IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 49, NO.

12, DECEMBER 2021 3897

Aging Assessment of Corona-Exposed

HTV-SiR/EPDM Blends Loaded
With Nanofillers
Muhammad Zaheer Saleem , Mohammad Akbar, Life Senior Member, IEEE, and Shahid Alam

Abstract— Exposure of insulating systems to strong electric of undesirable conduction processes, dielectric and thermal
field and other environmental stresses may cause loss of their losses, tracking, corrosion at metal–material contacts, corona
desired properties. In high-voltage applications, phenomena, such discharges, unexpected flashovers, space charge effects, and
as corona discharges and unexpected flashovers, may deteri-
orate the surface as well as bulk conditions of an insulating even breakdown of insulators may take place [5]–[8].
material and thereby affect its lifetime. In this article, sev- Attempts to examine the individual or combined effect
eral types of corona-exposed HTV-SiR/ethylene propylene diene of several of the above-listed factors have been extensively
monomer (EPDM) blends filled with different concentrations reported in the literature. A few of these studies in the
of nano-sized boron nitride and silicon carbide particles are context of the present work that focuses on analyzing the
evaluated and the induced modifications of their properties are
presented and discussed. The diagnosis is based on measured induced modifications in/on the polymeric insulators due to
data of surface partial discharge (PD) and volume current. For corona discharges are summarized here. In [9], silicone rubber
the latter, experiments were performed at different levels of samples filled with different concentrations of ATH (50 wt%
electric field between 0.5 and 4 kV/mm and ambient temperature and above) and exposed to ac and negative dc corona under
ranging from 22 ◦ C to 70 ◦ C. Results of the conducted exper- normal fog (PH 7.2) and acid fog (PH 3.3) were investigated.
iments revealed the degradation of surface properties through
an increase in the PD magnitude. It was also observed that The obtained results revealed loss of hydrophobicity and
corona aging of the samples decreases the threshold electric field penetration of nitric acid species into the materials under ac
particularly at elevated temperatures, above which space charge voltage in the acid fog condition. In another study performed
effect in the materials may become significant. Moreover, it was under both the polarities of dc voltage on silicone rubber
observed that the blend compositions loaded with nanofillers filled with nano-SiO2 , more surface degradation and loss of
retard surface PD and bulk deterioration.
hydrophobicity were observed under negative dc corona [10].
Index Terms— Aging, ethylene propylene diene monomer As far as comparison between ac and dc corona on surface
(EPDM), nanocomposites, partial discharge (PD), silicone rubber, deterioration is concerned, stronger impact of the ac voltage
volume current and space charge.
was reported [11].
Since corona causes degradation of insulating materials,
I. I NTRODUCTION attempts have been made to design better insulation systems
to counteract/lessen its effect. Realization of these has been
I DENTIFYING potential aging threats to the desirable prop-
erties of high-voltage insulating systems is essential for
their proper and realistic design. Moreover, knowledge about
made more effective with the emergence of polymeric com-
posites, where a mixture of base matrix and filler particles
is prepared for achieving specific requirements in various
these is important for minimizing loss of assets, human life,
applications. For example, in [12], the performance of sil-
hazards, and interruption of electric power supply. Materials
icone rubbers filled with various concentrations of micro-/
may degrade due to various factors, including environmental
nano-SiO2 was evaluated for determining the most suitable
stresses, locally enhanced electric fields, charge injection into
composition to retard both surface partial discharges (PDs)
the bulk at metal–material contacts, deposition of ions on
and loss of hydrophobicity. The performed measurements
the interfaces between insulating media under HVDC con-
demonstrated that the desired characteristics are achieved for
ditions, and accumulation of pollutants [1]–[4]. As a conse-
sample doped with 5 wt% nano-SiO2 . A similar study on
quence, modification of applied electric field, intensification
silicone rubber material filled with micro-ATH/nano-Al2O3
Manuscript received August 24, 2021; revised October 13, 2021; has been conducted in an attempt to enhance the resistance
accepted November 10, 2021. Date of publication November 24, 2021; against corona discharges [13]. In another work, the effect
date of current version December 17, 2021. This work was supported
by the Higher Education Commission (HEC) of Pakistan under Project of micro-/nano-sized ZnO filler on breakdown characteris-
10346/KPK/NRPU/Research and Development/HEC/2017. The review of this tics of low-density polyethylene (LDPE) under corona aging
article was arranged by Senior Editor S. J. Gitomer. (Corresponding author: was investigated [14]. As an outcome, it is reported that
Muhammad Zaheer Saleem.)
The authors are with the Faculty of Electrical Engineering, Ghulam Ishaq the addition of 2 wt% microfiller and 3 wt% nanofiller in
Khan Institute of Engineering Sciences and Technology, Topi, Swabi 23460, the base matrix gave better results in comparison to the
Pakistan (e-mail: zaheer.saleem@giki.edu.pk). other compositions. Similarly, in [15], it was found that
Color versions of one or more figures in this article are available at
https://doi.org/10.1109/TPS.2021.3128768. 7 wt% nano-boron nitride (BN) filler in EPDM is the opti-
Digital Object Identifier 10.1109/TPS.2021.3128768 mum loading to impede the effect of surface discharges.
0093-3813 © 2021 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission.
See https://www.ieee.org/publications/rights/index.html for more information.

