Download Thesis-Reporttt-4

Power Transformer Faults Analysis by FRA
Measurements in Electrical Power System
By
Waqar Ahmed
CIIT/SP14-MS (EE)-003/WAH
MS Thesis
In
Electrical Engineering
COMSATS Institute of Information Technology
WAH Cant – Pakistan
Fall 2015
1
Power Transformer Faults Analysis by FRA
Measurements in Electrical Power System
A Thesis Presented to
COMSATS Institute of Information Technology, Wah Cant
In partial fulfilment
Of the requirement for the degree of
MS (Electrical Engineering)
By
Waqar Ahmed
CIIT/SP14-MS (EE)-003/WAH
FALL 2015
2
Power Transformer Faults Analysis by FRA
Measurements in Electrical Power System
A Post Graduate Thesis submitted to the name of Department of Electrical Engineering
as partial fulfilment of the requirement for the award of Degree of MS (Electrical
Engineering).
NAME
REGISTRATION #
Waqar Ahmed
CIIT/SP14-MS (EE)-003/WAH
Supervisor
________________________
Prof. Engr. Dr. Muhammad Amin
HoD, Department of Electrical Engineering
Wah Campus
COMSATS Institute of Information Technology (CIIT)
Wah Cant
MAY 2015
3
Final Approval
This thesis titled
Power Transformer Faults Analysis by FRA
Measurements in Electrical Power System
By
Irfa Nisar
CIIT/SP14-MS (EE)-017/WAH
Has been approved
For the COMSATS Institute of Information Technology, Wah Cant
External Examiner: __________________________________________
Supervisor: ________________________________________________
Prof. Engr. Dr. Muhammad Amin
Electrical Engineering/Wah Campus
HoD: _____________________________________________________
Prof. Engr. Dr. Muhammad Amin
4
HoD (Electrical Engineering/Wah Campus)
Certificate of Originality
Date: _____________
I, Mr. Waqar Ahmed, Registration no. CIIT/SP14-MS(EE)-017 /WAH, student of MS(EE) class,
hereby declare that the material printed in my thesis titled “Power Transformer Faults Analysis
by FRA Measurements in Electrical Power System” is my own original work and has neither
been submitted, printed or published as research work, thesis, book or publication by another
person, in any form, in any University, Research Organization, Journal etc., in Pakistan or
abroad, nor a substantial part of this material has been accepted for the award of any degree at
CIIT or any other educational institution.
I further declare that the originality of contents through plagiarism software has also been
verified.
Student’s Name: Waqar Ahmed
Registration # CIIT/SP14-MS (EE)-017/WAH
Signature: _________________________
---------------------------------------------------------------------------------------------------------------Certified that the originality of the contents of above mentioned research thesis is verified
through plagiarism software and found similarities within acceptable range.
Supervisor Name: Prof. Dr. Muhammad Amin
Signature: _____________________
H.O.D Name: Prof. Dr. Muhammad Amin
Signature: ______________________
5
Date: _________________________
Date: __________________________
Declaration
I Irfa Nisar, registration # CIIT/SP14-MS (EE)-017/WAH hereby declare that I have produced
the work presented in this thesis, during the scheduled period of study. I also declare that I have
not taken any material from any source except referred to wherever due that amount of
plagiarism is within acceptable range. If a violation of HEC rules on research has occurred in this
thesis, I shall be liable to punishable action under the plagiarism rules of the HEC.
Date: ______________
Signature of the Student: _________________________
Waqar Ahmed
CIIT/SP14-MS (EE)-003/WAH
6
Certificate
It is certified that Waqar Ahmed, registration # CIIT/SP14-MS(EE)-003/WAH has carried out all
the work related to this thesis under my supervision at the Department of Electrical Engineering,
COMSATS Institute of Information Technology, Wah Cant and the work fulfils the requirement
for award of MS degree.
Date: __________________
Supervisor: ________________________________
Prof. Engr. Dr. Muhammad Amin
HoD Electrical Engineering Department
Head of Department:
______________________
Prof. Engr. Dr. Muhammad Amin
Electrical Engineering Department
7
DEDICATION
To my
Parents, Supervisors, Co. supervisors
Who always guided me
8
Acknowledgement
I would like to thank Comsats Institute of Information and Technology Wah Cant. Special thanks
to the following people for the generous support and contribution they have made to write this
thesis. For meticulously reviewing the text and offering good suggestions.
9
Waqar Ahmed (CIIT/SP14-MS (EE)-003/WAH)
ABSTRACT
Power Transformer Faults Analysis by FRA
Measurements in Electrical Power System
To safe people and belongings from harm or wound, electric defects in a power grid as in
electrical equipment such as Power Transformer must be absolved rapidly. In past days of power
systems the defects clarification was done by the service staff, which optically diagnose the
faults and by hand monitored a transformer to remove the faults up to some extent. As come out
faults became more and the working demands of the electric power grid became more rigorous,
the demand for automatic fault sanction became an essential. The Power Transformer is one of
the highly cost and significant electrical equipment of a Power Transmission System; the loss of
transformer failure can be very costly. To avoid these failures, different techniques, methods for
protecting and monitoring are being processed. These losses also cost money and this money
always are charged to the consumer. A power grid station is consisted of three main sections as
power transmission, power distribution as well as power generation plants. It also includes
transmission cables, distribution system, and substations. The Power Transformer is high cost
and essential electrical instrument of a Power Transmission Section. As it is essential elements in
electrical power, as it has capability to variant voltage as well as current states, which is able
transformers to produce power in electric system, to transfer and disseminate electric power and
employ power at an efficient and desirable states. It is that part of electrical instrument which
required uninterrupted check out and fast monitoring, as it is very costly and basic element of
power system to perform efficiently.
To avoid this, different methods, techniques and systems for monitoring and protecting of Power
Transformers in service are being developed. By the condition required for knowing about the
ability of the detection system, different manipulators are fitted with better data providing during
10
their conclusion process. Restorative processes are chosen antecedent to transformer failures to
avoid fall-time and control functioning and monitoring cost. The eventual goal of this research is
Power Transformer Faults Analysis by FRA Measurements in Electrical Power System for
incipient faults diagnosing method that is able to analyze internal defects in transformers. The
complete model and the graphs that are showing the disturbance in the required system are
simulated in the MATLAB. This research presents a transfer function for transformer faults
analysis and simulations to differentiate internal faults data and study its properties.
