International Journal on Electrical Engineering and Informatics - Volume 5, Number 2, June 2013
The Implementation of Needle-Plane Electrode Configuration and Test
Methods for Partial Discharge Inception Voltage Characteristic
Measurement of Mineral Oil
Ferdinand Sipahutar1,3, Suwarno1, Ahmad Azhari Kemma1,3, Norasage Pattanadech2,
Fari Pratomosiwi2, and Michael Muhr2
1
School of Electrical Engineering and Informatics, Institut Teknologi Bandung,
Jl. Ganesha 10, Bandung Indonesia
2
Institute of High Voltage Engineering and System Management, TU Graz,
Inffeldgasse 18, A - 8010 Graz, Austria
3
PT PLN (Persero), Jakarta, Indonesia
Abstract: The investigation of the Partial Discharge Inception Voltage characteristic is
performed by many researchers using the needle-plane electrode configuration and
various test methods. This was conducted due to the capability of Partial Discharge
Inception Voltage characteristic to represent or determine the condition of insulating
liquid. This paper discusses the implementation of the needle-plane electrode
configuration and two test methods to find out the characteristics of Partial Discharge in
Partial Discharge Inception Voltage level of mineral oil. For this purposes, the mineral
oil which used was Nynas Nitro 4000x with water content less than 10 ppm. In
experiment, the test circuit was set up according to IEC 60270. The Ramp Method as
the first test procedure was conducted in this experiment according to IEC 61294 with
ramp rate of rise test voltage 1 kV/s until Partial Discharge Inception Voltage occurred.
Meanwhile, a Combine Method as the second test procedure was used as comparative
Partial Discharge Inception Voltage test technique. With this combine method, the test
voltage was applied to the test object with rate of rise test voltage 1 kV/s until 70% of
the Partial Discharge Inception Voltage value obtained from the ramp method. Then the
test voltage was increased in steps with 1 kV/step with step duration of 1 minute until
Partial Discharge Inception Voltage obtained with apparent charge ≥ 100 pC. The rest
time between consecutive tests was 5 minutes. The needle tip radius that used as high
voltage electrode were 10 µm and 20 µm, meanwhile brass plane electrode with
diameter 75mm and 50mm was used as the grounded electrode. The gap distance
between the needle electrodes toward ground electrode was fixed at 50 mm. The
calculation of electric field stress of the needle-plane electrode configuration was done
by using simulation of Finite Element Method (FEM). Based on the Partial Discharge
Inception Voltage test result, the needle electrodes with tip radius 10 µm will produce
electric field stress that higher than other needle tip, meanwhile the Partial Discharge
Inception Voltage is lower which tested using both test method. By using the combine
method, the Partial Discharge Inception Voltage value, charge quantity and the number
of Partial Discharge will be lower than the ramp method. The results also showed that
the Partial Discharge pulse currents using both test method was about 0.2 – 0.85 mA.
The time duration of Partial Discharge pulse was in the range of 1.01 – 8.38 µs and the
rise time were between 68 - 301 ns. It was found that the Partial Discharge Inception
Voltage test result agree with the Weibull distribution
Keywords: Partial Discharge Inception Voltage; Electrode; Ramp method; Combine
method; Weibull; CDF; PDF ; CV; Finite element method
Received: February 15th, 2013. Accepted: May 31th, 2013
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Ferdinand Sipahutar, et al.