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 3898 IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 49, NO. 12, DECEMBER 2021

TABLE I
S PECIFICATIONS OF THE S TUDIED B LENDS F ILLED W ITH D IFFERENT C ONCENTRATIONS OF N ANOFILLERS

Another contribution showing enhanced lifetime of nano- is examined using the current density versus applied electric
Al2 O3 filled polyimide materials under corona discharge is field plot. Finally, the role of filler and its concentration in
reported in [16]. A comparative analysis of the silicone rubber retarding the degradation process is analyzed.
filled with nano-SiO2 and nano-Al2 O3 is performed in [17],
in which more improvement (in terms of resistance against II. E XPERIMENTAL W ORK
heat build-up due to discharges) is observed in nano-SiO2 filled A. Preparation of Blends
samples.
In the present study, flat samples of polymeric blends filled
Apart from determining appropriate concentration of micro-
with different concentrations of nanofillers were fabricated.
/nano-sized fillers in a single-base material, research initiatives
The thickness of each sample was 2 mm and its length
considered a blend of two base materials with suitable addi-
and width were 150 and 110 mm, respectively. To prepare
tives in an attempt to enhance the electrical and mechanical
these samples, high-temperature vulcanized silicone rubber
properties of insulating materials [18]–[21]. These studies are
(HTV-SiR) and EPDM were used as the two base materials,
mainly performed on blends having various compositions of
while nano-sized (50 nm) BN and silicon carbide (SiC) were
two base materials (SiR and EPDM) and nanofillers, such as
used as fillers. Moreover, for vulcanization and fast curing,
SiO2 , ATH, TiO2 , and Al2 O3 . However, the reported results
dicumyl peroxide (DCP) was used as a curing agent. In the
of such studies are limited demanding further experimentation
preparation process, first, blending of the two base materials
and analysis. In particular, studies on HTV-SiR and EPDM
was carried out in a two-roller mill mixing machine working
blends filled with nanoparticles to understand their corona-
at a constant temperature of 110 ◦ C. Initially, EPDM was
induced degradation are quite rare. Moreover, the diagnostic
passed through the roller for 2 min, and then, it was mixed
techniques, such as image saturation, digital image process-
for five more minutes with HTV-SiR. Thereafter, filler and
ing, and nuclear resonance magnetic detection [22]–[24],
DCP were added to the blend and the compound was mixed
are mainly used to report the impact of corona discharge
for 20 min. The vulcanization was then performed using an
exclusively on the surface characteristics of the material, such
electric heat-press machine with dual heat plates by applying
as hydrophobicity and tacking/erosion. However, its effect
a pressure of 10 MPa at a temperature of 180 ◦ C for a duration
on the bulk of the material that may appear under various
of 3 min. Finally, postcuring was carried out at 150 ◦ C for 2 h.
scenarios, such as elevated temperature, strong electric field,
The detailed composition of each prepared blend is given
and aged conditions of the test specimens, is rarely studied.
in Table I.
These factors may facilitate charge injection at metal–material
interface [25] leading to space charge accumulation and,
hence, modification of the applied field strength. This may B. Corona Aging
eventually cause the failure of insulating system [26]. A schematic view and a photograph of the experimental
In the present study, in addition to the assessment of setup used to expose the test sample to corona discharges are
degradation on the surface due to corona discharges, induced shown in Fig. 1. It consists of a 30-kV, 30-kVA regulated
effects in the bulk of the materials are also investigated. voltage supply, measuring circuit, corona chamber, protection
For this purpose, seven different types of HTV-SiR/EPDM scheme, and data acquisition system. To measure and record
blends, including unfilled and those incorporating different discharge current, a PicoScope was connected to a personal
concentrations of boron nitride and silicon carbide nanofillers, computer. Moreover, the corona chamber was equipped with
were prepared. Samples of the materials were first aged under a 12-V dc air compressor electric pump along with inlet and
corona discharge and then diagnosed through measurements outlet for air flow to minimize any possible ozone impact.
of surface PD and volume current following the standard Corona discharges were produced using a circular electrode
procedures. The latter was performed at different intensities suitably equipped with 31 stainless-steel needles, each having
of applied electric field in the range of 0.5–4 kV/mm while a tip radius of 40 μm. This arrangement resembles an experi-
changing temperature from ∼22 ◦ C to 70 ◦ C. The results mental setup used earlier for a similar study [9]. The needles
obtained for both the virgin and aged samples are compared for were placed in four circular layers, the innermost with one,
determining the degree of damage (deterioration). Moreover, while the second, third, and fourth layers contain 6, 12, and
possible accumulation of space charge in each studied sample 12 needles, respectively. The spacing between two consecutive

