Transient voltage distribution in transformer winding (experimental investigation)
1 like517 views
This document discusses an experimental investigation into the non-linear voltage distribution in transformer windings caused by very fast transient overvoltages (VFTOs) resulting from switching operations. A high-frequency circuit model of a 100 kVA transformer was developed using the EMTP software, and simulation results were compared with experimental findings, revealing a significant non-uniform voltage distribution that can damage insulation. The study highlights the importance of series capacitances and the effect of design parameters on the transient response in transformer windings.
![IJRET: International Journal of Research in Engineering and Technology ISSN: 2319-1163
__________________________________________________________________________________________
Volume: 02 Issue: 04 | Apr-2013, Available @ http://www.ijret.org 579
TRANSIENT VOLTAGE DISTRIBUTION IN TRANSFORMER WINDING
(EXPERIMENTAL INVESTIGATION)
Kanchan Rani1
, R. S. Gorayan2
1
M.tech Student, 2
Professor, Electrical Department IIT (BHU), VARANASI, U.P India,
kanchan.rani.eee11@itbhu.ac.in, rsgorayan.eee@iitbhu.ac.
Abstract
In this work, the non-liner voltage distribution in transformer winding is investigated that occurs due switching and lightning.
Transformer winding is modeled in the alternative transients program (ATP) version of Electromagnetic transients program (EMTP-
RV). EMTP software is used to simulate the very fast transient overvoltage. An experimental setup that consist of , Recurrent surge
generator, CRO and transformer winding model has been developed and voltages measured at different point along the transformer
winding. Simulation results show good agreement with the experimental result.
Index Terms: Very fast transient overvoltages, internal resonance, impulse voltage distribution, disc winding
-----------------------------------------------------------------------***-----------------------------------------------------------------------
1. INTRODUCTION
It is well known that switching operation in the Gas insulated
switchgears (GIS) produces very fast transient over voltages
(VFTO). VFTO have very short rise time of .1µsec or less and
its main oscillating frequency range is in between 1MHz to
50MHz [1].
The distribution of these transient over voltages in transformer
winding is highly non uniform. It has been observed that 60
Percent of these voltages appears across first 10 percent length
of the winding. This non uniform voltage distribution can
damage the transformer insulation [2].
This work deals with the voltage distribution in the
transformer winding when its terminal is excited with impulse
voltage. Study is aimed to analyze the nature of the internal
voltage amplification and voltage stress at various points of
transformer winding with impulse excitation. A transformer
winding model is developed on the EMTP software.
Simulation results are compared with the experimental results
and a satisfactory result are obtained.
2. TRANSFORMER WINDING MODEL
For the study of the transients response of the transformer a
high frequency circuit model of 100 KVA transformer model
has been developed based on geometry and configuration.
While calculating phenomena associated with such high
frequencies, the capacitance of transformer winding is
important, although it is of no importance at power frequency
voltage levels. The most detailed model of the transformer is
one in which every turn of the winding is represented and all
capacitances and inductances are included. Such a model may
be prohibitive in terms of memory and complexity. The details
can be reduced, by taking some assumption, to simplify L, C,
network without losing much accuracy. A schematic diagram
of the developed model is shown as in Figure1
Fig. 1: Simplified Equivalent model for Transformer Winding
It is assumed that the winding is uniform i.e. all the series
capacitance are equal and all shunt capacitance are equal and
all series inductances are equal.
3. TEST TRANSFORMER AND CALCULATION
OF WINDING PARAMETERS
3.1. Test Transformer description
To determine the transient’s voltage distribution in the
transformer windings, it is necessary to calculate the
parameters of the winding i.e. inductance and capacitance. The
study has been done on 100 KVA single phase transformer
having continuous disk type H.V. winding. The transformer
data is given in Table 1.](https://image.slidesharecdn.com/transientvoltagedistributionintransformerwindingexperimentalinvestigation-140804001024-phpapp02/85/Transient-voltage-distribution-in-transformer-winding-experimental-investigation-1-320.jpg)
![IJRET: International Journal of Research in Engineering and Technology ISSN: 2319-1163
__________________________________________________________________________________________
Volume: 02 Issue: 04 | Apr-2013, Available @ http://www.ijret.org 580
Table 1: Test Transformer data
Rating 100 kVA
H.V. voltage 11 kV
L.V. voltage 433V
Frequency 50Hz
Insulation between core and
L.V. winding
Bablised Paper
Insulation over conductor Paper
Insulation over layer Paper
Insulation over L.V. and H.V.
winding
Bablised paper
Table 2 and 3 present core and windings data for the Test
Transformer.