1. Introduction
Monitoring of the transformer oil is important to be kept due to the occurrences of Partial
Discharge will generate stress within the liquid insulation. Actually, there are many factors that
may affect the quality of the mineral oil that usually used as the insulation for transformer. The
moisture effect, particle, thermal stress and electrical stress are several factors that should be
eliminated. The Partial Discharge events in liquid insulation may lead complete breakdown,
especially while the degradation of the insulations material occur [1-2]. Therefore, to maintain
the condition of transformer oil, the continuity monitoring is needed. One of the methods that
used to monitoring oil condition in transformer is Partial Discharge measurement. This method
is an important diagnostic technique and used as non-destructive test for the insulation of high
voltage [1]. The occurrence of Partial Discharge in mineral oil is strongly associated with the
cavity formation within the mineral oil. The evolution of these cavities will induce the rise of
series Partial Discharge pulses of ascending magnitude. Such Partial Discharge Pulses can be
used as an indicator to determine the value of the Partial Discharge Inception Voltage (PDIV)
in insulating liquid [3]. The information of the Partial Discharge Inception Voltage
characteristic in mineral oil that obtained from measurement can be used as useful indicator to
monitor the degradation of the insulation of high voltage components [4].
In many case, Partial Discharge Inception Voltage is an alternatively important indicator
that most researchers use for representing the integrity of the liquid insulation [5].The
definition of Partial Discharge Inception Voltage of an insulating liquid according to the IEC
61294 is the lowest voltage at which an apparent charge occurs equal or exceeding 100 pC
when the sample is tested under the specified conditions [6]. Some researchers report that the
characteristic features of partial discharge phenomena greatly depend on experimental
conditions such as electrode geometry, shape and amplitude of applied voltage, liquid nature
and purity [7]. Therefore, the electrode geometry and shape have an important role for Partial
Discharge Inception Voltage measurement. The electrode geometry and shape will affect the
Partial Discharge Inception Voltage measurement which is related to the deployment of electric
field stress around the electrode and especially at the tip. This factors also being a reason for
investigation of Partial Discharge Inception Voltage characteristic of the liquid insulation by
using the needle-plane electrode configuration that has been used by many research groups as
seen in [8, 9, 10]. The highest electric field was obtained at the tip of needle electrode [11].
There are doubts about the effectiveness of ramp method as the test procedure which
recommended by IEC61294 [12]. The advantage of Ramp Method is short test duration to
obtain Partial Discharge Inception Voltage value but may have a highly chance to lead
breakdown events. The Combine Method as the comparator of the Ramp Method can used for
Partial Discharge Inception Voltage measurement and able to reduce the chance of the
breakdown events than Ramp Method. But the combine method requires long test duration to
obtain Partial Discharge Inception Voltage value.
The discussion about distribution pattern of partial discharge data is also important to
perform. This is done to determine the characteristic of test data obtained by experiment. So
the probability of data such as cumulative distribution function (cdf) and probability density
function (pdf) of Partial Discharge can be known. Based on numerical analysis, partial
discharge fit to the two parameter of Weibull function [13]. This Weibull distribution is widely
used for data analysis due to its relative simplicity and flexibility. Besides of that, this paper
proposes the CDF and PDF of Partial Discharge Inception Voltage value so it can be used to
determine the occurrence probability of Partial Discharge Inception Voltage value. In this case,
the Partial Discharge Inception Voltage data was analyzed by using simple formula that used to
determine the distribution of Breakdown Voltage (BDV) data [14].
2. Experiment Setup and Data Analysis
The experiments were divided into two parts. First, we simulated the electric field
simulation of the electrode configuration system by FEM simulation. Second, we carried out
laboratory scale experiment. The moisture content in this measurement was kept less than 10
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The Implementation of Needle-Plane Electrode Configuration and Test
ppm which was measured by using Karl Fischer Coulometer.
A. Electrode Configuration
The measurement of Partial Discharge Inception Voltage was performed in a test vessel.
Tungsten needle electrode with tip radius 10 µm and 20 µm were used as high voltage
electrode. The length of needle electrode is 45 ± 0.5 mm. Brass plane electrodes with 75 mm
and 50 mm diameter were used as the grounded electrode. The gap distance between the needle
- plane electrode was fixed at 50 mm. Figure 1, depicts the electrode configuration for Partial
Discharge Inception Voltage measurement.