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 SALEEM et al.: AGING ASSESSMENT OF CORONA-EXPOSED HTV-SiR/EPDM BLENDS LOADED WITH NANOFILLERS 3899

Fig. 2. Schematic of the constructed geometry in the 3-D domain for

performing computation.

element-based software, Comsol Multiphysics. For the compu-

tational domain, the electrodes arrangement described earlier
in Section II-B was used. A schematic view of the constructed
geometry in the 3-D domain is shown in Fig. 2. For the
simulations, the boundary condition on the bottom electrode
Fig. 1. Experimental setup for corona discharge study of the test sample under was set to 0 V, whereas 20 kV was applied to the multineedle
ac voltage. (a) Schematic illustration and (b) photographic representation. top electrode. A condition of zero charge was kept on the outer
boundaries limiting the computational domain.
The obtained electric field profiles at four different gap
layers was 10 mm. The length (height) of the needles in each
spacings of 1, 16, 32, and 48 mm from the tip of innermost
layer, starting from the outermost to the innermost, was 9, 11,
needle along the x- and y-axes are shown in Fig. 3(a) and (b),
12, and 12 mm. The optimal gap between the central (inner-
respectively. As seen, the variation of profile is dependent on
most) needle and the lower (ground) electrode was 50 mm
the distance from the tip of electrode, being strong at 1 mm and
as calculated through simulation (described in Section III) for
weak near the grounded electrode. A nearly uniform electric
maintaining uniform electric field on the surface of the sample.
field of 0.3 kV/mm is achieved at a gap length of 48 mm
Using the test setup described above, 20 kV was applied
both along the length and width of the computational domain,
between the multineedle electrode and the earthed electrode
represented by the x- and y-axes, respectively. Accounting for
to produce corona discharges to age the materials. The exper-
the 2-mm thickness of the test sample, a distance of 50 mm
iment continued uniterrupted for 72 h on each sample. The
(between the tip of the innermost needle and bottom electrode)
chosen duration of test was considered appropriate as time
was kept fixed in this study.
spans for conducting such measurments are not yet standard-
The electric field along the z-axis of the computational
ized [9], [12]. The air flow rate in the chamber was maintained
domain (starting from the tip of the innermost needle to the
at 5 L/min to eliminate any ozone impact. Furthermore, the
grounded electrode) is also examined and the obtained profile
temperature (21 ◦C–23 ◦ C) and humidity (55% ± 5%) were
is shown in Fig. 4. As seen, the field is varying along the
kept practically constant throughout the study.
gap showing the highest value at the tip of the needle and
III. C ALCULATION OF E LECTRIC F IELD decreasing with increasing distance from it. The maximum
field strength is observed to be approximately 6 kV/mm that
A relation between the displacement vector D (C/m2 ) and
is above the ionization threshold of air (∼3 kV/mm), thus
charge density ρ (C/m3 ) as described by the Gauss law is
ensuring the occurrence of corona discharges from the needles.
∇ · D = ρ. (1)
IV. D IAGNOSTIC AND C HARACTERIZATION S TUDIES
The displacement vector D is linked with electrostatic
field E (V/m) as For determining the corona-induced modifications on the
surface as well as in the bulk of the studied materials, various
D = ε0 εr E (2) analyses were made using both direct measurement and the
where ε0 is the permittivity of vacuum and εr is the relative diagnostic techniques.
permittivity.
For determining the optimal location beneath the needles A. Corona Current Measurement
in corona chamber (shown in Fig. 1) giving nearly uni- In recent years, a few studies of this nature on polymeric
form electric field, (1) was solved numerically using finite materials have been conducted under harmonic voltage both in

