Digital distancerelaymodelingandtestingusinglabvie wandmatlabsimulink

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Digital Distance Relay Modeling and Testing Using LabVIEW and
MATLAB/Simulink
Thesis · June 2015
DOI: 10.13140/RG.2.1.2013.4647
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Ayache Mati
University M'Hamed Bougara of Boumerdes
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Registration Number:…..…../2015
People’s Democratic Republic of Algeria
Ministry of Higher Education and Scientific Research
University M’Hamed BOUGARA – Boumerdes
Institute of Electrical and Electronic Engineering
Department of Power and Control
Final Year Project Report Presented in Partial Fulfilment of
the Requirements for the Degree of
MASTER
In Electrical and Electronic Engineering
Option: Power Engineering
Title:
Presented by:
- MATI Ayache
- BEGBAGUI Merouane
Supervisor:
Pr. BENTARZI Hamid
Digital Distance Relay Modeling and Testing
Using LabVIEW and MATLAB/Simulink

II
II
Dedication
Every challenging work needs self-efforts as well as
guidance of Elders those who were very close to our heart.
My humble effort I dedicate to my sweet and loving
Mother and my family members,
Whose affection, love, encouragement and prays of day and
night make me able to get such success and honor.
Along with all my friends, hardworking and respected
Teachers
Merouane BEGBAGUI

I
Dedication
I have a great pleasure to dedicate this modest work
To my Beloved Mother, my Dear Father
To my Dear Sisters, Brothers, Uncles, Aunts and Cousins
To all my Friends
To all my Teachers from primary school to my last year of
university
And to all with whom I spent wonderful moments
Ayache MATI

III
ACKNOWLEDGEMENT
In the name of Allah, the Most Gracious and the Most Merciful
Alhamdulillah, all praises to Allah for the strengths and His blessing in completing
this project.
We would like to express our deepest and sincere gratitude to our project
Supervisor Pr. H.BENTARZI. It was a great privilege and honor to work and study
under your supervision, we would like also to thank the other teachers for their
precious help during our work. Thank you very much.
Last but not least, we are infinitely grateful to our family members, particularly
our parents for their patience, unwavering support, continuous encouragement,
and belief in us throughout our whole life. We would have never made it this far
without them beside us every step of the way.
Finally, a special thanks go to all IGEE members.

IV
Abstract
Numerical relays are developed due to the advancement in the application of
microprocessor technology in relaying industry. Numerical relays can communicate with
its peers. They are economical and are easy to operate, adjust and repair. Designing of
numerical relays helps to produce new prototypes and protection algorithms.
In conventional transmission line protection, a three–zone stepped directional distance
scheme is used to provide the primary as well as remote backup protection. The voltage
and current measurements are needed by the distance relay for determining the
impedance.
In this work, a new design model of mho distance relay has been implemented
first in PC using LabVIEW, then tested using Power System Simulink Model under
several operating and fault conditions. Finally, the relay prototype has been realized using
acquisition card NI USB-6009, which acquires real-time signals of the currents and the
voltages, processes them digitally and outputs tripping signal to the circuit breaker. The
obtained results show that the relay operates correctly under different fault types for
different locations.

V
Table of Contents
Dedication I
Acknowledgment III
Abstract IV
Table of Contents V
List of Figures VII
List of tables VIII
Introduction 1
Chapter One Distance protection philosophy
1.1 Introduction ...................................................................................................................... 3
1.2 Distance relays ................................................................................................................. 3
1.3 Distance relay zones ........................................................................................................ 4
1.4 Inputs signals to the relay................................................................................................ 4
1.5 Distance protection comparators.................................................................................... 5
1.5.1 Phase comparator ............................................................................................. 5
1.5.2 Magnitude comparator..................................................................................... 6
1.6 Distance protection characteristics ................................................................................ 6
1.6.1 Mho characteristic............................................................................................ 6
1.6.1.1 Mho characteristic phase comparator......................................................... 6
1.6.1.2 Mho characteristic amplitude comparator ................................................. 7
Chapter Two Digital and numerical relays
2.1 Introduction....................................................................................................................... 9
2.2 Relay performance ........................................................................................................... 9
2.3 Relay technology............................................................................................................ 10
2.4 Generalized Numerical relay structure........................................................................ 11

V
2.4.1 Isolation and analog signal scaling module................................................ 12
2.4.2 Anti-aliasing filter module............................................................................ 13
2.4.3 Analog-to-digital converter........................................................................... 14
2.4.4 Phasor estimation algorithms........................................................................ 15
2.4.5 Relay algorithm and trip logic implementation ......................................... 17
Chapter Three Distance relay design model
3.1 Introduction..................................................................................................................... 18
3.2 Proposed Relay model and tools required................................................................... 18
3.2.1 Hardware Part................................................................................................. 19
3.2.1.1 Isolation and Analog Signal Scaling ........................................... 19
3.2.1.2 Signal Conditioning Circuit: (Low-pass Filters) ....................... 21
3.2.1.3 Acquisition Card (NI USB-6009) ............................................... 24
3.2.2 Software Part................................................................................................... 26
3.2.2.1 LabVIEW model numerical distance relay................................. 26
Chapter Four Implementation and Testing
4.1 Introduction..................................................................................................................... 31
4.2 Power System Simulink Model.................................................................................... 31
4.3 Testing procedures ......................................................................................................... 32
4.4 Testing results................................................................................................................. 32
4.5 Testing results discussion.............................................................................................. 36
4.6 Implementation............................................................................................................... 37
Conclusion....................................................................................................... …………..38
References