Tip radius
Tip radius
Tip radius
Tip radius
10 µm
20 µm
10 µm
20 µm
Needle Electrode
50 mm
50 mm
75 mm
50 mm
Figure 1. Electrode configuration for Partial Discharge Inception Voltage (PDIV) measurement
B. Testing Circuit
The test circuit for Partial Discharge Inception Voltage measurement was set up according
to IEC 60270 [15]. The discharge was measured with Power Diagnostics ICM and
Oscilloscope Yokogawa DLM series at the same time. With ICM, we recorded the Partial
Discharge Inception Voltage and Partial Discharge patterns. The coupling device was
connected to the coupling capacitances and to the ICM. This configuration was chosen to
depict the real condition of electrical system. In addition, this configuration was used to avoid
the possible destruction of measuring equipment in case of the breakdown occurs. Meanwhile
with oscilloscope, we used to recorded the Partial Discharge pulse current signal.The shunt
resistor was directly connected to the oscilloscope via 50 ohm matching impedance. Figure 2,
illustrates the test circuit of Partial Discharge Inception Voltage measurement.
Current limiting resistor
Coupling Capacitances
Step Up Test Vessel
(16 litre oil)
C
Coupling Devices
C
Insulation Condition
Capacitive voltage divider 200 kV
Shunt Resistor
Coaxial cable 50 Ω
Personal Computer
Voltage Regulator
G
MatchingImpedance
Coaxial cable 50 Ω
Coaxial cable 50 Ω
Pre‐amplifier
Oscilloscope
Figure 2. Test circuit for Partial Discharge Inception Voltage (PDIV) measurement
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Ferdinand Sipahutar, et al.
C. Testing Procedure
The Ramp Method (as specified in IEC 61294) and the Combine Method were used to
investigate Partial Discharge Inception Voltage characteristic of mineral oil. According to IEC
61294, Partial Discharge Inception Voltage measurement is done by applying the ramp test
voltage with rate of rise test voltage 1 kV/s until the first discharge with its apparent charge ≥
100 pC occur. The measurement of Partial Discharge Inception Voltage was conducted ten
times for every test object. The combine method procedure is a method to generate Partial
Discharge Inception Voltage by means of increasing the voltage with the rate of rise test
voltage 1 kV/s until 70% of average Partial Discharge Inception Voltage value that obtained
from Ramp Method. Then, the voltage was increased in steps with rate of rise test voltage 1
kV/step until the Partial Discharge Inception Voltage value (100 pC detection) occurred. After
the Partial Discharge Inception Voltage value was achieved, the test voltage was decreased
until zero. The rest time between consecutive tests was 5 minutes. Figure 3, describes the test
procedure of Partial Discharge Inception Voltage measurement using ramp method and
combine method.
PDIV (Charge = 100 pC)
PDIV (Charge = 100 pC)
1st
PDIV
3rd
PDIV
2nd
PDIV
10th
PDIV
70 % of average PDIV
1 kV/s
1 kV/s
1 kV/s
1 kV/s
1 kV/s
zero volt
zero volt
PDIV pulse
zerovolt
zerovolt
1 minute
1 minute
a)
5 minute
b)
Figure 3. Test procedure of Partial Discharge Inception Voltage measurement according to a)
IEC 61294, b) Combine Method
D. Data Analysis
The plot of Partial Discharge Inception Voltage test results is an useful information to
forecast the possibility of failures. Some action and appropriate plans to manage and controls
such failures can be conducted by using data plot. Weibull analysis is widely used for data plot
and data analysis due to its relative simplicity and flexible. In addition, the failure analysis and
forecasting of small number of population data can be conducted using Weibull analysis [16].
In many case, Weibull analysis is applied to analyze breakdown voltage and partial discharge
data. The guide for statistical analysis of electrical insulation breakdown data can be seen in
[17]. Based on numerical analysis, partial discharge is fit with Weibull distribution of two
parameter [18]. In this thesis, PDIV characteristics test results were analyzed using Weibull
distribution to obtain the cumulative distribution function (cdf) and the probability density
function (pdf). The formula for data analysis is complied with IEEE 930-2004. The Weibull
statistical analysis of Partial Discharge Inception Voltage characteristics test results is
conducted using the following formula.
