applied
sciences
Article
Non-Uniform Distribution of Contamination on
Composite Insulators in HVDC Transmission Lines
Zhijin Zhang *, Xinhan Qiao * , Shenghuan Yang and Xingliang Jiang
State Key Laboratory of Power Transmission Equipment & System Security and New Technology,
Chongqing University, Chongqing 400044, China; yangshenghuan@cqu.edu.cn (S.Y.); xljiang@cqu.edu.cn (X.J.)
* Correspondence: zhangzhijin@cqu.edu.cn (Z.Z.); qiaoxinhan@cqu.edu.cn (X.Q.); Tel.: +86-138-8320-7915 (Z.Z.)
Received: 17 September 2018; Accepted: 12 October 2018; Published: 17 October 2018
Featured Application: The proposed pollution non-uniformity coefficient K provides guidance
for insulation design and field anti-pollution works, which helps prevent the occurrence of
pollution flashover accidents.
Abstract: In recent years, the air particulate pollutants formed by the combustion of fossil fuels and
the emission of industrial waste gases have constantly been produced, and the polluted particles
deposit also seriously affects social production and people’s lives. For instance, pollution-induced
flashover is seriously threatening the safe operation of the power system, while insulator pollution
non-uniformity has great influence on the flashover voltage of insulators. Therefore, in this paper
both field contamination experiments of HVDC (High Voltage Direct Current) transmission lines
and wind tunnel contamination simulation tests were conducted, and pollution non-uniformity
coefficient KT/B , KW/L and KH/M were proposed and obtained. The results showed that the degree of
contamination on top surface and leeward side is heavier than that on bottom surface and windward
side. Thus, in the DC energized condition, contamination along the string is also non-uniform,
and serious pollution occurs mainly in the high voltage terminal. In order to explain the uneven
distribution phenomenon along the string, the coupling-physics model of composite insulator string
was established and using the finite element method, the electric field around the insulator was
simulated. Furthermore, basing on the field charging theory, the value of electric field force on
particles around the insulator surface was calculated and the mechanism of non-uniformity along the
insulator sting was then explained. The results are very important for guiding insulation design and
field anti-pollution works.
Keywords: contamination; non-uniform distribution; composite insulators; electric field; HVDC
transmission lines
1. Introduction
Because of the deterioration of the atmosphere environment in China, the operating HVDC
transmission lines are still under high pollution flashover risks [1,2]. Pollution flashover of insulator is
a serious threat to safe operation of the power grid. It risks causing large-scale power outages, and
badly impacting development of the social economy [3–5]. The primary cause of pollution flashover is
contaminants accumulating and depositing on the insulator surface. Besides this, it is important to
further study insulator contamination rules to better guide the anti-pollution works of transmission
line and substation outdoor insulation.
Plenty of research [6–8] has been done through simulation and pollution tests to reveal insulator
contamination mechanisms. Literature [6] has put forward a power law relationship between the
pollution accumulation rate and wind velocity through a simplified wind tunnel contamination
Appl. Sci. 2018, 8, 1962; doi:10.3390/app8101962
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Appl. Sci. 2018, 8, 1962
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experiment. Literature [7] built a pollution deposit model of rail insulator using a gas–solid aerosol
flow simulation to show the rules of wind velocity affecting pollution deposits and distribution.
Through a simulation and wind tunnel test, literature [8] concluded that the DC voltage results in a
larger contaminant deposition rate of particles on the insulator surface and a larger increasing rate
than AC voltage and non-energized conditions.
Not only does the contamination degree have an effect on flashover voltage, but also the
contamination non-uniformity has great influence on flashover voltage, many documents have
conducted in-depth research on this [9–16]. In literature [9], we can find that the uniform distribution
of the pollution has given a weaker dielectric rigidity than the one obtained in non-uniform pollution.
Besides, the influence of non-uniform pollution distribution on DC composite insulators on their
flashover performance was analyzed [10], and a correction formula for the non-uniform pollution
flashover voltage was proposed. The test results showed that the flashover voltage U50 decreases with
the increase of T/B, where T/B is ratio of the salt deposit density (SDD) on the top surface to that on
the bottom surface. Similar conclusions can be found in references [11,12].
In literature [13], DC pollution flashover tests of insulators under fan-shaped non-uniform
pollution were presented, and the influence of fan-shaped non-uniform pollution on flashover voltage,
arc propagation, and critical leakage distance were investigated. Research results indicate that a
reduction in the ratio W/L from 1/1 to 1/15 gave a median 35% ± 4% decrease in flashover strength,
where W/L is ratio of the salt deposit density (SDD) on the windward surface to that on the leeward
surface. Thus, in literature [14], artificial pollution tests of 4 types of porcelain and glass insulators
with ring-shaped non-uniform pollution were carried out. Experimental results indicate that the
non-uniform pollution degree K (the SDD ratio of inner part to outer part) has significant effects
on insulator flashover performance. AC (Alternating Current) pollution flashover tests of 7-unit
insulators in all three different non-uniform pollution conditions were carried out in reference [15].
The results indicate that the increase of uneven pollution degree J (J = SDD2 /SDD1 , SDD1 and SDD2
represent different parts of the insulator’s SDD, specifically, SDD2 represents SDD of bottom surface,
leeward side, inner ring side, SDD1 represents SDD of top surface, windward side, outer ring side
respectively.) from 1 to 15 will give a 39% raise of U50 under non-uniform pollution on top and bottom
surfaces, a 23% decrease for fan-shaped non-uniform pollution and a 21% higher U50 with ring-shaped
non-uniform pollution.
What is more noteworthy is that, in literature [16], the effect of pollution non-uniformity
distribution on the insulators performance under ac voltage has been studied with three types of
distribution: Transversal, periodic longitudinal and non-periodic longitudinal. Transversal and
periodic longitudinal distribution are similar to W/L and T/B non-uniform pollution noted above.
However, the effect of non-periodic longitudinal distribution on the insulator’s performance is indeed
a new discovery, which showed that this category has allowed the identification of the existence of a
minimum voltage of about 42% of those acquired under uniform distribution.
From the above analysis, we can see that the contamination non-uniformity did have great
influence on flashover voltage, but few of the reports on pollution non-uniformity in energized
condition were presented. Natural exposure tests with −280 kV DC voltage energization were carried
out for 5 years in reference [17]. The results show that insulators near the line and ground sides of a
string collect more contaminant than the middle when DC voltage is applied. However, the specific
values and influencing factors of non-uniformity are not given.
In this paper, both field contamination experiments of HVDC transmission lines and wind
tunnel contamination simulation tests in dc energized condition were conducted, and pollution
non-uniformity coefficients KT/B , KW/L and KH/M were proposed and obtained. Thus, the effects
of particle diameter, wind velocity and relatively humidity on pollution non-uniformity were
quantitatively computed. In order to explain the uneven distribution phenomenon along the string,
the coupling-physics model of composite insulator string was established. Furthermore, basing on field
Appl. Sci. 2018, 8, 1962
Appl. Sci.
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2018, 8,
8, xx FOR
FOR PEER
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14
33 of
theory, the
the
mechanism
of non-uniformity
non-uniformity
along insulator
insulator
sting was
was
then
revealed.
