ENS6126: Master of Engineering Progress Report: Transformer Protection

This report, submitted as a progress report for a Master of Engineering program, details the methods for modern transformer protection. The project focuses on reducing fault current and magnetizing inrush current using wavelet transform and digital filters to mitigate harmonics. The report covers the background of transformer losses, different current losses, and current transformer issues. The proposed approach involves wavelet transform, digital filters (specifically FIR filters), and the analysis of results using MATLAB. Preliminary results and discussions include simulations of fault current and inrush current, and the application of FIR filters. The report concludes by summarizing the methods for protecting transformers through the reduction of fault current and harmonics, and the implementation of the steady flow of electric power.

ENS6126 Master of Engineering 1
Progress Report
Modern Transformer Protection
John Citizen
Student # 12345678
26 May 2099
Supervisor: Dr Jane Public

Abstract
The advancement in Modern Power System has gained a design of wide range of
Transformers With sizes of few KVA to several hundred of MVA. Huge Transformers
are used to step up a voltage of about 25KV to transmission level, such as 330KV.The
Transformers are availed in various sizes to step down the voltages from 330KV to
130KV and then its distributed in level of 33KV ,then its again stepped down for
domestic supply to 415V.The transformer has to be protected for reliable Power
System. The losses due to thermal stress and electrodynamics forces of the transformer
has to be decreased to make steady flow of supply. To ensure the supply magnetising
inrush current and fault current of transformer has be reduced. In this project the fault
and magnetising inrush current has been identified using wavelet transform and
continuous monitoring of the system will help to handle the fault current so it can be
reduced. The harmonics are formed by the non-linear devices placed in the power
system. These harmonics are the multiple integers of the fundamental frequency. These
Harmonics Frequencies are due to the voltage and current distortions. Distortions in
voltage and current will results problem in power quality. So approximation of
harmonics is most important for the efficiency of the system. The Quality of the system
has to be maintained as per the given standards and to protect the system from damages
due to loads. A filtering device has been used to filter the unwanted frequencies. This
device will allow only some specific frequencies and reduce the distortions. Therefore a
digital filter has been designed to reduce the harmonics and improve the quality of the
power in the system. This project is to explain the methods of protection of transformer
by reducing the fault current and magnetising inrush current using Wavelet Transform
and to reduce the harmonics in the power system using Digital Filter. There are various
types of digital filter has been used to improve the efficiency and reduce the distortions
to maintain the quality of the system. Digital Filters are basically classified in two types
depending upon the impulse response as IIR and FIR filters. The FIR filter have linear
Phase response and there won’t be any phase distortion and it will maintain the stability.
Therefore a Transformer protection methods has been given using Wavelet Transform
and FIR filter based algorithms and analysed using MATLAB.
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Table of Contents
List of Figures..........................................................................................................................iii
1. Introduction....................................................................................................................1
1.1 Introduction................................................................................................................1
1.2 Objectives....................................................................................................................2
1.3 Significance.................................................................................................................2
1.4 Report Organisation...................................................................................................3
2. Background.....................................................................................................................5
2.1 Literature Review.............................................................................................................5
2.2 Transformer losses...........................................................................................................9
2.3 Different current losses in transformer........................................................................10
2.4 Current Transformer Issues..........................................................................................14
3. Proposed Approach......................................................................................................17
3.1 Wavelet transform..........................................................................................................17
3. 2 Continuous wavelet transform.....................................................................................18
3.3. Wavelet based algorithm..............................................................................................19
3.4 Digital filters...................................................................................................................20
3.5 Infinite impulse response (IIR) filter............................................................................22
4. Preliminary Results and Discussions..........................................................................29
4.1 Wavelet based Algorithm Result.............................................................................29
5. Conclusion.....................................................................................................................35
References.............................................................................................................................37
