IEEE International Symposium on; 07/1990
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ABSTRACT: Charge carrier mobility was determined for plain and doped
low-density polyethylene (LDPE) using DC transient currents. Barium
titanate was used as a strongly polar dopant and titanium dioxide as a
semiconductor dopant. The values of the mobility obtained were on the
order of 10<sup>-10</sup> cm<sup>2</sup> v<sup>-1</sup> s<sup>-1</sup>.
Results indicate that the inclusion of 1% by weight of BaTiO<sub>3</sub>
and TiO<sub>2</sub> has a considerable effect on the conduction
properties of the polymer. BaTiO<sub>3</sub> increased the charge
carrier mobility by a factor of three and also increased the
conductivity of the polymer. TiO<sub>2</sub> increased the charge
carrier mobility by a factor of five. Charge trapping and space charge
formation were modified by the introduction of titanium dioxide
Conduction and Breakdown in Solid Dielectrics, 1989., Proceedings of the 3rd International Conference on; 08/1989
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ABSTRACT: An experimental investigation of space charges in LDPE
(low-density polyethylene) and XLPE (cross-linked polyethylene) cables
with different semiconductor layers is presented. The space-charge
distribution was investigated using the field probe technique as a
direct method. It was found that the structure of the semiconducting
layers as well as the voltage polarity of the conductor have a marked
effect on the space-charge distribution. The results provide direct
experimental evidence on the polarity of space charges formed in HVDC
(high-voltage, direct-current) cables. Their distribution helps to
explain the reduction of the breakdown voltage that occurs on polarity
reversal
IEEE Transactions on Electrical Insulation 01/1989;
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ABSTRACT: The effect of titanium dioxide as a semiconductive additive and
barium titanate as a highly polar additive on the DC transient currents
in low-density polyethylene is investigated. Experiments were made using
thick specimens under a high electric field (>25×10<sup>6</sup>
V/m) and a constant temperature of 40°C. Results indicate that the
incorporation of these additives has an effect on the DC transient
currents in low-density polyethylene
Electrical Insulation and Dielectric Phenomena, 1988. Annual Report., Conference on; 11/1988
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ABSTRACT: A test method that uses a capacitive field probe to investigate
the space charge distribution in low-density polyethylene (LDPE) is
described. Specimens of 7-mm thickness were stressed under 100 kV DC at
room temperature and for different time periods. The results indicate
that the LDPE insulation layer between electrodes is occupied by
positive and negative homocharges. The dependence of space charge
distribution on the stressing time is also evident
IEEE Transactions on Electrical Insulation 07/1988;
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ABSTRACT: The effect of dissolved gases (02, air and N2) and a widerange of concentration of organic additives (quinoline,toluene and naphthalene) on the electrohydrodynamic headdue to co-field motion in transformer oil and liquid paraffinhas been measured fof both uniform and nonuniform fieldsusing direct voltages. The effect of gap length on thehead was also examined. The results indicate that all thedissolved gases investigated as well as toluene and napthalenereduced the developed head, whereas quinoline increased thehead. With a highly nonuniform field the effect of 02 andtoluene was found to be strongly dependent on the polarityof the point electrode.
IEEE Transactions on Electrical Insulation 03/1979;