Research
results
charging
theory,
the mechanism
of non-uniformity
along insulator
sting
was
then revealed.
Research
theory,
mechanism
of
along
sting
then
revealed.
Research
results
are
valuable
for
field
pollution
level
mapping
works
and
for
DC
lines
outdoor
insulation
design.
results
are
valuable
for
field
pollution
level
mapping
works
and
for
DC
lines
outdoor
insulation
design.
are valuable for field pollution level mapping works and for DC lines outdoor insulation design.
2. Natural Pollution Test
Test in
in the
the Operating
Operating HVDC
HVDC Transmission
TransmissionLines
Lines
2. Natural Pollution Test
in
the
Operating
HVDC
Transmission
Lines
2.1.
The Sample
Sample Arrangement
Arrangement and
Contamination
Distribution
2.1. The
The
and Contamination
Contamination Distribution
Distribution
2.1.
Sample Arrangement
and
The
contamination
samples
were
arranged
in
The contamination
contamination samples
samples were
were typical
typical type
type suspension
suspension composite
composite insulators
insulators arranged
arranged in
in
The
typical
type
suspension
composite
insulators
different
towers
in
a
certain
±
800
kV
HVDC
transmission
line
corridor.
The
tower
views
and
diagram
different
towers
in
a
certain
±800
kV
HVDC
transmission
line
corridor.
The
tower
views
and
diagram
different towers in a certain ±800 kV HVDC transmission line corridor. The tower views and diagram
of
test
were
shown
in
and
test
of test
test samples
samples arrangement
arrangement were
were shown
shown in
in Figure
Figure 1.
1. The
The sample
sample arrangement
arrangement and
and test
test procedures
procedures
of
samples
arrangement
Figure
1.
The
sample
arrangement
procedures
were
based
exactly
on
guideline
[18].
were
based
exactly
on
guideline
[18].
were based exactly on guideline [18].
(a)
(a)
(b)
(b)
1. Field
Field pollution
pollution test
test of
of transmission
transmission line
lineoperating
operatinginsulators.
insulators. (a)
(a)the
the±
±800
transmission
Figure 1.
800 kV
kV transmission
Figure
1.
Field
pollution
test
of
transmission
line
operating
insulators.
(a)
the
±800
transmission
line
view;
(b)
Diagram
natural
contamination
insulator
string
sample
arrangement.
line view; (b) Diagram natural contamination
contamination insulator
insulator string
string sample
sample arrangement.
arrangement.
The contamination
contamination
period
from
2014 to November
2017.to
to the
contamination
period
was was
from March
MarchMarch
2014 to
to November
November
2017. According
According
toAccording
the meteorological
meteorological
The
period
was
from
2014
2017.
the
meteorological
monitoring
statistics
nearthe
thatfrequency
location, the
frequency
wind speed
within
0.5–5.4 95%
m/s
monitoring statistics
statistics
near that
that
location,
the
frequency
of wind
wind
speedofwithin
within
0.5–5.4
m/s reaches
reaches
95%
monitoring
near
location,
of
speed
0.5–5.4
m/s
reaches
95%
during
test
period.
And
basing
on
the
TSP
(total
suspended
particles)
monitoring
data
during test
test period.
period. And
And basing
basing on
on the
the TSP
TSP (total
(total suspended
suspended particles)
particles) monitoring
monitoring data
data near
near that
that area,
area,
during
≤
near
that
area,
the
cumulative
probability
particles
d
50
µm
is
about
and
PM
hold
the
the
cumulative
probability
of
particles
d
p ≤of
50
μm
is
about
90%,
and
PM
10 90%,
hold
the
majority
of
p
10
the cumulative probability of particles dp ≤ 50 μm is about 90%, and PM10 hold the majority of the
majority
of
the
TSP.
After
the
contamination
period,
contamination
distribution
on
insulator
surface
TSP.
After
the
contamination
period,
contamination
distribution
on
insulator
surface
were
obtained,
TSP. After the contamination period, contamination distribution on insulator surface were obtained,
were
obtained,
as is shown
in Figure 2.
as is
is shown
shown
in Figure
Figure
2.
as
in
2.
Figure 2. Field
Field pollution test
test of transmission
transmission line operating
operating insulators.
Figure
Figure 2.
2. Field pollution
pollution test of
of transmission line
line operating insulators.
insulators.
The following
following phenomena
phenomena can
can be
be observed.
observed. Contamination
Contamination distribution
distribution on
on insulator
insulator surface
surface is
is
The
distribution
non-uniform. Contamination
Contamination
degree
on top
top surface
surface and
and leeward
leeward side
side is
is heavier
heavier than
than that
that on
on bottom
bottom
non-uniform.
Contamination degree
degree on
surface
and
windward
side.
Thus,
in
the
DC
energized
condition,
contamination
along
the
string
is
surface and windward side. Thus, in the DC energized condition, contamination along the string is
also
non-uniform,
and
serious
pollution
occurs
mainly
in
the
high
voltage
terminal
and
ground
also non-uniform, and serious pollution occurs mainly in the high voltage terminal and ground
Appl. Sci. 2018, 8, 1962
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Appl. Sci. 2018, 8, x FOR PEER REVIEW
of 14
surface and windward side. Thus, in the DC energized condition, contamination along the4string
is also non-uniform, and serious pollution occurs mainly in the high voltage terminal and ground
terminal. In order to quantify contamination non-uniformity, ESDD (equivalent salt deposit density,
terminal. In order to quantify contamination non-uniformity, ESDD (equivalent salt deposit density,
mg/cm2)2and NSDD (non-soluble pollution deposit density, mg/cm2)2of the samples will be measured.
mg/cm ) and NSDD (non-soluble pollution deposit density, mg/cm ) of the samples will be measured.
2.2.
2.2.Contamination
ContaminationNon-Uniformity
Non-UniformityofofOperating
OperatingHVDC
HVDCComposite
CompositeInsulator
Insulator
Following
guidelinesininliterature
literature[18],
[18],
ESDD
NSDD
of samples
the samples
measured
Following the
the guidelines
ESDD
andand
NSDD
of the
werewere
measured
based
based
on
the
method
shown
in
Figure
3:
Firstly,
moderately
purified
water
was
used
to
clean
up the
on the method shown in Figure 3: Firstly, moderately purified water was used to clean up the surface
surface
of the polluted
insulator,
the conductivity
of theliquid
dirtyafter
liquid
after filtering
was measured,
of the polluted
insulator,
then thethen
conductivity
of the dirty
filtering
was measured,
the salt
the
salt quantity
attached
to surface
each group
sheds
was calculated
separately,
and finally,
quantity
attached
to surface
of eachofgroup
sheds was
calculated
separately,
and finally,
based based
on the
on
theofareas
of the insulator
the converse
salt quantity
ESDD
was calculated;
the dirty
areas
the insulator
surface,surface,
the converse
salt quantity
to ESDD to
was
calculated;
the dirty liquid
was
liquid
was
filtered
after
cleaning
the
insulator,
then
the
insoluble
materials
were
left
on
the
filtering
filtered after cleaning the insulator, then the insoluble materials were left on the filtering paper to
paper
to dry
were weighed.
Lastly, referring
to thearea,
surface
the converse
of the of
quantity
of
dry and
wereand
weighed.
