See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/261344615
The influence of voltage and frequency variations on insulation quality of a high
voltage cable
Conference Paper · July 2013
DOI: 10.1109/EUROCON.2013.6625098
CITATIONS
READS
3
4,014
5 authors, including:
Celal Kocatepe
Celal Fadil Kumru
Yildiz Technical University
T.C. Süleyman Demirel Üniversitesi
56 PUBLICATIONS 205 CITATIONS
29 PUBLICATIONS 143 CITATIONS
SEE PROFILE
SEE PROFILE
Ramazan Ayaz
Hakan Akca
Yildiz Technical University
Ege University
23 PUBLICATIONS 126 CITATIONS
21 PUBLICATIONS 104 CITATIONS
SEE PROFILE
All content following this page was uploaded by Ramazan Ayaz on 26 September 2014.
The user has requested enhancement of the downloaded file.
SEE PROFILE
EuroCon 2013 • 1-4 July 2013 • Zagreb, Croatia
The Influence of Voltage and Frequency Variations
on Insulation Quality of a High Voltage Cable
Celal Kocatepe #1, Celal Fadl Kumru#1, Ramazan Ayaz #1, Oktay Arkan #1, Hakan Akça#1
#
Department of Electrical Engineering, Yildiz Technical University
Davutpasa Campus 34210,Esenler, Istanbul, Turkey
1
kocatepe@yildiz.edu.tr
cfkumru@yildiz.edu.tr
1
ayaz@yildiz.edu.tr
1
oarikan@yildiz.edu.tr
1
hakca@yildiz.edu.tr
1
Abstract— Insulation quality issue has had a significant place
in high voltage systems for long years. Especially for high voltage
cables, which is one of the most crucial elements in power
systems, the measurements of dissipation factor or tan delta has
a great importance on the insulation life time. Besides, when the
power system parameters such as frequency and voltage level are
not steady, tan delta measurement values will also be changed.
Therefore, tan delta and dielectric loss measurement should be
realized in case of unsteady power system conditions to get more
exact results. In this study, tan delta measurement of a 20,1/34,5
kV, single core high voltage cable is carried out. By changing the
frequency and voltage level, dissipation factor, capacitance (Cs),
insulation resistance (Rs) and dielectric losses (Pk) measurement
values are obtained.
Keywords: Tan delta, dielectric loss, High Voltage (HV) cable, HV
measurement, XLPE cable.
the equivalent circuit of the insulating material. In this case,
phase angle between current and voltage differs from 90o.
Tangent of this angle is expressed as "dielectric loss factor"
and consumptive power on the resistance is called "dielectric
loss".
Dissipation factor and capacity analysis were discussed in
several studies in the literature. In the study of A. Ponniran
and M. S. Kamaruddin, they investigated the change of the
tan and capacity parameters by taking account of the ageing
on the underground XLPE cables [5]. P. Werelius and his
friends presented their studies that the frequency response of
insulation material in terms of capacity and dielectric loss
factor depends on not only insulation material but also
temperature of material [7]. T. J. Person and R. F. Eaton
examined the effect of the dielectric loss on the power cables
with different polymer materials in their study [8]. G.
I. INTRODUCTION
Tanimoto and his friends investigated tan delta values by
The reliability of the high voltage equipment used in
different polyethylene materials at high temperatures [9]. W. J.
electric power systems such as power cables, power
K. Raymond and his friends introduced measurement of
transformers, capacitors etc. significantly depends on material
dissipation factor in paper-insulated lead-covered cable
insulation [1-2]. Dielectric losses which occur in high voltage
insulation at ultra-high frequency in their study [10]. In the
equipment are an important indicator of the insulation [1-4].
study by J. C. Hernández-Mejía and his friends, characteristics
Therefore, tan delta and capacitance values of the insulation
of tan delta on aged and non-aged medium voltage cable at
material are important parameters for determining the
very low frequency are examined [11]. S. Kim and his friends
dielectric performance of high voltage cables [5].