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List of Figures
Figure 1 Magnetizing inrush current..........................................................................................11
Figure 2 Harmonic distortion.....................................................................................................13
Figure 3 Basic Circuit of Relay....................................................................................................15
Figure 4 Circuit to implement the Relay.....................................................................................16
Figure 5 Wavelet based algorithm flow chart............................................................................19
Figure 6 Digital filters.................................................................................................................20
Figure 7 Magnitude response for the filters...............................................................................21
Figure 8 Infinite impulse response (IIR) filter.............................................................................22
Figure 9 Structure of FIR Filter...................................................................................................25
Figure 10 Digital Filter Design Flow Chart..................................................................................26
Figure 11 Magnitude Response of the Filter..............................................................................27
Figure 12 Simulation Diagram of Transformer for Fault.............................................................29
Figure 13 the output Waveform for fault current......................................................................30
Figure 14 Output Waveform for inrush Current.........................................................................30
Figure 15 Output waveform of FIR Filter....................................................................................33
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1. Introduction
1.1 Introduction
Generally Transformers are considered as a most reliable unit, but there is a
chance of failure because of internal fault, due to stresses from external sources. Fuse
has been used for smaller distribution Transformer. Sometimes inverse definite
minimum time or instantaneous over current and Earth fault relays has been used for
Transformer Protection. For this type of protection downstream power system co-
ordination is necessary.so this could lead to time delay. Therefore this method cannot be
used for Large Power Distribution which could lead to unstable system and generate
more power losses.
A Device where the electrical energy from one circuit is transferred to another
by a magnetic field without changing the frequency, this is done by a transformer. At
this modern times it is essential to have transformers that have reduced loss and to
transmit electric power at a greater level. The life span of a transformer is reduced due
to the effect of overload that increases the temperature of the transformer. Filters are
used for reducing the loss of electric power in the transformers. The aim of the report is
to provide a transformer protection for the purpose of steady electrical flow by using
wavelet transform algorithm and algorithm based on filter. This project also explains the
current transformer issues and their restrain characteristics. By providing a continuous
the supply magnetizing inrush current and fault current of the transformer, it has been
reduced the fault current of the transformer. The required hardware for the
implementation of the reduced electrical losses is been given in this project. The
methods to protect the transformer through minimizing the fault current by using the
wavelet transformation algorithm and to reduce the harmonics by using the digital filter
will be explained in this project. The result of this implementation of the steady flow
electric power will be given in MATLAB, which is a programming language that
includes data visualization and creating user interface, also includes developing and
running algorithms. The report will provide the harmonic distortions, different varieties
of current in the transformer and external and internal short circuits. Various types of
digital filter has been used to progress the efficiency and to reduce the distortions to
maintain the quality of the system. Digital Filters are basically classified in two types
depending upon the impulse response as IIR and FIR filters. The FIR filter have linear
Phase response and there won’t be any phase distortion and it will maintain the stability.
Digital filters will be used for reducing the electric losses and the distortion are
protected.
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1.2 Objectives
The objective of the project is to reduce the loss due to thermal stress and
electrodynamics forces of the transformer and to maintain a steady flow of electric
current, to maintain the quality of the system and to protect the reliable power system of
the transformer. It also aims at reducing problems related to power quality by
decreasing the distortions in the current. To reduces the higher voltage electricity into
lower voltage systems that is used by the end users.
1.3 Significance
1. In a distribution system a better regulation of voltage is been produced by the
transformer that acts as a booster to it. The transmission of power occur in
higher rate that is not economical, the voltage level is been enhanced by the
transformers by producing a voltage with greater level at a very low loss. The
power transformers assist in maintaining the power quality and control and
simplifies the electrical networks.
2. The transformer that is generated in electrical power is a cost effective
transformer with a low voltage level, if this low voltage power is transmitted in
in the receiving end it results in a greater linear circuit that causes the line losses.
The increase in the voltage power causes the reduction in the ohmic.
3. Power transformer can electrically segregate the circuits.
4. Power transformer can decrease or increase the capacitor’s value, a resistance or
an inductor in an AC circuit. Power transformer thus perform as an impedance
transferring device.