Table 2: Transformer Core data
Diameter of core 375 mm
Width of window 375 mm
Height of window 1335 mm
CRGO lamination .33 mm
Distance between center of
adjacent limb
685 mm
Table 3: Transformer Winding data
Winding L.V. H.V.
Type of winding Helical Disc
Current density 2.75 A/mm2 2.92 A/mm2
Cross area of
conductor
55 mm2 8.637 mm2
Number of disc - 10
Inside diameter 405mm 571mm
Outside
diameter
507mm 649 mm
Mean length of
turn
1432mm 1916mm
3.2 Determination of the transformer winding
parameters
Capacitance calculation:
Disc to disc capacitance for the winding have been calculated
from the principle of electrostatic energy conservation [3].
Net series capacitance is given as:
Cs=
Where, D =mean winding diameter
N=number of disc in the transformer
n =number of turn per disc
h=width of copper strip conductor
= inter –disc space
=thickness of insulation
Disc to ground capacitance for winding have been calculated
assuming that the coil, core leg and the metal tank form
cylindrical electrode system.
Net shunt capacitance is given as:
Where, a = Radius of core
b = Inner radius of L.V. winding
c = Outer radius of H.V. winding
d = Inner radius of H.V. winding
Axial length of the H.V. winding
Inductance calculation [4]:
We have,
L= .001a
If <.2, then
=4
4. TRANSFORMER WINDING RESPONSE TO
IMPULSE VOLTAGES
When analyzing the impulse voltage distribution in the
transformer winding a capacitive network is considered. In
other words, the presence of series capacitances between](https://image.slidesharecdn.com/transientvoltagedistributionintransformerwindingexperimentalinvestigation-140804001024-phpapp02/85/Transient-voltage-distribution-in-transformer-winding-experimental-investigation-2-320.jpg)
![IJRET: International Journal of Research in Engineering and Technology ISSN: 2319-1163
__________________________________________________________________________________________
Volume: 02 Issue: 04 | Apr-2013, Available @ http://www.ijret.org 581
winding sections causes the transformer to respond to abrupt
impulses as a network of capacitances for all frequencies
above its lower natural frequencies of oscillations.
And are the total ground capacitance and series
capacitance of the transformer winding respectively. The ratio
has been denoted by the distribution constant α.
To improve the transients response and to reduce the disc to
disc voltage gradient the value of α is as small as possible.
One way to reduce the value of α is to increase the value of
which can be achieve by interleaving and inter-shielding [5].
4.1. Simulation Result
The behavioral response of the high voltage winding of the
transformer have been analyzed using EMTP by simulating
the circuit shown in Fig-1. An impulse voltage source having
peak voltage 40 volt is apply on the excitation terminal and the
voltage at various node is measured. The node voltage at 2nd
,3rd
and last node is shown in below with isolated neutral. fig -
2, fig-3 and fig-4 show the node voltages when α is 10,3.5 and
1 respectively .
Fig2 : node voltage when α =10 at a- 2nd
node b- 3rd
node c-
last node
b
c
Fig4: node voltage when α = 1 at a. 2nd
node b. 3rd
node c.
last node
a
b
c
Fig3: node voltage when α =3.5 at a. 2nd
node b.3rd
node
c. last node
a
..