11
Table of contents
1 Introduction ...................................................................................... 18
1.1
Statement of problem ............................................................................................................................. 19
1.2
Objective of Research work ................................................................................................................... 20
1.3
Organization of thesis ............................................................................................................................ 21
2 Literature Review ............................................................................ 24
2.2
Research Methodology........................................................................................................................... 26
2.2.1 Theoretical Studies .....................................................................................................................................26
2.2.2 Experimental Set Up ..................................................................................................................................26
2.2.3 Method of Analysis ....................................................................................................................................27
2.3
Study of Electrical Power system .......................................................................................................... 27
2.4
Power transformer Assessment Review................................................................................................. 28
2.4.1 Out comings of Power System ...................................................................................................................30
2.4.2 High cost of repairing & controlling ..........................................................................................................31
2.4.3 Development of Electricity Need ...............................................................................................................31
2.5
Power Transformer Faults .................................................................................................................... 32
2.6
Types of Transformer faults .................................................................................................................. 34
2.6.1 Transformer External faults .......................................................................................................................34
2.6.2 Transformer Internal Faults ........................................................................................................................35
3.1
Introduction ........................................................................................................................................... 39
3.2
Power transformer Fault Analysis Techniques ..................................................................................... 39
3.2.1 FRA vs. Typical Dissolved Gas Analysis (DGA) ......................................................................................40
3.2.2 FRA vs. Typical Faults Analysis by using Swarm Optimization (SVM) ...................................................41
3.2.3 Transformer Fault Detection by Bayesian Network and RSR theory ........................................................41
3.2.4 A Novel Algorithm to diagnose Incipient Transformer Faults ...................................................................41
3.2.5 Multi-Kernel Support Vector classifier for Fault Analysis of Transformers..............................................42
3.2.6 Mathematical equivalence techniques to measure transfer functions of transformers ...............................42
3.2.7 Propagation characteristics of UHF partial discharge in power transformers ............................................42
3.2.8 Extreme frequency technique based on FRA .............................................................................................43
3.2.9 Propagation characteristics of UHF partial discharge using FDTD ...........................................................43
12
3.3
Frequency Response Analysis ................................................................................................................ 43
3.3.1 Impulse Frequency Response .....................................................................................................................46
3.3.2 Frequency Sweep technique .......................................................................................................................46
3.4
Transfer function ................................................................................................................................... 46
4.1
Design Objectives ................................................................................................................................... 49
4.2
Proposed Work ...................................................................................................................................... 49
4.2.1 Proposed Work System Diagram ...............................................................................................................50
4.2.2 Description of Proposed Work ...................................................................................................................51
4.2.3 Block Diagram of Proposed work ..............................................................................................................51
4.2.4 Description of proposed work ....................................................................................................................52
4.2.5 Electric circuit components ........................................................................................................................53
5.1
Frequency 60HZ .................................................................................................................................... 57
5.2
FREQUENCY 50HZ.............................................................................................................................. 60
5.3
FREQUENCY 55 HZ............................................................................................................................. 63
6.1
Conclusion .............................................................................................................................................. 67
7.1
References .............................................................................................................................................. 69
13
List of figures
Figure 1: Power generation and transmission plant .................................................................................... 25
Figure 2: Power Transformer ...................................................................................................................... 29
Figure 3: Conceptual failure model of transformer..................................................................................... 30
Figure 4: Fault Distribution of power transformer ...................................................................................... 31
Figure 5: Power transformer age classifications ......................................................................................... 33
Figure 6: RLC Simulink Simple model ...................................................................................................... 45
Figure 7: Proposed System Diagram .......................................................................................................... 50
Figure 8: Block diagram of proposed work ................................................................................................ 51
Figure 9: Results at Bus 1 (60Hz) ............................................................................................................... 57
Figure 10: Results at Bus 2 (60Hz) ............................................................................................................. 58
Figure 11: Results at Bus 3 (60Hz) ............................................................................................................. 59
Figure 12: Results at Bus 1 (50Hz) ............................................................................................................. 60
Figure 13: Results at Bus 2 (50Hz) ............................................................................................................. 61
Figure 14: Results at Bus 3 (50Hz) ............................................................................................................. 62
Figure 15: Results at Bus 1 (55Hz) ............................................................................................................. 63
Figure 16: Results at Bus 2 (55Hz) ............................................................................................................. 64
Figure 17:Results at Bus 3 (55Hz) .............................................................................................................. 65
14
List of tables
Table 1: Primary reasons of transformer losses .......................................................................................... 36
Table 2: Severity characteristics of Power transformer .............................................................................. 37
15
List of Equations
Eq 1:
Eq 2:
Eq 3:
Eq 4:
Eq 5:
Eq 6:
Eq 7:
V = 4.44Φ. f.T ...................................................................................................................... 35
V ∝ Φ.f ................................................................................................................................. 35
Φ ∝ V/f ................................................................................................................................. 35
H(ω) = V2(ω)/V1 (ω) ........................................................................................................... 47
TF1 = R (ω) ⁄ V (ω) .............................................................................................................. 47
TF2 = R (ω) ⁄ I (ω) ................................................................................................................ 47
TF3 = I (ω) ⁄ V (ω) ................................................................................................................ 47
16
Chapter 1
Introduction
17
1
Introduction
To safe people and belongings from harm, electric defects in a power grid as in electrical
equipment such as Power Transformer must be cleared rapidly. In past days of power systems
the defects clarification was done by the service staff, which optically diagnose the faults and by
hand monitored a transformer to remove the faults up to some extent [1]. As come out faults
became more and the working demands of the electric power grid became more rigorous, the
demand for automatic fault sanction became an essential. The Power Transformer is one of the
highly cost and significant electrical equipment of a Power Transmission System; the loss of
transformer failure can be very costly [2]. To avoid these failures, different techniques, methods
for protecting and monitoring are being processed. These losses also cost money and this money
always are charged to the consumer [3].
So the main objective of this work is to analyses the transformer faults in the electrical system by
the compensation of the insulation failures between windings and ground terminal, breakdown
between different phases, breakdown occur in between contact turns and transformer core faults
[1]. Since many operational cases of transformer failures are caused by input current
problems and thus, the rapid distortion of inflow current from incipient fault is more
necessary to avoid. Therefore, measures must be taken to ensure that the Power transformer
operates precisely to differentiate between fault and non-fault conditions to ensure service
reliability [3]. Many techniques are applied to compensate and to control the transformer faults
by using different protection devices. This research emphasizes on the compensation of the
incipient faults to overcome the breakdown in the system. For compensation of the Power
Transformer faults different POWER TRANSFORMER MODELING techniques are used like
DGA, DPA, PDA and FRA [4]. By using these techniques the power transformer faults can be
analyze and improves as well as insulation between windings and core loss can be compensate
according to the situation [3].
Now a day’s many different methods are used to reduce and control transformer internal faults.
Major fault diagnostic and detection techniques includes such as dissolved gas analysis (DGA),
Degree of polymerization (DPA), partial discharge analysis (PDA), frequency response
analysis(FRA), and transformer function measurement use different parameters.
18
In this work FRA technique is used to analyses the incipient faults that occurred in Power
Transformers by developing model in Matlab Simulink. In FRA technique, power transformer
can be made up of composite network of resistance, capacitances and inductances [5]. All
modelling results executed for 132/11 kV, 40MVA power transformer that specifically
established on data provided for this design [6]. Any change in values of capacitances,
resistances and inductances will lead noticeable variations in frequency behaviour of
transformer.
Although various techniques are used in literature to analyze the incipient faults problem but it
still motivates the researchers to develop the new methodologies or improve the existing ones to
reduce the winding losses in the power transformer by the compensation of the insulation
windings and earth, different phases, breakdown occur in between adjacent turns and transformer
core faults [5].
1.1 Statement of problem
The incipient faults reduction in the power transformer is of the great importance because of
their economic, financial demands to the consumer and the company. To reduce incipient
faults the in the electrical power system, the windings and transformer core loss power must be
controlled or compensated internal losses will increase if the winding and core loss is not to be
controlled.
In this work FRA technique is used to analyses the incipient faults that occurred in power
Transformers by developing model in Matlab Simulink and compensate the insulation windings
and earth, different phases, breakdown occur in between adjacent turns and transformer core
faults. This reduction in the internal faults helps to improve the power system and also reduce the
electricity crises that have to face by overall world.
In this research work our main attention is reduce and analyses the internal faults that mostly
occurred in transformer. Under strains from high powered, current go around conductor pass
through insulators as slowly degenerate of insulation procedures, hence, short circuit was
19
occurred and power transformer break down. When an internal fault presents, irregularities in
potential, electric flow and different electrical arguments will analyzed. Therefore, features that
specifically modify unnatural response in transformers could identify by FRA method and
proposed a transfer function that predicts a method of analyzing incipient faults.
So to analyze the incipient faults that occurred in Power Transformer by designing the model by
using MATLAB SIMULINK software and using FRA measurements for analyzing and
reducing incipient faults by implementing FRA technique in proposed model.
1.2 Objective of Research work
The main objective of this thesis is to analyze reliability of power transformer faults by
Frequency Response Analysis (FRA). This thesis demonstrates application of frequency
response analysis technique to power transformer assessment. The reliability assessment of
power transformer assessment resulted qualitative and quantitative frequency response analysis.
This research work focus on analysis of internal faults that occurred in power transformer in
electrical power system by analyzing different fault analysis techniques. So this research works
using FRA technique in proposed model to detect internal faults in power transformer. So to
analyze the internal faults that occurred in Transformer by designing the model by using
MATLAB SIMULINK software and using FRA measurements for analyzing and reducing
internal faults.
The qualitative analysis of the faults analysis results sets and describe qualitative importance.
The qualitative results help in focusing attention on main apparatus of power transformer that
contributed to the unreliability of the system.
20
1.3 Organization of thesis
The thesis research work is arranged in following pattern:
Chapter 1: This chapter defines introduction, the objectives of this project, statement of problem
and its importance.
Chapter 2: It describes some literatures reviews on previous works in the field of study, the
research methodology, a brief review of the electrical power system, review of power
transformer, study of power transformer faults analysis, description of fault analysis techniques,
details of transformer faults, its area of transformer failures, transformer applications. Also
describes the monitoring and controlling techniques of transformers which have been proposed
in recent years.