; ,
1
(1)
The F(t;α,β) is defined as the cumulative distribution function, α is defined as a scale
parameter, β is defined a shape parameter that related to the range of Partial Discharge
Inception Voltage, whilst t is defined as a measured variable and in this case is Partial
Discharge Inception Voltage value.
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The Implementation of Needle-Plane Electrode Configuration and Test
.
,
Simple approximation :
.
. 100%
(2)
The F(i;n) is defined as an estimation of CDF, i is defined as the rank order of data, and n is
defined as weights of small data sets. The expressions for the CDF is present the probability of
Partial Discharge Inception Voltage occurring with the rising of test voltage. The probability
density function
of Weibull distribution can be calculated using the formula as follows
[19].
.
. exp
(3)
The f(x) is defined as probability density function, α is defined as scale parameter, is defined
as shape parameter, x is defined as measured variable. For calculation, we determine:
ln
(4)
where ln (ti) is the natural logarithm.
For each probability of PDIV value, we expressed a percentage of value:
ln
,
ln 1
(5)
The weighted average of Xi and Yi is calculated using the equations as follows:
∑
∑
and
∑
(6)
∑
By using equation (2-17) the β and α parameter can be calculated as follows:
∑
∑
exp
–
}
(7)
The lower and upper bounds of the 90% confidence interval for the percentile:
exp
/
exp
and
/
(8)
For fitting data, the Kolmogorof-Simirnov method is introduced because is appropriate for
small samples [20].
P0 (Xi) = P0 (X ≤ Xi) = CDF (Xi)
;
(9)
1…
(10)
D+ = Fn – Fo and D- = Fo – Fn-1
(11)
D = Maximum of all D+ and D- ( ≥ 0) ; for i = 1, ….. n
(12)
According to the Kolmogorof-Simirnov method, Fo(Xi) is defined as the CDF evaluated at
Xi, Fn(Xi) is defined as a empirical distribution function, D or ks is defined as the distance test,
n is defined as the number of data, and X is defined as the data value. The test error α = 0.05,
CV(0.05), was used for fitting data.
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Ferdinand Sipahutar, et al.
Table 1. shows the critical value of Kolmogorof-Simirnov error.
Table 1. Kolmogorov-Simirnov Critical Value (CV) for α (0.20 and 0.05) [20]
Number of sample
CV (0.20)
CV (0.05)
4
0.494
0.624
0.446
5
0.564
0.411
6
0.521
7
0.381
0.486
8
0.358
0.457
9
0.339
0.432
0.322
10
0.411
3. Test Results and Discussion
According to the simulation results, we can see that the electric field stress for plane
diameter 75 mm is higher than plane diameter 50 mm which tested using the needle electrode
tip radius 10 µm and 20 µm respectively as shown in table 2. From table 2, we can conclude
that small tip radius will generates high electric field stress and will influencing the inception
voltage of the partial discharge. Figure 4 shows the comparison of the Partial Discharge
Inception Voltage value and standard deviation for all electrode configurations which tested
using both test methods. The quantity of charge can be seen on Figure 5. The test results show
that the average Partial Discharge charge (QIEC) of the needle electrode with tip radius 20 µm
which higher than Partial Discharge charge of the needle electrode with tip radius 10 µm and
this is related to the increasing of Partial Discharge Inception Voltage value.