5. Power transformer can also be used to avoid DC current passing starting from
one circuit to another circuit.
6. Each single show gadget or recording gadget can be perused in the wire lengths
between the distinctive channels for get to, not caused by wire length going
between accuracy.4mA to zero level, to decide the open circuit or sensor is
harmed (0mA state) is extremely helpful, in the simple expansion of two-line
outlet surge and lightning assurance gadgets, is helpful for safe mine blast.
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7. The capacitive protection of the beneficiary causes obstruction on the blunder,
both for 4 ~ 20mA wire circle, the recipient protection is normally 250
(specimen Uout = 1 ~ 5V) that protection sufficiently little to create huge
mistakes, in this manner, can permit the link length longer than the voltage
telemetry framework further
8. In the present source yield protection is sufficiently expansive, the attractive
field sensor coupled to the wire the voltage circle won't have a huge effect, on
the grounds that the obstruction caused by the current is little, as a rule utilizing
turned combine can decrease the impedance resistance. Less defenseless to
parasitic thermocouples and weight drop along the wire protection and
temperature float of the transmission line can be extremely economical contorted
match wire better.
1.4 Report Organisation
This report contains five topics namely introduction, Background of the project,
proposed approach, preliminary results and discussions and conclusion, which are
arranged as below
Introduction provides a general description about the Power transformers the
magnetic field that is changed by the transformers is given. The objective of the report
and its significance of implementation of the transformer is been explained. The
objective is gives as to provide a steady flow of electric power. The aim of the report is
given as to provide a transformer protection for the purpose of steady electrical flow by
using wavelet transform algorithm and algorithm based on filter. The main theme of the
project is given in the introduction part. A description about the MATLAB and the
definition of the filters is given.
The Background topics presents the clear vision about the project background. This
explains about the transformer losses, different current losses in the transformer and
current transformer issues. This topic also includes the literature review related to the
journals Modern Protection of Three-Phase and Spare Transformer Banks by Michael
Thompson, Faridul Katha Basha, and Craig Holt, article about Transformers Fault
Detection Using Wavelet Transform by Y. Najafi Sarem, E. Hashemzadeh, and M.A.
Layegh , a journal about Simulation Of Transformer For Fault Discrimination Using
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Wavelet Transform & neural Network by Laxminarayan Sonwani, Dr. Dharmendra
Kumar Singh and Durga Sharma and journal about A Review Of Design Digital Filter For
Harmonics Reduction In Power System by Prashant Nagare, Dr. Sachin Pable, Dr. A.K.
Kureshi. In transformer losses explanation is given about Copper loss, Dielectric loss
and Radiation and induction loss. The Different current losses in transformer topic
explains about the hysteresis loss eddy current loss and a graph that shows the inrush
current is caused when application of source voltage to a reenergized transformer gives
rise to sudden increase in current is been explained. The hardware that are required to
implement the relay is been given and a figure of basic circuit of the relay is given and a
figure Circuit to implement the Relay is also provided
The topic Proposed Approach addresses the wavelet transform, continuous wavelet
transform, wavelet based algorithm, digital filters and Infinite impulse response filter.
Preliminary Results and Discussions describe the Wavelet based Algorithm Result and
figures of Simulation Diagram of Transformer for Fault, the output Waveform for fault
current, Output Waveform for inrush Current and Output waveform of FIR Filter. FIR
Based Algorithm is also been explained
Conclusion gives the summary of the project.