Chapter 3: This chapter shows the process of developing and constructing the model of fault
analysis of power transformer system based on FRA. The causes were identified as the event
causing every possible fault by developing a fault analysis model. Furthermore in this chapter we
conduct the qualitative faults analysis of power transformer. Fault response analysis (FRA) of the
power transformer was performed to investigate the causes for the fault in power transformer
operation. By qualitative analysis of the FRA, we found the irregularities of power transformer
system.
Chapter4: present simulations were performed using the Matlab/Simulink software, and the
simulation results were recorded and described. First step is to analyze which type of fault that
occurred in transformer, whether the fault occurred in winding in power transformer by the
compensation of the insulation windings and earth, different phases, breakdown occur in
between adjacent turns and transformer core faults. To obtain calculated results, the faults are
computed using standard frequency responses. The results for these various responses are then
brought together using techniques employed for “generalized frequency responses analysis” to
perform calculations. This result will help the decision making in order to betterment of power
transformer system.
Chapter 5: It presents measuring faults detection values of power transformer system
components. In this research, I had presented applications and results of the importance measures
21
analysis of a power transformer system, by using frequency responses measures and comparing
results with standards of frequency required. In this chapter, all the simulations results have been
simulated by different values of frequency responses. I had also simulated results, by taking
different values of current and voltages at three busses in electrical system.
Chapter 6: This chapter had presented a summary of the research carried out in this thesis and
concluded the results and giving idea for some useful future research issues.
Chapter 7: In chapter 7, I had concluded references and sources from where the material has
been cited over it.
22
Chapter 2
Power transformer Evaluation
23
2
Literature Review
A power grid station is consists of three main sections as power transmission, power distribution
as well as power generation plants. It also includes transmission cables, distribution system, and
substations [2]]. The Power Transformer is high cost and essential electrical instrument of a
Power Transmission Section. As it is essential elements in electrical power, as it has capability to
alter voltages as well as current values, which is able the transformers to produce power in
system, to transfer, disseminate electric power and enforced power at an efficient and desirable
states [4]. It is that part of electrical instrument which required uninterrupted check out and fast
monitoring, as it is very costly and basic element of power system to perform efficiently [5]. To
avoid this, different methods, techniques and systems for monitoring and protecting of Power
Transformers in service are being developed. By the condition required for knowing about the
ability of the detection system, different manipulators are fitted with better data providing during
their conclusion process [7]. Restorative processes are chosen antecedent to transformer failures
to avoid fall-time and control functioning and monitoring cost.
An advanced electric system is very huge and composite network consists of generators,
transformers, transmission lines, distribution lines, and other devices [8]. The purpose of the
electric power system is to make, supplying, transmit electric power. This power system is also
known as the grid station and can be classified into the generators that provide the energy,
mostly electricity production comes from coal, natural gas, biomass, nuclear fission, wind, solar,
and hydraulic plant [4].
The transmission system that contain the energy from the generating plant to the load centre,
and the distribution system that carries the power to nearby homes and industries, such system as
those shown in Figure 2.1.
The Power Transformer is one of the highly cost and significant electrical equipment of a Power
Transmission System; the loss of transformer failure can be very costly. To avoid these failures,
different techniques, methods for protecting and monitoring are being processed [5]. These
losses also cost money and this money always are charged to the consumer.
24
The transformer set up at power stations or substation should be work fault free over a retentive
period of time. Transformers depend on a number of elements to produce required voltage and
current [9]. The primarily function of the power transformer is to cut down the transmission cost
in electrical power system. It cut down the transmission limitations by reducing the required
current for transmission. The cost step down is carried by increasing the transmission voltage in
the system. For long transmission lines, very high voltages up to 800 kV are used while for
average transmission 500 and 450 kV is carried out [11]. To fulfil the requirement of voltages
and power, power transformers are demanded from generation to clients. The voltage adjusted is
done by step up or step down transformers. Step up transformer increases the voltage on
secondary side while step down transformer decreases the voltage on the secondary winding side
of transformer [10].
Figure 1: Power generation and transmission plant
Power transformers are mostly very certain, with a 25-30 years designing period [8]. In
performance period of transformer could be as more as 40-70 years with continuous monitoring.
25
Therefore, the in-services failures of a transformer is actually risky to inferior by bursts and fire,
greatly damaging to surrounding through oil outflow, expensive to amend or repair, and results
in significance failures [11].
As power transformer period, which added the chances of losses? Losses are mostly set off by
severe states, such as lighting strikes, switching transients, short circuits, or other disturbance.
When the transformer is new, it is necessary electrical and mechanical power to stand with
uncertain system states [12].
2.2 Research Methodology
Methodology of research thesis can be divided into following different sections.
2.2.1 Theoretical Studies
Theoretical studies generally pay attention on clear and complete understanding of the object and
the problem. Various heuristic techniques developed in past few years for analyzing and solving
the faults and the reduction of losses in power transformer. The back off of these techniques will
also be studied in the theoretical studies.
2.2.2 Experimental Set Up
In the experimental set up, FRA technique is used to compensate the emerging faults of the
Power Transformer and by compensation of internal faults than transformer condition will
improved and the breakdown loss will be reduced from the power system of the our required
need of electricity. The whole experimental work will be done on the MATLAB.
26
2.2.3 Method of Analysis
The requirement of the proposed research is that by using the FRA technique, to reduce the
breakdown losses in the power transformer by the compensation of the insulation windings and
earth, different phases, breakdown occur in between adjacent turns and transformer core losses
and then we analyses the results without FRA that how much improvement in the breakdown
loss reduction appears. The results of the power transformer of our requirement with and the
without FRA will be shown as the graphical representation in the MATLAB and then will
propose a transfer function of incipient faults analysis of our demand.
2.3 Study of Electrical Power system
A power grid station is consisted of three main sections as power transmission, power
distribution as well as power generation plants. It also includes transmission cables, distribution
system, and substations [6]. An advanced electric system is very huge and composite network
consists of generators, transformers, transmission lines, distribution lines, and other devices. The
purpose of the electric power system is to make, supplying, transmit electric power. This power
system is also known as the grid station and can be classified into the generators that provide the
energy, mostly electricity production comes from coal, natural gas, biomass, nuclear fission,
wind, solar, and hydraulic plant [12].
Electric power is generated, transmitted and distributed in course of AC current. Since the
electric power is obtained at grid stations which are installed generally away from consumers
areas, it can only be deported to them by a wide transmission lines [11]. At many points in the
line of the power system, it may be required to change some features (e.g voltage, a.c to d.c,
frequency, power factor etc.) of electric power system. This can be done by suitable equipment
called Sub-station [9]. For example, a Power Transmission sub-station, generation voltage
(132kV) is stepped down to a low voltage (33kV) for transmission of electric power. The
assembly of equipment like transformer used for this purpose is grid station. It will be variant
voltage states of electric power supply [10]. The power transformer is essential component
employed to change the voltage level according to the needs of proposed model.
27
2.4 Power transformer Assessment Review
Power transformer is one of vital electricity component in electrical power. It brings a vital role
both in transferring and disseminating system by transmitting the electricity potential, from one
potential level to another, under magnetic induction [14]. When a failure happened on a
transformer, it means that the electricity supply could not be done to clients.
Power Transformer is high cost and essential electrical instrument of a Power Transmission
Section. As it is essential elements in electrical power, as it has capability to variant voltages as
well as current values, which is able, the transformers to produce electricity, to transfer,
disseminate electric power and enforced power at efficient and desirable states [11]. It is that part
of electrical instrument which required uninterrupted check out and fast monitoring, as it is very
costly and basic element of power system to perform efficiently [14].
The Power Transformer is one of the highly cost and significant electrical equipment of a Power
Transmission System; the loss of transformer failure can be very costly. To avoid these failures,
different techniques, methods for protecting and monitoring are being processed. These losses
also cost money and this money always are charged to the consumer [13].
Power transformers are mostly very certain, with a 25-30 years designing period [8]. In
performance period of transformer could be as more as 40-70 years with continuous monitoring.
Therefore, the in-services failures of a transformer is actually risky to inferior by bursts and fire,
greatly damaging to surrounding through oil outflow, expensive to amend or repair, and results
in significance failures [11].