VII
List of Figures
Figure 1.1 Transmission line with distance relay ................................................................3
Figure 1.2 Distance relay protection zones ........................................................................4
Figure 1.3 Definition of the mho characteristic phase comparator..................................7
Figure 1.4 Definition of the mho characteristic amplitude comparator. .........................8
Figure 2.1 Generalized numerical relay structure ……………........................................... 12
Figure 2.2 Isolation and analog scaling of a voltage signal .......................................... 13
Figure 2.3 Isolation and analog scaling of a current signal ........................................... 13
Figure 2.4 Specifications of a low-pass filter .................................................................. 14
Figure 2.5 Phasor representation of a sinusoidal quantity ............................................. 16
Figure 3.1 the general block diagram of the proposed protection scheme................... 18
Figure 3.2 CS100-VP current transformer Module......................................................... 19
Figure 3.3 Current Transformer Electrical Connection.. ............................................... 19
Figure 3.4 ASTONIA Potential transformer 220/12V ................................................... 20
Figure 3.5 Voltage divider with equal Resistors ............................................................ 20
Figure 3.6 The circuit of Sallen & Key LPF ................................................................... 22
Figure 3.7 Design of the fifth order BLPF....................................................................... 22
Figure 3.8 NI USB-6009 Modules. ................................................................................... 24
Figure 3.9 Process of measuring analog signals in order to be used in computers..... 25
Figure 3.10 Block Diagram for Phasor Estimation Algorithm using Recursive DFT.. 27
Figure 3.11 Block Diagram for Mho Distance Relay ...................................................... 28
Figure 3.12 numerical distance relay front panel .............................................................. 29
Figure 3.13 Mho distance relay flow-chart ....................................................................... 30
Figure 4.1 Power system SIMULINK model ................................................................. 32
Figure 4.2 Phase A to ground fault ................................................................................... 33
Figure 4.3 Phase B to ground fault ................................................................................... 33
Figure 4.4 Phase C to ground fault.................................................................................... 34
Figure 4.5 Phase A to phase B fault ................................................................................... 34
Figure 4.6 Phase B to phase C fault ................................................................................... 35
Figure 4.7 Phase C to phase A fault ................................................................................... 35
Figure 4.8 Three phases fault ABC..................................................................................... 36
Figure 4.9 Numerical mho distance relay prototype......................................................... 37

VII
List of tables
Table 1.1 Fault impedance Algorithm for various fault types ......................................5
Table 3.1 Capacitors values .............................................................................................. 24
Table 4.1 power system data and Relay setting .............................................................. 31

Introduction
Page 1
INTRODUCTION
Today, the major challenging task for an electrical engineer is ensuring a high
level of continuity of service to customers even under system disturbance. However, a
number of undesirable but unavoidable nature events or human-error incidents may
occur and disrupt this condition. The cause of accident includes lightings, wind
damage, ice loading, tree falling, bird shorting, aircraft colliding, vehicles hitting,
people contacting, digging into underground cable, and so on.
To avoid damage to the equipment of the utilities, long interruption service to the
customers and possible personal hazards, proper protective relays are necessary to
take suitable corrective actions during these abnormal conditions. Originally, all
protective relays were electromechanical type, which are still being widely used in
many systems. Solid state relays were introduced in the 1950‟s and are commonly
used today for their relative accuracy, sensitivity, ease of testing and maintaining.
Recently, researchers have been trying to develop a more reliable, secure and fast
acting relay with small space and power consumption by using microprocessor
technology.
Distance protection is the most widely used method to protect transmission lines. The
fundamental principle of distance Relying is based on the local measurement of voltages and
currents, where the Relay responds to the impedance between the relay terminal and the fault
location. There are many types of distance relay characteristic such as mho, reactance,
admittance, quadrilateral polarized-mho, offset mho etc. Every type of characteristics has
different intended function and theories behind.
In order to understanding the function of relays, software relay models must be realized,
modeling of protective relays offer an economic and feasible alternative to studying the
performance of protective relays. Relay models have been long used in a variety of tasks,
such as designing new relaying algorithms, optimizing relay settings. Electric power utilities
use computer-based relay models to confirm how the relay would perform during systems
disturbances and normal operating conditions and to make the necessary corrective
adjustment on the relay settings.
LabVIEW software for National Instruments has been used as interfacing software.
This makes the modeling process and analysis easier because LabVIEW has many
features and functions that can be used together with data acquisition card from
National Instruments. LabVIEW is a graphical programming language that uses icons
instead of lines of text to create applications. In contrast to the text-based

Introduction
Page 2
programming languages, where instructions determine program execution, LabVIEW
uses data flow programming, where the flow of data determines execution.
The goal of this paper is to explain the building process of LabVIEW model for
distance relay. Inside the modeling, fault detection, apparent impedance calculation
for all types of faults, and zone coordination were designed and implemented. A Mho
type distance characteristic was chosen to be as the protection scheme. For this relay,
the developed model can be included in one block set only by creating the subsystem
for the developed model.
This study is divided into four main chapters:
-Chapter one: presents an overview of distance protection philosophy, and its
important aspects.
-Chapter two: deals with generalities of digital and numerical relays.
-chapter three: illustrates the design model in LabVIEW and tools required for the
proposed distance relay.
-Chapter four: deals with the implementation, simulation, and testing the mho
distance relay developed in LabVIEW.

CHAPTER 1
Distance protection philosophy
 Introduction
Distance relays
Distance relay zones
Inputs signals to the relay
Distance protection comparators
Distance protection characteristics

Chapter I Distance protection philosophy
Page 3
Distance protection philosophy
1.1 Introduction
This chapter presents an overview of distance protection systems, because methodologies
for designing and modeling these systems are developed later in this paper. The important aspects
of distance protection are discussed. These aspects include the principles of operation of distance
relay, and the operating characteristics and criteria to set distance protection zones. The input
signals to the relay and the principles of operation of amplitude and phase comparators are
discussed. Finally, distance protection Mho characteristics are presented.
1.2 Distance relays
Protections based on distance relaying have been used in the power grid generally and in
transmission lines particularly in order to detect the fault rapidly and disconnect the faulted part
only. This maintains a reliable operation of the power system and ensures continuity of power
supply. The basic principle governing the operation of a distance relay is the ratio of the voltage
V to the current I at the relaying point as shown in Figure1.1. The ratio (V/I) represents the
measured impedance Z of the faulty line between the relay location and the point of fault
occurrence. Then, the measured impedance is compared to the set impedance, and if this Z is
within the reach of the relay then it operates.[7]
Figure1.1.Transmission line with distance relay

Page 4
1.3 Distance relay zones
Distance relays have instantaneous directional zone 1 protection and one or more time
delayed zones [1,2]. The tripping signal produced by zone 1 is instantaneous; it should not reach
as far as the busbar at the end of the first line so it is set to cover only 80-85 % of the protected
line. The remaining 20-15% provides a factor of safety in order to mitigate against errors
introduced by the current and voltage transformers, and line impedance calculations. The 20-15
% at the end of the line is protected by zone 2, which operates in t2 seconds.
The reach setting of the Zone 2 protection should be at least 120% of the protected line
impedance. In many applications it is common practice to set the Zone 2 reach to be equal to the
protected line section +50% of the shortest adjacent line.
Zone 3 provides the back-up and operates with a delay of t3 seconds. Zone 3 reach should be set
to at least 1.2 times the impedance presented to the relay for a fault at the remote end of the
second line section (GEC, 1990). Typical reach for a 3-zones distance protection are shown in
Figure1.2.
Figure 1.2 Distance relay protection zones
1.4 Inputs signals to the relay
On a three-phase power system, there are ten distinct types of possible faults: a three-
phase fault, three phase-to-phase faults, three phase-to-ground faults and three double-phase-to-
ground faults. The equations that govern the relationship between voltages and currents at the
relay location are different for each of these faults. We should therefore expect that it will take
several distance relays, each of them energized by a different pair of voltage and current inputs,
to measure the distance to the fault correctly. It is a fundamental principle of distance relaying
that, regardless of the type of fault involved, the voltage and current used to energize the
appropriate relay are such that the relay will measure the positive sequence impedance to the

