Modelling Relays for Power System Protection Studies

Tanta University
Faculty of Engineering
Electrical Power and Machines Engineering Department
Modelling Relays for Power System
Protection Studies
By
Project Team 2015/2016
Supervised By
Dr. Mohamed Abo Elazm Alaam
2016

Dedication
It will be honor for us to whole – heartedly thank our
supervisor Dr. Mohamed Abo Elazm. And furthermore,
we are appreciate everyone who provides us with any
help even minor especially staff members of Electrical
Power and Machines Engineering Department.
Project Team 2015/2016
Project Members:
1- Abd ElHamid Khaled El Zayat
2- Ahmed Hassan Hamad
3- Ahmed Wagih Abd ElRazek
4- Eslam Abd El-Maksoud Yousef
5- Mahmoud Serag Elsamanody
6- Mohamed Gamal Badr
7- Mona Mossad Taha
8- Nawal Atef El-Shreif
9- Rasha El-Sayed Shahin

Summary
Electrical power system is one of the more complex and important
systems ever built by human civilization. The role of electrical power system
in the development, sustenance and expansion of the economic activity of
modern societies is of the first order of importance. However, power system
sometimes fail due to adverse environment and aging of equipment when the
failures happen, protection of power system acquires a vital significance to
minimize the damages and to keep the operation of the system safe.
Numerical relays are result of the application of microprocessor
technology in the protection industry. These relays are in an extensive use in
modern protection schemes, and are very active area of research. Modelling of
numerical relays provides a valuable source of information for manufacturers,
utility engineers, educators and trainers.
The introduction of the phasor measurement unit (PMU) has greatly
improved the observability of the power system dynamics. Based on PMUs
different kinds of wide-area protection, emergency control and optimization
systems can be designed. A great deal of engineering, such as power system
studies and configurations and parameters settings, is required, a cost effective
solution could be based on standard products and standard system designs.
In Chapter one, are described the subject and organization of the book.
Literature review on modelling of protection system is also provided. Working
principle of studied relays namely; Overcurrent, Distance, Directional and
Differential are reviewed and discussed as well. Some background in wide area

protection of power systems and phasor measurement units also discussed as
well.
In Chapter two, has given an overview on relay technology. Numerical
relays concepts and the numerical relay modelling have also been described.
The structure of a generalized numerical relay has been established so that the
modelling of numerical relays is simplified. Major relevant modules and
functions of a generalized numerical relay have been outlined. These modules
include signal conditioning and scaling model, analogue anti-aliasing filtering
module, analogue-to-digital conversion module, phasor estimation algorithm
and relay logic. Basic concepts and information concerning each module has
been presented. The most common techniques and methods employed in each
module has also been described and developed.
In Chapter three, the Results which verify and validate the problem
statement, are presented
In Chapter four, Wide Area Protection system technology roadmap is
discussed which contained system structure, function configuration, key
technologies, and implementation. WAP is an ideal and practical solution.
However, in order to get more information, WAP has to depend on
communication networks and sometimes even depend on synchronization
signals. Therefore, many works are still expected to do for a more reliable
protection system.
In Chapter five, the Conclusion is introduced

Contents I
Contents
CHAPTER 1 1
Introduction 1
1.1 Literature Review of Protection System Modelling 1
1.2 Digital And Numerical Relay Models 2
1.3 Working Principle of Studied Relays 3
1.3.1 Over Current Relay 4
1.3.2 Directional Relay 5
1.3.3 Distance Relay 6
1.3.4 Differential Relay 7
1.4 Wide Area Protection 8
1.4.1 Definition 8
1.4.2 Phasor Measurement Units (PMUs) 9
CHAPTER 2 12
Problem statement 12
2.1 Introduction 12
2.2 Generalized Numerical Relay Structure 13
2.2.1 Analogue Signal Scaling Module 13
2.2.2 Analogue Anti-Aliasing Filtering 14
2.2.3 Sample and Hold 14
2.2.4 Multiplexer 14
2.2.5 Analogue to Digital Converter 15
2.3 Modelling 15
2.4 Digital and Numerical Relay Models 16
2.4.1 Introduction 16
2.4.2 The Methodology of Modelling Numerical Relays 17
2.5 Problem Statement 17
2.5.1 Vision 17

ContentsII
2.5.2 Statement Issue 18
2.5.3 Method 19
2.6 Embedding Relays into a Power System 23
2.6.1 The Effective of Embedding Protection System 28
CHAPTER 3 31
Substation Protection 31
3.1 introduction 31
3.2 Load Flow for IEEE 14 Bus System 32
3.3 Fault Cases 35
3.3.1 Generator Protection 36
3.3.2 XFMR Protection 37
3.3.3 Bus Protection 39
3.3.4 Transmission Line Protection 43
CHAPTER 4 54
Wide Area Protection 54
4.1 Definition 55
4.2 System Structure 56
4.3 Master Station 57
4.4 Slave Station 57
4.5 WAP Using Phasor Measurement Units (PMUs) 58
4.5.1 IEEE 14-bus 63
CHAPTER 5 69
Conclusions 69
References 72

List of Figures and Tables IX
List of Figures
Figure 2-1 Generalized Numerical Relay Structure.......................................13
Figure 2-2 Definite Time Overcurrent Protection..........................................23
Figure 2-3 IEEE 14BUS System .................................................................. 28
Figure 3-1: Sub System Of (“IEEE14 Bus”)..................................................35
Figure 3-2: Unit Generator Typical Protection Model...................................36
Figure 3-3: XFMR Typical Protection Model................................................37
Figure 3-4: Current On Both Sides Of The XFMR........................................38
Figure 3-5: Trip Signal Of Differential Relay And Over Current..................38
Figure 3-6: Bus Protection Model..................................................................39
Figure 3-7: Total Inner Feeder Current And Total Outer Feeder Current......40
Figure 3-8: Bus Voltage And Differential Relay Action................................40
Figure 3-9: Over Current And Distance Relay...............................................41
Figure 3-10: Total Inner Feeder Current And Total Outer Feeder Current....41
Figure 3-11: Bus Voltage And Differential Relay Action..............................42
Figure 3-12: Over Current Relay Trip Signal ................................................42
Figure 3-13: Distance Relay Trip Signal........................................................43
Figure 3-14: Transmission Line Protection Model........................................43
Figure 3-15: Transmission Line Current and Distance Relay Trip Signals...44
Figure 3-16: Over Current Relay Trip Signal.................................................45
Figure 3-17: Transmission Line Current and Distance Relay Trip Signal.....45
Figure 3-19: Transmission Line Current And Distance Relay Trip Signal....46
Figure 3-30: Over Current Relay Trip Signal................................................ 52
Figure 4-1: Diagram Of WAP System Architecture ..................................... 56
Figure 4-2: Phasor Measurement Unit (PMU) Structure............................... 60
Figure 4-3: Installing 3 Pmus In Buses 2, 6 And 9........................................ 63

List of Figures and TablesX
List of Tables
Table 2-1: Exciter Data...................................................................................24
Table 2-2: Generator Data..............................................................................24
Table 2-3: Bus Data........................................................................................25
Table 2-4: Line Data.......................................................................................26
Table 2-5: IEEE standard Protection relays.................................................. 27
Table 2-6: Study Cases of Fault.....................................................................29
Table 3-1: Load Flow Results........................................................................33
Table 3-2: Transmission line losses...............................................................34
Table 3-3: System total generation and demand............................................34
Table 4-1: Buses initial voltages and lines impedances. ...............................65
Table 4-2: Deducing voltage of remaining buses with aid of allocation of
PMUs at buses 2 ,6 ,9. Load flow analysis.....................................................66
PMUs at buses 2 ,6 ,9. Short circuit analysis (Three phase fault) at bus 5.....66
PMUs at buses 2 ,6 ,9. Short circuit analysis (Three phase fault) at bus13....67

1. Introduction 1
CHAPTER 1
Introduction
Modern numerical relays are widely employed in protection systems
nowadays. Designing and modelling 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.
Computer models of protective relays offer an economical and feasible
alternative to investigate the performance of relays and protection systems.
Computer models of relays permit investigators to observe in a very detailed
way the performance of processes in each internal module of the relay.
Designing new relaying algorithms or new relaying equipment is also
improved with relay modelling because relay designs are refined before
prototypes are built and tested. For specific problems and conflicting scenarios,
use of models open the possibility of creating new solutions when known
approaches do not work satisfactorily.
1.1 Literature Review of Protection System Modelling
Relay models have been used for a long time by manufacturers,
consultants and academics for designing new prototypes and algorithms, to
check and optimize the performance of relays already installed in power
systems and to train new protection personnel.