28
Figure 2: Power Transformer
The necessity equipment which defines the ideal transformer counts to wide limit, with the
features of core windings loss [19]. The characteristics which are very important in transformer
core material are permeability, saturation, resistivity and hysteresis loss. It is usually assumed
that, the core that most important method in transformer pattern building has been done [20]. The
building of a power transformer changes by the manufactures. The basic need is requires the
same and that has been change in past years. The main components of the power transformer are
the core, winding, insulation and tank.
As power transformer period, which added the chances of losses? Losses are mostly set off by
severe states, such as lighting strikes, switching transients, short circuits, or other disturbance.
When the transformer is new, it is necessary electrical and mechanical power to stand with
uncertain system states [12].
Transformer losses could have important profitable affect due to high span of times in supplies,
constructing, and instalment in adding to more component failures [7]. By the estimation of
Electric Power Research Institute (EPRI), improving the period of power transformer is almost
considered scheme of improving period of power transmission system and distribution [15].
29
This scheme begins with generator, transformers at the power station.
Insulation strength
Reducing strength with
time & after incidents
Insulation
spare margin
Insulation
stress
Failure
Incidents
New
Increasing age
Old
Figure 3: Conceptual failure model of transformer
Power transformer states requirement in power systems are as following:
2.4.1 Out comings of Power System
The out comings of power transformer may affect power system stability. It is tedious to
instantly evaluate the effect of break down for stability of grid station. For example, the failures
of a generator step-up transformer is usually more difficult than loss occur in transformer of
transmission side and the breakdown of transformer with high loading is much affecting than less
[10]. Safe operation of power transformers is also necessary due to uncertain losses and
30
breakdown can cause in a big accident and get increasing high values in output price, especially
in ever-growing surrounding.
2.4.2 High cost of repairing & controlling
In Electrical power system, transformers are the main components. When the faults occur or may
go wrong. Then it should be amend or even repair. The life period of power transformer is high
in order to avoid substitute. This is due to raise the attempt for amends and repairs the
transformer condition. In order to prevent, the repairing cost need to be reduced to degree where
a high powered transformer can be on working condition [17].
2.4.3 Development of Electricity Need
The electricity growth is increased to twice in 2010-2040 at yearly developing rate of 3.5 %
every year. Electricity growth need has the highest fashioned in advanced countries, the needs
grows by 5% per year over the ongoing period [11]. Accordingly, new requirement of power
system, specifically transformer should be developed. Likewise, more loads of power
transformers will be needed. The load rate and the high power transaction speed up the power
transformers physical conditions as a result of raising the operating tension [13].
20%
21%
tank/fluid
terminal
4%
magnetic circuit
22%
windings
accessories
33%
Figure 4: Fault Distribution of power transformer
31
2.5 Power Transformer Faults
In the life period of power transformer, the transformer has been integrating the effect of
thermal, mechanical, chemical, electrical and electromagnetic faults during normal pattern and
stable states. A fault may happen when any functional faults pass its power of the above
mentioned parameters. In addition, fault procedures in power transformers are mostly difficult
and so practice between producers, services, academics session is required to realize then [7].
Nowadays, power transformers are usually very suitable with expected utilities period of 30
years or more because of advancement in manufacturing and monitoring [17]. Also the design
parameter of system and the operation condition are alter, the condition of power transformer for
the equal type apparatus are also different. In such circumstance it is very tedious to found the
fault system for all circumstances of the power transformer system.
A practicable way of transformer’s failure could be described in Figure2.4, as define by CIGRE
Work Group [21]. Typically transformer functional loss mechanisms are illustrated by the
CIGRE Work Group [23]. Utilities describes thus bring out most power transformer losses are
not due to destruction, but also because of damage or getting on due to some failures in
manufacturing and construction design, utilities and maintenance. Sometimes a power
transformer failed without giving warning message [17]. However, the indication of proposing
fault and losses can be analyzed, precluded or removed.
Operational losses are usually prevailed with isolated effects such as lightning strikes or short
circuits. The changing failures over the period of a transformer, taking the mechanical losses
enforced on a winding [19]. When the transformer is fresh, the windings will be adjusted to
reduce the failures of electromagnetic power in short circuits. As the transformer insulation
becoming old, the paper insulation will contract and may cause in minimizing of clamping
pressure, hence minimizing the mechanical power [20].
Because of the automatic behaviour of operational faults it is different that it will be possible to
analyze when fault will occur. However, if operational power and operational losses could be
analyzed enough, it may be possible to find the circumstances by which the fault is to be
occurred [21].
32
An important task in managing transformer services period would be increased and maintaining
the assessment of required strengths and operational stresses would be minimized to some extent
[24].
11%
21%
0-9years
10-19years
14%
20-29years
30-39years
18%
Figure 5: Power transformer age classifications
The working of power transformer depends on insulator and cooling system, because these two
schemes are closely associated, the quantity of heat, in the core and winding carriers find out the
performance and duration of insulated windings and insulator [19]. The most important
properties that proposed the operating period of insulator, oil/paper insulation are chemical
purity, thermal stability, mechanical design and insulator power [21]. Faults in transformer may
or may not be potential to repair condition by simple curative action.
33
2.6 Types of Transformer faults
There are two main types of faults

Transformer External faults

Transformer Internal faults
2.6.1 Transformer External faults
There are three external faults in power transformer as listed below:

External Short - Circuit

High Voltage Disturbance

Under Frequency Effect
2.6.1.1 External Short - Circuit
The short-circuit may occur in two or three phases of electrical system. It depends on the voltage
values, which has been short circuited by the impedance value at point of fault. Copper loss of
the fault in transformer is unexpectedly high [23]. Thus, increasing copper loss may causes
excess internal heating in transformer? High fault current produces severe mechanical stresses in
the transformer [24]. The maximum mechanical faults occur during first cycle of same fault
current.
2.6.1.2 High Voltage Disturbance
High Voltage Disturbance is of two states as follows;

Transient Surge Voltage

Power Frequency Over Voltage
34
1. Transient Surge Voltage
High voltage and high frequency surge may occur in power system due to any of reasons;
(a) Arcing ground if neutral point is isolated.
(b) Switching operation of different electrical component
(c) Atmospheric Lightening Impulse
2. Power Frequency Over Voltage
There is always a chance of system in over voltage due to unexpected disconnection of high
load. Over voltage causes an increase in stress on the insulation of transformer. Increased in
voltages values may increase appropriate rate of flux. This is due to, increased in iron loss and is
appropriate large increase in magnetizing current [20].
2.6.1.3 Under Frequency Effect
As the given equation describes, number of turns in the winding is fixed
Eq 1:
V = 4.44Φ. f.T
Eq 2:
V ∝ Φ.f
Eq 3:
Φ ∝ V/f
So,
From, equation it is shows that if frequency decreases in system, then rate of flux in the core
increases, this criteria is similar to over voltage.
2.6.2 Transformer Internal Faults
The fault current is dependent on the value of earthen impedance and is also proportional to
the distance of the fault point from neutral point [19].The value of fault current depends on
the value of earthen impedance as well as the distance between the faulty point and neutral
point [20]. The fault current also depends up on leakage reactance of the portion of the
winding across the fault point and neutral.
35
The internal faults can be categorized as follows

Insulation breakdown between winding and earth

Insulation breakdown in between different phases

Insulation breakdown in between adjacent turns

Transformer core fault
2.6.2.1 Insulation breakdown in between different phases
Phase to phase failures in the transformer are very uncommon. These faults occur, and it will
give increase in significant value of current to operate instantaneous over current relay on the
primary side and the differential relay [23].
Table 1: Primary reasons of transformer losses
Sr.No
Transformer Failures Causes
1983
1996
2008
1
Surges Protection
31.3%
30.1%
12.8%
2
External short circuits
13.7%
19.8%
23.2%
3
Poor Manufacturer
11.6%
6.7%
2.3%
4
Deterioration of insulations
11.4%
8.4%
13.8%
5
Overloading
7.9%
3.4%
2.9%
6
Humidity
8.1%
7.4%
4.2%
7
Inadequate maintenance
6.4%
13.1%
12.01%
8
Shortage, Malicious, Mischief
3%
2.0%
1.5%
9
Loose Connections
2.5%
1.9%
5.8%
10
All Others
7.3%
7.9%
21.6%
36
2.6.2.2 Insulation breakdown in between adjacent turns
Power Transformer connected with electrical high voltage transmission system, is very likely to
be subjected to high magnitude [14].The voltage variations between insulation winding become
so high, it cannot attain the stress and causing insulation loss between internal turns of primary
and secondary windings of transformer. Very large number of Power Transformer losses comes
up from fault between turns. Internal adjacent turn losses may also be raised due to mechanical
forces between turns arises by external short circuit [17].