PDIV (kV), Std Deviation (kV), Electric Field Stress (kV/cm)
Table 2. The maximum electric field stress based on simulation
results at the needle tip using input 100 volt
Needle Tip Radius
Electric Field Stress (kV)
[Plane Diameter 50 mm]
Electric Field Stress (kV)
[Plane Diameter 75 mm]
10 µm
20 µm
13.7
8.1
15
8.8
50
40
30
20
10
0
75
50
75
Ramp Method
50
Combine Method
Test Method - Ground Electrode
PDIV [Needle Tip 10 µm]
PDIV [Needle Tip 20 µm]
Standard Deviation [Needle Tip 10 µm]
Figure 4.Test results of average PDIV, Standard Deviation and Electric Field Stress from
different test procedure and needle tip radius
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The Implementation of Needle-Plane Electrode Configuration and Test
Average PDIV (kV) and Average PD Charge (pC)
From Figure 4 we can see that the needle electrode with tip radius 10 µm generates lower
Partial Discharge Inception Voltage than needle electrode with tip radius 20 µm. These results
are in accordance with the maximum electric field stress that simulated for both tip radii. The
simulation results show that the value of electric field stress of the needle electrode with tip
radius 10 μm is nearly two times of needle electrode with tip radius 20 μm as stated in the
Table 2. The different of Partial Discharge Inception Voltage level may cause by the
randomness evolving of cavity within mineral oil and local heating process that influenced by
the electric field stress of the different needle tip dimensions. The electric field stress affects
also the aggressiveness of ions movement within mineral oil. This movement caused by the
high electric field stresses could evoke the kinetic energy for ions. When the movement of ions
toward area is near to the tip of the needle electrode, the possibility of discharge is high. Figure
4 also presents the standard deviation of Partial Discharge Inception Voltage value of the
needle electrode with tip radius 20 µm that higher than needle tip radius 10 µm by using ramp
method and combine method. This result indicates that the use of needle tip radius 10 µm for
Partial Discharge Inception Voltage measurement of mineral oil under room temperature is
better than using needle electrode with tip radius 20 µm. In addition, the combine method is
more sensitive to detect Partial Discharge Inception Voltage than ramp method. The reason of
this sensitivity is related to the development of cavities that requires sufficient energy to
discharge which influenced by local heating due to electric field stress. Under the constant test
voltage for 1 minute (in accordance with combine method), the discharge possibly occur when
cavities are already formed. Unlike the case of IEC 61294 test procedures, with rate of rise test
voltage 1 kV/s, the cavity establishment is not progressing well. Therefore, the Partial
Discharge Inception Voltage with charge ≥ 100 pC will be only detected when the electric field
stress is higher than combine method and occasionally occur near to the breakdown limit.
Hence, the measurement of Partial Discharge Inception Voltage using the combine method is
more secure from breakdown events than ramp method. According to the test results, the
standard deviation of Partial Discharge Inception Voltage value is better when using the needle
electrode with tip radius 10 µm than the needle electrode with tip radius 20 µm. Therefore, the
using of the needle electrode with tip radius 10 µm is highly recommended than the needle
electrode tip radius 20 µm.
500
450
400
350
300
250
200
150
100
50
0
75
50
Ramp Method
75
50
Combine Method
Test Method - Ground Electrode
PDIV [Needle Tip 10 µm]
PDIV [Needle Tip 20 µm]
Qiec - Ramp Method [Needle Tip 10 µm] Qiec - Ramp Method [Needle Tip 20 µm]
Figure 5.Test results of average Partial Discharge Charge (Qiec) from different test
procedure and needle tip radius
From Figure 5 we can see that the Partial Discharge charge (Qiec) is strongly influenced by
the Partial Discharge Inception Voltage value that related to the electric field stress. When the
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Ferdinand Sipahutar, et al.
electric field stress inside the mineral oil is high, then the Partial Discharge Inception Voltage
value is easy to obtained especially using the needle electrode tip radius 10 µm and plane
diameter 75 mm. With high electric field stress, the Partial Discharge charge production will
high. According to the test results, we can see the test method also influence the Partial
Discharge Inception Voltage and Partial Discharge charge value. This results is caused by the
combine method is easy to obtain the Partial Discharge Inception Voltage value in low voltage.