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 3900 IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 49, NO. 12, DECEMBER 2021

Fig. 5. Experimental setup for measuring PDs along the surface of the test
samples. (a) Schematic view and (b) photographic representation.

(two-input channel NI oscilloscope with a 12-bit enhanced

vertical resolution of ±20 V and a maximum sampling rate
of 100 MS/s) was used for acquiring the data. Furthermore,
for displaying the measurement in time domain, a PicoScope 6
software was used.
The test procedure was based on applying an ac voltage of
20 kV to the multineedle high-voltage electrode and measuring
Fig. 3. Results of the simulated electric field distributions along (a) x- and the discharge current through voltage drop across the shunt
(b) y-axes at different gap distances between the tip of innermost needle and
grounded electrode. In (a) and (b), the lines used for calculating electric field resistor in the ground circuit. The data were measured and
are labeled with black and green, respectively. recorded for 1 min both at the beginning of each experiment
when the samples were unaged (virgin) and after exposing
them to corona discharges for 72 h.

B. Surface PD Measurement
The experimental study of PDs along the surface of material
was carried out by following IEC standard 60270 using the
test setup shown in Fig. 5. A rod-plane electrode arrangement
was used as per ASTM standard D2257. The diameter of the
rod was 6 mm with an end-curvature radius of 1 mm. The
plane electrode on which the test sample was mounted was
grounded.
Before the commencement of this test, the PD measuring
system was calibrated to ensure accurate measurement. To ini-
tiate the experiment, an ac voltage was applied across the
electrodes and gradually raised till the PDs were detected.
Correspondingly, the corona inception voltage was recorded
Fig. 4. Simulated electric field along the z-axis (labeled with blue line) of
the computational domain starting from the tip of innermost needle to the
and PDs were measured for 30 s. Thereafter, PDs were also
grounded electrode. measured and recorded at a voltage level three times higher
than that of the inception voltage. To check the repeatability
of results, experiments were repeated at least three times.
the laboratory as well as in the field to determine their surface
degradation and contamination level [27]–[30]. The setup used C. Volume Current Measurement
in the present work for generation and monitoring of corona For examining the impact of corona discharge aging on
current is shown in Fig. 1. In this arrangement, a PicoScope the bulk of material, volume current was measured using

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 SALEEM et al.: AGING ASSESSMENT OF CORONA-EXPOSED HTV-SiR/EPDM BLENDS LOADED WITH NANOFILLERS 3901

Fig. 6. (a) Schematic of the standardized three-electrode system and

(b) pictorial view of the experimental setup for measuring volume current
of the sample.