1. Introduction2
Relay manufacturers were the first to develop relay models for
evaluating the performance of their designs. Those models implemented the
processes by substituting the values of inputs in equations representing the
relays to check if the outcomes were acceptable. The characteristics of
overcurrent relays were the first to be modelled. Mathematical models, were
developed in the form of algebraic equations for representing time-current
characteristics of overcurrent relays. The first transient model of a distance
relay was presented in, where the ninth-order state space mathematical model
of a mho element was developed.
MATLAB integrates mathematical computing, visualization, and a
powerful language to provide a flexible environment for technical computing.
MATLAB possesses a flexible software structure comprising libraries, models
and programs that enable integration of different model components in a single
package. SIMULINK is a package in MATLAB for obtaining time domain
solutions. This package shows an open system where new libraries and models
can be added with relative ease. The Power System Block Set enables transient
modelling of basic components of power systems. The combination of
MATLAB, SIMULINK and the Power System Block Set permits users to
model and simulate real-time power and related protection systems with high
accuracy.
1.2 Digital And Numerical Relay Models
Modelling and simulation of electric power systems has been a common
practice for more than thirty years. Computer models of major power system
components have been used in software packages such as short circuit
programs, load flow, stability programs, and electromagnetic transient
programs. Relay system modelling has been performed in a lesser degree.

1. Introduction 3
A successful relay model must produce the same output for the same
inputs than its real counterpart, even when there would not be a direct
correspondence to the actual microprocessor machine language coding within
the relay.
Utility engineers and consultants use relay models to select the relay
types suited for a particular application, and to analyse the performance of
relays that appear to either operate incorrectly or fail to operate on the
occurrence of a fault. Instead of using actual prototypes, manufacturers use
relay model designing to expedite and economize the process of developing
new relays. 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. The software models could be used for training young and
inexperienced engineers and technicians. Researchers use relay model
designing to investigate and improve protection design and algorithms.
However, choosing appropriate settings for the steady state operation of
overcurrent relays and distance relays is presently the most familiar use of
relay models.
1.3 Working Principle of Studied Relays
A Relay is a logical element which process the inputs (mostly voltage
and currents) from the system and issue a trip decision if a fault within its
jurisdiction is detected
Inputs to the Relays are
- Current from current transformer (CT)
- Voltage from voltage transformer (VT)

1. Introduction4
How Do Relays Detect Faults?
- When a fault takes place, the current, voltage, frequency, and other
electrical variables behave in a peculiar way. For example:
 Current suddenly increases
 Voltage suddenly decreases
- Relays can measure the currents and the voltages and detect that
there is an over-current, an under-voltage, or a combination of both.
- Many other detection principles determine the design of protective
relays.
Basic Elements of Relay
Sensing Element, Comparison Element and Control Element Relay To
trip or signal circuit (CB)
Advantages of Relay
- Maximum flexibility
- Provide multiple functionality
- Self-checking and communication facility
- It can be made adaptive for any system
1.3.1 Over Current Relay
Working Principle of Over Current Relay:
In an over current relay, there would be essentially a current coil. When
normal current flows through this coil, the magnetic effect generated by the
coil is not sufficient to move the moving element of the relay, as in this
condition the restraining force is greater than deflecting force. But when the
current through the coil increased, the magnetic effect increases, and after
certain level of current, the deflecting force generated by the magnetic effect

1. Introduction 5
of the coil, crosses the restraining force, as a result, the moving element starts
moving to change the contact position in the relay.
1.3.2 Directional Relay
A directional relay uses an additional polarizing source of voltage or
current to determine the direction of a fault. Directional elements respond to
the phase shift between a polarizing quantity and an operate quantity. The fault
can be located upstream or downstream of the relay's location, allowing
appropriate protective devices to be operated inside or outside of the zone of
protection. When fault currents can flow in more than one direction with
respect to the load current it is often desirable to determine which direction the
fault is flowing and trip the appropriate devices accordingly. This is usually
due to the need to de-energize only those parts of the power system that must
be de-energized to contain a given fault.
An important concept in the application of directional overcurrent relays
is polarization. Polarization is the method used by the relay to determine the
direction of current flow .for phase directional overcurrent relays, this is
accomplished by the use of voltage transformers, which provide a voltage
signal to the relay and allow it to distinguish the current direction.
Directional over-current protection comprises over-current relay and
power directional relay- in a single relay casing. The power directional relay
does not measure the power but is arranged to respond to the direction of power
flow.

1. Introduction6
1.3.3 Distance Relay
Is one type of relay, which functions depending upon the distance of
fault in the line. More specifically, the relay operates depending upon the
impedance between the point of fault and the point where relay is installed.
The working principle of distance relay or impedance relay is very
simple. There is one voltage element from potential transformer and an current
element fed from current transformer of the system. The deflecting torque is
produced by secondary current of CT and restoring torque is produced by
voltage of potential transformer.
In normal operating condition, restoring torque is more than deflecting
torque. Hence relay will not operate. But in faulty condition, the current
becomes quite large whereas voltage becomes less. Consequently, deflecting
torque becomes more than restoring torque and dynamic parts of the relay
starts moving which ultimately close the No contact of relay. Hence, clearly
operation or working principle of distance relay depends upon the ratio of
system voltage and current. As the ratio of voltage to current is nothing but
impedance a distance relay is also known as impedance relay. The operation
of such relay depends upon the predetermined value of voltage to current ratio.
This ratio is nothing but impedance. The relay will only operate when this
voltage to current ratio becomes less than its predetermined value. Hence, it
can be said that the relay will only operate when the impedance of the line
becomes less than predetermined impedance (voltage / current). As the
impedance of a transmission line is directly proportional to its length, it can
easily be concluded that a distance relay can only operate if fault is occurred
within a predetermined distance or length of line.

1. Introduction 7
1.3.4 Differential Relay
The differential relay is one that operates when there is a difference
between two or more similar electrical quantities exceeds a predetermined
value. In differential relay scheme circuit, there are two currents come from
two parts of an electrical power circuit.
These two currents meet at a junction point where a relay coil is
connected. According to Kirchhoff Current Law, the resultant current flowing
through the relay coil is nothing but summation of two currents, coming from
two different parts of the electrical power circuit. If the polarity and amplitude
of both currents are so adjusted that the phasor sum of these two currents, is
zero at normal operating condition. Thereby there will be no current flowing
through the relay coil at normal operating conditions. But due to any
abnormality in the power circuit, if this balance is broken, that means the
phasor sum of these two currents no longer remains zero and there will be non-
zero current flowing through the relay coil thereby relay being operated. In
current differential scheme, there are two sets of current transformer each
connected to either side of the equipment protected by differential relay. The
ratio of the current transformers are so chosen, the secondary currents of both
current transformers matches each other in magnitude. The polarity of current
transformers are such that the secondary currents of these CTs opposes each
other. From the circuit is clear that only if any nonzero difference is created
between this to secondary currents, then only this differential current will flow
through the operating coil of the relay. If this difference is more than the peak
up value of the relay, it will operate to open the circuit breakers to isolate the
protected equipment from the system. The relaying element used in differential
relay is attracted armature type instantaneously relay since differential scheme

1. Introduction8
is only adapted for clearing the fault inside the protected equipment in other
words differential relay should clear only internal fault of the equipment hence
the protected equipment should be isolated as soon as any fault occurred inside
the equipment itself. They need not be any time delay for coordination with
other relays in the system.
1.4 Wide Area Protection
System-wide disturbances in power systems are a challenging
problem for the utility industry because of the large scale and the complexity
of the power system. When a major power system disturbance occurs,
protection and control actions are required to stop the power system
degradation, restore the system to a normal state, and minimize the impact of
the disturbance. In some cases, the present control actions are not designed for
a fast-developing disturbance and may be too slow.
1.4.1 Definition
The meaning of wide-area protection, emergency control, and power
system optimization may vary dependant on people, utility, and part of the
world. Therefore, standardized and accepted terminology is important. Since
the requirements for a wide-area protection system vary from one utility to
another, the architecture for such a system must be designed according to what
technologies the utility possesses at the given time. Also, to avoid becoming
obsolete, the design must be chosen to fit the technology migration path that
the utility in question will take. The solution to counteract the same physical

1. Introduction 9
phenomenon might vary extensively for different applications and utility
conditions.
The potential to improve power system performance using smart wide-
area protection and control, and even defer High voltage equipment
installations, seems to be great. The introduction of the phasor measurement
unit (PMU) has greatly improved the observability of the power system
dynamics. Based on PMUs different kinds of wide-area protection, emergency
control and optimization systems can be designed. A great deal of engineering,
such as power system studies and configuration and parameter settings, is
required, a cost effective solution could be based on standard products and
standard system designs.
1.4.2 Phasor Measurement Units (PMUs)
- History
In 1893, Charles Proteus Steinmetz presented a paper on simplified
mathematical description of the waveforms of alternating current electricity.
Steinmetz called his representation a phasor. With the invention of phasor
measurement units (PMU) in 1988 by Dr. Arun G. Phadke and Dr. James S.
Thorp at Virginia Tech, Steinmetz’s technique of phasor calculation evolved
into the calculation of real time phasor measurements that are synchronized to
an absolute time reference provided by the Global Positioning System. We
therefore refer to synchronized phasor measurements as synchrophasors. Early
prototypes of the PMU were built at Virginia Tech, and Macrodyne built the
first PMU (model 1690) in 1992.

