Journal of Recent Trends in Electrical Power System
Volume 6 Issue 3
DOI: https://doi.org/10.5281/zenodo.10043379
ac
Analysis of the Effects of Dust Accumulation on
33kV Line Insulators
Igbogidi O. N., Amadi H.N.
Department of Electrical Engineering, Rivers State University,
Port Harcourt, Nigeria
Corresponding Author
E-Mail Id: hachimenum.amadi@ust.edu.ng
ABSTRACT
High voltage insulators always fail by having invisible and visible cracks and sometimes broken
into pieces making the power system vulnerable to preventable losses. It is imperative to select
the right type of insulator to withstand the nominal voltage based on design. Dust on the surface
of insulator tends to reduce the reliability of the h i g h v o l t a g e i n s u l a t o r b y
r e d u c i n g t h e reliability and quality of power systems since it will generally lead to regular loss
of power supply. To validate the insulator suitable for high voltage system, it is evident by
experimental procedures to note the effect of various kinds of artificial contaminations on
33kV insulators (porcelain and polymeric insulator types). Dust types utilized in the
experiment include cement dust, sea-salt, local dust and urea dust. Based on IEC 60507
standard, insulator specimens were polluted by artificial means. The specimens after
pollution were left unattended to up to 24hours for natural drying. This experimental
procedure continued for 7 days to get a significant and visible pollution on the surface of each
insulator. This process was ideally used to check the break-down voltages and leakage
currents as a way of probing into the effect of dust on the surface of the insulator . The
results realized in this process are clear indications that salt and urea contaminations will
affect porcelain and polymeric insulators more. In an attempt to compare, it was
seen that cement pollution does not significantly affect porcelain and polymeric
insulators. Maximum leakage currents associated with urea pollution and salt
pollution tend to be higher because urea can reabsorb water molecule. The results
also showed that polymeric insulators have higher break-down voltage than porcelain
insulators. Comparatively, the effect of contamination is more on porcelain insulators than
on polymeric insulators. Salt, cement and urea contaminations have higher effects on
porcelain insulators than on polymeric insulators. The break-down voltage of polymeric
insulators in salt contamination is 17% higher than in porcelain insulators, the break-down
voltage of polymeric insulators in cement contamination is 22% higher than in porcelain
insulators and the break-down voltage of polymeric insulators in urea contamination is 31%
higher than in porcelain insulator. The method of pollutions and collection of the test results
are in accordance with IEC 60507 standard.
Keyword: High voltage, breakdown voltage, leakage current, porcelain insulator, polymeric
insulator
INTRODUCTION
High voltage insulators provide support to
high voltage transmission lines by
separating the lines from ground
structures. High voltage insulators are
usually installed in high altitude to prevent
high voltage from making contact with the
earth structure. Irrespective of location, the
function of the insulator is to disallow
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current flow to the earth structure.
Depending on the location, they are prone
to pollution and contamination at different
levels. Insulators installed in heavily
polluted zones become more easily
contaminated uniformly or sometimes
non-uniformly.
Contaminations
may
include bird feces, natural dust, local dust
etc. When dust particles get mixed up with
fog, rain, moisture and dew contamination
is thus said to have existed on the surface
of the insulator. The insulator surface gets
gradual degradation leading to increased
leakage currents because of contamination
even when operated at the rated voltage.
Flashover is the resultant effect of this
scenario. Insulator characteristics are
generally altered if exposed to heavily
polluted areas.
Generally,
transmission
lines
and
distribution lines are run overhead
traversing through the cities, factories,
rivers, sea shores and industries that make
air pollution their daily activity. The idea
behind this is for power supply to get to
every place inhabited by man. The power
line gets contaminated in pollution prone
zone especially with cement, urea and sea
salt. Though the degree of degradation
because of contamination is also a function
of insulator material. Porcelain insulator
and polymeric insulator are good but with
higher preference on polymeric type
because of its simplicity, less in weight,
easy to handle and hydrophobicity
property. Porcelain insulators generally
may have early flashover due to pollution
or contamination of their surfaces [1].