examined the performance of tan delta at very low frequency
Cross-linked polyethylene (XLPE) insulated high voltage
on medium voltage cables [12].
cables are one of the most important components in power
Especially in a network, the voltage and frequency may be
systems. Although these cables have high mechanical strength,
variable due to harmonics. In such a case, tan analysis has to
low dielectric loss and low dielectric permittivity, there are
be done for different voltage and frequency values.
some factors that can deteriorate the dielectric materials and
In this study, tan, Cs, Rs, and Pk parameters of a 34,5 kV
affect the insulation performance of these cables [6].
underground XLPE cable is analyzed in different voltage and
Humidity, air cavity and water in the dielectric material of
frequency values by using CPC100/CPTD1 measurement
underground cables cause dielectric loss factor (tan delta),
device.
which is an important criterion in determining the
performance of cable, to increase. In company with the
II. BASIC THEORY
increase of these losses, insulation of the cable is exposed to
Generally, dielectric losses in insulation can be represented
voltage stress and heat. As a consequence of these changes,
by
a series (Rs) or parallel resistance (Rp). This equivalent
thermal and electrical breakdowns may occur [7].
The phase difference between current and voltage of the circuit models is shown in Fig. 1 where the resistance Rp, Rs
ideal capacitor is 90°. However, insulation materials which are represents the dielectric losses based upon conductivity, space
used in the applications do not exactly have an ideal capacitor. charge and dipole formation polarization, and the capacitance
Therefore, in addition to the capacitor, a resistance is used in Cp, Cs represent the capacitive elements of the insulation [13].
978-1-4673-2232-4/13/$31.00 ©2013 IEEE
964
EuroCon 2013 • 1-4 July 2013 • Zagreb, Croatia
III. EXPERIMENTAL SETUP
In this study, an experimental setup is configured to
measure the dissipation factor of a high voltage cable with the
changing frequency and voltage. As a test sample, a single
core, XLPE insulated medium voltage cable is selected.
Technical specifications of the high voltage cable are given in
Table I.
TABLE I
TECHNICAL SPECIFICATION OF HIGH VOLTAGE CABLE
Fig. 1. Equivalent parallel (a) and series (b) circuit of a high voltage
insulation
Properties
VDE Code
Nominal Voltage
Nominal cross-section (Cu)
Diameter of conductor
Conductor DC resistance (at 20°C)
Operating inductance
Operating capacitance
Current carrying capacity (in air)
Cable length
Overall diameter
When a voltage is applied to the terminals of both
equivalent circuits, active and reactive currents will flow
through Rp and Cp respectively. Normally, phase difference
between a capacitive element’s voltage and current is 90°
degrees. However, when the Rp is being taken into account,
the apparent current show a small angular deviation called
delta (). The tangent of this small angle is the dissipation
factor or tan delta. The tan delta formulas for parallel and
series equivalent circuits are as follows:
tan δ parallel =
1
ω ⋅ Rp ⋅ C p
tan δ series = ω ⋅ Rs ⋅ C s
[2.1]
[2.2]
As understood from the equations, the parallel and series
circuits show different characteristics along with the changing
frequency. Besides, the power losses in a dielectric insulation
for parallel and series circuit can be calculated as:
p L − parallel = ω ⋅ C p ⋅ U 2 ⋅ tan δ
p L − series =
ω ⋅ Cs ⋅U 2
⋅ tan δ
1 + tan 2 δ
Value
N2XSY
20,1 / 34,5 kV
1x95/16 mm2
11 mm
0,193 0,68 mH/km
0,16 μF/km
279 A
6m
38 mm
In general, tan delta measurements are carried out by
classical Schering Bridge method. However, this kind of
method and its measurement set-up are not practical for field
measurements. Therefore, digital measurement devices which
provide mobile use and convenience in field studies are
developed for tan delta measurements. In this work, the
measurements are realized by CPC100/CPTD1 measurement
device which is shown in Fig.2.
[2.3]
[2.4]
In parallel and series circuit, the equivalent capacitance Cp
and Cs have different values as given in Eq. 2.5. However,
while the tan delta value is too small, Cp and Cs values may be
considered same.