Table 2: Severity characteristics of Power transformer
Sr.No Transformer Conditions
Statements
1.
Minor
2.
Marginal
Primary function could be done but necessary repair
required
Reduction in Primary function
3.
Critical
Causes in reduction of Primary Function
4.
Catastrophic
Product becomes incompatible
2.6.2.3 Transformer core fault
Sometimes, insulation of bolts fails which also allows eddy current to flow through the bolt and
causing overheating [19]. Insulation failure in lamination and core bolts causes severe local
heating, which causes more core loss but cannot produce any measureable variations in input and
output current in the transformer [21]. Excessive over heating can head to failures of transformer
insulating oil with ejection of gases.
37
Chapter 3
Frequency Response Analysis &
Transfer Function
38
3.1 Introduction
Power transformer is one of vital electrical component in electrical system. It brings a vital role
both in transferring, disseminating system by transmitting the electricity potential, from one
potential level to another, under magnetic induction [9]. When loss occurred in a transformer, the
electricity supply could not be done to clients.
The Power Transformer is high cost and essential electrical instrument of a Power
Transmission Section. As it is essential elements in electrical power, as it has capability to alter
voltage as well as current values, which capable the transformers to produce electric power, to
transfer and disseminate electric power and employ power at an efficient and desirable states
[10]. It is that part of electrical instrument which required uninterrupted check out and fast
monitoring, as it is very costly and basic element of power system to perform efficiently [11].
The Power Transformer is one of the highly cost and significant electrical equipment of a Power
Transmission System; the loss of transformer failure can be very costly. To avoid these failures,
different techniques, methods for protecting and monitoring are being processed. These losses
also cost money and this money always are charged to the consumer [12].
The building of a power transformer changes by the manufactures. The basic need is requires the
same and that has been change in past years. The main components of the power transformer are
the core, winding, insulation and tank [14].
As power transformer period, which added the chances of losses? Losses are mostly set off by
severe states, such as lighting strikes, switching transients, short circuits, or other disturbance.
When the transformer is new, it is necessary electrical and mechanical power to stand with
uncertain system states [12].
3.2 Power transformer Fault Analysis Techniques
As come out faults became more and the working demands of the electric power grid became
more rigorous, the demand for automatic fault became an essential. The Power Transformer is
39
one of the highly cost and significant electrical equipment of a Power Transmission System; the
loss of transformer failure can be very costly [5]. To avoid these failures, different techniques,
methods for protecting and monitoring are being processed. These losses also cost money and
this money always are charged to the consumer [7].
So the main objective of this work is to analyses the transformer faults in the electrical system by
the compensation of the insulation breakdown between windings and earth, breakdown between
different phases, breakdown occur in between adjacent turns and transformer core faults. Since
many operational cases of transformer failures are caused by inrush current problems and
thus, the rapid distortion of inflow current from incipient fault is more necessary to avoid
[11]. Therefore, measures must be taken to ensure that the Power transformer operates precisely
to differentiate between fault and non-fault conditions to ensure service reliability. Many
techniques are applied to compensate and to control the transformer faults by using different
protection devices [12].
Now a day’s many different methods are used to reduce and control transformer internal faults.
Major fault diagnostic and detection techniques includes such as dissolved gas analysis(DGA),
degree of polymerization(DPA), partial discharge analysis(PDA), frequency response
analysis(FRA), and transformer function measurement use different parameters.
3.2.1 FRA vs. Typical Dissolved Gas Analysis (DGA)
In [1] the author used to describe DGA technique in order to analyze the internal fault detection
of Power Transformer by using wavelet network. WNs are very effective system for faults
detecting process proposed in present year. It also represents different analysis of WN
measurements for diagnosing of internal faults [2]. It equates and analyzes the network
procedures and simulating results of five WNs. According to this, the feed forward WN, this is
used for fault detection in power transformer. In this research paper, DGA is such kind of
optimization technique that has been used to modify WN [7]. The comparative analysis shows
that WN output power mostly depending upon on the energizing function for suitable levels
which measures in the capability of 85%–90% [3].
.
40
3.2.2 FRA vs. Typical Faults Analysis by using Swarm Optimization (SVM)
In [2] the author described different states of Power Transformer which is used particle Swarm
Optimization by using SVM. The requirements of SVM have different modifications on the
classified results [5]. The system is established on oil DGA technique; the executing levels of
transformer are classified into very good, better, best as considered fault states. As to classify
PSO algorithm rules to modify SVM categorizer could improve the conditions judgment
accuracy of transformer [2]. In this research, convergence factors, changing inertia and adaptive
variation particle of these methods are presented to improve the transformer faults analysis
algorithm.
3.2.3 Transformer Fault Detection by Bayesian Network and RSR theory
In [3] research, the author describes Transformer Fault Detection by using Bayesian Network
and RSR theory. Bayesian network’s has ability of handling with uncertain faults problems could
have finite solution to the undependable results ensure by transformer fault detection [21]. RSR
theory was used for reducing step down of BN classification system, which efficiently reduced
the difficulty of network complexity, also decreased i/p of system and improve for actual
analysis [19]. RSR is an efficient instrument to control incoherent and uncertain arising
problems. This paper focused on the application of artificial intelligence algorithm for
transformer fault detection, by combined BNC and RSR theory, and found a new algorithm
pattern for transformer fault detection [3].
3.2.4 A Novel Algorithm to diagnose Incipient Transformer Faults
In [4] the author used Novel Algorithm to diagnose Incipient Transformer Faults. In this research
work, a simple but efficient method is ensuring to analyze the internal faults in power
transformer [14]. It manipulates i/p voltage, o/p potential and i/p electric flow at the power
frequency and therefore current changing values can be calculated [16]. The set of algorithm is
41
used to differentiate mechanical transformer faults [17]. This research work represents an easy
and effective method to diagnose mechanical defects in power transformer.
3.2.5 Multi-Kernel Support Vector classifier for Fault Analysis of Transformers
In [5] author described Multi-Kernel Support Vector classifier for Fault Analysis of
Transformers. This research work includes method named as (MKSVC), to examine DGA
technique for fault detection of transformer [17]. MKSVC gives an idea to manipulate kernel
classifications by one dimensional collection of different kernels [23]. The MKSVC technique is
measured by using 315 fault data in comparing with different used systems. DGA is most famous
technique for diagnosing internal faults of transformers recently [18].
3.2.6 Mathematical equivalence techniques to measure transfer functions of transformers
In [6] the author used mathematical equivalence techniques to measure transfer functions of
transformers to find out different types of mechanical faults. The most commonly mechanical
defects that are mostly find out by using the TF and happen many times, are disc-space changes,
radial distortion and rotator shift [7]. A fault detection which includes fault type, position and
states of faults by using TF case study[15]. The TF technique is relative technique and evaluate
simulations should be analyzed with determine simulation results [16].
3.2.7 Propagation characteristics of UHF partial discharge in power transformers
In [7] the author describes the propagation characteristics of UHF partial discharge in power
transformers with complex winding structure. The detection of (UHF) Electromagnetic wave
(EM) produced by PD has been enforced in power transformer to detect insulation faults [8]. In
this system, Gaussian impulse with different magnitude and breath is used for substitute PD
electric flow [23]. In this research paper, the wavelet and no of occurrence of range for UHF
signs are acquainted using representation techniques. The outcomes tell that PD position
representing to winding is primary regulating element of generation feature of UHF signals [18].
42
3.2.8 Extreme frequency technique based on FRA
In [9] the author described extreme frequency technique for power transformer based on FRA
[20]. In this research work, a new high grade-frequency black-box system of the power trans is
presented for calculation of transferred brightening over voltages [21]. The experimental setup
was carried out on 130-kVA and 36-MVA three-phase power transformers [21]. The presented
calculation and measurement results confirm the validity of the proposed model for full and
chopped lightning impulse voltages [20].