.
b
.
c
a](https://image.slidesharecdn.com/transientvoltagedistributionintransformerwindingexperimentalinvestigation-140804001024-phpapp02/85/Transient-voltage-distribution-in-transformer-winding-experimental-investigation-3-320.jpg)
![IJRET: International Journal of Research in Engineering and Technology ISSN: 2319-1163
__________________________________________________________________________________________
Volume: 02 Issue: 04 | Apr-2013, Available @ http://www.ijret.org 583
Results also indicate that voltage distribution in the
transformer is highly non uniform with larger value of α as
compare to when value of α is low.
.
ACKNOWLEDGEMENTS
The authors wish to thank Prof. S.P. Singh, the Head of
Electrical Engineering, Indian Institute of technology (BHU)
Varanasi for providing necessary computational and
laboratory facility for successful completion of this work.
REFERENCES:
[1]. Y. Shibuya, S. Fujita and T. Shimomura “Effects of very
fast transients overvoltage on transformer” IEE, volume 146
No.4 july 1999 .
[2]. Gao Youhua ,Yuan Hong, Wang Erazi, and Cao Yundong
“Calculation Of Very Fast Transients Over-Voltage And Its
Distribution In Transformer Winding In 110 kV
GIS”.proceedingof international conference on electrical
machines and systems 2007 ,oct 8~11 Seoul Korea
[3] Robert M. Delvecchio, Bertrand poulin, Dilip Kumar M.
shah, Rajendra Ahuja “Transformer Design principle Chapter
12.
[4].Grover, F.W., “Inductance Calculations: Working
Formulas and Tables”, Dover Publication, Inc-1962.
[5] Mehdi Bagheri, Mehdi Vakilian, Arsalan Hekmati,
Rouhollah Heidarzadeh “Influence of Electrostatic Shielding
of Disc Winding on Increasing the Series Capacitance in
Transformer” Power Tech, 2007 IEEE Lausanne.
BIOGRAPHIES:
Obtained the Under Graduate degree
from B.B.D. National Institute of
Technology & Management, Lucknow.
Presently doing Post Graduation from
Indian Institute of Technology, BHU,
Varanasi
Obtained the Under Graduate and Masters
degree from University College of Engg.
Burla, Sambalpur University, Odissa, and
Ph.D. from Institute of Technology, BHU,
Varanasi. Presently, working as Professor
in IIT (BHU) Varanasi.](https://image.slidesharecdn.com/transientvoltagedistributionintransformerwindingexperimentalinvestigation-140804001024-phpapp02/85/Transient-voltage-distribution-in-transformer-winding-experimental-investigation-5-320.jpg)
Transient voltage distribution in transformer winding (experimental investigation)
- 1. IJRET: International Journal of Research in Engineering and Technology ISSN: 2319-1163 __________________________________________________________________________________________ Volume: 02 Issue: 04 | Apr-2013, Available @ http://www.ijret.org 579 TRANSIENT VOLTAGE DISTRIBUTION IN TRANSFORMER WINDING (EXPERIMENTAL INVESTIGATION) Kanchan Rani1 , R. S. Gorayan2 1 M.tech Student, 2 Professor, Electrical Department IIT (BHU), VARANASI, U.P India, kanchan.rani.eee11@itbhu.ac.in, rsgorayan.eee@iitbhu.ac. Abstract In this work, the non-liner voltage distribution in transformer winding is investigated that occurs due switching and lightning. Transformer winding is modeled in the alternative transients program (ATP) version of Electromagnetic transients program (EMTP- RV). EMTP software is used to simulate the very fast transient overvoltage. An experimental setup that consist of , Recurrent surge generator, CRO and transformer winding model has been developed and voltages measured at different point along the transformer winding. Simulation results show good agreement with the experimental result. Index Terms: Very fast transient overvoltages, internal resonance, impulse voltage distribution, disc winding -----------------------------------------------------------------------***----------------------------------------------------------------------- 1. INTRODUCTION It is well known that switching operation in the Gas insulated switchgears (GIS) produces very fast transient over voltages (VFTO). VFTO have very short rise time of .1µsec or less and its main oscillating frequency range is in between 1MHz to 50MHz [1]. The distribution of these transient over voltages in transformer winding is highly non uniform. It has been observed that 60 Percent of these voltages appears across first 10 percent length of the winding. This non uniform voltage distribution can damage the transformer insulation [2]. This work deals with the voltage distribution in the transformer winding when its terminal is excited with impulse voltage. Study is aimed to analyze the nature of the internal voltage amplification and voltage stress at various points of transformer winding with impulse excitation. A transformer winding model is developed on the EMTP software. Simulation results are compared with the experimental results and a satisfactory result are obtained. 