1. Introduction10
- Definition
Phasor Measurement Units (PMUs) are considered as a promising tool
for future real-time monitoring, protection, analysis, and control. A PMU can
measure waveforms of voltages and currents typically at a rate of up to 60
samples per cycle, using a common synchronizing signal from the Global
Positioning System (GPS). The GPS not only provides time tagging for all the
measurements but also ensures that all phase angle measurements are
synchronized to the same time as well. A PMU located at any bus can provide
direct synchronized measurements of magnitudes and angles for voltage
phasor at that bus, and for current phasors of branches incident to that
particular bus, assuming that the PMU has sufficient number of channels.
Observability analysis is a fundamental component of real time state
estimation. Installing PMU at each bus offers complete observability of the
system. However, installing large number of PMUs in a system leads to
increase in complexity and cost of communication facilities which can be
higher than that of the PMUs themselves. Reduction of number of installed
PMUs will definitely reduce monitoring and communications costs. The
aforementioned issues demonstrate the importance of optimal PMU placement
in electrical networks.

12 2. Problem statement
CHAPTER 2
Problem statement
2.1 Introduction
This chapter discusses the problem statement of relay modelling and
how to embed such a model on a real power system. Generally, Problem
statement can be divided into three parts (Vision, Statement issue and
Method). “Vision” part, will answer the question of what does the world look
like when solving the problem? “Statement issue” part, will describe the
problem using specific issue and the last part “Method”, will describe the
process used to solve the problem.
In this chapter we will firstly indicate information about relay structure
especially microprocessor relays such as (numerical and digital relays) and the
functionality of each of the internal modules of the generalized microprocessor
relay will be discussed, then we will define the meaning of Modelling as an
entrance to understand relay modelling, then the problem statement of relay
modelling will be indicated in form of three parts mentioned above (“Vision”,
“Statement issue” and “Method”) and finally relay modelling embedded in a
real power system and the various types of relays required to protect power
system equipment such as generator, transformer, bus and transmission line
according to IEEE standard will be explained.

2. Problem statement 13
2.2 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 the amount of information commonly available. It’s
possible to recreate the majority of modern digital and numerical relay
equipment.
The following figure 2.1 is shown the schematic of a generalized
numerical relay structure and the functionalities of each module of the
generalized relay model is developed next.
Figure 2-1: Generalized Numerical Relay Structure
2.2.1 Analogue Signal Scaling Module
The analogue signal scaling 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

2. Problem statement14
suitable for use by the data acquisition system. Since analogue-to-digital
converts accept only voltage signals this module also converts current to
equivalent voltages.
2.2.2 Analogue Anti-Aliasing Filtering
The analogue 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).
2.2.3 Sample and Hold
The basic function of sample and hold in an analog input system is to
capture an input signal and hold it constant during the subsequent ADC
conversion cycle.
2.2.4 Multiplexer
The analogue multiplexer consists of an array of analogue switches controlled
with digital logic. The analogue multiplexer uses the digital control logic to
select a specific analogue input and direct it to its output. In the generalized
relay model of Figure 2.1, the analogue multiplexer is applied to select one
sample-and-Hold output channel at a time for subsequent analogue scaling and
analogue-to digital conversion. During a sample interval, the multiplexer
brings all the sampled-and held signals one a time for analogue-to-digital
conversion. The multiplexer is not relevant for modelling of numerical relays,

because the multiplexer does not affect the analogue inputs. So it is assumed
here to be accomplished seamlessly.
2.2.5 Analogue to Digital Converter
.
An analogue-to-digital converter (A/D converter or ADC) takes the
instantaneous value of an analogue voltage and converts it into an n-bit number
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 technique can be used
to achieve this conversion. The full-input voltage ranges for an ADC are
typically 0 to +5 or 0 to +10 volts for unipolar operation, and -5 to +5 or -10
to +10 volts for bipolar operation.
2.3 Modelling
Modelling is a proven and well-accepted engineering technique. We
build architectural models of houses and high rises to help their users visualize
the final product.
We may even build mathematical models to analyse the effects of winds
or earthquakes in our buildings. A model provides the blueprints of a system.
Models may encompass detailed plans, as well as more general plans that give
a 30,000-foot view of the system under consideration. A good model includes
those elements that have broad effect and omits those minor elements that are
not relevant to the given level of abstraction. Every system may be described
from different aspects using different models, and each model is therefore a
semantically closed abstraction of the system. A model may be structural,

emphasizing the organization of the system, or it may be behavioural,
emphasizing the dynamics of the system.
Modelling is also important because description of system behaviour by
experimentation might not be feasible due to experiment may be to too
dangerous, cost of experimentation might be too high.
To sum up, modelling can do the following:
- Models help us to visualize a system as it is or as we want it to be.
- Models permit us to specify the structure or behavior of a system.
- Models give us a template that guides us in constructing a system.
- Models document the decisions we have made.
2.4 Digital and Numerical Relay Models
2.4.1 Introduction
The objective of the proposed theses is to develop a methodology for
designing protection systems. This methodology should facilitate the process
of designing numerical relay models. .
The methodology should embed the models within a power system modelled
in a software program such as MATLAB, in such a way to recreate the
protection system working along with the modelled power system. With this
arrangement, the methodology should help in investigating the interaction
between the protection system and the power system under specific scenarios.
Manufacturers, consultants and academics for designing new prototypes and
algorithm, to check and optimize the performance of relays already installed in

power systems and to train new protection personnel, have used relay models
for a long time.
2.4.2 The Methodology of Modelling Numerical Relays
The proposed protection system model designing methodology is
divided in major two-steps. .
The first step consists of designing numerical and digital relay models
with the help of a computer program such as MATLAB. For designing, the
numerical and digital relay model structure is based in the structure of the
generalized numerical relay.
The second step is embedding the designed numerical relay models into
a power system modelled in and MATLAB program or any other modelling
programs such as EMTP and ETAP.
Now and from the previous information, it is easy to state the problem
of modelling relays with the help of its parts as mentioned before. The
following topic indicates problem statement of relay modelling.
2.5 Problem Statement
As mentioned at the beginning of this chapter, problem statement can be
divided into three types Vision, Statement issue and Method. These types will
be explained in details in this section.
2.5.1 Vision
It’s now clear that with the usage of modelling relays flexible, economic
and feasible protection to electric power system is provided. These relays are
widely used in today’s power system. Designing and modelling of numerical

relays are crucial tasks in developing new devices and algorithm.
Modelling of digital and numerical relays is employed by utility engineers and
educators to assess the performance of relays installed in power systems ad to
train new protection personnel. Digital and numerical relay models are
employed by manufactures and researchers to develop new relay prototypes
and protection algorithm.
So solving this problem will make it easier and simple and of course the
world needs the problem of relay modelling to be solve.
2.5.2 Statement Issue
The development in relaying technology have not solved definitively all the
protection issues, and therefore, substantial investigations and research on
protection and protective relaying continuous.
The following are the most relevant topics currently being investigated
in the field of protective relaying.
- Setting and adjustment of relays and interrelation of protective relays
with different component of the power system especially control elements.
- Behaviour of relays during different operating states of power systems
- Designing of new relay algorithms, relay functions and protection schemes
- Engineering of new relay products
- Education and training of protection personal
Most of times, it is impossible to investigate the mentioned topics on
real systems due to operation, security and economical restrictions. Several
approaches and resources have been developed to overcome these difficulties.
These include Real Time Digital Simulator (RTDS), Real Time Playback
Simulator (RTPS) and software packages for modelling protective relays. So
all the previous difficulties are solved by modelling technique.