3.2.9 Propagation characteristics of UHF partial discharge using FDTD
In [8] the author used to examine UHF PD (partial discharge) Signal Propagation in Power
Transformers by FDTD Modelling. The UHF method for analyzing PD sources in power
transformers has become increasingly important in recent research [9]. This paper is concerned
with ultra-high frequency (UHF) PD signal propagation in power transformers in the presence of
conducting obstacles, which may represent the core, winding or other internal structures [10]. A
study of the propagation of UHF signals excited by PD in a simple power transformer model has
been carried out using FDTD simulation software [11]. The direction of flow of PD current plays
a significant role that can affect the observed differential time delay by 1 or 2 ns when all other
parameters are kept constant [18].
3.3 Frequency Response Analysis
Frequency Response Analysis (FRA) is method of analyzing circumstances and internal fault
identifying of power transformers. The primary estimation of this technique is that transformer
physical and insulating material throughout manufacturing levels are varied [13]. FRA technique
is progressively used to analyze winding physical variations. In FRA technique, the TF of
transformer is examined in different frequency values and established on this analysis different
internal faults could analyze [18].
43
In this work FRA technique is used to analyses the incipient faults that occurred in Power
Transformers by developing model in Matlab Simulink. In FRA technique, power transformer
can be made up of composite network of resistance, capacitances and inductances [11]. All
modelling results executed for 132/11 kV, 40MVA power transformer that specifically
established on data provided for this design. Any change in values of capacitances, resistances
and inductances will lead noticeable variations in frequency behaviour of transformer [13].
Although various techniques are used in literature to analyze the incipient faults problem but it
still motivates the researchers to develop the new methodologies or improve the existing ones to
reduce the winding losses in the power transformer by the compensation of the insulation
windings and earth, different phases, breakdown occur in between adjacent turns and transformer
core faults.
In this work, FRA technique is used to analyses the incipient faults that occurred in Power
Transformers by developing model in Matlab Simulink and compensate the insulation windings
and earth, different phases, breakdown occur in between adjacent turns and transformer core
faults. This reduction in the internal faults helps to improve the power system and also reduce the
electricity crises that have to face by overall world [23].
According to FRA technique, RLCM system is specifically needed for power arrangement faults
detection that is capable to represent a physical mean of transformer monitoring [24]. Resistance,
inductor, Capacitance circuit system is acquired for every portion in power system; any variation
in transformer physical composition can head to variant in winding function. The power system
is used to identify some possible variations in frequency results because of changes in
transformer’s circumstances [22].
44
A simple RLC model is shown in fig as describes:
Figure 6: RLC Simulink Simple model
The frequency range for FRA is usually from 12Hz up to 3MHz and the measure is established
on the frequency responses of a transformer is evaluated by its capacitance and inductance
disturbances, which are find by the geometrical structure of the transformer and features of
materials used. However, mechanical faults alter the capacitive and inductive characteristics,
which produce deflections in the FRA spectrum [14]. This means that FRA is a relative method,
in which measurements are taken at beginning level is compared with values taken at a before
level, then the variations in measurements of the frequency responses are detected to analyze
mechanical variations inside the transformer [15].
Frequency response can be evaluated directly by sweep through frequency method or can be
finding by impulse response methods [17]. Both methods have favours and limitations. For
example, the impulse response method requires low evaluating time period, but it is most
disturbances sensitive. On the other hand, the frequency sweep method requires longer time for
the evaluation, but it is not much disturbance tender.
45
3.3.1 Impulse Frequency Response
In the impulse frequency response, an impulse voltage that has enough frequency values is
enforced to the object and both the taking voltage and other resulting responses voltage or
current are measured together [11]. This frequency response method is established the transfer
function which describes that the transfer function doesn’t account on the enforced signal when
the system is linear and time invariant. Then measured signals are mathematically changed into
the frequency domain by using Fast Fourier Transform (FFT). The ratio among the FFT of the
response signal and the enforced signal is the frequency response of the represent transfer
function [15]. Disadvantages of the stimulate source that can develop enough power in the define
frequency estimation, minimized power state of put in impulse at increasing frequencies extent
the high limit of calculated frequency response, and the requirement for noise keeping methods
are some of limitations of the impulse response [16].
3.3.2 Frequency Sweep technique
In this method, a sinusoidal voltage is enforced and the measureable values and level of the
reaction voltage or current are measured at distinct frequencies values. This means that this is a
direct method for finding the frequency response values, since the final result is already available
after sweeping the after the already defined frequency limit [19].
3.4 Transfer function
The measurements of the transfer function are very tender diagnostic method to analyze
mechanical changes of the dynamic component of a power transformer [17]. Distortion
influenced by short circuit currents or transfer power may cause in changes of the transfer
function [20]. For evaluation of transfer function with impulse frequency response method
represented in this research work with a frequency constants low-states sinusoid signal with
finding voltage V1 is applied at one end of power transformer and then take up again at another
end which is going to be taken voltage V2.
46
The transfer function is given by
Eq 4:
H(ω) = V2(ω)/V1 (ω)
When input voltage V (t), input current I (t) and resistance response R (t) are evaluated than three
transfer functions may be followed as:
Eq 5:
Eq 6:
Eq 7:
TF1 = R (ω) ⁄ V (ω)
TF2 = R (ω) ⁄ I (ω)
TF3 = I (ω) ⁄ V (ω)
TF1 is a transfer function which consists of input voltage and its response. TF2 is transfer
functions which contain input current and its response. TF3 is transfer function which having
input current and voltage that is the response of V (ω).
For the study of FRA technique, a model is required which is capable to present a physical mean
of transformer construction. Research studies also proved that RLCM model is specifically
needed for power transformer faults analysis [22]. In this model which having the geometrical
properties and dielectric dimensions, it is proposed that transformer windings consist of certain
different portions. A RLC model is supposed for each section, such that is appropriate all
electrical and physical dimensions of this portion. Hence, any alterations in transformer physical
construction can extent to variations of transformer winding transfer function.
47
Chapter 4
Design of power transformer fault
analysis based on FRA
48
4.1 Design Objectives
The main objective of this thesis is to analyze reliability of power transformer faults by
frequency response analysis (FRA). This thesis demonstrates the application of frequency
response analysis technique to power transformer assessment. The reliability assessment of
power transformer assessment resulted qualitative and quantitative frequency response analysis.
This research work focus on analysis of internal faults that occurred in power transformer in
electrical power system by analyzing different fault analysis techniques. So this research works
using

FRA technique in proposed model to detect internal faults in power transformer

So, as to analyze the incipient faults that occurred in Power Transformer by designing the
model by using MATLAB SIMULINK software
The qualitative results help in focusing attention on main apparatus of power transformer that
contributed to the unreliability of the system.
4.2 Proposed Work
The proposed power transformer faults analysis by FRA method is designed using a simulation
technique in Matlab Simulink software. The design is proposed to save the power transformer by
internal faults and protect interference due to input currents.
This research emphasizes on the compensation of the incipient faults to reduce the breakdown in
the power system. For the compensation of the Power Transformer faults different POWER
TRANSFORMER MODELING techniques are used like DGA, DPA, PDA and FRA. By using
these techniques the power transformer faults can be analyze and improves as well as insulation
between windings and core loss can be compensate according to the situation.
In this work FRA technique is used to analyses the incipient faults that occurred in
49
Power Transformers by developing model in Matlab Simulink and compensate the insulation
windings and earth, different phases, breakdown occur in between adjacent turns and transformer
core faults. This reduction in the internal faults helps to improve the power system and also
reduce the electricity crises that have to face by overall world.
According to FRA technique, RLCM system is specifically needed for power arrangement faults
detection that is capable to represent a physical mean of transformer monitoring. Resistance,
inductor, Capacitance circuit system is acquired for every portion in power system; any variation
in transformer physical composition can head to variant in winding function. The power system
is used to identify some possible variations in frequency results because of changes in
transformer’s circumstances.
4.2.1 Proposed Work System Diagram
Figure 7: Proposed System Diagram
50
4.2.2 Description of Proposed Work
The proper description of the proposed work is as follow
In this matlab Simulink system, a three-phase, 60 Hz, 735 kV power system transmitting power
from a power plant consisting of six 350 MVA generators to an equivalent network through a
600 km transmission line. The transmission line is split in two 300 km lines connected between
buses B1,B2, and B3. In order to increase the transmission capacity, each line is series
compensated by capacitors representing 40% of the line reactance.