a standardized three-electrode system, consisting of high-

voltage, measuring, and grounded electrodes. A schematic of
the test setup showing a sample placed between the electrodes
is given in Fig. 6(a). A photograph of the complete system
encompassing different components is shown in Fig. 6(b).
The high-voltage electrode was connected to a Glassman dc
source (model FJ60R2) capable of generating up to 20 kV.
Similarly, the measuring electrode was connected to a highly
sophisticated Keysight electrometer (B2891A) with a current
measurement range of 1 fA–20 mA. The data acquisition
Fig. 7. Corona discharge current recorded for 1 min both on the virgin
was accomplished through a LabVIEW software installed (unaged) and aged samples of the studied blends. (a) A. (b) B. (c) C.
in a personal computer. To eliminate any electromagnetic
disturbances, the three-electrode system was placed inside
a grounded metal-enclosed oven shown by the dotted line First, the temperature of the oven was set and maintained
in Fig. 6(a). at the desired value. This was followed by placing the elec-
The measurements were made by applying voltage stepwise. trodes holding the test sample in the oven for 30 min to
First, 1 kV was applied to the test specimen, which gave a acquire isothermal conditions. Afterward, the same procedure
spike of capacitive current followed by gradually decreasing as adopted earlier at room temperature was repeated at 40 ◦ C,
polarization current. The current was allowed to reach a nearly 60 ◦ C, and 70 ◦ C.
steady-state value to determine the conductivity of the sample.
The voltage was then raised to different levels in the range V. R ESULTS AND D ISCUSSION
of 3–8 kV and the corresponding steady-state current was
measured, which facilitated the evaluation of field dependence A. Corona Discharge Current
of the conductivity. Each experiment was repeated at least The results of the measured current for 1 min both at the
three times to check the repeatability of results. Moreover, beginning and at the end of each experiment during the corona
to ensure zero impact of residual polarization, the sample was aging test are shown in Fig. 7. To offer clarity, data obtained
short-circuited and grounded for sufficiently long time after for virgin (unaged) samples are presented in black, while the
each measurement. current recorded after 72 h of aging is shown in red. It can
These experiments were extended to elevated temperatures be seen that all the measured values are in the mA range.
to obtain the temperature dependence of the conductivity. Furthermore, it is worth noting that the density of current

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 3902 IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 49, NO. 12, DECEMBER 2021

TABLE II
D IFFERENT PARAMETERS OF THE R ECORDED C ORONA D ISCHARGE C URRENT

Fig. 8. Phase-resolved PD patterns recorded for 30 s on the studied blends. In (a), (c), and (e), data are shown for the virgin samples (represented by ∗ ).
(b), (d), and (f) Measurements for aged materials (denoted by ^).

TABLE III
PD M AGNITUDE M EASURED ON THE B LEND M ATERIALS AT A V OLTAGE L EVEL T HREE T IMES H IGHER T HAN T HAT OF THE I NCEPTION V OLTAGE

spikes is affected by the composition of the test sample. For impact, maximum recorded peaks and average of the rms
example, it is the highest for unfilled sample (designated as values during both the positive and negative cycles of the
blend A) and the lowest for blends denoted as C and F. discharge current are shown in Table II. For better comparison,
However, blend C filled with BN showed relatively better data are represented as a ratio, where the numerator and
results compared to the blend F doped with SiC. Similarly, denominator indicate the measured values at the beginning
higher resistance of other polymeric samples filled with BN and at the end of each experiment, respectively. As it can be
against discharges can be observed. seen, the denominator is generally greater than the numerator
Comparing the measurements of unaged and corona-aged showing higher corona current after aging. This ratio is lower
samples, it can be seen that corona discharges degrade the than unity for sample A (without filler) and samples D and G
properties of polymeric materials. In order to quantify the (doped with 5% of BN and SiC fillers, respectively) reflecting

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 SALEEM et al.: AGING ASSESSMENT OF CORONA-EXPOSED HTV-SiR/EPDM BLENDS LOADED WITH NANOFILLERS 3903

TABLE IV
PD I NCEPTION V OLTAGE OF THE B LEND M ATERIALS

more profound effect of corona aging. On the other hand,

it is close to unity for materials C and F containing 3% of
nanofillers, which reflects their better performance. It has also
been observed that discharges of higher peaks and more rms
values occur during the positive cycle, which is consistent with
the observations made in an earlier study [31].