2.5.3 Method
The following flowcharts show examples of Methods which are used
to model various types of relays mentioned in this book.
1- Over Current Relay

2- Distance Relay

3- Differential Relay

4- Directional Relay

23 2. Problem statement
2.6 Embedding Relays into a Power System
In the “IEEE14 Bus system” shown in Figure 2.2, the protection system
is applied according to IEEE standard using relays mentioned in table 2-5.
A load flow in case of normal operation is also run on this system and
the resulted data is shown in chapter 3
Figure 2-2: IEEE 14-Bus System

IEEE14 Bus system parameters
Exciter
No
1 2 3 4 5
KA 200 20 20 20 20
TA 0.02 0.02 0.02 0.02 0.02
TB 0.00 0.00 0.00 0.00 0.00
TC 0.00 0.00 0.00 0.00 0.00
VRmax 7.32 4.38 4.38 6.81 6.81
VRmin 0.00 0.00 0.00 1.395 1.395
KE 0.19 1.98 1.98 0.70 0.70
TE 0.0012 0.001 0.001 0.001 0.001
TF 1.0 1.0 1.0 1.0 1.0
Table 2-1: Exciter Data
Generator Bus No 1 2 3 4 5
MVA 615 60 60 25 25
Xl (P.U) 0.2396 0.00 0.00 0.134 0.134
Ra (P.U) 0.00 0.0031 0.0031 0.0014 0.0041
Xd (P.U) 0.8979 1.05 1.05 1.25 1.25
X’d (P.U) 0.2995 0.1850 0.1850 0.232 0.232
X’’d (P.U) 0.23 0.13 0.13 0.12 0.12
T’do 7.4 6.1 6.1 4.75 4.75
T’’do 0.03 0.04 0.04 0.06 0.06
Xq (P.U) 0.646 0.98 0.98 1.22 1.22
X’q (P.U) 0.646 0.36 0.36 0.715 0.715
X’’q (P.U) 0.4 0.13 0.13 0.12 0.12
T’qo 0.00 0.3 0.3 1.5 1.5
T’’qo 0.033 0.099 0.099 0.21 0.21
H 5.148 6.54 6.54 5.06 506
D 2 2 2 2 2
Table 2-2: Generator Data

Bus NO Generator Load Bus
Type
Generator
P Q P Q Q (max) Q(min)
1 1426.8 0.00 0.00 0.00 2 6150 -6150
2 246 -260.76 133.455 133.455 1 307.5 -246
3 0.00 0.00 579.33 116.85 2 246 0.00
4 0.00 0.00 293.97 0.00 3 0.00 0.00
5 0.00 0.00 46.74 9.84 3 0.00 0.00
6 0.00 0.00 68.88 46.125 2 147.6 -36.9
7 0.00 0.00 0.00 0.00 3 0.00 0.00
8 0.00 0.00 0.00 0.00 2 147.6 -36.9
9 0.00 0.00 181.425 102.09 3 0.00 0.00
10 0.00 0.00 55.35 35.67 3 0.00 0.00
11 0.00 0.00 21.525 11.07 3 0.00 0.00
12 0.00 0.00 9.84 9.84 3 0.00 0.00
13 0.00 0.00 9.84 9.84 3 0.00 0.00
14 0.00 0.00 91.635 30.75 3 0.00 0.00
*Bus type: (1) swing bus, (2) generator bus (PV bus), and (3) Load Bus
(PQ Bus)
Table 2-3: Bus Data
From
Bus
To
Bus
Resistance
(P.U)
Reactance
(P.U)
Line
Charging
(P.U)
Tap Ratio
1 2 0.01938 0.05917 0.0528 1
1 5 0.05403 0.22304 0.0492 1
2 3 0.04699 0.19797 0.0438 1
2 4 0.05811 0.17388 0.0374 1
2 5 0.05695 0.17388 0.034 1
3 4 0.06701 0.17103 0.0346 1
4 5 0.01335 0.04211 0.0128 1
4 7 0.00 0.20912 0.00 0.978
4 9 0.00 0.55618 0.00 0.969
5 6 0.00 0.25202 0.00 0.932
6 11 0.09498 0.1989 0.00 1
6 12 0.12291 0.25581 0.00 1
6 13 0.06615 0.13027 0.00 1
7 8 0.00 0.17615 0.00 1

Table 2-4: Line Data
IEEE Standard Protection Relays
7 9 0.00 0.11001 0.00 1
9 10 0.03181 0.08450 0.00 1
9 14 0.12711 0.27038 0.00 1
10 11 0.08205 0.19207 0.00 1
12 13 0.22092 0.19988 0.00 1
13 14 0.17093 0.34802 0.00 1
Generator
Stator protection
 Phase Faults
 Differential over current relay (87G) (Primary)
 Over current instantaneous and time delayed (50/51) (Backup)
 Negative sequence over current relay (46) (Backup)
 Voltage control over current relay (51V) (Backup)
 Distance relay (21) (Backup)
 Ground Faults
 Over/under voltage relay (59/27)
 Ground fault over current relay (51G)
 Negative sequence over current relay (46)
Rotor Protection
 Ground Fault
 Ground over voltage relay
 Loss of excitation
 Loss of excitation relay (40)

Table 2-5: IEEE Standard Protection Relays
BUS
 Differential over current protection (87B)
 Over current relay (50/51)
 Distance relay (21)
Transmission Line
 Distance relay (21)
 Over current Relay (50/51)
Transformer
 Differential over current relay (87T)
 Instantaneous and time delayed over current relay
(50/51)
 Restricted earth fault relay (87N)
 Over current ground fault relay (50/51N)
 Directional over current relay (67)
 Over excitation relay (24)
 Over load relay (49)

2.6.1 The Effective of Embedding Protection System
In order to make sure that the protection system runs effectively on the
power system through different fault, we might choose a subsystem from the
IEEE 14 bus system in Figure 2.3
Figure 2-3: Subsystem of IEEE14 Bus
Using subsystem, which contains (BUS1, BUS2 and BUS5), in the
above figure, each bus represents a substation which contains (inner feeders
and outer feeders).
If there is a fault occurs on Subsystem, its protection will operate to clear
this type of fault.
The substation protection consists of four panels, (Bus panel, generator
panel, transformer panel and transmission line panel). Each panel contains the
typical protection functions as mentioned in Table 2.1
In our relay modelling, we choose some relays according to standard
required to protect the various equipment of the system.

The results of modelling of these relays and the power system model in which
these relays are embedded are shown in Chapter 3.
Such a relays are shown in the following table.
Table 2-6: Study Cases of Fault
Fault location Fault Type Relays used
BUS 1
 SLG Fault
 3-phase Fault
 87B
 50/51
 21
Transmission line Be-
tween (bus1&5) and be-
tween (bus 1&bus2)
 SLG Fault
 3-phase Fault
 50/51
 21
Transformer (between
generation and bus 1)
 3-phase Fault  87T
 50/51

3. Substation Protection 31
CHAPTER 3
Substation Protection
3.1 Introduction
Electric power may flow through several substations between
generating plant and consumer, and may be changed in voltage in several steps.
The task of protection and control in substations and in power grids is the
provision of all the technical means and facilities necessary for the optimal
supervision, protection, control and management of all system component and
equipment in high and medium-voltage power systems.
The task of control system starts with the position indication of the HV
circuit breaker and ends in complex systems for substation automation,
network and load management as well as for failure- and periodical
maintenance. For all these functions the data acquisition at the switch yard and
the command execution at the switch yard are part of the network control and
management.
The purpose of power system control as a subdivision of power system
management is to secure the transmission and distribution of power in the more
complex power systems by providing each control centre with a continually
updated and user friendly overall vision of the entire network. All important
information is transmitted via communication links from the substations to the
control Centre where it is instantly evaluated and corrective action are taken.
The growing amount of data acquired, the increasing communication
bandwidth and the performance and memory capacity of modern computers
have resulted in replacement for conventional panels for direct process control

3. Substation Protection32
by computer based control systems with screen or video based displays. In few
cases, conventional mimic panels are still kept for power grid overview.
Load management is directly influencing the system load. With the help
of ripple control communication via the power network. It is selectively
disconnecting and reconnecting consumers. On the basis of actual and
forecasted load figures it is possible to level out loads curves, to make better
usage of available power resources, or buy or sell energy on the market. It
would be beyond the scope of this book to describe in detail all the subsystems
and component belonging to network control. Therefore, this chapter presents
several system fault cases and how the protection system interacts to these
cases to provide the maximum reliability and sensitivity for protection.
In Chapter 2, the relay modelling can be completely designed and tested
by a software program such as MATLAB program which contains power
system equipment’s such as buses, transformers and transmission lines. In this
Chapter, relays such as overcurrent, differential over current and distance are
applied in a local protection system applied for “IEEE 14 bus system”.
3.2 Load Flow for IEEE 14 Bus System
The following tables indicate load flow results for “IEEE14 bus” using
typical parameters mention in Chapter2.