(
C s = C p ⋅ 1 + tan 2 δ
)
[2.5]
Eq. 2.1 and 2.2 give good results for a fixed (50 Hz)
frequency. However, dielectric loss factor is oppositely
changed for varying frequency in both equations. Therefore,
frequency dependence of dielectric loss factor should be
investigated [14].
Fig. 2. CPC100/CPTD1 Tan delta measurement device
978-1-4673-2232-4/13/$31.00 ©2013 IEEE
965
EuroCon 2013 • 1-4 July 2013 • Zagreb, Croatia
TABLE III
ATMOSPHERIC CONDITION OF LABORATORY
The device has two measurement probes. One of them is
high voltage probe whereby high voltage is applied to the
conductor/screen and the other one is measurement probe
whereby the measurement data is collected. As given in Table
II, the device can measure tan delta up to 12 kV AC and
400Hz.
TABLE II
OPERATING RANGES & TECHNICAL SPECIFICATION OF MEASUREMENT
DEVICE
Terminal
U/f
High
Voltage
Output
0-12 kV AC
15 – 400 Hz
THD
< 2%
I
S
tmax
300 mA
3600 VA
>2 min
100 mA
1200 VA
> 60 min
Relative
Humidity
(%)
29
Temperature
(°C)
14,7
Atmospheric
Pressure
(mmHg)
766,57
First of all, for a fixed 50 Hz frequency, the voltage applied
to the cable is changed at 2 kV intervals and the data collected
are given in Table IV.
TABLE IV
MEASUREMENT DATA FOR FIXED FREQUENCY & CHANGING VOLTAGE
Voltage Frequency CpCs Rp
Rs Tan Pk
(kV)
(Hz)
(pF) (G) ()
(%) (mW)
2
50
884,996 19,75 660,8 0,0182 0,2
The experimental setup for tan delta measurement is given
in Fig. 3.
Fig. 3. Experimental setup for tan delta measurement
50
885,007 19,17 674,43 0,0188
0,8
6
50
885,031 18,81 687,84 0,0191
1,9
8
50
885,042 17,91 723,79 0,0201
3,6
10
50
885,070 15,08 843,12 0,023
6,6
12
50
885,194 10,26 1209,6 0,0365 13,6
In Fig. 5, tan delta changes are given according to
measurement results which are carried out for different
frequencies between 50 Hz – 350 Hz and voltage levels from
2kV up to 12 kV at 2kV intervals. As can be seen in Fig. 5,
tan delta is increasing in parallel to the raise in voltage level
for each frequency value. Additionally, frequency increment
also cause tan delta value to increase.
0.055
50 Hz
150 Hz
250 Hz
350 Hz
0.05
0.045
Tan Delta [%]
High voltage is applied to the conductor and measurement
probe is connected to the cable screen as in real application.
Besides, the XLPE insulation is guarded at both sides to
prevent discharges and surface charges which may affect the
measurement sensitivity. Additionally, each measurement is
carried out for five times and the average value is calculated
to increase the accuracy of the measurements. The
measurements are realized in Yildiz Technical University
High Voltage Laboratory and the experimental setup is given
in Fig. 4.
4
0.04
0.035
0.03
0.025
0.02
0.015
2
4
6
8
Test Voltage [kV]
10
12
Fig. 5. The relation between tan delta and voltage level
Fig. 4. The measurement setup prepared in high voltage laboratory
IV. MEASUREMENT RESULTS AND ANALYSIS
The measurements of insulation quality parameters of a
high voltage cable are carried out for different frequencies and
voltages. During the measurements, atmospheric conditions of
the laboratory are taken and the average values are given in
Table III.
978-1-4673-2232-4/13/$31.00 ©2013 IEEE
Therefore, it is concluded from the figure that any raise in
voltage level and frequency is increasing the tan delta value
and weakening the insulation material.
The next measurement data is obtained at 2kV, 6kV, 8kV
and 12kV voltage levels, to make a detailed analyze of the
frequency effect on dissipation factor. The measurement result
obtained for 12 kV voltage and different frequencies are given
in Table V.