Lastly, referring
to the surface
the area,
converse
of the quantity
insoluble
insoluble
materials
to
NSDD
was
calculated.
materials to NSDD was calculated.
Figure 3. The flowchart of the measuring of the ESDD and NSDD.
Figure 3. The flowchart of the measuring of the ESDD and NSDD.
In this test, 64 series of measurements were made. Each group was taken for calculating
In this test,non-uniformity
64 series of measurements
werebottom
made.surface,
Each group
was side
takenand
forleeward
calculating
contamination
of top surface and
windward
side,
contamination
non-uniformity
of
top
surface
and
bottom
surface,
windward
side
and
leeward
side,
high voltage groups and middle groups respectively. The SDD and relative standard deviation error
high
voltage
groupsby
and
middle
groups
respectively. The SDD and relative standard deviation error
(σ) were
calculated
the
equation
as follows:
(σ) were calculated by the equation as follows:
n
∑ SDDi
i =1SDD i

SDD =
SDD = i =1 n
n
n
s
σ=
n(
(1)(1)
n
∑ (SDDi − SDD2)2 )/(n − 1)/SDD × 100%
1
σ = (i=(SDD
i − SDD) ) / (n − 1) / SDD ×100%
(2)
(2)
where SDDi is a calculated SDDi =1from test results, and n is the number of measurements made.
To better understand contamination non-uniformity of insulators, KT/B , KW/L , KH/M , K*T/B ,
where SDDi is a calculated SDD from test results, and n is the number of measurements
made.
K*W/L and K*H/M were proposed and calculated as follows:
To better understand contamination non-uniformity of insulators, KT/B, KW/L, KH/M, K*T/B, K*W/L

and K*H/M were proposed and calculated
as follows:
KT/B = NSDDT /NSDDB





K T/B ==NSDD
NSDDT WNSDD
/NSDD

B L
  KW/L

KKH/M ==NSDD
NSDDH /NSDD
M
(3)
W NSDDL
 KW/L

∗
=
ESDD
/ESDD
T
B
T/B


KH/M = NSDDH NSDDM


K∗
= ESDDW /ESDDL

(3)

  K*W/L= ESDD ESDD
T/B = ESDD
T H /ESDD
B M
K∗H/M
K*W/L = ESDDW ESDDL
 L , NSDDH and NSDDM , are the NSDD of top surface, bottom
where NSDDT , NSDDB , NSDDW , NSDD
*H/M = ESDDH ESDDM
K
surface, windward side, leeward side,
high
voltage group and middle group respectively, as is ESDD.
The
Contamination
degree
and
calculated
K
are Hshown
in Table
1. the NSDD of top surface, bottom
where NSDDT, NSDDB, NSDDW, NSDDL, NSDD
and NSDD
M, are
surface, windward side, leeward side, high voltage group and middle group respectively, as is ESDD.
The Contamination degree and calculated K are shown in Table 1.
Appl. Sci. 2018, 8, 1962
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Table 1. Contamination degree and non-uniformity results for field operating insulators.
NSDD (mg/cm2 )
NSDDT
NSDDB
NSDDW
NSDDL
NSDDH
NSDDM
Average value
σ
0.342
13.5%
0.167
11.1%
0.208
8.6%
0.301
9.6%
0.316
9.3%
0.193
8.2%
ESDDB
ESDDW
ESDDL
ESDDH
2 ) REVIEW
Appl. Sci.ESDD
2018, 8, (mg/cm
x FOR PEER
ESDDT
ESDDM5 of 14
Average value
0.061
0.031
0.037
0.054
0.056
0.035
Table 1. Contamination degree and non-uniformity results for field operating insulators.
σ
13.6%
9.1%
8.8%
10.5%
10.2%
8.7%
NSDD
L
NSDD
H
NSDDK*
M
K (mg/cm2) NSDD
KT/B T NSDD
K*T/B B NSDD
KW/LW NSDD
K*W/L
KH/M
H/M
Average
value
1/0.51
1/1.45
1/1.46 0.316
1/0.61 0.1931/0.62
Average
value 1/0.49
0.342
0.167
0.208
0.301
σ
13.5%
11.1%
8.6%
9.6%
9.3%
8.2%
ESDD (mg/cm2) ESDDT ESDDB ESDDW ESDDL ESDDH ESDDM
It can be seen from the table that both KT/B and K*T/B are around 1/0.51, which means that
Average value
0.061
0.031
0.037
0.054
0.056
0.035
the amount of contamination
on13.6%
the top 9.1%
surface is
2 times10.5%
than that
of the bottom
surface. Thus,
σ
8.8%
10.2%
8.7%
KW/L , K*W/L , KH/M , K*
1/1.46,
respectively,
this we can get two
K*T/B 1/0.61,
KW/L 1/0.62
K*W/L
KH/M from
K*H/M
K H/M are 1/1.45,
KT/B
1/0.49
1/0.51
1/1.45
1/1.46
1/0.61
1/0.62
conclusions, on Average
the onevalue
hand, the
contamination
on
insulator
surfaces
is very
uneven, on the other
hand, the value of K and K* is almost equal. The above data is very important for guiding insulation
can be seen from the table that both KT/B and K*T/B are around 1/0.51, which means that the
design andItfield
anti-pollution works.
amount of contamination on the top surface is 2 times than that of the bottom surface. Thus, KW/L,
The
measurement
of contamination non-uniformity on insulator surface in operating HVDC
K*W/L, KH/M, K*H/M are 1/1.45, 1/1.46, 1/0.61, 1/0.62 respectively, from this we can get two conclusions,
transmission
lines
is complicated
and on
dangerous
work which
plenty
manpower.
But by using
on the one
hand,
the contamination
insulator surfaces
is veryneeds
uneven,
on theof
other
hand, the value
wind tunnel
simulation
the
factors
particle
diameter,
wind insulation
velocity, design
relative
humidity
and
of K and
K* is almostmethod
equal. The
above
dataof
is very
important
for guiding
and
field
anti-pollution
works.
electric field can also be considered. It may be a useful way for obtaining contamination non-uniformity
measurement
of contamination
non-uniformity
on insulator
surface
operating measurements.
HVDC
K, withoutThe
so much
time-consuming,
danger
and sometimes
irregular
fieldinpollution
transmission lines is complicated and dangerous work which needs plenty of manpower. But by
Because the non-uniformity of NSDD is almost equal to that of ESDD, only the non-uniformity of
using wind tunnel simulation method the factors of particle diameter, wind velocity, relative
NSDD humidity
is considered
in the
wind
tunnel
simulation.
and electric
field
can also
be considered.
It may be a useful way for obtaining contamination
non-uniformity K, without so much time-consuming, danger and sometimes irregular field pollution
3. Contamination
Test
in Wind
Tunnel
measurements.
Because
the non-uniformity
of NSDD is almost equal to that of ESDD, only the nonuniformity of NSDD is considered in the wind tunnel simulation.
3.1. Samples
3. Contamination Test in Wind Tunnel
The sample was big-small sheds composite insulators named Type-A. The technical parameters
and structure
of the sample are shown in Table 2 and Figure 4, in which H is structure height, D is
3.1. Samples
big-shed diameter, and d is small-shed diameter.