Page 5
fault. Once this is achieved, the zone settings of all relays can be based upon the total positive
sequence impedance of the line, regardless of the type of the fault. We will now consider various
types of fault, and give the appropriate voltage and current inputs to be used for the distance
relays responsible for each of these fault types[1,3,5].In the following table we are going to see
fault impedance algorithm for various fault types:
Table 1.1 Fault impedance Algorithm for various fault types
Fault Type Algorithm
AB or ABG (VA-VB)/(IA-IB) (1)
AC or ACG (VA-VC)/(IA-IC) (2)
BC or BCG (VB-VC)/(IB-IC) (3)
AG VA/(IA+3K0I0) (4)
BG VB/(IB+3K0I0) (5)
CG VC/(IC+3K0I0) (6)
ABC or ABCG (1)=(2)=(3)
Where:
A, B and C indicates faulty phases, G indicates ground fault.
VA, VB and VC indicate voltage phases
IA, IB and IC indicate current phases
Z0 = line zero-sequence impedance
Z1 = line positive-sequence impedance
K1 = residual compensation factor where k0 = (Z0-Z1)/KZ1. K can be 1 or3 depend on the relay
design.
I0 =1/3( IA + IB + IC)
1.5 Distance protection comparators
Relay measuring elements whose functionality is based on the comparison of two
independent quantities are essentially either amplitude or phase comparators.[6,8]
1.5.1 Phase comparator
A phase comparator checks the difference between the phase angles of the two composite
signals and operates if the difference is within a specified range.

Page 6
The composite signals in a phase comparator are denoted by S1 and S2. An angular displacement
is considered positive if S1 leads S2. A phase comparator operates if the following condition is
satisfied (1.1)
1.5.2 Magnitude comparator
A magnitude comparator compares the amplitude of the two composite signals and
operates if the amplitude of one signal is greater than the amplitude of the other signal.
The composite signals in an amplitude comparator are denoted by SO and SR, operating and
restraining signals, respectively. The comparator operates if the following condition is satisfied.
| | | | (1.2)
1.6 Distance protection characteristics
The parameters of the composite signals in a comparator determine the shape, size and
position of the operating characteristic in the impedance plane. The operating characteristics of
distance relays are usually geometric figures, such as circles, straight lines or their combinations.
However, in numerical relays it is possible to design operating characteristics of almost any
shape. The most common operating characteristics employed by distance relays are impedance,
offset impedance, mho, reactance, and quadrilateral characteristics. There are methods used for
obtaining different operating characteristics by the phase and magnitude comparators, special
focus will be on Mho characteristic because it is very used.
1.6.1 Mho characteristic
1.6.1.1 Mho characteristic phase comparator [6]
The phase comparator signals S1 and S2 for producing the mho characteristic are defined
as follows:
(1.4)
Dividing these equations by the line current Ir -φr, give the following equations.
(1.5)
(1.6)

Page 7
As seen in Figure 1.3, the impedances S'1 and S'2 are placed in the extremes of the constant ZR θz
impedance. When the system impedance Zr φr is inside the operating characteristic, as shown on
Figure (1.3(a)), the angle between S'1 and S'2 fulfills equation (1.1) and the relay operates. In
Figure (1.3(b)) is shown the case of Ir φr lying outside the operating characteristic. Now, the
angle between S'1and S'2 is outside the range specified in Equation (1.1), and the relay does not
operate. The constant parameter ZR θz marks the diameter of the circular characteristic that
passes through the origin.
Figure 1.3 Definition of the mho characteristic phase comparator
1.6.1.2 Mho characteristic amplitude comparator
The following SO and SR inputs are used in amplitude comparators that implement the
mho characteristic. In Figure 1.4, the radius of the mho circular characteristic is ZR θ.
(1.7)
(1.8)
Dividing these equations by Ir -φr leads to the following equations.
(1.9)
(1.10)
When the system impedance Zr φr is inside the characteristic, the absolute value of the
impedance S’R is less than the absolute value of the radius S’O as shown in Figure 1.4(a).

Page 8
the condition specified in Equation (2.2) is satisfied and the relay operates. When the system
impedance Zr φr is outside the characteristic, the absolute value of S’R is larger than the absolute
value of S’O and the relay does not operate as shown in Figure 1.4(b).
Figure 1.4 Definition of the mho characteristic amplitude comparator.

CHAPTER 2
Digital and numerical relays
Introduction
Relay performance
Relay technology
Generalized Numerical relay structure

Chapter II Digital and numerical relays
Page 9
Digital and numerical relays
2.1 Introduction
Modern digital and numerical relays are widely employed in protection systems
nowadays. Designing and modeling of numerical relay require establishing a generalized
numerical relay structure, which is composed by the more relevant and common internal modules
employed by typical numerical relays. The present chapter discusses the functionality of each of
the internal modules of the generalized numerical relay, namely signal conditioning and scaling
module, analog anti-aliasing filtering module, analog-to-digital conversion, phasor estimation
algorithm and relay logic. The most common techniques and methods employed in each of these
internal modules are enumerated and reviewed.
2.2 Relay performance
The following characteristics are related to good performance of a relay in a power system [4],
[9].
Reliability
The reliability of a relay is directly in correspondence with the concepts of dependability
and security. A relay is said to be dependable when it operates in the occurrence of a fault
relevant to its protection zone. Security is reached either when the relay will not operate for a
fault outside its operating zone, or when the system is in a healthy state.
Selectivity
Selectivity is the ability that a relay has to only open those breakers that isolate the faulted
element. Selectivity discrimination can be achieved by time grading or by unit protection.
Selectivity by time grading means that different zones of operation are graded by time and
that in the occurrence of a fault, although a number of protections equipment respond, only
those relevant to the faulty zone complete the tripping function. Selectivity by unit protection
means that the relay will only operate under certain fault conditions occurring within a clearly
defined zone.
Speed
In the occurrence of a fault, the greater the time in which the fault is affecting the power
system, the greater is the risk that the power system falls into an unstable operation point.
Relays are the greater is the risk that the power system falls into an unstable operation point.
Relays are therefore required to clear the fault as quickly as possible.