B. Phase-Resolved PD Pattern
The phase-resolved PD patterns obtained for both the virgin
and corona-aged samples using the procedure described in
Section IV-B are shown in Fig. 8. These results present the
discharge level and number of pulses corresponding to the
phase angle of the ac voltage. To have better illustration and
more noticeable values of PD, data recorded at three times
higher voltage of the corona inception voltage is shown in
Fig. 8. As seen, PDs occur mostly in the first and third
quadrants of the ac cycle. Furthermore, the level of discharge
is affected by the composition of studied materials. This is
better elucidated in Table III, from which it is clear that the
PD magnitude is lower for the filled samples compared to
the unfilled sample A. Nevertheless, the desired characteristics
have shown dependence on the filler type and its concen-
tration in the base material. For example, we can see that
with 1% addition of nanoparticles, PD level decreases more
pronouncedly with BN compared to SiC. It is interesting to
note, however, that increasing concentration of filler above
a certain threshold lowers the resistance of the test sample
against surface discharges instead of improving it. An example
of this behavior can be seen in the first row of Table III
for blends D and G (containing 5% of nanofillers) where the
PD level is even more than that for the unfilled sample A.
The negative impact (of higher concentration of filler) is
attributed to the agglomeration phenomenon caused by the
uneven distribution of filler particles in the base material. This
results in a weak interaction between the base matrix and filler
particles [32]. Among the studied samples, the lowest PD level
was measured on sample C, which incorporates 3% of BN in
the blend of silicone rubber and EPDM.
By comparing the measurements shown in Fig. 8 and the
data given in Table III, one can clearly see that regardless of
the composition, PD magnitude is higher for aged samples
than their virgin counterparts. This reveals that by exposing a Fig. 9. Recorded volume currents for materials: (a) A, (b) C, and (c) F
at different test voltages and ambient temperatures. The first spike in all the
polymeric sample to corona discharges, its surface deteriorates, figures corresponds to an application of 1 kV, followed by 3, 5, 7, and 8 kV.
which results in lowering the resistance to PDs. However,
the degree of degradation, and consequently the increase in
PDs, is observed to be dependent on the composition of the 7.5 to 9.7 nC. Here, although the change (of the PD level)
sample. For blend A for example, the PD level varies from 7 to for sample D is small, however, the preaged measurements on
13.1 nC (Table III), while for sample D, it changes from this sample showed even higher discharges than the unfilled

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 3904 IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 49, NO. 12, DECEMBER 2021

Fig. 10. Comparison of the measured volume currents for virgin (denoted
by ∗ ) and aged (represented by ^) samples of blend G at different applied
voltages and two ambient temperatures.

blend A. As far as the role of filler type in suppressing PDs in

aged samples is concerned, BN nanoparticles provided better
performance compared to its SiC counterpart.
Apart from the above-described results, the effect of filler
in the studied materials was also analyzed on the PD inception
voltage (Vincp ) and a comparison is shown in Table IV. As can
be seen, Vincp is the highest for BN-doped blend C and
the lowest for the unfilled sample A. After exposing these
materials to corona discharges, test samples A and C exhibited
the maximum and the minimum decline of Vincp , respectively.
These observations are consistent with the findings reported
above, where the blends filled with 3% of nanofillers provided
better performance in the context of resistance to aging.