966
EuroCon 2013 • 1-4 July 2013 • Zagreb, Croatia
TABLE V
MEASUREMENT DATA FOR FIXED VOLTAGE & CHANGING FREQUENCIES
0.085
50 Hz
Voltage Frequency CpCs Rp
(kV)
(Hz)
(pF) (G)
Rs
()
Tan (%)
0.08
Pk
(mW)
0.075
0.07
50
885,194 10,26 1209,6 0,0365
13,6
12
100
885,149 4,637 648,12 0,0405
30,6
12
150
884,933 2,572 541,1 0,0462
52,6
12
200
884,89 1,757 432,31 0,0487
76,5
12
250
884,898 1,332 369,68 0,0527
101,7
0.055
12
300
884,862 1,15 319,68 0,0533
124,1
0.05
12
350
884,834 0,981 267,14 0,0534
145,1
0.045
12
400
884,811 0,794 249,74 0,0572
176,6
Loss Index [%]
12
0.06
0.05
0.06
0.04
2
The measurements are carried out for 50 Hz up to 400 Hz
frequencies at 50 Hz regular intervals. The results obtained are
shown in Fig. 6.
As it is understood from the Fig. 6 that, increase in
frequency cause a rise in tan delta value for each of four
voltage levels. Especially, when the applied voltage is nearly
closed to nominal voltage level, the increment of tan delta is
more.
0.055
0.065
2 kV
6 kV
8 kV
12 kV
4
6
8
Test Voltage [kV]
10
12
Fig. 7. The relation between loss index and voltage
In Fig. 7, the loss index value is increasing with the
increased voltage level. It is concluded that increase in voltage
level particularly above 10 kV causes an increase in loss index.
To analyze the frequency effect on loss factor, the
measurements are carried out for fixed 12kV voltage and the
results obtained are given in Fig. 8. It is clearly seen from the
Fig. 8 that the frequency increment is causing an increase in
loss index.
0.15
12 kV
0.14
0.13
0.04
Loss Index [%]
Tan Delta [%]
0.045
0.035
0.03
0.025
0.11
0.1
0.02
0.015
50
0.12
100
150
200
250
300
Test Frequency [Hz]
350
0.09
400
0.08
50
Fig. 6. The relation between tan delta and frequency for four voltage levels
The loss index which diagnoses about the insulation quality
of dielectric material is acquired by multiplying the relative
permittivity and tan delta (r·tan). The dielectric permittivity
value for XLPE insulation is approximately considered 2,3 for
all calculations [12]. The curve given in Fig. 7 is acquired by
using the measurement results which is realized to see the
effect of the voltage increment on the loss index. The
measurements are carried out for fixed 50 Hz frequency and
changing voltage level at 2 kV regular intervals.
978-1-4673-2232-4/13/$31.00 ©2013 IEEE
100
150
200
250
300
Test Frequency [Hz]
350
400
Fig. 8. The relation between loss index and frequency
V. CONCLUSION
In this study, the changes of tan delta, dielectric loss factor,
and other electrical parameters of a 20,1/34,5 kV nominal
rated high voltage cable are analyzed according to the
different frequency and voltage levels. CPC100/CPTD1
digital measurement device is used to realize the
measurements.
According to the measurements which are performed for
different voltages, it is concluded that dissipation factor and
dielectric losses are increasing with the raised voltage levels.
Thus, the results showed that the voltage increment applied to
967
EuroCon 2013 • 1-4 July 2013 • Zagreb, Croatia
the cable damages the cable insulation due to the dielectric
power losses.
The measurements for different frequencies are also carried
out to realize the frequency dependence of the cable insulation.
The measurement results proved that dielectric losses and tan
delta value in the cable insulation are considerably increasing
for higher frequency levels. For this reason, it understood that
changing frequency deteriorates the insulation quality of
dielectric material.