Table 3-1: Load Flow Results
Bus ID Generation Load Bus Load Flow
MW MVAR MW MVAR ID MW MVAR Amp %PF
Bus1
H_1 232.40 -16.561 0 0
Bus2 H_2 156.88 -20.405 86171.8 -99.2
Bus5 H_5 75.516 3.844 41184.5 99.9
Bus2
H_4 40.0 43.533 21.70 12.7
Bus1 H_3 -152.5 27.678 85679.7 -98.4
Bus3 H_3 73.237 3.560 40510.5 99.9
Bus4 H_4 56.133 -1.562 31025.0 -100
Bus5 H_5 41.519 1.157 22947.8 100
Bus3
H_3 0.00 25.063 94.200 19
Bus2 H_2 -70.91 1.602 40547.2 -100
Bus4 H_4 -23.28 4.461 13553.1 -98.2
Bus4
H_4 0.00 0.000 47.800 -3.9
Bus2 H_2 -54.45 3.033 30941.8 -99.8
Bus3 H_3 23.659 -4.824 13698.4 -98.0
Bus5 H_5 -61.15 15.816 35835.7 -96.8
Bus7 Z_7 28.071 -9.689 16847.2 -94.5
Bus9 L_9 16.081 -0.435 9126.4 -100
Bus5
H_5 0.00 0.000 7.600 1.60
Bus1 H_1 -72.75 2.241 41218.5 -100
Bus2 H_2 -40.61 +2.085 23030.2 99.9
Bus4 H_4 61.670 -14.194 35835.7 -97.5
Bus6 L_6 44.099 12.437 25946.6 96.2
Bus5
H_50 0.00 0.000 7.600 1.60
Bus1 H_1 -72.753 2.241 41218.5 -100
Bus2 H_2 -40.615 -2.085 23030.2 99.9
Bus4 H_4 61.670 -14.194 23030.2 -97.5
Bus6 L_6 44.099 12.437 25946.6 96.2
Bus6
L_6 0.00 12.770 11.200 7.50
Bus1 L_11 7.357 3.564 4411.1 90.0
Bus1 L_12 7.787 2.504 4413.4 95.2
Bus3 L_13 17.750 7.218 10339.3 92.6
Bus7
Z_7 0.00 0.00 0.00 0.00
Bus8 T_8 0.00 -17.174 9341.1 0.00
Bus9 L_9 28.070 5.782 15587.6 97.9
Bus4 H_4 -28.070 11.392 16476.6 -92.7
Bus8
T_8 0.000 17.635 0.00 0.00 Bus7 Z_7 0.00 17.635 9341.1 0.0
Bus9
L_9 0.00 0.00 29.502 -4.584
Bus10 L_10 5.224 4.216 3670.3 77.8
Bus7 Z_7 -28.070 -4.980 15587.6 98.5
Bus14 L_14 9.424 3.608 5517.4 93.4
Bus4 H_4 -16.080 1.740 8843.5 -99.4
Bus10
L_10 0.00 0.00 9.000 5.800
Bus9 L_9 -5.211 -4.182 3670.3 78.0
Bus11 L_11 -3.789 -1.618 2263.5 92.0
Bus11
L_11 0.00 0.00 3.500 1.800
Bus6 L_6 -7.302 -3.448 4411.1 90.4
Bus10 L_10 3.802 1.648 2263.5 91.8
Bus12
L_12 0.00 0.00 6.100 1.600
Bus6 L_6 -7.715 -2.354 4413.4 95.6
Bus13 L_13 1.615 0.754 975.2 90.6
Bus13
L_13 -15.2 0.00 0.00 13.500
Bus6 L_6 -17.538 -6.801 10339.3 93.2
Bus12 L_12 -1.609 -0.749 975.2 90.7
Bus14 L_14 5.647 1.749 3249.2 95.5
Bus14
L_14 0.00 0.00 14.900 5.00
Bus9 L_9 -9.308 -3.361 5517.4 94.1
Bus13 L_13 -5.592 -1.639 3249.2 96.0

Table 3-2: Transmission Line Losses
Branch From To Bus Flow To From Bus Flow Losses %Bus Voltage Vd
%Drop
in Vmag
ID MW MVAR MW MVAR KW KVAR From To
1_2 156.888 -20.405 -152.590 27.687 4297.9 7272.8 106.0 104.5 1.50
1_5 75.516 3.844 -72.753 2.241 2763.2 6085.6 106.0 102.0 4.05
2_3 73.237 3.560 -70.914 1.602 2323.3 5262.4 104.5 101.0 3.5
2_4 56.133 -1.562 -45.456 3.033 1676.8 1470.6 104.5 101.8 2.73
2_5 41.519 1.157 -40.615 -2.085 903.8 -927.9 104.5 102.0 2.55
3_4 -23.286 4.461 23.659 -4.824 373.4 -362.7 101.0 101.8 0.77
4_5 -61.155 15.816 61.670 -14.19 514.3 1622.3 101.8 102.0 0.18
4_7 28.071 -9.689 -28.070 11.392 1.7 1703.1 101.8 106.2 4.38
4_9 16.081 -0.435 -16.080 1.740 1.3 1304.9 101.8 105.6 3.82
5_6 44.099 -12.437 -44.094 -8.016 4.4 4421.3 102.0 107.0 5.05
6_11 7.357 3.564 -7.302 -3.448 55.4 116.1 107.0 105.7 1.31
6_12 7.787 2.504 -7.715 -2.354 71.8 149.5 107.0 105.5 1.48
6_13 17.750 7.218 -17.538 -6.801 212.1 417.8 107.0 105.0 1.96
7_8 0.00 -17.174 0.000 17.635 0.0 461.1 106.2 109.0 2.85
7_9 28.070 5.782 -28.070 -4.980 0.0 801.9 106.2 105.6 0.56
9_10 5.224 4.216 -5.211 -4.182 12.9 34.1 105.6 105.1 0.49
9_14 9.424 3.608 -9.308 -3.361 116.1 246.9 105.6 103.6 20.4
10_11 -3.789 -1.618 3.802 1.648 12.6 29.5 105.1 105.7 0.59
12_13 1.615 0.754 -1.609 -0.749 6.3 5.7 105.5 105.0 .48
13_14 5.646 1.749 -5.592 -1.639 54.1 110.2 105.0 103.6 1.46
1341.5 30125.3
Table 3-3 shows that the total generation in the system (MW and Mvar)
is equal to the system total load demand and system losses (MW and Mvar),
and from that we get that the system model we work on is healthy and ready
for our next step.
Table 3-3: System Total Generation and Demand
MW MVAR MVA %PF
Source (Swing Buses) 232.404 -16.561 232.993 99.75 leading
Source (Non-Swing Buses) 40.00 99.003 106.778 37.46 lagging
Total Demand 272.404 82.441 28.605 95.71 lagging
Total Motor Load 259.000 73.500 269.227 96.20 lagging
Total Static Load 0.002 -21.184 21.184 0.01 leading
Total Constant Load 0.00 0.00 0.00
Total Generic Load 0.00 0.00 0.00
Apparent Losses 13.401 30.125
System Mismatch 0.00 0.00

3.3 Fault Cases
“IEEE14 bus” is protected by the relays that created and applied on as
mentioned before in Chapter 2, the system imbedded with relays is tested and
protected correctly, and to justify that we zoomed on subsystem as mentioned
in chapter 2.
Figure 3-1: Sub System Of (“IEEE14 Bus”)

3.3.1 Generator Protection
Figure (3.2) shows the typical protection of unit generator, the relays
responsible to detect any fault considered should trip, for our case of study we
just modelled three protections relays differential, over current relay and
distance relay.
In this chapter we have not include generator protection because that the
generator modulation does not enable us to apply internal faults and show the
protection behavior.
Figure 3-2: Unit Generator Typical Protection Model

3.3.2 XFMR Protection
The fault applied on the star side of the transformer. From the typical
protection of transformer, the relays responsible to detect that fault should trip,
for our case of study we just modelled two protections relays differential and
over current relay. And for the three phase fault condition the primary
protection (Differential Relay) must detect the fault because of the fault
happened in the zone of the differential relay, and the secondary protection
also detect the fault and after the delay time it will trip, but in this condition
we made the primary and secondary trip at the same time that they detect the
fault.
Figure 3-3: Transformer Typical Protection Model

Following figures show the current on both sides of the transformer and
protection system trip signals due to fault case.
Figure 3-4: Current on Both Sides of The Transformer
Figure 3-5: Trip Signal of Differential Relay and Over Current

3.3.3 Bus Protection
In the Following, different fault cases (single line to ground fault and
three-phase fault) and the protection system action due to fault cases is shown.
The fault applied on the bus within the primary protection (differential)
zone but also as mentioned in the previous paragraph the primary and the
secondary protection (over current and distance relay) detect the fault at the
same time and the secondary should be delayed with safety margin time, and
in our study case we made the both primary and secondary trip at the same
time.
Figure 3-6: Bus Protection Model