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2. Background
2.1 Literature Review
As per (Sonwani, Kumar Singh & Sharma, 2015), the Fault discrimination of the
transformer is simulated by using neural network and wavelet transform. The simulation
of power transformer fault discrimination is done by using Mat lab. The wavelet
transform is used to identifying the non-stationary signals like magnetizing fault current
and inrush current. The wavelet transform process is almost equal to the Fourier
transform. It provides the decomposition of signal in the function form. It has the ability
to abstract information since transient signal in both frequency and time domain.The
artificial neural network is utilized for detecting the discrimination of fault current and
inrush current. It is powerful tool. It is used at artificial intelligence. The artificial neural
network has the ability to detect & automate the knowledge, has been proposed for
discrimination. The neural network is used for protecting the power transformer. To
reduce the maintainability and damage of the power system, the protective relays are
used. Because it has ability to separate the faulty part from the good part. It has the
interconnection between artificial neurons. It leads to the simulation of nervous system
in the human brain. For the discrimination process of power system, the input data is
imported to artificial neural network, but it is not possible. Because the dimension of
wavelet is too huge. The convergence of artificial neural network is difficult due to the
result of importing huge input data. To reduce the dimension of input, the spectral
energy wavelet signal is planned with (∆t) time length. The output is produced at three
phases. So the data window is separated into three. The methodology of this project is to
plan & demonstrating a power system at MATLABthrough Simulink library. The
received output signal is imported to the wavelet transform with the help of wavelet
toolbox. This is done at MATLAB. The signal of wavelet decomposition is provided the
approximate coefficients of signals also it provided the detailed coefficient of signal. By
using this signal the fault current is classified. The fault current may be internal fault
current or inrush current. It is detected by using neural network toolbox. The featured
data is mined after wavelet analysis. It is given to the neural network. Because it is used
to provide the more accurate and reliable information. By using this data, one could
reduce the number of neuron present at the middle layer. It is needed for simple neural
network architecture. For identifying the discriminating fault of power system, the
neural network Input, Output and Hidden layer is used. The discrimination fault of
power system is detected using wavelet transformer and neural network.
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As per (Nagare & Pable, 2016), the harmonics of power system is reduced using a
designed digital filter. The non-linear devices are created the harmonics in the power
system. The Power system quality damages are occurred due to the harmonics. Because
the harmonics created the distorted voltage and current. The limitation of harmonics is
very important to maintain the efficiency of the power system quality. Harmonics is the
sinusoidal components. It is a repetitive waveform. It contains the frequencies. The
filter is used to reject the unwanted frequencies. The Electric arc furnaces, Magnetic
Circuits and Power Electronics are sources for generating harmonics. These three are
nonlinear devices. The consequence of harmonics is explained in that paper.to decrease
the harmonics effect in the filter by using filter, one could know the magnitude and
phase of the harmonics. Because it is necessary to design the filter. To evaluate the
harmonics, multiple algorithms are used. The algorithms are mostly depending on the
Fast Fourier Transform (FFT) and Discrete Fourier Transform (DFT) method. The
digital filter is designed to control the harmonic problems and increase power quality by
distributing electrical power to the system. The many filters are used to reduce the
harmonic in the power system and increase the power system quality. The IIR and FIR
filters are discussed to reduce the harmonics. The FIR and IIR filters are designed for
reducing the harmonic distortion in the power system. These two filters are basic digital
filters. The IIR filters are most often used for harmonic distortion. Because it is
implemented with less coefficients. The transfer function of the FIR and IIR filter
impulse response is provided. The structure of the FIR filter is viewed. The design
procedure for the FIR filter is provided as the flowchart. The FIR and IIR filter
differentiation also provided. Many types of windows are used for design and analysis
the filter and spectral. The mathematical equations for these windows are provided. The
given windows are Hanning, Bartlett, Hamming, Kaiser, rectangular and Blackman
window. The harmonics problem in the electrical system design pollutes the power.
This paper is helpful to find out which loads are accountable for great level of alteration
and to identify their distortion level. The harmonic measurements results are helpful to
find out the quality of electric power. This paper provides the information to reduce the
harmonics and to increase the quality of electric power.
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According to the author (Sarem, 2012), the transmission and generator applications
are done by using spare and three phase transformer. The modern protection technology
is used in spare and three phase transformer banks. This technology is used for reduce
the complexity of wiring, detect the faulted equipment and provide automatic, easy
reconfiguration to facilitate the transmission facility to service. Here transmission and
generator applications use this Three-single-phase-and-spare transformer banks. This
bank is used to increase the fault tolerance by the single phase transformer which
replaces the fault one and produces speed repair of the critical path. For speeding up the
critical path modern protection method is used. This method involves precise intimation
of the fault in the transformer. For this purpose TOOLS configuration is used. In this
paper two major applications are analysed. They are the transmission substation
autotransformer and the sub transmission grid and the generator step up transformer.