The sample was big-small sheds composite insulators named Type-A. The technical parameters
and structure of the sample are shown in Table 2 and Figure 4, in which H is structure height, D is
2. Structure
parameters of the tested insulators.
big-shed diameter, andTable
d is small-shed
diameter.
Parameters (mm)
Table
2. StructureMaterial
parameters of the tested insulators.
Sample
D
Sample
Material
Silicon
Type-A
Silicon rubber
Type-A
rubber
d
H
Parameters (mm)
135 d 105 H 660
D
135 105 660
Figure 4. Structure of the samples.
Figure
4. Structure of the samples.
Appl. Sci.
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8, x1962
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Appl. Sci. 2018, 8, x FOR PEER REVIEW
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The contaminants were simulated by SiO2 powder. After screening, 250 mesh, 400 mesh, 800
The
contaminants
were
simulated
bybySiO
After
screening,
250250
mesh,
400 mesh,
800
2 powder.
were
simulated
SiO
2 powder.
After
screening,
mesh,
400 mesh,
800
meshThe
andcontaminants
2000 mesh SiO
2 powder
samples
were
obtained
for
wind
tunnel
contamination
test.mesh
The
and
2000
mesh
SiO
powder
samples
were
obtained
for
wind
tunnel
contamination
test.
The
optical
2
mesh
and
2000
mesh
SiO
2
powder
samples
were
obtained
for
wind
tunnel
contamination
test.
The
optical microscope magnification of SiO2 powder sample is shown in Figure 5 and diameter situations
microscope
magnification
of SiO2 powder
sample
is shown
in Figure
5 and
diameter situations of
optical
microscope
magnification
2 powder
sample
is shown
indiameter
Figure
5 and
are shown of
in SiO
Table
3, where
d is the
particle
. diameter situations
of tested
SiO2 powder
tested
SiO
powder
are
shown
in
Table
3,
where
d
is
the
particle
diameter.
2 2 powder are shown in Table 3, where d is the particle diameter.
of tested SiO
(a)
(a)
(b)
(b)
Figure 5. SiO2 powder samples used in the tunnel test: (a) optical microscope; (b) 250 and 2000 mesh
Figure
SiO
samples
Figure5.5.specimen
SiO2 2powder
powder
samplesused
usedininthe
thetunnel
tunneltest:
test:(a)
(a)optical
opticalmicroscope;
microscope;(b)
(b)250
250and
and2000
2000mesh
mesh
powder
enlargement.
powder
powderspecimen
specimenenlargement.
enlargement.
Table 3. Diameter situations of tested SiO2 powder.
Table 3. Diameter situations of tested SiO powder.
Table 3. Diameter situations of tested SiO22powder.
Powder Specification (mesh)
d (10%)
d (50%)
d (90%)
D50 (μm)
Specification
(mesh)d (10%)
d (10%) dd(50%)
(50%)
d (90%)
D50 (µm)
Powder Powder
Specification
(mesh)
d
(90%)
D
5046.5
(μm)
250
35.3
46.5
57.8
250
35.3
46.5
57.8
46.5
250
35.3
46.5
57.8
46.5
400
22.3
27.7
35.2
27.7
400
22.3
27.7
35.2
27.7
400
22.3
27.7
35.2
27.7
800 800
11.811.8
15.9
15.9
17.617.6
15.9 15.9
800 2000
11.8
15.9
2000
2.8 2.8
4.2
5.8
4.2
4.2
5.817.6
4.2 15.9
2000
2.8
4.2
5.8
4.2
Note:
(10%),10%
10%particle
particle
size
is smaller
this value;
d (50%),
50% particle
size isthan
smaller
than
Note: d
d (10%),
size
is smaller
thanthan
this value;
d (50%),
50% particle
size is smaller
this value;
Note:
d (10%),
10% size
particle
size is
smaller
thanDthan
this
value;
d (50%),
50%
particle
sizesize,
is smaller
than
d (90%),
90%dparticle
smaller
than
this
value,
particle
size,
cumulative
probability
distribution
50 , average
, average
particle
cumulative
this
value;
(90%),
90%isparticle
size
is smaller
this value,
D50
of
particle
size
is
50%.
this
value; ddistribution
(90%), 90% of
particle
size
is smaller
probability
particle
size
is 50%. than this value, D50, average particle size, cumulative
probability distribution of particle size is 50%.
3.2. Experimental
Experimental Devices
Devices
3.2.
3.2. Experimental
Devices
The tests
tests were
were
carriedout
outininaacirculating
circulatingwind
windtunnel,
tunnel,asasshown
showninin
Figure
The
power
The
carried
Figure
6. 6.
The
testtest
power
is
is
provided
by
the
YDTW-50/50kVA
test
transformer.
The
range
of
wind
speed
in
the
wind
tunnel
The
tests
were
carried
out
in
a
circulating
wind
tunnel,
as
shown
in
Figure
6.
The
test
power
is
provided by the YDTW-50/50kVA test transformer. The range of wind speed in the wind tunnel is
is 0–7
adjustable
accuracy
is 0.1
It
is range
mainly
of contaminated
section,
provided
byand
the
YDTW-50/50kVA
test
ofcomposed
wind of
speed
in the wind
tunnel
is
0–7
m/sm/s
and
the the
adjustable
accuracy
is transformer.
0.1
m/s.m/s.
It is The
mainly
composed
contaminated
section,
fan
fan
section
and
test
section.
The
front
end
of
the
test
section
is
equipped
with
a
six
angle
cellular
0–7
m/s and
andtest
the section.
adjustable
is mainly
composed
of acontaminated
section,
fan
section
Theaccuracy
front endisof0.1
them/s.
testItsection
is equipped
with
six angle cellular
devices
devices
to
reduce
the
air
flow
turbulence,
a
deflector
for
equalizing
airflow
is
installed
at
the
corner
of
section
and
test
section.
The
front
end
of
the
test
section
is
equipped
with
a
six
angle
cellular
devices
to reduce the air flow turbulence, a deflector for equalizing airflow is installed at the corner of the
the
wind
tunnel.
Other
equipment
includes
frequency
converter,
anemometer,
electronic
balance
of
to
reduce
the Other
air flow
turbulence,
a deflector
for equalizing
is installed
at the balance
corner of
wind
tunnel.
equipment
includes
frequency
converter,airflow
anemometer,
electronic
ofthe
0.1
0.1 mg
accuracy,
temperature
hygrometer,
air
particulate
mattercollection
collectioninstrument,
instrument,
scrubbing
tools,
wind
tunnel.
Other
equipment
includesair
frequency
converter,
anemometer,
electronic
balance of
0.1
mg
accuracy,
temperature
hygrometer,
particulate
matter
scrubbing
tools,
Ultrasonic
fogtemperature
generator, etc.
etc.
mg
accuracy,
hygrometer, air particulate matter collection instrument, scrubbing tools,
Ultrasonic
fog
generator,
Ultrasonic fog generator, etc.
(a)
(a)
(b)
(b)
Figure
Figure6.
6.Wind
Windtunnel
tunnel test
test device.
device. (a)
(a)Diagram
Diagramof
ofwind
wind tunnel;
tunnel; (b)
(b) Wind
Wind tunnel.
tunnel.