Therefore, the generation of Partial Discharge charge will also influence by the Partial
Discharge Inception Voltage value which related to the electric field stress. Besides of the
Partial Discharge Inception Voltage and Partial Discharge charge value, the characteristic of
Partial Discharge such as pulse current, duration of pulse current, and also the rise time of
Partial Discharge current can be obtained. Table 3 depicts the characteristic of Partial
Discharge current.
Table 3. The maximum electric field stress based on simulation results at the needle tip using
input 100 volt
Ground Plane Electrode (mm)
Rise
Pulse
Pulse
Time Duration Current
Gap Distance 50 mm
Needle tip
radius (µm)
Ramp Method
Combine Method
75 mm
50 mm
75 mm
50 mm
10
0.39-0.46
0.27-0.47
0.29-0.37
0.2-0.32
20
0.54-0.85
0.41-0.65
0.34-0.51
0.36-0.44
10
1.40-2.57
1.39-3.67
1.06-2.01
1.08-2.26
20
2.79-8.38
2.69-6.99
1.01-2.78
1.25-2.23
10
73-180
83-227
68.8-173.6
71-153
20
151-276
107-301
90.4-172.8
131-188
From table 3 we can see the characteristic of Partial Discharge current such as pulse
current, pulse duration and the rise time. According to the test results, high electric field stress
will generates high Partial Discharge pulse current. The configuration of the needle electrode
with tip radius 10 µm toward the ground plane electrode with tip radius 75 mm will produce
Partial Discharge pulse current which higher than plane electrode diameter 50 mm tested using
both test methods. Moreover, Partial Discharge pulse duration and Partial Discharge rise time
is shorter than the cofiguration of the needle electrode tip radius 10 µm and 20 µm toward the
ground plane diameter 50 mm. In addition, we can see also that the needle electrode with tip
radius 20 µm will generates Partial Discharge pulse current, Partial Discharge pulse duration
and Partial Discharge rise time which higher than the needle electrode with tip radius 10 µm
for appropriate configuration. We can conclude also that the test methods will influence the
value and range of Partial Discharge pulse current, Partial Discharge pulse duration and also
Partial Discharge rise time.
Figure 6a and 6b represent the cumulative distribution function and probability density
function of Partial Discharge Inception Voltage value of ramp method and combine method
respectively. The numerical analysis of Partial Discharge Inception Voltage value of ramp
method and combine method is in accordance with the Weibull distribution. The compliance of
data to the Weibull distribution for each test method is proved by using Kolmogorov-Simirnov
(KS) method. The congruence of Partial Discharge Inception Voltage data to the Weibull
distribution is indicated by D+ and D- parameter. While the maximum value of D+ or D- less
than critical value of KS that presented in the table 1, then hypothesis of dataagrees with the
Weibull distribution is accepted. The Confidence Interval (CI) for lower and upper bounds is
90% confidence limit for the percentiles 0.1%, 1%, 5%, 10%, 30%, and 95%. The higher
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The Implementation of Needle-Plane Electrode Configuration and Test
100%
18%
90%
16%
80%
14%
70%
12%
60%
10%
50%
8%
40%
6%
30%
20%
4%
10%
2%
0%
Probability Density Function (%)
Cumulative distribution function (%)
frequently density function of PDIV value using ramp method for plane diameter 75 mm and
50 mm is in the 31.2 – 34.3 kV for needle tip 10 µm and 39.5 – 40.2 kV for needle tip 20 µm.
Meanwhile, for combine method, the higher frequently density function lies in the 25.4 - 26.2
kV for needle tip 10 µm and 31.2 - 34 kV for needle tip 20 µm. The probability density
function of Partial Discharge Inception Voltage value can be used as information to determine
the frequently density of the occurrence of Partial Discharge Inception Voltage. Table 4 shows,
the pdf for all electrode configurations.