2. TRANSFORMER WINDING MODEL For the study of the transients response of the transformer a high frequency circuit model of 100 KVA transformer model has been developed based on geometry and configuration. While calculating phenomena associated with such high frequencies, the capacitance of transformer winding is important, although it is of no importance at power frequency voltage levels. The most detailed model of the transformer is one in which every turn of the winding is represented and all capacitances and inductances are included. Such a model may be prohibitive in terms of memory and complexity. The details can be reduced, by taking some assumption, to simplify L, C, network without losing much accuracy. A schematic diagram of the developed model is shown as in Figure1 Fig. 1: Simplified Equivalent model for Transformer Winding It is assumed that the winding is uniform i.e. all the series capacitance are equal and all shunt capacitance are equal and all series inductances are equal. 3. TEST TRANSFORMER AND CALCULATION OF WINDING PARAMETERS 3.1. Test Transformer description To determine the transient’s voltage distribution in the transformer windings, it is necessary to calculate the parameters of the winding i.e. inductance and capacitance. The study has been done on 100 KVA single phase transformer having continuous disk type H.V. winding. The transformer data is given in Table 1.
- 2. IJRET: International Journal of Research in Engineering and Technology ISSN: 2319-1163 __________________________________________________________________________________________ Volume: 02 Issue: 04 | Apr-2013, Available @ http://www.ijret.org 580 Table 1: Test Transformer data Rating 100 kVA H.V. voltage 11 kV L.V. voltage 433V Frequency 50Hz Insulation between core and L.V. winding Bablised Paper Insulation over conductor Paper Insulation over layer Paper Insulation over L.V. and H.V. winding Bablised paper Table 2 and 3 present core and windings data for the Test Transformer. Table 2: Transformer Core data Diameter of core 375 mm Width of window 375 mm Height of window 1335 mm CRGO lamination .33 mm Distance between center of adjacent limb 685 mm Table 3: Transformer Winding data Winding L.V. H.V. Type of winding Helical Disc Current density 2.75 A/mm2 2.92 A/mm2 Cross area of conductor 55 mm2 8.637 mm2 Number of disc - 10 Inside diameter 405mm 571mm Outside diameter 507mm 649 mm Mean length of turn 1432mm 1916mm 3.2 Determination of the transformer winding parameters Capacitance calculation: Disc to disc capacitance for the winding have been calculated from the principle of electrostatic energy conservation [3]. Net series capacitance is given as: Cs= Where, D =mean winding diameter N=number of disc in the transformer n =number of turn per disc h=width of copper strip conductor = inter –disc space =thickness of insulation Disc to ground capacitance for winding have been calculated assuming that the coil, core leg and the metal tank form cylindrical electrode system. Net shunt capacitance is given as: Where, a = Radius of core b = Inner radius of L.V. winding c = Outer radius of H.V. winding d = Inner radius of H.V. winding Axial length of the H.V. winding Inductance calculation [4]: We have, L= .001a If <.2, then =4 4. TRANSFORMER WINDING RESPONSE TO IMPULSE VOLTAGES When analyzing the impulse voltage distribution in the transformer winding a capacitive network is considered. In other words, the presence of series capacitances between