Figure 6. Wind tunnel test device. (a) Diagram of wind tunnel; (b) Wind tunnel.
Appl. Sci. 2018, 8, 1962
Appl. Sci. 2018, 8, x FOR PEER REVIEW
7 of 14
7 of 14
3.3. Experimental Methods
The wind tunnel contamination test procedure is as follows: Before the test, wash the insulators
samples thoroughly
thoroughly with
with Na
Na33PO44 solution
solution to
to remove
remove all
all traces
traces of
of grease
grease and
and dirt
dirton
oninsulators
insulators surface,
surface,
and then put the insulators in a dry and clean
place
and
let
them
dry
naturally
to
prepare
for
the
clean place and let them dry naturally to prepare for the test.
test.
During the test, firstly control the parameters such as wind
wind speed,
speed, particle
particle (SiO
(SiO22) concentration
in the wind tunnel to be stable and meet the test setup requirements, then suspend samples into the
where the
the concentration
concentration of
of particles
particlesin
inthe
thewind
windtunnel
tunnelisis15
15mg/m
mg/m3, the diameter of the
wind tunnel, where
400, 800
800 and
and 2000
2000meshes
meshesrespectively,
respectively,the
thewind
windvelocity
velocityisis1 1m/s,
m/s,33m/s,
m/s, 55 m/s
m/s and
particles is 250, 400,
7 m/s
m/s respectively,
respectively, relatively
relatively humidity
humidity is
is 60%,
60%, 70%,
70%, 80%
80% and 90% respectively. Finally electrify the
insulator with voltage of DC + 35 kV. Contamination
Contamination particles
particles were
were accumulated
accumulated in
in 88 h.
h.
4. Simulation Test Results
4.1. The
The Contamination
Contamination Distribution
Distribution of
of Insulators
Insulators in
4.1.
in Wind
Wind Tunnel
Tunnel
When
the
wind
speed
is
5
m/s,
the
diameter
of
the
particles
400
meshes,
relatively
humidity
When the wind speed is 5 m/s, the diameter of the particles
is is
400
meshes,
relatively
humidity
is
is 60%
non-energized
condition,
thecontamination
contaminationdistribution
distributionofofType-A
Type-Aisisshown
shownin
inFigure
Figure 7a.
7a.
60%
in in
non-energized
condition,
the
When
with voltage
voltage of
of DC
DC ++ 35
35 kV,
kV, the
the contamination
contamination distribution
distribution of
of Type-A
Type-A is
is
When electrify
electrify the
the insulator
insulator with
shown
in
Figure
7b.
shown in Figure 7b.
(a)
(b)
Figure 7. The
The contamination
contamination distribution
distribution of
of different
different insulators.
insulators. (a)
(a) Sample
Sample in
in non-energized
non-energized condition;
condition;
(b) Sample with voltage of DC + 35 kV.
From the test results, conclusions can be made
made as
as follows:
follows:
(1) As
7a, contamination
contamination distribution
obviously non-uniform
non-uniform on
insulator
(1)
As is
is shown
shown in
in Figure
Figure 7a,
distribution is
is obviously
on insulator
surface.
surface. Contamination
Contamination degree
degree of
of leeward
leeward side
side of
of insulator
insulator is
is greater
greater than
than that
that of
of windward
windward side
side
and
fan-shaped
pollution
layer
gets
formed
at
leeward
side.
Thus,
the
contamination
degree
and fan-shaped pollution layer gets formed at leeward side. Thus, the contamination degree of
of
the
surfaceisishigher
higherthan
than
that
of the
bottom
surface.
Inposition
the position
towards
aira flow,
a
the top
top surface
that
of the
bottom
surface.
In the
towards
air flow,
thicker
thicker
pollution
layer
get formed
round
Thistoisthe
due
the air pressure
in the
pollution
layer will
alsowill
getalso
formed
at roundatbar.
Thisbar.
is due
airtopressure
in the position
position
direct
to
the
incoming
air
flow
getting
increased,
causing
more
pollution
particles
to
direct to the incoming air flow getting increased, causing more pollution particles to adhere on
adhere
on
the
insulator
surface.
the insulator surface.
(2)
As
(2) As is
is shown
shown in
in Figure
Figure 7b,
7b, the
the effect
effect of
of DC
DC voltage
voltage on
on the
the contamination
contamination degree
degree is
is obvious.
obvious.
Contamination
degree
in
the
dc
energized
condition
is
heavier
than
that
in
a
non-energized
Contamination degree in the dc energized condition is heavier than that in a non-energized
condition.
condition. Besides
Besidesthis,
this,contamination
contamination distribution
distribution along
along the
the insulator
insulator sting
sting is
isobviously
obviously uneven,
uneven,
and
middle
and the
the contamination
contamination degree
degree of
of the
the high
high voltage
voltage area
area is
is much
much heavier
heavier than
than that
that of
of the
the middle
area
along
the
insulator
sting,
which
is
consistent
with
that
observed
at
the
operating
HVDC
area along the insulator sting, which is consistent with that observed at the operating HVDC
transmission
transmission lines.
lines.
Appl. Sci. 2018, 8, 1962
8 of 14
4.2. Effect of Wind Speed on Contamination Non-Uniformity
When the test is completed, turn off the power and take the sample out of the tunnel, brush the
contamination into a beaker and then filter and weigh the contamination. Then KT/B , KW/L , KH/M
were calculated in Formula (1). When the wind speed is 1 m/s, 3 m/s, 5 m/s and 7 m/s respectively,
the diameter of the particles is 250 meshes, relative humidity is 60% in DC energized condition, and
the results are shown in Table 4.
Table 4. Average NSDD, KT/B , KW/L , KH/M under different wind speed.
Wind Speed (m/s)
NSDD
(mg/cm2 )
σ
KT/B
KW/L
KH/M
1
3
5
7
0.12
5.7%
1/0.48
1/0.81
1/0.49
0.16
6.8%
1/0.52
1/1.22
1/0.56
0.21
7.3%
1/0.51
1/1.45
1/0.65
0.32
6.5%
1/0.55
1/1.75
1/0.71
As is shown in Table 4, average NSDD of the Type-A increased with the increase of the wind speed.
NSDD increases from 0.12 to 0.32 when the wind speed increases from 1 m/s to 7 m/s, which illustrates
that increased wind speed contributes to contamination. Besides this, the KT/B value remains almost
constant and stable at around 0.5. However, the KW/L value presents a downward trend, which means
that the contamination growth rate of the leeward side is larger than that of the windward side with the
increase of wind speed. It is noteworthy that when the wind speed is small, such as 1 m/s, the amount
of contamination accumulated on the windward side is greater than that on the leeward side, but the
opposite is true when the wind speed is higher. Besides this, the KH/M value also presents a downward
trend, which indicates that with the increase of wind speed, the effect of electric field on the growth of
contamination at high voltage terminal is weakened.
4.3. Effect of Particles Diameter on Contamination Non-Uniformity
When the wind speed is 5 m/s, the diameter of the particles is 250, 400, 800 and 2000 meshes
respectively, and relative humidity is 60% in DC energized condition. The results are shown in Table 5.
Table 5. KT/B , KW/L , KH/M with different particles diameter.