24
34
44
upper confidence bound [needle 10 µm]
lower confidence bound [needle 20 µm] cdf data points [needle 20 µm]
upper confidence bound [needle 20 µm] lower confidence bound [needle 10 µm]
pdf data points [needle 10 µm]
pdf data points [needle 20 µm]
10 µm [α = 34.1715, β = 15.1088, D+ = 0.1764]
20 µm [α = 42.2330, β = 10.4032, D+ = 0.1830]
[Confidence Interval (CI) =90%]
0%
14
cdf data points [needle 10 µm]
54
Partial Discharge Inception Voltage (kV) ‐ Ramp Method
a)
40%
80%
30%
60%
20%
40%
10%
20%
0%
Probability Density Function (%)
Cumulative distribution function (%)
100%
0%
16.0
26.0
36.0
cdf data points [needle 10 µm]
upper confidence bound [needle 10 µm]
lower confidence bound [needle 20 µm]
cdf data points [needle 20 µm]
upper confidence bound [needle 20 µm]
lower confidence bound [needle 10 µm]
pdf data points [needle 10 µm]
pdf data points [needle 20 µm]
10 µm [α = 28.3766, β = 27.1657, D+ = 0.2796]
20 µm [α = 33.7061, β = 21.1148, D+ = 0.2991]
[Confidence Interval (CI) =90%]
Partial Discharge Inception Voltage (kV) ‐ Combine Method
b)
Figure 6. Weibull CDF and PDF of Partial Discharge Inception Voltage value for Plane
diameter 50 mm (a) Ramp Method b) Combine Method
Table 4. The highest value of probability density function of PDIV for all the needle-plane
electrode configurations
Plane 75 mm
Test Method
Needle tip 10 µm
Needle tip 20 µm
Ramp Method
33.6 % (31.2 kV)
16.10 % (39.5 kV)
Combine
Method
38.7 % (25.4 kV)
19.31 % (31.2 kV)
Plane 50 mm
Needle tip 10
Needle tip 20 µm
µm
16.18% (34.3
13.44% (40.2 kV)
kV)
34.96% (26.2
22.44% (34 kV)
kV)
Conclusion
The electrode geometry such as the needle tip radius, the shape of ground electrode and
also the gap distance will influence the Partial Discharge Inception Voltage characteristic
(inception voltage, Partial Discharge charge, Partial Discharge current) of mineral oil. Besides
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Ferdinand Sipahutar, et al.
of that, the test method for Partial Discharge Inception Voltage measurement is also an
important parameter to be considered. According to the test results, the combine method
procedure is more sensitive to detect Partial Discharge Inception Voltage at low voltage and
more secure from breakdown events than the ramp method which recommended by IEC 61294.
In addition, the standard deviation of Partial Discharge Inception Voltage value for all the
needle electrode tip radius 10 µm that tested using both test methods is better than the needle
electrode tip radius 20 µm. Therefore we can conclude that the combine method is feasible to
be used in Partial Discharge Inception Voltage measurement and according to the test results,
the needle electrode with tip radius 10 µm is recommended for Partial Discharge Inception
Voltage measurement of mineral oil. In addition, the configuration of the needle electrode tip
radius 10 µm and plane diameter 75 mm, is strongly recommended due to its good
performance and its feasibility for Partial Discharge Inception Voltage characteristic
measurement of mineral oil. Finally, the test results for Partial Discharge Inception Voltage
obtained from experiment test agree with Weibull distribution and by using the cdf and pdf
value, the frequently density of the occurrence of Partial Discharge Inception Voltage can be
known. It found that the highest frequently density function of Partial Discharge Inception
Voltage value using ramp method for plane diameter 75 mm and 50 mm is in the 31.2 – 34.3
kV for needle tip radius 10 µm and 39.5 – 40.2 kV for needle tip 20 µm. Meanwhile, for
combine method, the higher frequently density function lies in the 25.4 - 26.2 kV for needle tip
radius 10 µm and 31.2 - 34 kV for needle tip 20 µm.