Generally speaking, leakage current is
dependent upon the surface resistance
which has a direct relationship with
hydrophobicity property of the insulator
material especially composite polymeric
insulators. Because of hydrophobicity,
insulators hardly get to flashover condition
especially polymeric type as leakage
Journal of Recent Trends in Electrical Power System
Volume 6 Issue 3
DOI: https://doi.org/10.5281/zenodo.10043379
current is discouraged. Though leakage
current occurs and must be prevented to
avert future damage. To this end, IEEE
and IEC 60507 have come up with
standard laboratory tests for performance
evaluation of insulators in outdoor
pollution [2].
Manmade
contamination
experiment
(otherwise
known
as
artificial
contamination) was carried out on 33kV
porcelain and polymeric insulators where
each has five specimens to evaluate effect
of insulator contamination. The tests were
conducted
for
three
kinds
of
contaminations such as salt, urea and
cement. The idea was to check the breakdown voltages and leakage currents of the
insulators when subjected to different
types of contaminations.
RELATED WORKS
It is obvious that there is significant
reduction of flashover voltage on glass and
ceramic insulators even when the
insulators are of high deposits of salt due
to environment prone pollution and
hydrophobicity damping effect of silicone
type of insulator material especially if the
glass type has RTV coverings which
would have made it possible in winter
period to get flashovers [1].
Contamination distribution effect on
insulators in alternating current (AC)
system and the description of the
significance of 3 essential classes of nonuniform contamination spread on the
surface of the insulators are generally:
movement as a result of the directions of
the wind or rain or both, longitudinal
periodic due to aerodynamic configuration
of sheds and the fact that rain naturally
washes away the top surfaces and the third
one being longitudinal non-periodic which
is a function of the electric field which
attracts deposit of contaminations on
insulator surface adjacent phase wire or by
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the position of the insulator especially in a
string
insulator
configuration.
Hydrophobic properties are improved with
the addition of defensive layer known as
defensive coating. Very large resistance,
dry band arc and less leakage currents are
achieved using separators that are
degraded provided a perfect defensive
coating is made to repel water due to the
presence of water-films in the coating [3].
Insulators that can withstand pollution
flashover voltages are used with oil bath.
A surface having oil may generally be
unpollutable because of the total mixture
of oil and the insulator particles. By
construction, the insulator may be cap and
pin type or have pedestal post and weather
shield to prevent pollution. The surface of
the lowest insulator in the chain has full
pollution deposits because of the presence
of wind and oil creeping properties. By
this leakage currents are minimized with
maximum resistance since the insulator
surface will be entirely covered with oil.
The situation allows oil to run over all
parts of the insulator surface thereby
getting all visible contaminations soaked
exhibiting the characteristic of a water
repellent in the process. Insulators that fall
in this category always perform optimally
in terms of surface contamination.
New or fresh oil is always recommended if
the existing oil is mixed with dirt and
water (polluted or contaminated oil). Most
of the time, wind play a major role in the
pollution of insulators and total withdrawal
from service especially if oil bath is not
adequately protected from the action of
wind and rain. By this, regular checks are
necessary to prevent flashover voltages.
Generally speaking, voltage spread or
distribution on insulators particularly the
porcelain type is generally non-uniform
especially when operated wet which will
eventually lead to discharges on the
Journal of Recent Trends in Electrical Power System
Volume 6 Issue 3
DOI: https://doi.org/10.5281/zenodo.10043379
surface thereby giving room for
flashover voltages. It is recommended to
glaze with appropriate resistance the
porcelain insulator to get fixed
resistances into the insulator provided
the insulator is segmented and shunted
with the required fixed resistances. This
technique is seamless and effective in
the prevention of loss of insulators due
to contamination in the power system.
The art of glazing involves the use of
glass with a little size of the particles of
tin oxide. Technically, the art of glazing
permits a minute current steaming
resulting from frequent heating due to
increased resistivity. This process makes
the surface of the insulator to remain dry
thereby preventing flashover as leakage
currents and arc are not encouraged [4].
Silicone composite materials when used
as coatings are more efficient than when
other equivalent materials are used. The
reason for this success is the fact that
silicone composite materials possess
hydrophobicity properties that make the
insulator to withstand pollution due to
factory and industrial operations [5].