4.2.3 Block Diagram of Proposed work
Fault
Breaker
Machine
Initialized
13.8/735kv
Transformer
B1
Circuit
Breaker
330Mvar
Series
Compensat
or 1
Circuit
Breaker
B2
100MW
735/230kv
Transformer
250MW
Figure 8: Block diagram of proposed work
51
330Mvar
Series
Compensat
or 2
B3
30000MVA
Source
4.2.4 Description of proposed work
This demonstration use of three-phase blocks to study transients on a series-compensated 735-kV
transmission system is as follows;
In this proposed matlab Simulink system, a three-phase, 60 Hz, 735 kV power system
transmitting power from a power plant consisting of six 350 MVA generators to an equivalent
network through a 600 km transmission line. The transmission line is split in two 300 km lines
connected between buses B1, B2, and B3. In order to increase the transmission capacity, each
line is series compensated by capacitors representing 40% of the line reactance. Both lines are
also shunt compensated by a 330 Mvar shunt reactance. The shunt and series compensation
equipment are located at the B2 substation where a 300 MVA 735/230 kV transformer with a 25
kV tertiary winding feeds a 230 kV, 250 MW load. The series compensation subsystems are
identical for the two lines. For each line, each phase of the series compensation module contains
the series capacitor, a metal oxide varistor (MOV) is protecting the capacitor, and a parallel gap
protecting the MOV. When the energy dissipated in the MOV exceeds a threshold level of 30
MJ, the gap simulated by a circuit breaker is fired. CB1 and CB2 are the two line circuit
breakers.
The generators are simulated with a Simplified Synchronous Machine block. Universal
transformer blocks (two-windings and three-windings) are used to model the two transformers.
Saturation is implemented on the transformer connected at bus B2. Voltages and currents are
measured in B1, B2, and B3 blocks. These blocks are three-phase V-I Measurement blocks
where voltage and current signals are sent to the Data Acquisition.
4.2.4.1 Fault and Line Switching
The transient performance of this circuit when a line-to-ground and three-phase to ground faults
are applied on line 1. The fault and the two line circuit breakers CB1 and CB2 are simulated with
blocks from the three-phase library. Open the dialog boxes of CB1 and CB2. See how the initial
breaker status and switching times are specified. A line-to-ground fault is applied on phase A at t
52
= 1cycle. The two circuit breakers which are initially closed are then open at t = 5 cycles,
simulating a fault detection and opening time of 4 cycles. The fault is eliminated at t = 6 cycles,
one cycle after line opening.
4.2.4.2 Line-to-Ground Fault
By double click the Data Acquisition block and open the three scopes. Start the simulation. As
the system has already been initialized (1500 MW generation at the 13.8 kV bus) with the Load
Flow utility of the Power, the simulation starts in steady state. At t = 1 cycle a line-to-ground
fault is applied and the fault current reaches 10 kA. During the fault, the MOV conducts at every
half cycle and the energy dissipated in the MOV builds up to 13 MJ.
At t = 5 cycles the line protection relays (not simulated) open breakers CB1 and CB2 and the
energy stays constant at 13 MJ. As the maximum energy does not exceed the 30 MJ threshold
level, the gap is not fired. After breaker opening the fault current drops to a small value and the
line and series capacitance start to discharge through the fault and the shunt reactance. The fault
current extinguishes at the first zero crossing after the opening order given to the fault breaker (t
= 6 cycles). Then, the series capacitor stops discharging and its voltage oscillate around 220 kV.
4.2.4.3 Three-Phase-to-Ground Fault
Change the fault type to a three-phase-to-ground fault by checking Phases A, B, and C in the
Fault Breaker block. Restart the simulation. Notice that during the fault the energy dissipated in
the MOV builds up faster that in the case of a line-to-ground fault. The energy reaches the 30 MJ
threshold level after 3 cycles, one cycle before opening of the line breakers. As a result, the gap
is fired and the capacitor voltage quickly discharges to zero through the damping circuit.
4.2.5 Electric circuit components
By the design of power transformer fault analysis using FRA Measurements, a model of the
power transformer is required to generate the fault data required to analyze the transformer
53
internal faults by simulating frequency responses. The Simulink Power system library browser in
the Matlab/Simulink environment is used to model the power transformer fault analysis system,
in which different values of frequencies are used with the standard required. The following
components are used in faults simulation model:
 Three-phase breaker
 Three-phase voltage source
 Three-phase transformer
 Three -phase fault
 Three-phase V-I measurements
 Scope
 Current measurements
4.2.5.1 Three-phase breaker
The Three-Phase Breaker block carries out a three phase circuit breaker which is connected in
series with three phase elements that are to be switched. The breaker timing can be determined
internally or externally by applying an external logic signal.
4.2.5.2 Three phase voltage source
In Three-Phase voltage source, the voltages values can be measured out by applying voltages at
three different phases. This block is implemented with internal RLC impedances values, these
voltages source are connected in Y connection with neutral point that can be internally
connected.
4.2.5.3 Three phase transformer
In three phase transformer block, three-phase transformer is using in this project to measure the
faults variation at three different position by using three phase of transformer.
54
4.2.5.4 Three-Phase faults
The Three-Phase Fault block carries out a three-phase circuit breaker where the clearing and
confining times can be determined. These faults can be determined by external Simulink signal,
or from an internal control timer. The Three-Phase Fault block uses three breaker blocks that
can be either switched open and close to phase-to-phase faults, phase-to-ground faults, or a
combination of phase-to-phase and ground faults. In this project, some types of faults are
simulated by the condition required for frequency responses of transformer faults detection.
4.2.5.5 Three phase V-I measurements
In the three Phase V-I measurements block, different values of current and voltages can be
measured. When connected with three phase element in series, it changes the three phase to line
currents and voltages.
4.2.5.6 Scope
The Scope block is to show signals produced during simulation. The Scope block may have
multiple axes with independent y-axes. The Scope block allows the variation of time and the
range of input values. The Scope displayed results can be changed by adjusting values of
different parameter during the time of simulations.
4.2.5.7 Current measurements
In current measurement block, different values of current waveform could be displayed.
Different current measurements were used in the design of the Simulink model system in order
to evaluate the every phase currents at several parts of the transformer.
55
Chapter 5
Results & Implementations
56
5.1 Frequency 60HZ
BUS 1
Figure 9: Results at Bus 1(60Hz)
57
BUS 2
Figure 10: Results at Bus 2 (60Hz)
58
BUS 3
Figure 11: Results at Bus 3 (60Hz)
59
5.2 FREQUENCY 50HZ
BUS 1
Figure 12: Results at Bus 1 (50Hz)
60
BUS 2
Figure 13: Results at Bus 2 (50Hz)
61
BUS 3
Figure 14: Results at Bus 3 (50Hz)
62
5.3 FREQUENCY 55 HZ
BUS 1
Figure 15: Results at Bus 1 (55Hz)
63
BUS 2
Figure 16: Results at Bus 2 (55Hz)
64
BUS 3
Figure 17:Results at Bus 3 (55Hz)
65
Chapter 6
Conclusion
66
6.1 Conclusion
This thesis will introduce an emergency field that is POWER TRANSFORMER FAULTS
Analysis. It will describe technologies and techniques that take in place into power transformer
fault analysis in systems. Furthermore simulations tools such as Matlab Simulink will be
presented which are mainly used by the researchers of this technology field. Also it is being
shown in practice how to create a complete Simulink model in Matlab Simulink, including the
setting up step by step frequency response of transformer, the detection of faults at certain levels.
The conclusion from this research arises is that Frequency Responses can compensate the
internal faults in power system but there need different values of the frequencies and their
regarding voltages and current values variations, and their values fully according to the load and
for internal core and windings faults, the transformer values have to be measured at the regular
interval and by using the number of buses in power system, although it also responsible for the
cost.
It is also seen that there are some other Faults Analysis methods that can be used for the power
transformer faults compensation in the power system like DGA, RSR, MKSVC and UHF Partial
Discharge etc. But it is seen from the whole work that the FRA is better than the other techniques
in some aspects like it compensate and remove the internal faults from the system in frequency
time response less than the other methods.