Page 10
Sensitivity
The relay is said to be sensitive if the relay operates to the minimum value of faulted
input signals.
Discrimination
This property allows the relay to distinguish between faults and some transient
phenomena like: an overload or transient over current in the case of transformers which is
caused by the inrush current. In addition, power swings in interconnected systems must not be
considered as faults.
2.3 Relay technology
The relay application for protection of power system date back nearly 100 years ago. Since
then, the technology employed to construct relays have improved dramatically relay size, weight,
cost and functionality. Based on the technology employed for their construction, relays can be
chronologically classified as electromechanical, static or solid-state, digital and numerical [5,6].
Electromechanical relays
The first relays employed in the electric industry were electromechanical devices. These
relays worked based on creating a mechanical force to operate the relay contacts in response
to a fault situation. The mechanical force was established by the flow of a current that
reflected the fault current through windings mounted in magnetic cores. Due to the nature of
its principle of operation, electromechanical relays are relatively heavier and bulkier than
relays constructed with other technologies. Besides, the burden of these relays can be
extremely high, affecting protection purposes. However, electromechanical relays were so
largely employed, tested and known that even modern relays employ their principle of
operation, and still represent a good choice for certain conditions of application.
Solid-state relays
With the advances on electronics, the electromechanical technology presented in the
relays of the first generation started to be replaced by static relays in the early 60’s. Static
relays defined the operating characteristic based in analog circuitry rather than in the action of
windings and coils. The advantages that static relays showed over electromechanical relays
were a reduced size, weight and electrical burden.
However, static relays showed some disadvantages since analog circuitry is extremely
affected by electromagnetic interference and the ranges of current and voltages values are
strongly restricted in analog circuits, affecting the sensitivity of the relay.

Page 11
Digital relays
Incorporating microprocessor into the architecture of relay to implement relay and logic
functions started happening in the 80’s. Digital relays incorporated analog-to-digital converter
(ADC) to sample the analog signals incoming from instrument transformers, and used
microprocessor to define the logic of the relay. Digital relays presented an improvement in
accuracy and control over incoming signals, and the use of more complexes relay algorithms,
extra relay functions and complementary task.
Numerical relays
The difference between numerical relays and digital relays lies in the kind of
microprocessor used. Numerical relays use digital signal processors (DSP) cards, which
contain dedicated microprocessors especially designed to perform digital signal processing.
2.4 Generalized Numerical relay structure
The generalized numerical relay concept, which is directly derived from open system
relaying, consists of a minimum set of hardware modules and functions of modern digital and
numerical relays. With the generalized numerical relay and with the amount of information
commonly available, it is possible to recreate the majority of modern digital and numerical relay
equipment. The following hardware modules and functions constitute the generalized numerical
relay. [6]
Isolation and analog signal scaling: Current and voltage waveforms from instrument
transformers are acquired and scaled down to convenient voltage levels for use in the
digital and numerical relays.
Analog anti-aliasing filtering: Low-pass filters are used to avoid the phenomena of
aliasing in which the high frequency components of the inputs appear to be parts of the
fundamental frequency components.
Analog-to-digital conversion: Because digital processors can process numerical or
logical data only, the waveforms of inputs must be sampled at discrete times. To achieve
this, each analog signal is passed through a sample- and-hold module, and conveyed, one
at a time, to an Analog-to-Digital Converter (ADC) by a multiplexer.
Phasor estimation algorithm: A software algorithm implemented in a microprocessor
estimates the amplitude and phase of the waveforms provided to the relay.
Relay algorithm and trip logic: The equations and parameters specific to the protection
algorithm and the associated trip logic are implemented in the software of the
microprocessor used in the relay. The microprocessor calculates the phasors representing
the inputs, acquires the status of the switches, performs protective relay calculations, and

Page 12
finally provides outputs for controlling the circuit breakers. The processor may also
support communications, self-testing, target display, time clocks, and other tasks.
In Figure 2.1 the schematic of a generalized numerical relay structure is shown. The
functionalities of each module of the generalized relay model are developed in next sections.
Figure 2.1 Generalized numerical relay structure
2.4.1 Isolation and analog signal scaling module
The isolation and analog signal scaling module acquires the voltage and current signals
from the transducers of the power system. This module provides electrical isolation from the
power system and scales down the acquired inputs to levels suitable for use by the data
acquisition system. Since analog-to-digital converters accept only voltage signals, this module
also converts currents to equivalent voltages.
In Figure 2.2 is shown a schematic diagram of the circuit for isolation and analog scaling of a
voltage signal. The output of a voltage transformer is applied to an auxiliary transformer that
reduces the voltage level and provides electrical isolation to the rest of the relay equipment. After
the auxiliary voltage transformer, the voltage is further reduced by a potentiometer to a level
suitable for use by the data acquisition system. A metal oxide varistor (MOV) is used at the input
of the auxiliary transformer to protect the data acquisition system from transients in the input
signals.

Page 13
Figure 2.2 Isolation and analog scaling of a voltage signal
In Figure 2.3 is shown the isolation and analog scaling circuit used for processing currents. A
current from a current transformer is reduced to a lower level by an auxiliary current transformer.
The secondary of the auxiliary current transformer is passed to a resistor to convert the current to
an equivalent voltage.
Figure 2.3 Isolation and analog scaling of a current signal
2.4.2 Anti-aliasing filter module
The analog inputs must be applied to low-pass filters and their outputs should be sampled
and quantized. The use of low-pass filter is necessary to limit the effects of noise and unwanted
components of frequencies over the folding frequency (half of the sampling frequency).
The nature of the relaying task dictates the total amount of filtering required. Distance protection
based on impedance measurements uses information contained in the sinusoidal steady state
components of 50 Hz. Therefore, filtering must preserve the steady state components and reject
other components. Common analog low-pass filters used in these relays are of third to fifth order
with cutoff frequency of about 90 Hz. The cutoff frequency of 90 Hz implies that a sampling rate
of at least three samples per cycle (180 Hz) must be used in order that that the information