Actually, rain seldom washes the surface
of the insulator even when operated
within an industrial-based pollution
prone area or severe marine pollution
prone area. Very importantly, rain fall
may not be regular that will guarantee
the washing of the surface of the
insulator
for
optimal
utilization.
Insulator
surface
contamination
generally reduces dielectric properties of
the insulator in a manner that can
guarantee a sharp rise in leakage current
that would be sufficient to cause a
flashover [6].
It has been noted that salt accompanied
with pollutants are generally very uneasy
for water to dissolve since oil on the
insulator surface may be acting like grease.
Based on this, it is noted that grease causes
substantial number of flashovers especially
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Journal of Recent Trends in Electrical Power System
Volume 6 Issue 3
DOI: https://doi.org/10.5281/zenodo.10043379
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in areas of high pollution. When subjected
to harsh operating and environmental
conditions petroleum products attains
reasonable stability height because of what
they contain. It is important to note that
silicone and jellies from the family of
petroleum are very popular classes of
grease. The moment current flows
temperature rises and this will give birth to
the jellies becoming weak (soft) thereby
making it to melt. If current flow is
stopped then cooling takes place and the
jellies retain their properties before the
temperature rise. It is important to note
that the material at this time of temperature
rise shows the true nature of the material
and are unfit for harsh environmental and
operating conditions. That is to say, they
are better used in environments devoid of
high risks of pollution [7].
MATERIALS AND METHOD
Pollution and Energization Technique
The experimental set-up to ascertain the
action of dust on 33kV line insulators in
this work is comprised of porcelain
insulator, polymeric insulator, salt,
cement, dust, demineralized water and rain
water. This was conducted at the
Transmission Company of Nigeria (TCN),
Afam Station by way of artificial
contamination. Five specimens in the order
of A, B, C, D and E were drawn from each
of porcelain insulator and polymeric
insulator to determine their break-down
voltages and leakage currents. The
measurements were recorded separately
for porcelain specimens and polymer
specimens each as dry, cement, urea and
salt pollutions respectively.
Table 1: Relevant Data Considered in the Pollution and Energization Experiment.
S/No. Parameters
Dimension/Unit
1
2
3
4
5
6
7
8
9
mm
mm
mm
mm/kV
no.
mm
mm
mm
mm
Insulator Length
Creepage Distance
Dry Arcing Distance
Specific Creepage Distance
Sheds
Diameter of Shed
Shed Spacing
Shed Thickness
Core Diameter
Test (Experiment) Procedure
The insulator specimens were dusted and
cleaned properly to remove all traces of
dirt and grease that were found on their
surfaces. There after the insulators were
washed using de-mineralized water to keep
them clean and later subjected to natural
drying which lasted for 24hours. Then the
insulators were surface polluted by
spraying as recognized by IEC 60507.
Insulator surface was sprayed with the
polluted solution and specimens were
dried by natural means for 24hours. This
process continued for 7 days to achieve a
Specimens
Porcelain Polymeric
510
510
910
915
380
385
25
25
8
3
90
245
45
160
3
-20.5
--
uniform layer on the surfaces of the
insulators. Similarly, urea and cement
pollutions were sprayed on the test
insulators following the same procedure
until a contamination layer was formed.
This same method was applied using salt
to contaminate the specimens and all were
tested
(energized)
accordingly
as
measurements were taken in each case for
porcelain insulator and polymeric insulator
samples respectively.
The Insulator specimens were mounted in
vertical position and energized (powered)
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Journal of Recent Trends in Electrical Power System
Volume 6 Issue 3
DOI: https://doi.org/10.5281/zenodo.10043379
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with one side of the test insulator linked to
high voltage source and the other linked to
earth. An earth clearance of two meters
was maintained while the experiment was
conducted.
Based on voltage control principle, voltage
was supplied in steps and corresponding
leakage current was recorded while
voltage was increased gradually until
break-down occurs. In each sequence, the
voltage at the break-down point was
considered the break-down voltage.
RESULTS AND DISCUSSION
Break-Down Voltage (BDV) and
Leakage Current (LC) for 33kV
Porcelain Insulators
The 33kV porcelain specimens were
conditioned and contamination was
applied using spraying technique for seven
days
until
a
heavy
covering
(contamination) was seen. The specimens
were powered after contamination
following experimental procedure. Then
the break-down voltages and leakage
currents were recorded accordingly as
shown in Table 2.