D50 (µm)
NSDD
(mg/cm2 )
σ
KT/B
KW/L
KH/M
46.5
27.7
15.9
4.2
0.21
7.7%
1/0.51
1/1.45
1/0.65
0.25
5.5%
1/0.56
1/1.42
1/0.63
0.30
4.2%
1/0.62
1/1.40
1/0.60
0.35
3.6%
1/0.66
1/1.36
1/0.58
As is shown in Table 5, decreased particle diameter contributes to contamination. When particle
diameter decreased from 46.5 to 4.2 µm, NSDD increased by 66.6%. Thus, particle diameter has an
effect on all three kinds of non-uniformity. With the decrease of particle diameter, KT/B value is closer
to 1. For example, KT/B changed from 1/0.51 to 1/0.66 when particle diameter decreased from 46.5 to
4.2 µm. Which shows that the larger the particles diameter is, the more obvious the non-uniformity
degree of contamination on top and bottom surfaces is. Large particles are not easily adhered to the
lower surface due to gravity, which can explain the change of KT/B .
Similarly, with the decrease of particle diameter, KW/L value is also closer to 1, for example, KW/L
changed from 1/1.45 to 1/1.36 when particle diameter decreased from 46.5 to 4.2 µm, which means
that the contamination growth rate of the leeward side is lower than that of the windward side with
the decrease of particle diameter. This is because small particles are more prone to cake in the position
towards air flow, and a thicker pollution layer will get formed at round bar (windward side).
Appl. Sci. 2018, 8, 1962
9 of 14
However, non-uniformity degree (KH/M ) of contamination on high voltage group and middle
group along insulator string is more obvious with the decrease of particle diameter, which illustrates
that the effect of electric field force on the contamination of smaller particles is more obvious.
4.4. Effect of Relatively Humidity on Contamination Non-Uniformity
When the wind speed is 5 m/s, the diameter of the particles is 250 meshes, relatively humidity is
60%, 70%, 80% and 90% respectively in DC energized condition, the results are shown in Table 6.
Table 6. KT/B , KW/L , KH/M under different relatively humidity.
Relatively Humidity
NSDD
(mg/cm2 )
Σ
KT/B
KW/L
KH/M
60%
70%
80%
90%
0.21
4.1%
1/0.51
1/1.45
1/0.65
0.23
5.6%
1/0.51
1/1.44
1/0.67
0.25
7.2%
1/0.53
1/1.45
1/0.70
0.26
7.7%
1/0.49
1/1.43
1/0.72
As is shown in Table 6, increased relatively humidity contributes to contamination. When relative
humidity increased from 60% to 90%, NSDD increased by 23.8%. The change of relative humidity has
little effect on KT/B and KW/L . With the increase of relative humidity, the KT/B value remains almost
constant and stable at around 0.5, with the KW/L value stable at around 1/1.44.
The change of relative humidity has a certain effect on KH/M , which is mainly manifested in the
increase of humidity making the K value trend closer to 1. The mechanism of the effect of humidity
on KH/M has not been studied. Based on the results, this paper only gives a theory that the change of
relative humidity will affect the charge of the polluted particles, which caused the change of electric
field force on polluted particles. As a result, the variation of contamination non-uniformity along
insulator sting is caused.
5. Discussion
This paper presents the pollution non-uniformity on insulator surface, then pollution
non-uniformity coefficient KT/B , KW/L and KH/M were proposed and obtained. Previous research
drew a conclusion that wind causes non-uniform distribution of pollution on the surfaces. However,
there is no literature to explain the mechanism of uneven distribution along the string. Therefore,
this chapter mainly explains this phenomenon by calculating the electric field force on contamination
particles, then future research directions are also expounded.
5.1. Numerical Calculation and Analysis of Electric Field Force
The uneven distribution of contamination along insulator string is due to the influence of electric
field force on contamination particles. Before calculating the electric field force, we need to get the
electric field distribution around the insulator. The electric field distribution of insulator strings
is solved by COMSOL, the control equations of computational domain under DC electric field are
as follows.
∇ · D = ρ, E = −∇V, D = ε 0 ε 1 E
(4)
where E is the electric field strength, in V/m; D is the electric flux density, in C/m2 ; U is the potential
value, in V; and the ε0 is the absolute dielectric constant of the vacuum, taking a value of 8.85 × 10−12
F/m; ε1 is relative dielectric constant of the medium, its value of silicon rubber insulator is 3.3; ρ is
charge density, in C/m3 . The contour line of the calculated electric field around Type-A is shown in
Figure 8.
Appl. Sci. 2018, 8, 1962
Appl.
Appl.Sci.
Sci.2018,
2018,8,8,x xFOR
FORPEER
PEERREVIEW
REVIEW
10 of 14
1010ofof1414
around
Type-A.
Figure8.8.Contour
Contourline
lineofofthe
theelectric
electricfield
fieldaround
aroundType-A.
Type-A.
Figure
The
The
electric
field
around
insulators
isisdistributed
distributed
unevenly
along
the
insulator
surface,
and
the
Theelectric
electricfield
fieldaround
aroundinsulators
insulatorsis
distributedunevenly
unevenlyalong
alongthe
theinsulator
insulatorsurface,
surface,and
andthe
the
electric
field
at
the
high
and
low
ends
is
larger.
The
maximum
value
occurs
at
the
surface
of
the
steel
electric
electricfield
fieldatatthe
thehigh
highand
andlow
lowends
endsisislarger.
larger.The
Themaximum
maximumvalue
valueoccurs
occursatatthe
thesurface
surfaceofofthe
thesteel
steel
foot
foot
close
totothe
the
high
voltage
end,
reaching
13
kV/cm.
the
surface
footclose
closeto
thehigh
highvoltage
voltageend,
end,reaching
reaching13
13kV/cm.
kV/cm.The
Theincrease
increaseofofcontamination
contaminationon
onthe
thesurface
surface
of
insulator
isismainly
mainly
causedby
theforce
forceofof
ofthe
the
electric
field
the
vertical
direction,
because
ofofthe
electric
field
ininin
the
vertical
direction,
because
the
theinsulator
insulatoris
mainlycaused
bythe
the
force
the
electric
field
the
vertical
direction,
because
the
the
vertical
force
will
deflect
the
polluted
particles
into
the
insulator
surface
so
as
to
increase
the
vertical
vertical force
force will
will deflect
deflect the
the polluted
polluted particles
particles into
into the
the insulator
insulator surface so asas toto increase the
the
contamination
contamination
amount.
we
calculate
YYaxis
field
ofofthe
the
path
A-C,
asas
contaminationamount.
amount.Therefore,
Therefore,we
wecalculate
calculateY
axiscomponent
componentofofelectric
electricfield
fieldof
thepath
pathA-C,
A-C,as
shown
in
Figure
9.
shown
in
Figure
9.
shown in Figure 9.
Figure
Figure
9.9.YYaxis
component
ofofelectric
electric
field.
Figure9.
axiscomponent
componentof
electricfield.
field.
It
ItItcan
can
be
seen
from
the
graph
that
the
YYaxis
axis
components
ofofelectric
electric
field
atathigh
high
voltage
group
canbe
beseen
seenfrom
fromthe
thegraph
graphthat
thatthe
theY
axiscomponents
componentsof
electricfield
fieldat
highvoltage
voltagegroup
group
and
middle
group
are
0.305
kv/cm,
0.24
kv/cm,
respectively.