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nand Sipahuttar was born in Gunung Siitoli, Indonesiaa in 1979. Hee
Ferdin
obtaineed bachelor deegree from Noorth Sumatra University
U
Indoonesia in 2003.
He joined Indonesiann Electric Pow
wer Company, PT. PLN in 2005. Currentlyy
o Electrical Engineering
E
annd Informatics,,
he is a master studeent at School of
Bandu
ung Institute of
o Technologyy. He interessts in SCADA
A system andd
Diagno
osis of High Voltage
V
equipments.
Suwarrno was born in
i Indonesia in 1965. He receeived BSc and MSc from Thee
Departtment of Electriical Engineeringg, Bandung Insttitute of Technoology, Bandung,
Indoneesia in 1988 andd 1991 respectivvely. He receivedd PhD from Naggoya University,
Japan in 1996 in thee field of Highh Voltage Electtrical Insulationn. Suwarno is a
professor in The Schoool of Electrical Engineering andd Informatics Innstitut Teknologii
ung and currentlyy he is the Dean of the School. Suwarno
S
is a mem
mber IEEE.
Bandu
215
Ferdinand Sipahutar, et al.
Ahm
mad Azhari Kemma
K
was born
b
in Makasssar, 1981. Hee obtained hiss
bach
helor degree frrom Bandung Institute
I
of Technology (ITB
B), Departmentt
of Electrical
E
Engiineering, majooring Electroniic Engineeringg in 2004. Hee
joineed Indonesian Electric
E
Powerr Company, PT
T. PLN in 20055. Currently hee
is a master studennt at School of
o Electrical Engineering
E
annd Informatics,,
dung Institute of Technologyy. His research interests are power system
m
Band
proteection and Diagnosis of Highh Voltage equippments.
Norasage Pattanaadech receiveed B.Eng and M.Eng degreee in electricall
engiineering from King Mongkkut's Institute of Technologgy Ladkrabangg
(KM
MITL) in 1997 and Chulalonngkom Universsity in 2001 reespectively. Hee
joineed Mahanakom
m University off Technology in
i 200 - 2003 before
b
workingg
in King
K
Mongkut Institute of Teechnology Laddkrabang, Banggkok, Thailandd
untill now. He is currently
c
also studying for PhD
P
in the Insstitute of Highh
Volttage Engineerring and Sysstem Management, Graz University off
Tech
hnology, Austrria. His researrch activities have been maainly involvedd
Partial discharge in inssulating liquid,, solid insulatoor characteristiics, high voltaage testing andd
magnetic Comppatibility.
equipmennt, and Electrom
I
in 19985. He receivved B.Eng. andd
Fari Pratomosiwi was born in Indonesia
ng. degrees in
i electrical engineering from
f
Bandungg Institute off
M.En
Tech
hnology (ITB),, Indonesia in 2007 and 20009, respectivelly. Now, he iss
curreently PhD studdent in the Innstitute of Higgh Voltage Enngineering andd
Systeem Managemeent, Graz Univversity of Techhnology, Austtria. His majorr
reseaarch interests are high voltaage insulating materials for substitutes off
insullating mineral oils
o and partiall discharge.
H
Voltage Enngineering andd
Michael Muhr is ann emeritus professor at the High
m Managemennt of Graz Uniiversity of Technology (TU Graz),
G
Austria..
System
Since 1990, he has been the Headd of the Instituute and Test Institute of Highh
ge Engineeringg and System Management of
o TU Graz. He
H is a memberr
Voltag
ÖVE, ÖGE, DKE, IEEE,
I
IEC andd CIGRE (connvenor of 5 woorking groups)..
He haas published more
m
than 170 publications
p
annd reports and also
a more thann
160 lectures. He received Honnorary Doctorral „Dr.h.c.“ of the Westt
mian Universitty of Plzen.
Bohem
216