67
Chapter 7
References
68
7.1 References
1. Weigen Chen, Chong Pan, Yuxin Yun, and Yilu Liu,“Wavelet Networks in Power
Transformers Diagnosis Using Dissolved Gas Analysis”, IEEE Trans. Power Delivery
vol. 24, no.1; January 2009
2. Jinling Lu, Mijia Wu "Condition Assessment for Power Transformer Based on Improved
Particle Swarm Optimization and Support Vector Machine”, IEEE, 2011
3. Qi-jia XIE Hui-xiong ZENG Ling RUAN Xiao-mingHai-long ZHANG “Transformer
Fault Diagnosis based on Bayesian Network and Rough SetReduction Theory”, IEEE,
2013
4. J. Chong and A. Abu-Sia da, “A Novel Algorithm to detect Internal Transformer Faults”,
IEEE Trans. Power Delivery, 2011
5. Y. J. Yin, J. P. Zhan, C. X. GU, Q. H. Wu and J. M. Zhang “Multi-Kernel Support Vector
Classifier for Fault Diagnosis of Transformers”, IEEE Trans. Power Delivery, 2012,
vol.21, no.5; May 2013
6. EbrahimRahimpour, Mehdi Jabbari and Stefan Tenbohlen, “Mathematical Comparison
Methods to Assess Transfer Functions of Transformers to Detect Different Types of
Mechanical Faults”, IEEE, 2013
7. Xu Zhao, Yonghong Chen, Yongpeng Meng, Kai Wu and Yuhan Niu “The propagation
characteristics of UHF partial discharge in power transformers with complex winding
structure”, IEEE, 2012
8. M. Ishak, M. D. Judd and W. H. Siew “A Study of UHF Partial Discharge Signal
Propagation in Power Transformers using FDTD Modeling”, April 2011.
9. DaliborFilipović-Grčić, BožidarFilipović-Grčić, and Ivo Uglešić, “High frequency model
for the power transformer based on frequency response analysis”, IEEE Trans. Power
Delivery, vol. 23, no. 4; October, 2008.
10. Toshiyuki Saida and Shin Yamada, Shigemitsu Okabe, Masanori Koto and Genyo Ueta,
“Development of High Frequency Circuit Model for Oil-immersed Power Transformers
and its Application for Lightning Surge Analysis”, IEEE Transaction on Dielectric
insulation, vol.18, no. 2; April 2011.
69
11. A.Akbari, AziranH.Firoozi, M.Kharezi and A.Farshidnia,“Power transformer modeling
by using FRA measurements”, IEEE Electrical Insulation, vol.18, no.7; June, 2009.
12. Essam Al-Ammar, George G. Karady and Orlando P. Hevia, “Improved Technique for
Fault Detection Sensitivity in Transformer Maintenance Test”, IEEE, 2007
13. DaliborFilipović-Grčić, BožidarFilipović-Grčić, and Ivo Uglešić, “High-Frequency
Model of the Power Transformer based on Frequency-Response Measurements”, IEEE,
2015
14. Jimmy Cesar Gonzales Arispe, Enrique Esteban Mombello, “Detection of Failures within
Transformers by FRA Using Multi resolution Decomposition”, IEEE Trans. Power
Delivery, vol. 29, no. 3; June 2014
15. Higemitsu Okabe, Masanori Koto, Genyo Ueta, Toshiyuki Saida and Shin Yamada,
“Development of high frequency circuit model for oil-immersed power transformers and
its application for lightning surge analysis”, IEEE Transaction on Dielectric and
Electrical Insulation, vol.18, no. 2; April 2011
16. EbrahimRahimpour,
EbrahimRahimpour
and
Stefan
Tenbohlen,“Mathematical
Comparison Methods to Assess Transfer Functions of Transformers to Detect Different
Types of Mechanical Faults”, IEEE Trans. Power Delivery, vol. 25; October 2014.
17. S.D. Mitchell, J.S. Welsh, R.H. Middleton and B.TPhung, “Practical Implementation of a
Narrowband High Frequency Distributed Model for Locating Partial Discharge in a
Power Transformer”, IEEE Journal of Electrical Engineering, 2007
18. G. Robles, R. Albarracín and
J. M. Martínez-Tarifa, “Shielding Effect of Power
Transformers Tanks in the Ultra-high-frequency Detection of Partial Discharges”, IEEE
Power Engineering Society, 2013
19. Vladimiro Miranda, Adriana R. Garcez Castro, and Shigeaki Lima “Diagnosing Faults in
Power Transformers With Auto associative Neural Networks and Mean Shift “, IEEE
Trans. Power System, vol. 27, no. 3; JULY 2012
20. Abu-Siada, and Syed Islam “A Novel Online Technique to Detect Power Transformer
Winding Faults”, IEEE Trans. Power Delivery, vol. 27, no. 2; April 2012
21. Wei Zhan, Ana E. Goulart, MiladFalahi and PreethiRondla “Development of a Low-Cost
Self-Diagnostic Modulefor Oil-Immerse Forced-Air Cooling Transformers”, IEEE Trans.
Power Delivery, vol. 30, no. 1; Feburary 2015
70
22. A.W. Galli, G.T. Heydt and P.F. Ribeiro, “Exploring the power of wavelet analysis”,
IEEE Computer Applications in Power, October 1996, pp.37-41
23. Thomas Baumann, Alain J. Germond, Dani el Tschudi, “Impulse test fault diagnosis on
power transformer using Kohonen’s self-organization neural network”, IEEE Neural
Network Computing for the Electric Power Industry, pp.199-205, 2010
24. M.G. Morante and D.W. Nicoletti,“A wavelet-based differential transformer protection”,
IEEE Trans. Power Delivery, vol. 14, pp. 1351-1358, Oct. 1999
25. Dey P, Das P and Chakrabothy A.K, “Implementation of Power Transformer Differential
Protection Based on Clarke’s Transform and Fuzzy Systems”, IEEE International Journal
of Engineering Research & Technology, vol. 1; Sept. 2012
26. Yu, Qingguang, et al. "Overview of FRA Measurements." Electric Utility Deregulation,
Restructuring and Power Technologies, 2004 (DRPT 2004). Proceedings of the 2004
IEEE International Conference on. Vol. 2. IEEE, 2004
27. D. Ribbenfjärd, “Electromagnetic Transformer Modelling Including the Ferromagnetic
Core”, Doctoral Thesis in Electrical Systems, Stockholm, Sweden, 2011
28. T. Leibfried, K. Feser, “Monitoring of Power Transformers Using the Transfer Function
Method”, IEEE Transactions on Power Delivery, Vol. 14, No. 4, pp. 1333–1341, October
2005.
29. E. Rahimpour, M. Jabbari, S. Tenbohlen, “Mathematical Comparison Methods to Assess
Transfer Functions of Transformers to Detect Different Types of 80 Mechanical Faults”,
IEEE Transactions on Power Delivery, Vol. 25, No.4, pp. 2544−2010, October 2010.
30. M. Bigdeli, M. Vakilian, E. Rahimpour, “A New Method for Detection and Evaluation of
Winding Mechanical Faults in Transformer through Transfer Function Measurements”,
Advances in Electrical and Computer Engineering, Vol. 11, No. 2, pp. 23−30, May 2011.
31. C. Sweetser, T. McGrail, “Winding Frequency Response Analysis Using Sweep
Frequency Response Analysis (SFRA) Method”, IEEE SERA specification, March 2003.
32. E. Barbisio, F. Fiorillo, C. Ragusa, “Predicting Loss in Magnetic Steels Under Arbitrary
Induction Waveform and With Minor Hysteresis Loops”, IEEE Transactions on
Magnetics, Vol. 40, No. 4, pp. 1810−1819, July 2004.
71
33. E. Barbisio, F. Fiorillo, C. Ragusa, “Predicting Loss in Magnetic Steels Under Arbitrary
Induction Waveform and With Minor Hysteresis Loops”, IEEE Transactions on
Magnetics, vol. 40, no. 4, pp. 1810−1819, July 2004.
34. A. Cataldo, L. Tarricone, F. Attivissimo, A. Trotta, “A TDR Method for Real−Time
Monitoring of Liquids”, IEEE Transactions on Instrumentation and Measurement, Vol.
56, issue 5, pp. 1616−1625, October 2007.
35. P. Karimifard, G. B. Gharehpetian, S. Tenbohlen, “Determination of Axial Displacement
Extent Based on Transformer Winding Transfer Function Estimation Using VectorFitting Method”, European Transactions on Electrical Power, Vol. 18, pp. 423−436, May
2008.
72