- 3. IJRET: International Journal of Research in Engineering and Technology ISSN: 2319-1163 __________________________________________________________________________________________ Volume: 02 Issue: 04 | Apr-2013, Available @ http://www.ijret.org 581 winding sections causes the transformer to respond to abrupt impulses as a network of capacitances for all frequencies above its lower natural frequencies of oscillations. And are the total ground capacitance and series capacitance of the transformer winding respectively. The ratio has been denoted by the distribution constant α. To improve the transients response and to reduce the disc to disc voltage gradient the value of α is as small as possible. One way to reduce the value of α is to increase the value of which can be achieve by interleaving and inter-shielding [5]. 4.1. Simulation Result The behavioral response of the high voltage winding of the transformer have been analyzed using EMTP by simulating the circuit shown in Fig-1. An impulse voltage source having peak voltage 40 volt is apply on the excitation terminal and the voltage at various node is measured. The node voltage at 2nd ,3rd and last node is shown in below with isolated neutral. fig - 2, fig-3 and fig-4 show the node voltages when α is 10,3.5 and 1 respectively . Fig2 : node voltage when α =10 at a- 2nd node b- 3rd node c- last node b c Fig4: node voltage when α = 1 at a. 2nd node b. 3rd node c. last node a b c Fig3: node voltage when α =3.5 at a. 2nd node b.3rd node c. last node a .. . b . c a
- 4. IJRET: International Journal of Research in Engineering and Technology ISSN: 2319-1163 __________________________________________________________________________________________ Volume: 02 Issue: 04 | Apr-2013, Available @ http://www.ijret.org 582 4.2 Experimental results The transient response of the transformer winding is investigated using experimental set up as shown in Fig 5 Fig 5 : Experiment set-up In the experiment the same impulse voltage as in simulation was injected to the transformer winding model using the recurrent surge generator and the voltage at various node is observed using CRO. CONCLUSIONS The result obtained from the EMTP simulation closely agrees with the experimental results. Impulse response of transformer winding is oscillatory. If the oscillation frequency equals the transformer natural frequency, then oscillatory transients response can trigger internal resonance. Voltage at different node shows that oscillation is reduced as the value of α is decreases. a b c Fig 8 : node voltage when α =1 at a. 2nd node b. 3rd node c. last node a b c Fig 7: node voltage when α =3.5 at a. 2nd node b. 3rd node c. last node a Fig 6: node voltage when α = 10 at a. 2nd node b. 3rd node c. last node b c
- 5. IJRET: International Journal of Research in Engineering and Technology ISSN: 2319-1163 __________________________________________________________________________________________ Volume: 02 Issue: 04 | Apr-2013, Available @ http://www.ijret.org 583 Results also indicate that voltage distribution in the transformer is highly non uniform with larger value of α as compare to when value of α is low. . ACKNOWLEDGEMENTS The authors wish to thank Prof. S.P. Singh, the Head of Electrical Engineering, Indian Institute of technology (BHU) Varanasi for providing necessary computational and laboratory facility for successful completion of this work. REFERENCES: [1]. Y. Shibuya, S. Fujita and T. Shimomura “Effects of very fast transients overvoltage on transformer” IEE, volume 146 No.4 july 1999 . [2]. Gao Youhua ,Yuan Hong, Wang Erazi, and Cao Yundong “Calculation Of Very Fast Transients Over-Voltage And Its Distribution In Transformer Winding In 110 kV GIS”.proceedingof international conference on electrical machines and systems 2007 ,oct 8~11 Seoul Korea [3] Robert M. Delvecchio, Bertrand poulin, Dilip Kumar M. shah, Rajendra Ahuja “Transformer Design principle Chapter 12. [4].Grover, F.W., “Inductance Calculations: Working Formulas and Tables”, Dover Publication, Inc-1962. [5] Mehdi Bagheri, Mehdi Vakilian, Arsalan Hekmati, Rouhollah Heidarzadeh “Influence of Electrostatic Shielding of Disc Winding on Increasing the Series Capacitance in Transformer” Power Tech, 2007 IEEE Lausanne. BIOGRAPHIES: Obtained the Under Graduate degree from B.B.D. National Institute of Technology & Management, Lucknow. Presently doing Post Graduation from Indian Institute of Technology, BHU, Varanasi Obtained the Under Graduate and Masters degree from University College of Engg. Burla, Sambalpur University, Odissa, and Ph.D. from Institute of Technology, BHU, Varanasi. Presently, working as Professor in IIT (BHU) Varanasi.