C. Volume Current
The recorded data of volume current both at different levels
of test voltage and ambient temperature for three test samples
(A, C, and F) are shown in Fig. 9. Moreover, a comparison of
results obtained at 40 ◦ C and 70 ◦ C for material G both in the
virgin and aged conditions is presented in Fig. 10. As shown
in Fig. 9, the volume current is time-varying having an initial
spike of capacitive current at each applied voltage followed
by a decaying polarization current and finally stabilizing as
a steady-state current. The latter is used for determining
conductivity of the test sample and is observed to be affected Fig. 11. Current density versus applied electric field characteristics of studied
by the applied voltage, composition of the sample, and the blends (a) A, (b) C, and (c) G at different ambient temperatures. The data
ambient temperature. For instance, incorporation of nanofillers points fit with broken lines with slope 1 corresponding to ohmic conduction,
while the solid lines are representing nonlinear behavior.
of different types in the base material yields different results.
Thus, current at the same applied voltage of sample C
(containing 3% of BN) is lower than that of sample F doped Comparing the current–time characteristics as shown in
with 3% of SiC. Similarly, increasing temperature is elevating Fig. 10, it can be seen that results are differently affected when
the whole profile and shortening the total time required for performed on aged samples. Here, the current gets quickly
recording one complete set of data. For blend C, the time stabilized and its deviation from those obtained for virgin
span is about 36 h at 22 ◦ C, while at 70 ◦ C, it reduces to samples at different levels of test voltage is more pronounced
less than 11 h, thereby implying that much faster mitigation at elevated temperatures. A difference of close to one order
of polarization processes occurs at higher temperature. During of magnitude can be seen at 70 ◦ C. In order to investigate
these experiments, deviations from average values of at least such a large change, current density J (calculated using the
three different measurements were found to be less than ±10% steady-state value) versus applied electric field E (test voltage/
indicating good repeatability of the results. thickness of the material) plotted in log–log coordinates is

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 SALEEM et al.: AGING ASSESSMENT OF CORONA-EXPOSED HTV-SiR/EPDM BLENDS LOADED WITH NANOFILLERS 3905

examined using the procedure described in [33]. According [3] L. He and R. S. Gorur, “Source strength impact analysis on polymer
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 3906 IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 49, NO. 12, DECEMBER 2021