 Single Line to Ground Fault
Figure (3.7) shows the total input feeder current and the total output feeders
current. Figure (3.8) shows the bus voltage before and after fault, also shows
the main protection (Differential Relay) trip action.
Figure 3-7: Total Inner Feeder Current and Total Outer Feeder Current
Figure 3-8: Bus Voltage and Differential Relay Action

Figure 3-9: Over Current and Distance Relay
 Three phase fault
Figure (3.10) shows the total input feeder current and the total output
feeders current. Figure (3.11) show the bus voltage before and after fault, also
shows the main protection (Differential Relay) trip action.
Figure 3-10: Total Inner Feeder Current and Total Outer Feeder Current

Figure 3-11: Bus Voltage and Differential Relay Action
Figure (3.12) shows over current relay trip signals and the trip signals timing
are different due to different phase shift of the current, when the current ex-
ceeds the setting current (Iset) the relay will produce the trip signal. Figure
(3.13) shows the trip signals of distance relay protection due to three phase
fault.
Figure 3-12: Over Current Relay Trip Signal

Figure 3-13: Distance Relay Trip Signal
3.3.4 Transmission Line Protection
Figure 3-14: Transmission Line Protection Model

For the transmission line fault cases, the fault occurred in the middle of
the lines between bus (1&5) and between bus (1&2) and to prove that the
protection system works correctly the fault must be cleared from both sides.
1- Transmission line between bus1 and bus5
 Single line to ground fault
First: the fault seen from bus 1 and will introduce the protection system
action. Figure (3.15) shows the current signals in transmission line before and
after the fault ,also shows the action of primary protection (distance relay).
Figure (3.16) shows the secondary protection (over current relay) trip signal
and if the current exceeds the setting value the relay produce the trip signal.
Figure 3-15: Transmission Line Current and Distance Relay Trip Signals

Second: the fault seen from bus 5 and will introduce the protection system
after the fault ,also shows the action of distance relay. Figure (3.18) shows
the over current relay trip signal and if the current exceeds the setting value
the relay produce the trip signal
Figure 3-17: Transmission Line Current and Distance Relay Trip Signal

The previous two cases prove that the protection system operates
correctivly .
after the fault ,also shows the action of distance relay. Figure (3.20) shows the
over current relay trip signal and if the current exceeds the setting value the
relay produce the trip signal.

Second: the fault seen from bus 5 and will introduce the protection
system action. Figure (3.21) shows the current signals in transmission line
before and after the fault ,also shows the action of distance relay. Figure (3.22)
shows the over current relay trip signal and if the current exceeds the setting
value the relay produce the trip signal.

correctly .
2-Transmission line between bus1 and bus2
 Single line to ground fault

system action. Figure (3.25) shows the current signals in transmission line

correctly .

system action .Figure (3.29) shows the current signals in transmission line

The previous two cases prove that the protection system operates correctly .
To varify that the modelling can work with any system we applied it at
IEEE 39 bus system and we get the expected result.
The results of IEEE39 bus system will be shown in the presentation .
Conclosion
 After the previus fault cases in these chapter the local protection
system prove that it can work correctivly and achive maximum
protection needed.
 As expected to reduce the effective size of the problem dimension and
simplify the problem solution. and like that the fault location,
isolation and service restoration (FLISR) is implemented on a real
distribution network.
 provision of all the technical means and facilities necessary for the
optimal supervision, protection, control and management of all
system component and equipment is achieved

4. Wide Area Protection54
CHAPTER 4
Wide Area Protection
Existing protection system is a distributed control system, which
mainly using local information to detect power system fault and abnormal
state. Due to limited information, existing protection system has many
deficiencies, mainly in the following aspects:
1) Protective relaying uses step-style setting principle to coordinate,
sometimes delay time will be very long and even is difficult on setting and
cooperation in certain operating conditions.
2) Protective relaying criterion is mainly based on local measurement.
Protective relay settings are developed that cover many different operating
arrangements. Usually settings are calculated for “worst case” and then
checked for adequacy during other operating conditions. Therefore, it is
difficult to adapt to different operating conditions for give setting.
3) Protective relaying aims to removal fault elements, and it is relatively
independent with security and stability devices, therefore protective relaying
and security stability devices are lack of coordination ability. Protective
relaying cannot consider the consequence and implications to power system
security and stability due to fault removal, sometimes even leads to chain-trip
events.
4) Routine backup power auto-switch is based on one substation
information, and it is difficult to adapt to various operating conditions of power
systems.

4. Wide Area Protection 55
Routing backup power auto-switch cannot achieve remote restoration
ability, and is difficult to consider the effect of distributed generation and
overload by backup power auto-switch operation.
Based on above issues, it is required to develop a new protection and
control systems that based on wide area information, called Wide Area
Protection (WAP) system. The amount of available information to protection
system shall be increased in order to enhance selectivity, sensitivity, and
reliability, and achieve a more intelligent and adaptive control system.
Therefore, it is necessary to study WAP technology roadmap which contained
system structure, function configuration, key technologies, and
implementation.
4.1 Definition
WAP is a control and protection system based on power grid information
through network communication. WAP can determine fault location and clear
fault selectively and quickly, then analysis the effect of power system stability
after faulty components disconnection and take appropriate control actions.
WAP consists of master and slave station. With wide area information, WAP
can solve the setting and matching difficulty of protective relaying, and can
shorter the delay time of back-up protection. WAP also can improve the level
of power system security and stability operation, and coordinate protective
relaying and stability control. Obtain real-time wide area information reliably
and accurately is the key point to build WAP. The reliability of network,
synchronization accuracy, and the efficiency of communication protocols are
key technologies of WAP. Full use of wide area information to get smarter,
more reliable and more adaptable control strategy that coordinated protective
relaying and stability control is the core contents of WAP.

4.2 System Structure
WAP system can be descripted as: Getting real-time information of
regional power grid through communications network, and with wide area
information to determine fault location, and remove the fault components from
power system quickly and selectively, and has certain security and stability
control ability. WAP system consists of master and slave station; system
structure is shown as Figure 4-1.
Figure 4-1: Diagram of WAP System Architecture
Master station mainly issues protection and control functions that
require multi-substation information which are collected through
communication network by slave station. Master station can analysis power
grid operation mode and status, determine fault location and send
corresponding commands to slave station.

Slave station is responsible for acquisition of electrical and state
quantities, and issues the protection and control functions that only require
local-substation information. Slave station sends information that master
station required to master station through communication network. At the same
time, slave station can receive, verify and execute master control command.
As protection is concerned, master and slave station both aims at back-
up protection.
4.3 Master Station
WAP should take full advantage of current differential protection to
improve selectivity and sensitivity of backup protection when synchronization
signal is available and healthy and to improve system reliability with wide area
redundancy information.
In the case of lost synchronization signal, current differential protection
is invalid, and pilot direction protection can be used, which does not depend
on synchronization signal.
In the case of CB failure, WAP can send remote trip command to the
CBs of adjacent components and substations. With such strategy, backup
protection operating time can be shorted within 0.2s or even less.
4.4 Slave Station
Protective equipment should be close to the object to be protected. Based
on this principle, any protection or control function which needs only local
information should be implemented in slave station. Meanwhile, slave stations
send information that master station required, and receives, verify and execute
commands from master station.

In the consideration of security, any trip command must be verified by
corresponding slave station. In general, slave station can use pick-up signal,
over current, under voltage or low impedance to verify the corresponding CB
trip command.
Traditionally, distributed protective relaying should match step by step
in the setting value and delay time. When all the information is collected in
slave station, all the protection functions can match automatically based on
accurate fault location. The following protection and control function can be
integrated in slave station:
1) Distance relay of transmission line;
2) Zero-sequence overcurrent relay of transmission line;
3) Current differential relay of power transformer;
4) Voltage blocking overcurrent of power transformer;
5) Current differential relay of bus;
6) Low frequency shedding;
7) Low voltage shedding;
8) Others that required.
4.5 WAP Using Phasor Measurement Units (PMUs)
PMU is monitoring device and being used effectively in real- time
monitoring system to assure reliable and secure supply to end users. In PMU
all the electrical parameters are measured in frequency domain with both
magnitude and phase angle of voltage and current. Through Global Positioning
System (GPS) all the measurements of PMUs are time stamped with common
time reference signal. Synchronization of power system measurements is
achieved by GPS with time mismatch of less than 1μs.