Page 14
needed to perform the distance relay functions is retained and errors due to aliasing are avoided.
In practice, the sampling rate must be at least four samples per cycle (240 Hz).
Low-pass filters specifications:
Low-pass filters are designed to pass frequencies, from zero to a frequency ωp with an
approximately unity gain. The frequency range [0, ωp] is called the pass band of the filter. High
frequencies, from a frequency ωs and up, are attenuated. The frequency range [ωs, ∞] is called
the stop band of the filter. The frequency range [ωp, ωs], between the pass and the stop band, is
called the transition band.
A graphical description of the specifications of a low-pass filter is provided in Figure2.4. The
hatched areas in the pass band and in the stop band indicate forbidden magnitude values in these
bands. In the transition band there are no forbidden values, but it is usually required that the
magnitude decrease monotonically in this band.
Figure 2.4: Specifications of a low-pass filter
The parameter δp is the tolerance of the magnitude response in the pass band. The desired
(nominal) magnitude response in the pass band is 1. The parameter δs is the tolerance of the
magnitude response in the stop band. The nominal magnitude response in the stop band is zero.
The –3 dB frequency is called the cutoff frequency, and it is defined as the frequency at which
the magnitude response of the filter is 1/√2 of its nominal value in the pass band.
2.4.3 Analog-to-digital converter
An analog-to-digital converter (A/D converter or ADC) takes the instantaneous value of
an analog voltage and converts it into an n-bit binary number that can be easily manipulated by a
microprocessor. The n-bit number is a binary fraction representing the ratio between the input
voltage and the full-scale voltage of the converter. A number of techniques can be used to

Page 15
achieve this conversion. The full-input voltage ranges for an ADC are typically 0 to +5 or 0 to
+10 volts for unipolar operations, and –5 to +5 or –10 to +10 volts for bipolar operation.
2.4.4 Phasor estimation algorithms
Algorithms are programs used in microprocessors that manipulate the samples of voltages
and currents to produce parameters of interest. Phasors are basic tools of AC circuit analysis,
usually introduced as a means of representing steady state sinusoidal wave forms of fundamental
power frequency. Measuring these voltage phasors in real time allows operators to see and
respond to approaching grid stability problems. Even when a power system is not quite in a
steady state, phasors are often useful in describing the behavior of the power system. For
example, when the power system is undergoing electromechanical oscillations during power
swings, the waveforms of voltages and currents are not in steady state and neither is the
frequency of the power system at its nominal value. Under these conditions, as the variations of
the voltages and currents are relatively slow, phasors may still be used to describe the
performance of the network, the variations being treated as a series of steady state conditions
Phasor estimation of voltage and current waveform using DSP technique are discussed in this
chapter. [10]
Any sinusoid can be represented by phasor which is arotating vector with a fixed amplitude,
frequency and phase angle. Phasor representation of a sinusoid is given in Figure 2.5.The
amplitude of the phasor is equal to the rms value of thesinusoid. The phase angle of the phasor is
the distance of apoint in the sinusoid from the reference.
A sinusoid can be given by:
( ) (2.1)
ω being the frequency of the signal in radian per second, Φ is the phase angle in radian and Xm
is the peak amplitude.

Page 16
Figure 2.5 Phasor representation of a sinusoidal quantity
The phasor representation of this sinusoid will have amplitude of Xm/√2 and rotating
anticlockwise with a fixed frequency ω.
A sinusoid at nominal frequency is sampled at N times the nominal frequency i.e. . The
sinusoid can be given by:
( ) (2.2)
M samples of the sinusoid xm :{ m=0, 1… M-1} are obtained from:
( Φ) (2.3)
To extract the fundamental frequency component from a signal corrupted with other frequency
components, set k=1 in equation to obtain the phasor estimate for M data samples.
√
∑ ( )
√
∑ ( )
√
[ ]
√
(2.4)
Equation (2.4) is the estimated phasor for fundamental frequency.
As new samples arrive it is necessary to update the estimated phasor. The algorithm that does not
take into account data from previous window and estimate the phasor afresh is called non-

Page 17
recursive algorithm. The phasor estimate for N samples from n=1 to n=N by non-recursive
algorithm is given by:
√
∑ [ ( ) ( )] (2.5)
A modified algorithm which saves computation taking into account data from previous window
is called as recursive algorithm which can be given by the equation below:
̂ =
√
( ) ( )
(2.6)
Last sample in the window being (N + m) the phasor is given as:
̂ =
√
( ) (2.7)
2.4.5 Relay algorithm and trip logic implementation
The estimated phasors of voltages and currents are used in the implementation of
protection algorithms in numerical relays. A relay algorithm is a set of equations whose
evaluation and comparison with certain predetermined levels determines the operation of the
relay. The equations and parameters that represent the relay algorithm of distance relay have been
developed in chapter1, and are implemented through computational code at the interior of the
relay microprocessor.

CHAPTER 3
 Distance relay design model
 Introduction
Proposed Relay model and tools required
Hardware Part
Software Part

Chapter III Distance relay design model
Page 18
Distance relay design model
3.1 Introduction
The principles of operation and application procedures of distance relay have been
presented in previous chapters. The concept of generalized numerical relay, whose structure is
constituted by the typical operational modules and functions of modern digital and numerical
relays, has been introduced.
A new distance relay design model is proposed in this chapter. The Proposed Relay model
and tools required are discussed and it is divided in two major parts, hardware part and
software part. Finally, flowchart summaries the whole function of the developped Mho
distance relay.
3.2 Proposed Relay model and tools required
The methodology for modeling distance numerical relays is proposed in this chapter.
The proposed protection system model designing methodology as shown in figure 3.1 consists
of two major parts: Hardware and Software.
Figure 3.1 the general block diagram of the proposed protection scheme.
Power
supply
Circuit breaker Transmission line Load
CT PT
Signal Cond.Circuit
Acquisition card +
PC based program
Isolation and analog signal scaling
Numerical distance relay

Page 19
3.2.1 Hardware Part
3.2.1.1 Isolation and Analog Signal Scaling
As it is mentioned in chapter two, Current and Voltage waveforms from instrument
transformers are required and scaled down to convenient voltage levels for use in the digital
and numerical relay.
Current Transformers
Smicro ModuleCS100-VP current
transformer Figure (3.2).
Figure 3.2. CS100-VP current transformer Module
These current sensors are based on principle of Hall Effect and null balance method with
galvanic isolation between input and output. The output voltage from the current sensor is the
perfect image of the primary (input) current Figure 3.3. The sensors provide wide application
capability for electronic measurement of DC, AC, pulsed currents or their combinations and
can also be used as a feedback element to control or regulate the electric devices.
Figure 3.3 Current Transformer Electrical Connection.
Where:
o Ip: primary current (input).
o Im: Secondary current (output).