Based
on
the
calculated
field
strength,
and
middle
group
are
0.305
kv/cm,
0.24
kv/cm,
respectively.
Based
on
the
calculated
field
strength,
and middle group are 0.305 kv/cm, 0.24 kv/cm, respectively. Based on the calculated field strength,
we
particles.
we
calculate
the
forces
acting
on
the
vertical
direction
ofofcontamination
contamination
particles.
wecalculate
calculatethe
theforces
forcesacting
actingon
onthe
thevertical
verticaldirection
directionof
contamination
particles.
The
The
movement
ofofair
air
ions
will
cause
neutral
atmosphere
dust
totobe
be
charged.
Research
shows
Themovement
movementof
airions
ionswill
willcause
causeneutral
neutralatmosphere
atmospheredust
dustto
becharged.
charged.Research
Researchshows
shows
that
[19]
31%
of
the
fly
ash
particles
in
nature
have
positive
charges,
26%
of
fly
ash
particles
that
have
that[19]
[19]31%
31%ofofthe
thefly
flyash
ashparticles
particlesininnature
naturehave
havepositive
positivecharges,
charges,26%
26%ofoffly
flyash
ashparticles
particleshave
have
negative
charges,
and
43%
of
particles
are
not
charged.
The
saturated
charge
of
contaminated
particles
negative
negative charges,
charges, and
and 43%
43% ofof particles
particles are
are not
not charged.
charged. The
The saturated
saturated charge
charge ofof contaminated
contaminated
can
be approximately
expressedexpressed
as:
particles
can
as:
particles
canbe
beapproximately
approximately
expressed
as:
22 2 εεpεp p 
Q
=
3πε
Ed
p
p
0
QQp p==33πε
Edp p εp + 2 
πε0 0Ed
εε ++22

pp

(5)
(5)
(5)
where
Qpp is
quantity of
of electric charge
of particle, in
C; EEisisthe
electric field
intensity ininV/m;
e is
where
whereQQ
pisisquantity
quantity ofelectric
electriccharge
chargeofofparticle,
particle,ininC;
C; E isthe
theelectric
electricfield
fieldintensity
intensity inV/m;
V/m;e eisis
elementary
charge; ddpp isisparticle
particle diameter,ininm;
m; εp is
the relative
dielectric constant
of particles,
elementary
elementarycharge;
charge; dp is particlediameter,
diameter, in m;εεp pis
isthe
therelative
relativedielectric
dielectricconstant
constantofofparticles,
particles,its
its
value
of
SiO
2
is
4.5.
In
order
to
simplify
the
analysis,
only
the
extreme
case
of
saturated
electricity
is
value of SiO2 is 4.5. In order to simplify the analysis, only the extreme case of saturated electricity is
Appl. Sci.
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8, 1962
x FOR PEER REVIEW
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11
14
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considered, so Formula (5) is used to characterize the quantity of electric charge of polluted particles.
its
value
of SiO
4.5. In
to simplify
theisanalysis,
only
the extreme
2 isforce
The
electric
field
onorder
polluted
particles
expressed
as Formula
(6).case of saturated electricity is
considered, so Formula (5) is used to characterize the quantity of electric charge of polluted particles.
(6)
The electric field force on polluted particles is fexpressed
e = Q p E as Formula (6).
field force in the vertical direction on particle
where fe is electric field force. The calculated felectric
(6)
e = Qp E
(take the diameter of 200 meshes as example) at the high voltage group and middle group are
−10 N and 7.18 × 10−11 N respectively. We can see that the calculated electric field force in the
1.67 × f10
where
field force. The calculated electric field force in the vertical direction on particle (take
e is electric
10
vertical
direction
particle
at the high
voltage
almost
1.6middle
times group
larger are
than
that
the
diameter
of 200on
meshes
as example)
at the
high group
voltageisgroup
and
1.67
× at
10−the
−
11
middle
group.
to further illustrate
the that
influence
of electricelectric
field force
thein
movement
of
N
and 7.18
× 10In order
N respectively.
We can see
the calculated
fieldon
force
the vertical
particles around
insulators,
we estimate
the acceleration
of times
particles
in vertical
direction.
The formula
direction
on particle
at the high
voltage group
is almost 1.6
larger
than that
at the middle
group.
fororder
calculating
the quality
ofthe
particles
is asoffollows.
In
to further
illustrate
influence
electric field force on the movement of particles around
insulators, we estimate the acceleration of particles in vertical direction. The formula for calculating
d
4
the quality of particles is as follows.
(7)
mg = ρ pπ ( p )3
d p2 3
4
3
mg = ρ p π( )
(7)
3
2
3
where ρp is the density of particles, its value of SiO2 is 2320 kg/m . The particles are subjected to
where ρp is the density of particles, its value of SiO2 is 2320 kg/m3 . The particles are subjected to
gravity and aerodynamic drag on the Y axis. It is observed from experiments that the movement of
gravity and aerodynamic drag on the Y axis. It is observed from experiments that the movement
particles near insulator is basically horizontal under non-energized condition, so there is balance
of particles near insulator is basically horizontal under non-energized condition, so there is balance
force on particles in the direction of Y axis, which means that fw = −fg, where fw is aerodynamic drag
force on particles in the direction of Y axis, which means that fw = −fg , where fw is aerodynamic drag
on particles and fg is gravity of particles. The formula for calculating the acceleration of particles is as
on particles and fg is gravity of particles. The formula for calculating the acceleration of particles is
follows.
as follows.
aa =
= ff/mg
/ mg
(8)
(8)
where
where ff is the resultant force, which is approximately equal to the force of the electric field in the
the
direction
direction of
of Y
Y axis. The calculated acceleration of different meshes particles at the high voltage group
and
and middle
middle group
group are
are shown
shown in
in Figure
Figure 10.
10. The calculated results
results show that the acceleration
acceleration in vertical
direction of the
the particles
particlesatatthe
thehigh
highvoltage
voltage
group
is
about
1.62
times
that
at middle
the middle
group.
group is about 1.62 times that at the
group.
This
This
calculated
is close
very close
the actual
KH/M Then,
value.we
Then,
we the
cantrajectory
get the trajectory
of
calculated
valuevalue
is very
to theto
actual
KH/M value.
can get
trend of trend
charged
charged
in the
11. “+” represents
a particle
withcharge
positive
and “−”
particles,particles,
as shownasinshown
the Figure
11.Figure
“+” represents
a particle with
positive
andcharge
“−” represents
represents
a particle
withcharge.
negative charge.
a particle with
negative
Figure
Figure 10.
10. The calculated Y-axis acceleration.
acceleration.
Appl. Sci. 2018, 8, 1962
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The trajectory
trajectory trend of charged particles.
Figure 11. The
It can
particle
moves
toward
thethe
shed’s
surface
duedue
to the
It
can be
be seen
seen from
fromFigure
Figure11
11that
thatthe
thecharged
charged
particle
moves
toward
shed’s
surface
to
effect
of
the
electric
field
force,
increasing
the
probability
of
particles
hitting
the
sheds
surface
of
the
the effect of the electric field force, increasing the probability of particles hitting the sheds surface of
insulator.