The PMU has roles for specific applications such as monitoring,
protection, state estimation and control in power systems. A rapid development
of processor and information technology, computer aided tools and data
collection techniques are being used widely for power plant monitoring and
control.
PMU has been increased worldwide in electrical utilities. The major
issues of PMUs are site location and its placement. Due to the association of
huge costs involved in PMUs and its communication infrastructure, it is not
necessary and also it will not be economically to place PMU in all substation
of the connected network.
PMUs installed on one bus can able to measure nearby buses. As result,
problem has been raised for number of PMUs to be installed in power system.
Optimization of PMU placement with complete observability of system
will help the utility to operate the network with more reliability.
Many investigations have been carried out by using different methods
for placement problem using both evolutionary algorithms and mathematical
programming approaches.
PMU can measure waveforms of voltages and currents typically at a rate
of up to 60 samples per cycle, using a common synchronizing signal from the
GPS. The GPS not only provides time tagging for all the measurements but
also ensures that all phase angle measurements are synchronized to the same
time as well. A PMU located at any bus can provide direct synchronized
measurements of magnitudes and angles for voltage phasor at that bus, and for
current phasors of branches incident to that particular bus, assuming that the
PMU has sufficient number of channels.

Installation of a typical 10 Phasor PMU is a simple process. A phasor
will be either a 3 phase voltage or a 3 phase current. Each phasor will,
therefore, require 3 separate electrical connections (one for each phase).
Typically, an electrical engineer designs the installation and interconnection of
a PMU at a substation or at a generation plant. Substation members will bolt
equipment rack to the floor of the substation following established seismic
mounting requirements. Then the PMU along with a modem and other support
equipment will be mounted on the equipment rack. They will also install the
GPS antenna on the roof of the substation as manufacturer instructions.
Substation members will also install "shunts" in all Current transformer (CT)
secondary circuits that are to be measured. The PMU will also require
communication circuit connection
Figure 4-2: Phasor Measurement Unit (PMU) Structure.

Installing PMU at each bus offers complete observability of the system.
However, installing large number of PMUs in a system leads to increase in
complexity and cost of communication facilities which can be higher than that
of the PMUs themselves. So, Reduction of number of installed PMUs will
definitely reduce monitoring and communications costs. Therefore,
importance of optimal PMU placement in electrical networks shall be
considered. The objective function is to minimize the overall cost of PMU
installation via minimizing the number of PMUs.
Several conventional optimization techniques have been proposed to
solve the optimal PMU placement problem (OPP), such as Binary Integer
Linear Programming (BILP). References and proposed the modification into
BILP technique with considering the effect of zero injection buses (ZIB). A
number of meta heuristic search algorithms and graph theory based algorithms
have been proposed to solve this optimization problem such as, modified
Binary Particle Swarm Optimization (BPSO), Genetic Algorithm (GA) ,
simulated annealing, graph theory, non-dominated sorting algorithm, Binary
Imperialistic Competition Algorithm (BICA), and Tabu search algorithm .
All these algorithms can provide complete observability of the system,
assuming that all substations of the network have the same degree of
importance. However, in reality, certain substations depict higher priority than
others. Those "highly prior" substations, commonly referred to as "critical
buses" or "important buses", need extra care during monitoring to avoid loss
of observability due to failure of any PMU. There is also a need to benefit
from existence of zero injection buses (ZIB).
The most important buses of the network are chosen based on:
(1) Topology of the network as well as on the basis of the transient
(2) Dynamic stability studies that have been performed on the system.

Types of most important buses are classified as:
(1) High Voltage buses: the high voltage bus is very important bus for
power system security. These buses should be monitored all the time for
system stability and security.
(2) High Connectivity buses: the high connectivity bus means that it has
large number of connected branches. It includes large number of current
phasors. So, the high connectivity buses are considered as important buses.
(3) Buses relevant to transient/dynamic stability: these buses of are
selected based on their relevance in preventing voltage collapses; minimizing
impacts of faults; and/or for their participation towards damping inter area
oscillations.
(4) Potential small signal control buses: which are buses where
controllers are placed. They include locations of FACTS devices, Energy
Storage Devices, high voltages direct current HVDC terminals, etc.
Assuming that a PMU should be placed at each important bus and
another PMU should be placed at a neighbour bus to present double monitoring
of these buses. However, there is no need to put a PMU at each important bus
to ensure direct observability at this bus. Therefore, ensuring double
observability at important buses from one direct PMU and one indirect PMU
is not a must. Observability from two PMUs indirectly for these important
buses is enough because the probability of failure of 2 PMUs is almost zero.
ZIB are the buses from which no current is being injected into the
system. The zero injection bus provides the availability of calculation of the
complex voltage of that zero injection bus or any one of its associating buses,
provided that all remaining associating buses are observable. There is also a
need to benefit from existence of zero injection buses (ZIB).

4.5.1 IEEE 14-bus
The system under study is the IEEE 14-bus system. It has five
synchronous machines, three of which are synchronous condensers used for
reactive power support and twenty branches. Single line diagram of this test
system is shown in Fig. 5.Node 7 is called a pure transit node; we also call it
no load node (is zero injected bus). There are no loads to consume the power,
no generators to inject the power either. The power injected by node 8 and
node 4 transmits to node 9 completely that is why it is named pure transit node.
According to PMU placement rule , for node7, as long as two current branches
are known; the left current branch can be calculated by pseudo measurement
(indirect measurement).
The chosen optimal placement results is installing 3 PMUs in buses2, 6 and 9.
Figure 4-3: Installing 3 Pmus In Buses 2 , 6 And 9

After choosing the optimal placement of PMUs through the system, we
have to check if that placement will lead to cover the whole system or not. That
is called “validation”. The program used to make load flow and short circuit
analysis is ETAP12.6.0.
 Steps for Validation
There are two steps to check for validation of choosing the number of
PMUs and their places on the buses through the system.
(1) Load Flow Analysis and Short Circuit Analysis: Using the parameters and
the initial values of the system, a load flow analysis and short circuit analysis will be possible
to achieve. The target of the load flow analysis short circuit analysis in our validation is to:
1. Determine the voltages as a phasor (magnitude and angle) of all buses.
2. Determine the currents of all the branches in the system.
(2) Observability Study: Now we know all voltages of buses and all currents branches,
in our observability study we will eliminate all voltages and currents except for:
a. The voltages of buses at which PMUS are existed
b. The currents of branches connected to the buses at which PMUs are existed
Then, we are now knowing voltages of PMUs buses and line currents
connected to each bus. Using these given voltages and currents to get the rest
of all voltages and currents of the system by these methods
a. If we know line current and voltage of one end of this line, we can get
the voltage at the other end using KVL.
b. Using zero injection bus, if we know all currents of lines connected to
that bus except one, using KCL we can get unknown line current.
After determining all voltages and currents of the system from the PMUs
(voltages of its buses and currents of its connected lines) using steps of

observability study, we will compare the results of the observability study with
the results of load flow study and short circuit study.
If the results of the studies are close with an acceptable error, then we
can say that the discussed placement of PMUs is accepted and can cover the
whole system.
 Results
Table 4-1 Buses Initial Voltages and Lines Impedances.
BUS Voltage Bus Z
mag ang from to MAG. ANG.
1 1.06 0 4 7 0.2045 89.9
2 1.045 -4.98 4 9 0.5389 89.9
3 1.01 -12.72 5 6 0.2349 89.95
4 1.019 -10.33 1 2 0.0623 71.85
5 1.02 -8.78 1 5 0.23 76.38
6 1.07 -14.22 2 3 0.204 76.705
7 1.062 -13.37 2 4 0.1856 71.76
8 1.09 -13.36 2 5 0.183 71.85
9 1.056 -14.94 3 4 0.183 68.6
10 1.051 -15.1 4 5 0.04418 72.34
11 1.057 -14.79 6 11 0.22 64.469
12 1.055 -15.07 6 12 0.283 64.337
13 1.05 -15.16 6 13 0.146 63.0667
14 1.036 -16.04 7 8 0.1762 90
7 9 0.11 90
9 10 0.09 68.78
9 14 0.2987 64.82
10 11 0.2089 66.859
12 13 0.298 42.143
13 14 0.3877 63.84