Page 20
Features:
o Noncontact measure the high current.
o Measures DC, AC and impulse currents
o Current sensing up to 200A peak
o Very fast response and high accuracy
o High overload capacity
o Temperature range -25°C to +85°C
In this circuit, three current transformers (CS100-VP modules) are used.
Potential Transformers
As it is mentioned in chapter 2 the output of a voltage transformer in transmission line is
applied to an auxiliary transformer that reduces the voltage level and provides electrical
isolation to the rest of the relay equipment. We have used 220/12V transformer.as shown in
figure 3.4.
Figure 3.4 ASTONIA Potential transformer 220/12V
In this circuit, three potential transformers are used.
The analog input that can be handled by the NI USB-6009 is 10V. So the maximum output
voltage of the potential transformer should be less than 10V.For this purpose we have used
voltage divider with two equal resistors R=2kΩ as shown in figure 3.5
Figure 3.5 Voltage divider with equal Resistors
Now the maximum output voltage of the voltage divider will be 6V and it is suitable for NI
USB-6009.

Page 21
3.2.1.2 Signal Conditioning Circuit: (Low-pass Filters)
The ideal low-pass filter response can be approximated by a rational function
approximation scheme such as the Butterworth response.[11]
The Butterworth response is shown in the following equation:
| ( )|
( )
(3.1)
Normalizing H0=1 and ωc= ω3db=1rad/sec
Then | ( )| ( ) ( )
( )
(3.2)
( ) => ( ) ( )
( )
( )
( )
(3.3)
Finding the roots of D(s):
( ) (3.4)
The poles are distributed over the circle of radius 1 ( ).Never a pole in the imaginary
axis.
Finding H(s) from H(s) H (-s):
H(s) is assigned all RHS poles and H (-s) is assigned all LHS poles
Following this procedure, the Butterworth LPF H(s) (H0=1, wc=1rad/sec) can be found for
various filters of order n.
( ) (3.5)
( )
√
(3.6)
( ) (3.7)
MATLAB is used to get this denominator polynomial (Butterworth polynomial) of the fifth
order filter.
Circuit design and implementation
We want to design of a fifth order Butterworth low-pass filter with a cutoff frequency of
80Hz.
For n=5:
( ) (3.8)
( )
( )( )( )
(3.9)

Page 22
To design of a fifth order Butterworth low-pass filter with a cutoff frequency of 80Hz and
gain of K=1 a Sallen & Key Topology is used.
The general form of the transfer function of a Sallen& Key Topology is:
( )
( )
(3.10)
If the gain k=1, the transfer function of the Sallen & Key will be:
( )
( )
(3.11)
Figure 3.6 The circuit of Sallen & Key LPF
To realize a 5th
order BLPF one Sallen& Key stage with a single op-amp is required for every
complex-conjugate pole pair. Since n=5 (odd), an additional negative pole is required and we
use an RC/voltage follower. Also we made the choice of K=1, which requires that the
inverting op-amp circuit be replaced by a voltage follower as shown in figure 3.7.
Figure 3.7 Design of the fifth order BLPF
Computation
To determine the resistance and the capacitance of the first stage shown in figure 3.7 we have:
Taking R1 =1KΩ, fc=80 Hz. we get: C1=2 μF

Page 23
( )
( ) ( )
(3.12)
To find the values of the resistors and the capacitors of the second and third stage:
From (3.9) and (3.12) we have:
( ) (3.13)
( ) (3.14)
Calculating the values of R21, R22, C21 and C22
Taking R1= R2 = 1KΩ and fc=80Hz
Frequency scaling => 2πfc=160π
We have: C21=2*Q1 =>C21=1.236
C22=1/2Q1 =>C22=0.809
Multiplying each capacitor by
C21=2.46 μF
C22=1.6 μF
So, R21= R22 = 1KΩ and C21=2.46 μF and C22=1.6 μF
Calculating the values of R31, R32, C31 and C32
Taking R31= R32 = 1KΩ and fc=80Hz
Frequency scaling => 2πfc=160π
We have: C31=2*Q2 =>C31=3.236
C32=1/2Q2 =>C32=0.309
Multiplying each capacitor by
C31=6.5μF
C32=618ηF
So, R31= R32 = 1KΩ and C31=6.5 μF and C32=618 ηF
Because these values of the capacitors are difficult to find an approximate existing capacitors
are used in this circuit. The capacitors used in the filer of this project are shown in the table
below:

Page 24
Table 3.1 Capacitors values
C1 C21 C22 C31 C32
Calculated value 2 μF 2.46 Μf 1.6 μF 6.5 μF 618 ηF
New value 2 μF 2.2μF 1μF || 470ηF 6.8μF 470ηF
3.2.1.3 Acquisition Card (NI USB-6009)
NI USB-6009 is a simple and low-cost multifunction I/O device from National Instruments.
Figure 3.8 NI USB-6009 Modules.
The device has the following specifications:
o 8 analog inputs (12‐bit, 10 kS/s)
o 2 analog outputs (12-bit, 150 S/s)
o 12 digital I/O
o USB connection, No extra power‐supply needed
o Compatible with LabVIEW, LabWindows/CVI, and Measurement Studio for
Visual Studio.NET
o NI‐DAQmx driver software
The NI USB-6009 is well suited for education purposes due to its small size and easyUSB
connection.
Physical input/output signals
Data acquisition involves gathering signals from measurement sources and digitizing-
the signal for storage, analysis, and presentation on a PC. Data acquisition (DAQ) systems
come in many different PC technology forms for great flexibility when choosing your system.
Scientists and engineers can choose from PCI, PXI, PCI Express, PXI Express, PCMCIA,
USB, Wireless and Ethernet data acquisition for test, measurement, and automation
applications.

Page 25
There are five components to be considered when building a basic DAQ system
o Transducers and sensors
o Signals
o Signal conditioning
o DAQ hardware
o Driver and application software
In this chapter we focus on Signals. The appropriate transducers convert physical phenomena
into measurable signals. However, different signals need to be measured in different ways.
For this reason, it is important to understand the different types of signals and their
corresponding attributes. Signals can be categorized into two groups:
o Analog
o Digital
Analog Signals
Analog input is the process of measuring an analog signal and transferring the
measurement to a computer for analysis, display, or storage. Figure 3.9. An analog signal is a
signal that varies continuously. Analog input is most commonly used to measure voltage
or current. You can use many types of devices to perform analog input, such as multifunction
DAQ (MIO) devices, high‐speed digitizers, digital multimeters, and Dynamic Signal
Acquisition (DSA) devices.
Figure 3.9 Process of measuring analog signals in order to be used in computers
An analog signal can be at any value with respect to time. A few examples of analog signals
include voltage, temperature, pressure, sound, and load.