Consequently, it is absolute that the frequency and voltage
increment are weakening the insulation material. When it is
considered that the power system parameters such as voltage
and main frequency are not steady, the dielectric losses in
high voltage cable insulation will not be similar with the
measured values which are obtained for nominal power
system conditions specified in standards. Therefore, it is
concluded that dielectric quality of high voltage cable
insulation changes with the voltage rise, electrical faults and
harmonic components in power system which may lead the
cable insulation to breakdown or early ageing.
REFERENCES
[1] X. Liu; J. Pu; J. Jiang; H. Ma, Z. Wang, “Research on dielectric loss
testing device for large-capacity and high-voltage electrical equipment”,
4th International Conference on Electric Utility Deregulation and
Restructuring and Power Technologies (DRPT), 2011, Page(s):649-652.
[2] E. Wasilenko; M. Olesz, “On-site loss tangent measurements of high
voltage insulation”, Sixth International Conference on Dielectric
Materials, Measurements and Applications, 1992, Page(s):170-173.
[3] A. Kumar; S. Sharma, “Measurement of dielectric constant and loss
factor of the dielectric material at microwave frequencies”, Progress In
Electromagnetics Research, PIER 69, 2007, Page(s): 47-54.
[4] B.D.Malpure; K. Baburao, “Failure analysis & diagnostics of power
transformer using dielectric dissipation factor”, International
978-1-4673-2232-4/13/$31.00 ©2013 IEEE
View publication stats
968
Conference on Condition Monitoring and Diagnosis, 2008, Page(s):
497-501.
[5] A. Ponniran; M. S. Kamarudin, “Study on the performance of
underground XLPE cables in service based on tan delta and
capacitance measurements ”, 2nd IEEE International Conference on
Power and Energy (PECon 08), 2008, Page(s): 39-43.
[6] R. Sarath; S. Das; C. Venkataseshaiah; N. Yoshmura, “Investigations
of growth of electrical trees in XLPE cable insulation under different
voltage profiles”, Annual Report Conference on Electrical Insulation
and Dielectric Phenomena, 2003, Page(s): 666-669.
[7] P. Werelius; J. Cheng; M. Ohlen; D. M. Robalino, “Dielectric
frequency response measurements and dissipation factor temperature
dependence”, Electrical Insulation (ISEI), Conference Record of the
2012 IEEE International Symposium on, 2012, Page(s): 296-300.
[8] T. J. Person; R. F. Eaton, “Reduction of dissipation factor in power
cable material systems containing metallocene- and post-metallocenecatalyzed polymers”, Electrical Insulation and Dielectric Phenomena,
CEIDP '09, 2009, Page(s): 735-738.
[9] G. Tanimoto; M. Okashita; F. Aida; Y. Fujiwara, “Temperature
dependence of tan in polyethylene”, Properties and Applications of
Dielectric Materials Proceedings of the 3rd International Conference
on, 1991, Page(s): 1068 - 1071 vol.2.
[10] W. J. K. Raymond; C. K. Chakrabarty; G. C. Hock, “Dissipation factor
measurement of PILC insulation at UHF”, Intelligent Systems,
Modelling and Simulation (ISMS), Third International Conference on,
2012, Page(s): 157-160.
[11] J. C. Hernández-Mejía; R. Harley; N. Hampton; R. Hartlein,
“Characterization of ageing for MV power cables using low frequency
tan diagnostic measurements”, Dielectrics and Electrical Insulation,
IEEE Transactions on, 2009, Page(s): 862-870.
[12] S. Kim; J. Lim; B. Kim; J. Lee; W. Choi; K. Lee; Y. Jung; T.
Kim,“The estimation of insulation on MV cables using the VLF tan diagnostic measurement”, Condition Monitoring and Diagnosis (CMD),
IEEE International Conference, 2012, Page(s): 1191-1196.
[13] Al-Arainy, A. A., Qureshi, M. I., Malik, N. H., Fundamentals of High
Voltage Engineering, Academic Publishing and Press, Saudi Arabia,
2005.
[14] C.L. Wadhwa, “High Voltage Engineering”, New Age Science, 2010.