Table 4-2: Deducing Voltage Of Remaining Buses With Aid Of Allocation
Of Pmus At Buses 2 ,6 ,9. Load Flow Analysis.
Table 4-3: Deducing Voltage Of Remaining Buses With Aid Of Allocation of
Pmus At Buses 2 ,6 ,9. Short Circuit Analysis (Three Phase Fault) At Bus 5.
BUS Voltage Bus i Z BUS Voltagecalculated BUS Voltageoriginal ERROR
mag ang from to MAG. ANG. MAG. ANG. mag ang mag ang mag ang
2 1.045 -4.98 2 1 1.48 6.35 0.0623 71.85 1 1.038 -10.04 1 1.06 0 0.1849 78.17
2 3 0.701 -9.68 0.204 76.705 3 1.01 -12.719 3 1.01 -12.72 0 -102.72
2 4 0.53 -4.5 0.1856 71.76 4 1.019 -10.25 4 1.019 -10.33 0.0014 -100.29
2 5 0.39 -5.53 0.183 71.85 5 1.024 -8.764 5 1.02 -8.78 0.004 175.31
6 1.07 -14.22 6 5 0.47 15.278 0.2349 89.95 5 1.128 -19.11 5 1.02 -8.78 0.22 105.14
6 11 0.076 -39.83 0.22 64.469 11 1.057 -14.789 11 1.057 -14.79 0 -104.79
6 12 0.0768 -32.69 0.283 64.337 12 1.051 -14.774 12 1.055 -15.07 0.0068 -68.6
6 13 0.18 -36.74 0.146 63.0667 13 1.044 -14.558 13 1.05 -15.16 0.012 -76.25
9 1.056 -14.94 9 4 0.17 11.658 0.5389 89.9 4 1.1 -19.215 4 1.019 -10.33 0.183 101.4
9 7 0.269 -25.83 0.11 90 7 1.051 -16.52 7 1.062 -13.37 0.059 64.33
9 10 0.064 -53.32 0.09 68.78 10 1.051 -15.099 10 1.051 -15.1 0 -105.1
9 14 0.094 -35.19 0.2987 64.82 14 1.036 -16.03 14 1.036 -16.04 0 -106
7 1.051 -16.52 7 8 0.1762 90 0.1589 77.02 8 1.0789 -16.428 8 1.09 -13.36 0.059 64.33
BUS Voltage Bus i Z BUS Voltage calculated BUS Voltage original ERROR
mag from to MAG. MAG. mag mag mag
2 0.5239 2 1 1.02389 0.0623 1 0.46 1 0.6342 0.1742
2 3 0.24494 0.204 3 0.4739 3 0.6071 0.1332
2 4 0.76207 0.1856 4 0.3825 4 0.28 -0.1025
2 5 1.65312 0.183 5 0.2214 5 0 -0.2214
6 0.1702 6 5 1.45582 0.2349 5 -0.1718 5 0 0.1718
6 11 0.27519 0.22 11 0.1096 11 0.2708 0.1612
6 12 0.16974 0.283 12 0.12216 12 0.251 0.12884
6 13 0.41609 0.146 13 0.10945 13 0.2711 0.16165
9 0.3431 9 4 0.56188 0.5389 4 0.0403 4 0.28 0.2397
9 7 0.10824 0.11 7 0.33119 7 0.3262 -0.00499
9 10 0.01579 0.09 10 0.3417 10 0.3415 -0.0002
9 14 0.08347 0.2987 14 0.3182 14 0.386 0.0678
7 0.3262 7 8 0.30652 0.1589 8 0.2775 8 0.4197 0.1422

Table 4-4: Deducing Voltage Of Remaining Buses With Aid Of Allocation of
Pmus at Buses 2 ,6 ,9. Short Circuit Analysis (Three Phase Fault) at Bus 13.
 Comments on Results
As shown in Table 2 voltage of remaining buses with aid of allocation
of PMUs at buses 2 ,6 ,9 is deduced from Load flow analysis with Total
error=5.616% .
of PMUs at buses 2 ,6 ,9 is deduced from Short circuit analysis (Three phase
fault) at bus 5 with Total error=6.994% .
of PMUs at buses 2 ,6 ,9 is deduced from Short circuit analysis (Three phase
fault) at bus 5 with Total error=4.424% .
The results of the studies are close in normal and abnormal cases with
an acceptable error. Therefore, we can say that the chosen placement of PMUs
is accepted and can cover the whole system.
BUS Voltage Bus i Z BUS Voltage calculated BUS Voltage original ERROR
mag from to MAG. MAG. mag mag mag
2 0.8455 2 1 0.35578 0.0623 1 0.8233 1 0.8839 0.0606
2 3 0.06202 0.204 3 0.8328 3 0.8661 0.0333
2 4 0.3063 0.1856 4 0.78865 4 0.747 -0.04165
2 5 0.48588 0.183 5 0.75658 5 0.6916 -0.06498
6 0.4996 6 5 1.7569 0.2349 5 0.0869 5 0.6916 0.6047
6 11 0.29 0.22 11 0.4358 11 0.6081 0.1723
6 12 0.4423 0.283 12 0.3744 12 0.2914 -0.083
6 13 1.97416 0.146 13 0.21137 13 0 -0.21137
9 0.7209 9 4 0.25289 0.5389 4 0.5846 4 0.747 0.1624
9 7 0.13872 0.11 7 0.70564 7 0.7453 0.03966
9 10 0.16713 0.09 10 0.70586 10 0.6963 -0.00956
9 14 0.48131 0.2987 14 0.5771 14 0.4718 -0.1058
7 0.7804 7 8 0.11649 0.1589 8 0.7619 8 0.7804 0.0185

5. Conclusions 69
CHAPTER 5
Conclusions
The scope of this book is to model the protection relays for power system
studies.
The performance of a protection system and power system in which the
relay is installed can be analysed using our developed methodology that would
allow relay model to be built up in a signal computational structure.
These analyses allow the user to examine the internal variables of the
relay as well as the interaction between different relay models and with other
elements of power system.
The work reported in this book shows that the objectives have been
fulfilled successfully
The local protection system prove that it can work correctively and
achieve maximum protection needed.
Provision of all the technical means and facilities necessary for the
optimal supervision, protection, control and management of all system
component and equipment is achieved.
Existing protection system is a distributed control system, which
mainly using local information to detect power system fault and abnormal
state. Due to limited information, existing protection system has many
deficiencies mentioned. So, it is required to develop a new protection system

5. Conclusions70
that based on wide area information, called Wide Area Protection (WAP). The
amount of available information to protection system shall be increased in
order to enhance the selectivity, sensitivity, and reliability, and achieve a more
intelligent and adaptive control system. Therefore, it was necessary to study
WAP system technology roadmap which discussed in Chapter 4.
Phasor Measurement Unit (PMU) is a good idea for WAP system and
considered as a promising tool for future real-time protection. Structure and
optimization allocation of PMUs also shown in Chapter 4

References72
References
[1] https://electricalnotes.wordpress.com/2013/01/01/types-of-over-
current-relay/
[2] http://www.electrical4u.com/over-current-relay-working-
principle-types/
[3] https://en.wikipedia.org/wiki/Protective_relay#Directional_relay
[4] http://electrical-engineering-portal.com/an-example-of-the-
effectiveness-of-directional-overcurrent-relays-ansi-67-67n
[5] http://www.electrical4u.com/distance-relay-or-impedance-relay-
working-principle-types/
[6] http://www.mytech-info.com/2013/11/principle-and-operation-of-
differential.html
[7] Paper: Journal of International Council on ElectricalEngineering,
Research and Engineering Practice of Wide areaProtection and
Control Systems
[8] G Phadke. Synchronized phasor measurements in power systems.
IEEE Comput. Appl. Power. 1993;6(2); 10-15.
[9] Anderson P.M, “Power System Protection”, IEEEPress power
engineering series, New York, 1998,ISBN: 0-7803-3427-2.
[10] “IEEE Guide for Protective Relay Application toTransmission
Lines”, Std.C37.113-1999, New York,2000, ISBN 0-7381-1832-x

References 73
[11] G. Benmouyal, E. O. Schweitzer, III, A. Guzmán,“Synchronized
phasor measurement in protectiverelays for protection, control, and
analysis of electricalpower systems” Western Protective Relay
Conference,Spokane, Washington, October 22–24, 2002.
[12] AEnshaee, RA Hooshmand, FH Fesharaki. A new method for
optimal placement of phasormeasurement units to maintain full
network ob-servability under various contingencies. Elect.
PowerSyst. Res. 2012; 89(1); 1-10.
[13] Nikolaos M Manousakis, George N Korres, Pavlos S
Georgilakis. Taxonomy of PMU PlacementMethodologies. IEEE
Trans. Power Syst. 2012; 27(2): 1070-1076.
[14] SideigAbdelrhmanDowi, Gengyin Li. Phasor Measurement Unit
Based on Robust Dynamic StateEstimation in Power Systems Using
M-Estimators. TELKOMNIKA Indonesian Journal of
ElectricalEngineering. 2014; 12(11): 7631-763.
[15] Mayadevi N, Vinodchandra SS, S Ushakumari. A Review on
Expert System Applications in PowerPlants. International Journal of
Electrical and Computer Engineering. 2014; 4(1): 116-126.

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