Page 26
Digital Signals
A digital signal cannot take on any value with respect to time. Instead, a digital
signal has two possible levels: high and low. Digital signals generally conform to
certain specifications that define characteristics of the signal. Digital signals are commonly
referred to as transistor‐to‐transistor logic (TTL). TTL specifications indicate
a digital signal to be low when the level falls within 0 to 0.8 V, and the signal is high between
2 to 5 V. The useful information that can be measured from a digital signal includes the state
and the rate.
3.2.2 Software Part
LabVIEW stands for Laboratory Virtual Instrument Engineering Workbench provided
by National Instrument. It is a programming language with graphical interface based on
structured data flow. LabVIEW uses programs represented by icons to create applications.
LabVIEW programs are called Virtual Instruments (VI). LabVIEW finds its application in
signal processing, data acquisition, hardware control etc. The graphical interface of LabVIEW
consists of front panel window and block panel window. Block panel is used to connect VIs
to construct logical operations. The inputs may be predefined or controlled from the front
panel and the output is reflected in the front panel. [12]
The Mho characteristic is best suited for the numerical protection of HV transmission lines as
it possesses an ideal distance relay characteristic. In the present work, the numerical distance
relay is designed and implemented. By using LabVIEW as software tool development, we can
use a relay for multiple zones using only one software environment with advanced built-in
analysis and signal processing libraries.
Since LabVIEW is based on graphical programming, the users can build instrumentation
called virtual instruments (VIs) using software objects. With proper hardware, these VI’s can
be used for remote data acquisition, design and analysis. The built in library of LabVIEW has
a number of VIs that can be used to design and develop any system. The model developed in
the block diagram window is able to sense the voltages/currents from the hardware circuit
model via USB 6009 kit. It is designed in such a manner that for any kind of fault it is capable
of detecting the fault type and location.
3.2.2.1 LabVIEW model numerical distance relay
The main job of using LabVIEW software program in this project is to interface the
real time hardware kit via tool kit USB6009.It is the only software program which facilitates
the data acquisition. Here also the main job is to model the Mho characteristic of the distance
relay.

Page 27
As we know any Virtual Instrument (VI) has two Windows Block Diagram and Front Panel.
Block Diagram
In this window we simulate all the algorithms needed in our design, including:
o Phasor estimation algorithms: recursive algorithm is used, this stage analyze the
signals coming from DAQ Assistant and gives us the amplitude and phase of each
voltage and current in the three phase system. SeeFigure (3.10).
Figure 3.10 Block Diagram for Phasor Estimation Algorithm using Recursive DFT.
o Input signals (SubVI): this SubVI calculates all the impedances that are mentioned in
table 1.1 and gives six impedances.
o Point location (SubVI): this SubVI draws the mho characteristic with three zones and
gives graphically the location of the six impedances mentioned before.
o Comparator (SubVI): this SubVI compare the six impedances calculated from input
signals (SubVI) with the transmission line impedance for the three zones.
o Fault loc (SubVI): this SubVI calculate the fault location for each type of fault.
The remaining blocks includes the zones time delay and other mathematical calculations. As
shown in Figure (3.11).

Page 28
Figure 3.11 Block diagram for Mho Distance Relay

Page 29
Front Panel:
This window is the HMI of the numerical distance relay. It is used to enter the
transmission line parameters, zones setting and time delay. It displays the amplitude and
phase of the three phase voltages and currents, fault type and location, and circuit breaker trip.
Besides there is a graph used to display the three zones of mho characteristic and the six
impedances as points. Figure (3.12).
Figure 3.12 numerical distance relay front panel.

Page 30
As a summary for the whole function of the developped Mho distance relay. The following
flow-chart explains the procedure step-by-step:
NO yes
NO Yes
NO yes
Figure 3.13 Mho distance relay flow-chart.
Start
Set relay setting (line parameters, zones length, time delay)
Calculate and plot zones of MHO relay
Measure currents and voltages using CT & PT
Filter the signals
Transfer signals to LabVIEW using NI USB-6009
Extract the amplitude and phase of the fundamentals using recursive
algorithm
Calculate the impedance
Zone 1
Zone 2
Zone 3
Delay
Delay
Trip signal

CHAPTER 4
 Implementation and Testing
Introduction
Power System Simulink Model
Testing procedures
Testing results
Testing results discussion
Implementation

Chapter IV Implementation and Testing
Page 31
Implementation and Testing
4.1 Introduction
This chapter will present the simulation of the mho distance relay developed in
LabVIEW, including testing procedures, results and discussion, and will end up with the
implementation of the proposed prototype.
4.2 Power System Simulink Model
To validate the relay model that has been developed in LabVIEW. MATLAB/SIMULINK
is used to simulate power system model for several operating and fault conditions as shown in
figure 1.The parameters of the power system model using SIMULINK and the settings of the
relay model using LabVIEW are mentioned in table 4.1.
Table 4.1 power system data and Relay setting
No Parameters Value
1 Line length 100 km
2 Voltage 220 KV
3 Frequency 50 Hz
4 Line resistance R1 0.01165 Ohm/Km
5 Line resistance R0 0.2676 Ohm/Km
6 Line reactance X1 0.2725 Ohm/Km
7 Line reactance X0 0.9495 Ohm/Km
Relay settings
Zones Settings Time delay (s)
1 One 80% 0
2 Two 120% 1
3 Three 160% 2

Page 32
4.3 Testing procedures
First step: set the transmission line parameters and zones settings in LabVIEW front
panel.
Second step: simulate faults in MATLAB/SIMULINK.
Third step: transfer data from MATLAB to LabVIEW.
Forth step: run the simulation in LabVIEW.
Figure 4.1 power system SIMULINK model
4.4 Testing results
The results of the test being performed are presented using figures which display the
LabVIEW front panel of the developed mho distance relay. We have tested seven different cases:

Page 33
Case one: phase A to ground fault at a distance of 70Km
Figure 4.2 Phase A to ground fault
Case two: Phase B to ground fault at a distance of 110Km.
Figure 4.3 Phase B to ground fault

Page 34
Case three: Phase C to ground fault at a distance of 140Km.
Figure 4.4 Phase C to ground fault
Case four: Phase A to phase B fault at a distance of 70Km.
Figure 4.5 Phase A to phase B fault

Page 35
Case five: Phase B to phase C fault at a distance of 110Km.
Figure 4.6 Phase B to phase C fault
Case six: Phase C to phase A fault at a distance of 140Km.
Figure 4.7 Phase C to phase A fault

Page 36
Case seven: Three phases fault ABC at a distance of 140Km.
Figure 4.8 Three phases fault ABC
4.5 Implementation
The implementation of the proposed mho distance relay is shown in figure 4.9.
It consists of:
o Three potential transformer (ASTONIA220/12V).
o Three current transformers (Smicro Module CS100-VP)
o Low-Pass Filters.
o Acquisition CardNI USB-6009.
o PC ( LabVIEW model for Mho distance relay)

Page 37
Figure 4.9 numerical mho distance relay prototype
Because the relay tester is not available, we have tested each stage alone.
Acquiring voltages
Three phase voltages were acquired using NI USB-6009
Figure 4.10 the acquired three phase voltages
Acquiring current
We have tested each current transformer alone,then using NI USB-6009 a voltage waveform
were acquired after that it transferred to current in LabVIEW as shown in figure 4.11.