[23] D. S. Prasad and B. S. Reddy, “Digital image processing techniques Mohammad Akbar (Life Senior Member, IEEE)
for estimating power released from the corona discharges,” IEEE Trans. received the bachelor’s degree in electrical engi-
Dielectr. Electr. Insul., vol. 24, no. 1, pp. 75–82, Feb. 2017. neering from the Engineering College, Peshawar,
[24] M. Bi, J. Yang, X. Chen, T. Jiang, A. Pan, and Y. Dong, “The research Pakistan, in 1970, the M.S. degree in electrical
on corona aging silicone rubber materials’ NMR characteristics,” IEEE engineering from the University of Tokushima,
Access, vol. 8, pp. 128407–128415, 2020. Tokushima, Japan, in 1977, and the Ph.D. degree in
[25] G. G. Raju, Dielectrics in Electric Fields. New York, NY, USA: Dekker electrical engineering from The University of Tokyo,
Inc., 2003. Tokyo, Japan, in 1980.
[26] G. C. Montanari, “Bringing an insulation to failure: The role of space He is a Renowned Power Engineer, possessing rich
charge,” IEEE Trans. Dielectr. Electr. Insul., vol. 18, no. 2, pp. 339–364, experience in applied research. While undergoing
Apr. 2011. postgraduate studies and later as a Post-Doctoral
[27] N. Bashir and H. Ahmad, “Odd harmonics and third to fifth harmonic Fellow with The University of Tokyo, he remained actively involved in
ratios of leakage currents as diagnostic tools to study the ageing of research dealing with polymeric insulators and high-altitude HVDC insulation
glass insulators,” IEEE Trans. Dielectr. Electr. Insul., vol. 17, no. 3, systems of Japanese electric utilities. Later, during his employment at Windsor
pp. 819–832, Jun. 2010. University, Canada, he explored more economical alternatives of SF6 gas for
[28] R. Ghosh, B. Chatterjee, and S. Chakravorti, “A novel leakage current practical use in high-voltage applications. Thereafter, during his ten years
index for the field monitoring of overhead insulators under harmonic tenure with the University of Petroleum and Minerals, Dhahran, Saudi Arabia,
voltage,” IEEE Trans. Ind. Electron., vol. 65, no. 2, pp. 1568–1576, he initiated a pioneering multimillion-dollar study dealing with pollution
Feb. 2018. problems of 380-kV high-voltage transmission lines in Saudi Arabia. The
[29] Z. Zhijin, L. Tian, J. Xingliang, L. Chen, Y. Shenghuan, and Z. Yi, study on successful completion offered design criteria of insulation systems
“Characterization of silicone rubber degradation under salt-fog environ- for safe and reliable operation of high-voltage transmission lines in the
ment with AC test voltage,” IEEE Access, vol. 7, pp. 66714–66724, Kingdom of Saudi Arabia. In October 1991, he took over as the first Chief
2019. Executive of WAPDA’s High Voltage and Short Circuit Laboratory (HVSCL),
[30] A. A. Salem, R. Abd-Rahman, S. Ahmed Al-Gailani, M. S. Kamarudin, Rawat, Islamabad, and provided meritorious services to the entire electrical
H. Ahmad, and Z. Salam, “The leakage current components as a diag- power sector and set several landmarks toward national self-reliance in the
nostic tool to estimate contamination level on high voltage insulators,” specialized field of power equipment testing and certification while also
IEEE Access, vol. 8, pp. 92514–92528, 2020. realizing a substantial saving of foreign exchange to the national exchequer.
[31] B. S. Reddy and S. Prasad D, “Effect of coldfog on the corona induced He pioneered goal-focused research on WAPDA’s problems, such as insulator
degradation of silicone rubber samples,” IEEE Trans. Dielectr. Electr. pollution of 500-kV transmission line, failure of distribution transformers,
Insul., vol. 22, no. 3, pp. 1711–1718, Jun. 2015. and failure of surge arresters, and offered pertinent feedback to the concerned
[32] M. Fairus, M. Hafiz, N. S. Mansor, M. Kamarol, and M. Jaafar, “Com- WAPDA’s formations. Simultaneously, he promoted the cause of engineering
parative study of SiR/EPDM containing nano-alumina and titanium profession through his dedicated voluntary services of multifaceted nature to
dioxides in electrical surface tracking,” IEEE Trans. Dielectr. Electr. the Pakistan Engineering Council, Ministries, and several other academic and
Insul., vol. 24, no. 5, pp. 2901–2910, Oct. 2017. research and development institutions. After his retirement as the General
[33] J. L. Auge, C. Laurent, D. Fabiani, and G. C. Montanari, “Investigating Manager, WAPDA, in December 2009, he switched over to academics and
DC polyethylene threshold by space charge. Current and electrolumines- served in different positions, such as a Professor, the Dean, the Director-
cence measurements,” IEEE Trans. Dielectr. Electr. Insul., vol. 7, no. 6, General, and the Vice-Chancellor. At present, he is a Professor and the Dean
pp. 797–803, Dec. 2000. of the Faculty of Electrical Engineering, GIK Institute, Topi, Pakistan. He has
published over 90 research articles in national and international journals and
conference proceedings.
Dr. Akbar received numerous recognitions and awards both at national and
Muhammad Zaheer Saleem was born in Shahkot, international levels from employers as well as professional societies.
Pakistan, in May 1996. He received the B.Sc. and
M.Sc. degrees in electrical engineering from the Shahid Alam was born in Peshawar, Pakistan,
University of Engineering and Technology (UET), in 1986. He received the M.Sc. degree in electrical
Lahore, Pakistan, in 2017 and 2019, respectively. power engineering and the Ph.D. degree in high-
He is currently pursuing the Ph.D. degree with the voltage engineering from the Chalmers University
Ghulam Ishaq Khan Institute of Engineering Science of Technology, Gothenburg, Sweden, in 2011 and
and Technology, Topi, Pakistan. 2016, respectively.
During the M.Sc. degree, he explored more eco- Currently, he is an Assistant Professor with the
nomical alternatives of SF6 gas for practical use in Faculty of Electrical Engineering, GIK Institute,
circuit breakers and other power equipment. He has Topi, Khyber Pakhtunkhwa, Pakistan. His research
published articles on SF6 gas alternatives. His major research areas are new interests include aging assessment and electrical
gaseous alternatives and corona-induced degradation of insulating polymeric characterization of polymeric composites and sur-
materials. face charge dynamics on insulating materials for HVDC applications.

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