Thus,
the amplitude
of particle
deflection
at theathigh
voltage
groupgroup
is greater
than that
the
the
insulator.
Thus,
the amplitude
of particle
deflection
the high
voltage
is greater
thanatthat
middle
group
due
to
a
larger
acceleration
of
particles,
causing
the
increasing
probability
of
sorption
of
at the middle group due to a larger acceleration of particles, causing the increasing probability of
contamination
particle,
which
explained
the
cause
of
non-uniform
contamination
distribution
along
sorption of contamination particle, which explained the cause of non-uniform contamination
the string. along the string.
distribution
Besides, after
after calculating
calculatingthe
theelectric
electricfield
fieldaround
around
field
insulators,
have
to transfer
Besides,
thethe
field
insulators,
we we
have
to transfer
the
the
situation
from
the
field
insulators
to
our
model.
According
to
the
steps
of
Section
5.1 above,
situation from the field insulators to our model. According to the steps of Section 5.1 above,
the
the acceleration
in vertical
direction
the particles
be obtained.
The calculated
results
show
acceleration
in vertical
direction
of theofparticles
can becan
obtained.
The calculated
results show
that
the
that
the
acceleration
in
vertical
direction
of
the
particles
at
the
high
voltage
group
is
about
2.51
times
acceleration in vertical direction of the particles at the high voltage group is about 2.51 times that at
thatmiddle
at the middle
that
aboutwe
1/0.40,
we clearly
can seethat
clearly
that
the
group. group.
Which Which
means means
that KH/M
inKtheory
about is1/0.40,
can see
there
is
H/M inistheory
there is35%
about
35%
in the of
result
thetest.
fieldThis
test. shows
This shows
thatmodel
the model
is more
accurate
in
about
error
inerror
the result
the of
field
that the
is more
accurate
in the
the application
of wind
tunnel
contamination,
however
there
some
errors
in the
application
application
of wind
tunnel
contamination,
however
there
are are
stillstill
some
errors
in the
application
of
of field
contamination.
main
reason
theerror
errorisisthat
thatthe
thescouring
scouring of
of the
the rainwater
rainwater reduced
field
contamination.
TheThe
main
reason
forfor
the
contamination inhomogeneity of field insulators between the high voltage group and middle
middle group.
group.
5.2. Future
Future Research
Research Directions
Directions
5.2.
On the
research
onon
insulator
contamination,
this this
paper
has conducted
deep
On
the basis
basisofofthe
thetraditional
traditional
research
insulator
contamination,
paper
has conducted
research,
but
further
work
also
need
to
be
done
to
apply
the
research
results
to
the
operation
of
deep research, but further work also need to be done to apply the research results to the operationthe
of
power
system.
Firstly,
based
on
the
results
of
this
study,
we
should
continue
to
study
the
characteristics
the power system. Firstly, based on the results of this study, we should continue to study the
of pollution flashover
(in non-uniform
distribution condition)
andcondition)
try to predict
characteristics
of pollution
flashover (incontamination
non-uniform contamination
distribution
and the
try
pollution
flashover
voltage.
Secondly,
the
contamination
prediction
model
is
still
needed,
and
to predict the pollution flashover voltage. Secondly, the contamination prediction model is then
still
the pollution
prediction
modelprediction
is combined
withisthe
pollution
flashover
prediction
model.
Finally,
needed,
and then
the pollution
model
combined
with
the pollution
flashover
prediction
the
pollution
flashover
warning
can
be
realized
and
measures
can
be
taken
in
advance
to
prevent
the
model. Finally, the pollution flashover warning can be realized and measures can be taken in advance
pollution
flashover
accident.
to prevent the pollution flashover accident.
6. Conclusions
6. Conclusions
This paper presents the pollution non-uniformity on insulator surface from both field
This paper presents the pollution non-uniformity on insulator surface from both field
contamination experiments of HVDC transmission lines and wind tunnel contamination simulation
contamination experiments of HVDC transmission lines and wind tunnel contamination simulation
tests, as well as the mechanism of non-uniformity along insulator sting. Conclusions can be made that:
tests, as well as the mechanism of non-uniformity along insulator sting. Conclusions can be made
that:
(1) The contamination on insulator surfaces is very non-uniform in operating HVDC transmission
lines,
the non-uniformity
is mainly
reflected
in three
aspects, such
as the topHVDC
and bottom
surface,
(1) The
contamination
on insulator
surfaces
is very
non-uniform
in operating
transmission
windward
and
leeward
side,
high
voltage
group
and
middle
group
area.
The
value
of
K
, KW/L ,
T/B
lines, the non-uniformity is mainly reflected in three aspects, such as the top and bottom
surface,
KH/M are 1/0.49,
1/1.45,side,
1/0.61
respectively.
Besides
this, thegroup
valuearea.
of K*The
andvalue
K is almost
windward
and leeward
high
voltage group
and middle
of KT/B,equal.
KW/L,
(2) K
The
effects
of
particles
diameter,
wind
velocity
and
relatively
humidity
on
pollution
H/M are 1/0.49, 1/1.45, 1/0.61 respectively. Besides this, the value of K* and K is almost equal.
non-uniformity
were quantitatively
computed
through
tunnel
simulation
Withnonthe
(2) The
effects of particles
diameter, wind
velocity
and wind
relatively
humidity
onresults.
pollution
increase
of
wind
speed
(particles
diameter
is
250
meshes,
RH
is
60%),
K
value
remains
almost
uniformity were quantitatively computed through wind tunnel simulation
results. With the
T/B
increase of wind speed (particles diameter is 250 meshes, RH is 60%), KT/B value remains almost
Appl. Sci. 2018, 8, 1962
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constant and stable at around 0.5. However, the KW/L value (within 1/0.81–1/1.75) and KH/M
value (within 1/0.49–1/0.71) presents a downward trend. With the decrease of particles diameter
(wind speed is 5 m/s, RH is 60%), the KT/B value (within 1/0.51–1/0.66) and KW/L (within
1/1.45–1/1.36) value are closer to 1, which means non-uniformity becomes smaller, while the
KH/M value (within 1/0.65–1/0.58) is the opposite. The change of relative humidity has little
effect on KT/B and KW/L . With the increase of relative humidity (wind speed is 5 m/s, particles
diameter is 250 meshes), KT/B and KW/L values remain almost constant and stable at around
1/0.5, 1/1.44 respectively. However, with the increase of humidity, the KH/M value (within
1/0.65–1/0.72) is closer to 1.
The electric field around insulators is unevenly distributed around the insulator surface, causing
different electric field force and the acceleration on particles in vertical direction at high voltage
group and middle group area, which is the cause of the non-uniform distribution of contamination
along the insulator string.
Author Contributions: Z.Z. and X.Q. conceived the overall outline of the manuscript and all the authors
contributed to the writing and revision of the paper.
Funding: This research was funded by Project [No. 2018CDYJSY0055] Supported by the Fundamental Research
Funds for the Central Universities and Science and Technology Foundation of the State Grid Corporation of China
[No. SGTYHT/14-JS-188].
Conflicts of Interest: The authors declare no conflict of interest.
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© 2018 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access
article distributed under the terms and conditions of the Creative Commons Attribution
(CC BY) license (http://creativecommons.org/licenses/by/4.0/).