Page 38
Figure 4.11 the acquired current
4.6 Testing results discussion
The following points may be mentioned about the testing results:
In the displayed figures, the three zones of protection are represented by three circles of
different radius, and the fault impedance is the solid point inside one of the circles which
will indicate the occurrence of a fault on the transmission line and which zone of
protection is concerned.
By testing the behavior of the developed relay model under different fault conditions, the
relay model was able to recognize the appropriate fault type.
From perspective impedance calculations, the relay model has the ability of indicating the
correct zone of operation in all cases.
The relay identifies the fault locations as expected, as the fault location is changed, the
measured impedance changes consequently.
The fault impedance increases when the fault is applied at higher distances due to the
increase of the impedance of the line with distance.
All the detected fault impedances are located on the first quadrant of the mho relay
characteristic trace which verifies the directionality of the mho relay which only senses
the faults situated in the forward direction.
The relay responds at different time delays depending on the zone of fault detection, for
zone one it responds almost instantaneously, for zone two it sends a trip signal after 1 sec
and for zone three the trip signal is generated after 2 sec.

References:
[1] M.P.Thakre, V.S.Kale, „distance protection for long transmission line using pscad‟, International
Journal of Advances in Engineering & Technology, Jan. 2014.
[2] Dr. Hamid H. Sherwali and Eng. Abdlmnam A. Abdlrahem, “Simulation of numerical distance
relays”, Al-Fatah University Tripoli- Libya, 2010.
[3] Omar G. Mrehel Hassan B. Elfetori AbdAllah O. Hawal ,‟ Implementation and Evaluation a
SIMULINK Model of a Distance Relay in MATLAB/SIMULINK‟,2013
[4] Auday A.H. Mohamad, Essar Gafar Ahmed „‟ Design a Fast Digital Protective Relay Algorithm
For High Voltage Transmission line‟‟ Received Feb. 2014, accepted after revision May 2014
[5] Stanley H . H or owitz and A r un G . Phadke,‟ Power System Relaying, Third Edition.2008
[6] Sandro Gianny Aquiles Perez, “Modeling Relays for Power System Protection Studies”, Ph.D
Research, University of Saskatchewan, Saskatchewan, Canada, July 2006.
[7] H.Bentarzi, A. Ouadi, M. Chafai and A. Zitouni, “ Distance Protective System Performance
Enhancement Using Optimized Digital Filter”, in Proc. CSECS '11 The 10th WSEAS International
Conference on CIRCUITS, SYSTEMS, ELECTRONICS, CONTROL & SIGNAL PROCESSING,
Montreux University, Switzerland, December, 29-31, 2011.
[8] Alstom, network protection & automation guide, edition may 2011
[9] Gerhard Ziegler, “Numerical Distance Protection Principles and Application”, Publicis
Corporate Publishing, Erlangen, Siemens, third edition, 2008.
[10] Sourav Mondal, Ch. Murthy, D. S. Roy, D. K. Mohanta,‟ Simulation of Phasor Measurement Unit
(PMU)Using Labview
[11] http://www.ece.uic.edu/~jmorisak/blpf.html
[12] Vinicius J. & Osvaldo S. “ Using LabVIEW in a Mini Power System Model Allowing Remote
Access and New Implementation.” International Conference on Engineering Education, 2007.

Conclusion
Page 39
Conclusion
In this work, a new protection scheme that is based on the Mho distance relay algorithm
has been implemented using LabVIEW. After that the implemented Mho distance relay has been
tested. Then, the relay prototype has been realized using acquisition card NI USB-6009.
At beginning, we have presented operation principles of distance relay. We also discussed some
key aspects of distance relay protection, such as protection zones, comparators, the input signals
to the relay and Mho operating characteristic.
Consequently, the structure of a generalized numerical relay is introduced. The major internal
modules of the generalized relay model are described. These modules are the analog signal
scaling module, analog anti-aliasing filtering module, analog-to-digital conversion module,
phasor estimation algorithm module and relay logic module. The most common techniques and
methods employed in each module of the generalized numerical relay have enumerated and
reviewed.
We have then proceeded to design a new distance relay model. We have presented the proposed
relay model and tools required. Therefore, we have divided our design in two major parts,
hardware part and software part. We ended up with a flowchart that summaries the whole
function of the developped Mho distance relay.
Finally, a Mho type distance relay has been successfully developed based on LabVIEW
software. By testing the behavior of the developed relay model under different fault conditions,
the relay model has been able to recognize the appropriate fault type. From perspective
impedance calculations, the relay model has the ability of indicating the correct zone of
operation in all cases. The relay identifiers the fault locations as expected, as the fault location is
changed, the measured impedance changes consequently.
After the test, it can be noticed that the obtained results satisfy the principle operation of
numerical distance relay and its characteristics using this new frame work. Moreover, it can be
concluded that this proposed scheme has the following advantages:
1. The Mho distance protection can rapidly and reliably operate during power faults.
2. This complex protection scheme can easily be implemented on PC.

Conclusion
Page 40
3. This project is suitable for education for showing to the power engineering students the
distance relay principle of function and how to adjust it for protecting the different zones
of the transmission line.
For enhancing more the performance of the relay, power swing blocking protection function may
be implemented that can be considered as further work. Besides, quadrilateral distance relay
which is very suitable for avoiding some power swing situation, can be implemented as extended
work.
For more sophisticated distance relay that may be proposed is to design an adaptive relay which
can choose which type of distance relay may be used (Mho or quadrilateral) for such situation
and it will decide if it will use power swing blocking protection function or not. Because, the use
of the last protection function has certain limitations.
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