Here the configuration is done in three ways. In the first one the fault transformer is
eliminated and the spare one is replaced. In second way of configuring, normal in
service transformers are replaced by the spare one. In the third configuration spare
transformer does not exist, for reconfiguring the banks high and low side phases are
used. There are some basic functions for the protection of the transformer which
includes ampere turns (AT) matched about the magnetic circuits. Closed magnetic
circuits are present in the single phase transformers. AT expressions are expressed
individually for each phase of the transformer for calculating the amount of current
flowing in the winding. Next is the fault protection of the winding, which will be tough
to spot the faults. In this we have two types of faults. They are turn-to-turn faults and
turn-to-ground faults. It has a high amount of short circuit current flowing and wastes
energy at the point of fault. Under this fault protection immediate protection of pressure
is used. In order to prevent the pressure relay is used. This relay find out the increase in
pressure created by the energy in the turns of the circuit. This provides the positive
intimation. Another protection is transformer restricted earth fault. This is used for
finding out the fault produced in the windings of the terminal. Two main elements are
used for this protection, one is current polarized direct element and the other is high
impedance differential element. Another protection method is negative sequence
differential protection, in this method sequence is negative because of the higher
sensitivity to all the faults. This method is not that much used for the single phase
transformer since this is very tough to be applied. This paper explains about the
conventions of the diagram and the compensation. Here autotransformer protection is
discussed. The transformer is protected in the bulk electric power substation application.
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This has two sides of bank that is high side is in ring bus, breaker-and-a-half bus, or
double-bus double-breaker arrangement and low side has a single breaker. Here bus
unloading is made and sometimes territory loading is done. Under this protection of
fault many schemes are used and implemented. Another method for protection is GSU
transformer that protects the single phase transformer in power generating station. Here
high side is taken as ring bus that is double breaker and low side is the single breaker.
Here many types of relay and their uses are explained. In programmable relays the
unconventional uses are simplified by the user configurable matrix. For achieving the
protection many relays are used in this paper. Modern system used in this paper
improves the sensitivity.
As per (Thompson, Basha & Holt, 2016), the protection of the transformers using
the wavelet transform by introducing the differential current signals. This method
detects the various types of faults in the circuit. This method is used for the single phase
transformer but not applied for the three-phase. The concept of inrush current is used
here. This paper provides the new method for shielding the transformer by means of
electrical signal. The inrush current is magnetized by removing the magnetic flux, even
after the transformer is cut from the foundation flux is remains in the field. When
voltage is applied to primary winding, after the transformer is electrified the initial
current occurs and this is called the magnetizing of inrush current. This inrush current
emerge high forces between windings and dependent elements. Stimulation is made and
extraction process is done. For the purpose of simulation MATLABsoftware is used in
this power process. Here simulation of power network is done by getting the
information from the line diagrams of the network used. After the simulation work is
over, pre-processing is done. The simulated information are pre-processed for the
training. This process involves passing difference in the current and sampling the
frequency using the sampling frequency. This result is used for the harmonics
extraction. Low pass filter is used in this method to reduce the high frequency and
eliminate the unwanted frequencies. The frequency higher than the Nyquist frequency is
eliminated. In the extraction of harmonics inrush current is used for the demonstration
purpose. Here the signal is converted from each period and is examined for the basic
frequency content. Two methods are used for protecting the transformer. They are in
general electric method and Westinghouse method. Signal energy is one of the factor for
the protection of transformer. Here signal energy is derived by using the parsval’s
theorem for wavelet transform. By giving certain conditions and values for the formula
we get the signal energy. An algorithm is used for the protection. A protection
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