Table 2: Break-Down Voltages and Leakage Currents of 33kV Porcelain Insulators
Condition
Dry
Salt
Cement
Urea
A
BDV
(kV)
118
112
95
110
LC
(µA)
26
100
37
90
B
BDV
(kV)
114
132
90
100
LC
(µA)
65
142
25
104
C
BDV
(kV)
115
101
100
110
LC
(µA)
110
92
89
122
D
BDV
(kV)
118
114
116
98
LC
(µA)
65
85
78
134
E
BDV
(kV)
122
120
122
105
LC
(µA)
32
65
32
154
Table 3: Graph of Break-Down Voltages and Leakage Currents of Porcelain
Insulator Samples.
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Journal of Recent Trends in Electrical Power System
Volume 6 Issue 3
DOI: https://doi.org/10.5281/zenodo.10043379
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Break-Down Voltage (BDV) and
Leakage Current (LC) for 33kV
Polymeric Insulators
The 33kV polymeric specimens were also
conditioned and contamination was
supplied using spraying technique for a
number of days until a heavy layer
(contamination)
was
noticed.
The
specimens
were
powered
after
contamination following experimental
procedure. Then the break-down voltages
and leakage currents were recorded
accordingly as shown in Table 4.
Table 4: Break-Down Voltages and Leakage Currents of 33kV Polymeric Insulators.
A
BDV
Condition (kV)
Dry
155
Salt
131
Cement
122
Urea
141
LC
(µA)
51
43
31
48
B
BDV
(kV)
149
149
125
135
LC
(µA)
48
50
38
48
C
BDV
(kV)
146
116
135
132
LC
(µA)
44
40
49
50
D
BDV
(kV)
145
123
144
136
LC
(µA)
45
44
53
41
E
BDV
(kV)
144
120
142
132
LC
(µA)
44
42
52
40
Table 5: Graph of Break-Down Voltages and Leakage Currents of Polymeric Insulator
Samples.
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Journal of Recent Trends in Electrical Power System
Volume 6 Issue 3
DOI: https://doi.org/10.5281/zenodo.10043379
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Table 6: Comparison of Break-Down Voltages for Porcelain and Polymeric Insulators.
Table 7: Comparison of Leakage Currents for Porcelain and Polymeric Insulators.
CONCLUSION
From the tests results, leakage current is
more on porcelain insulators subjected to
urea and salt pollutions and less in cement
contaminations due to the fact that breakdown occurred earlier in cement
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contamination and late in urea and salt.
Looking at average break-down voltages of all
samples, it may be noted that among all
pollutions, break-down voltage became low
in salt as well as in cement and higher in
urea. This implies that molecules of salt
and cement degrade the surface of the
insulator faster when than urea. Generally,
leakage currents are higher in urea
polluted insulators. Results showing
leakage currents indicate that average leakage
currents are higher in urea polluted insulators and
less in cement and salt pollutions.
Comparatively, the effect of contamination
or pollution on porcelain specimens is
higher than in polymeric insulators. Effect
of cement, urea and salt pollutions
(contaminations) is low in polymeric
insulators and higher in porcelain
specimens. With regards to test data, the
break-down
voltage
of
polymeric
insulators in salt contamination is 17%
higher than in porcelain insulators, the
breakdown voltage of polymeric insulators
in cement contamination is 22% higher
than in porcelain insulators and the breakdown voltage of polymeric specimens in
urea contamination is 31% higher
compared to porcelain specimens.
REFERENCES
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(1991).
Artificial
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Insulators to Be Used on AC
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Journal of Recent Trends in Electrical Power System
Volume 6 Issue 3
DOI: https://doi.org/10.5281/zenodo.10043379
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Cite as :
Igbogidi O. N., & Amadi H.N. (2023).
Analysis of the Effects of Dust
Accumulation on 33kV Line Insulators.
Journal of Recent Trends in Electrical
Power
System,
6(3),
19–26.
https://doi.org/10.5281/zenodo.10043379
HBRP Publication Page 19-26 2023. All Rights Reserved
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