Electrical Power System Analysis

Electrical Power System Analysis

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Description: Electric power is a natural physical phenomenon, a fundamental type of energy which mankind has learned to create and control for its benefit. Electricity is always energy produced by converting some other form of energy (heat, mechanical motion, solar light, or moving wind, etc.) into electric power. Electricity has two advantages over other forms of energy that have led to its wide popularity.

First, it is flexible: it can be transformed into heat, light, mechanical motion, radio signals, television images, and stereo sound. Second, it is very controllable: it can be turned on and off in a millionth of a second, and metered out precisely, from an amount so little that it would hardly move one grain of sand a tenth of a millimeter, to quantities that can power entire nations.

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Electrical Power System Analysis

1. Introduction

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Dr Houssem Bouchekara

Page 1


phenomenon, a fundamental type of energy
which mankind has learned to create and
control for its benefit.

Electricity is always energy produced by
converting some other form of energy (heat,
mechanical motion, solar light, or moving wind,
etc.) into electric power.

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Electricity has two advantages over other forms
of energy that have led to its wide popularity.

First, it is flexible: it can be transformed into
heat, light, mechanical motion, radio signals,
television images, and stereo sound.

Second, it is very controllable: it can be turned
on and off in a millionth of a second, and
metered out precisely, from an amount so little
that it would hardly move one grain of sand a
tenth of a millimeter, to quantities that can
power entire nations.

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History of Electric Power

Benjamin Franklin is known for his discovery of

Born in 1706, he began studying electricity in
the early 1750s. His observations, including his

He knew that lightning was very powerful and

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History of Electric Power

Between 1750 and 1850 there were many great
discoveries in the principles of electricity and
magnetism by Volta, Coulomb, Gauss, Henry,
Faraday, and others.

It was found that electric current produces a
magnetic field and that a moving magnetic field
produces electricity in a wire.

This led to many inventions such as the battery
(1800), generator (1831), electric motor
(1831), telegraph (1837), and telephone
(1876), plus many other intriguing inventions.

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History of Electric Power

In 1879, Thomas Edison invented a more
efficient lightbulb, similar to those in use today.

In 1882, he placed into operation the historic
Pearl Street steam–electric plant and the first
direct current (dc) distribution system in New
York City, powering over 10,000 electric

By the late 1880s, power demand for electric
dramatically raised electricity demand for
transportation and other industry needs.

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History of Electric Power

By the end of the 1880s, small, centralized
areas of electrical power distribution were
sprinkled across U.S. cities.

Each distribution center was limited to a service
range of a few blocks because of the
inefficiencies of transmitting direct current.

Voltage could not be increased or decreased
using direct current systems, and a way to
transport power longer distances was needed.

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History of Electric Power

To solve the problem of transporting electrical
Westinghouse developed a device called the

The transformer allowed electrical energy to be
transported over long distances efficiently.

This made it possible to supply electric power to
homes and businesses located far from the
electric generating plants.

The application of transformers required the
distribution system to be of the alternating
current (ac) type as opposed to direct current
(dc) type.

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History of Electric Power

hydroelectric power plant in 1896 initiated the
practice of placing electric power generating
plants far from consumption areas.

The Niagara plant provided electricity to Buffalo,
New York, more than 20 miles away. With the
demonstrated the superiority of transporting
electric power over long distances using
alternating current (ac).

Niagara was the first large power system to
supply multiple large consumers with only one
power line.

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The Structure of The Power System

Electric power systems are real-time energy
delivery systems.

Real time means that power is generated,
transported, and supplied the moment you turn
on the light switch.

Electric power systems are not storage systems
like water systems and gas systems.

Instead, generators produce the energy as the
demand calls for it.

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The Structure of The Power System

Figure 1 shows the basic building blocks of an
electric power system.

An interconnected power system is a complex
enterprise that may be subdivided into the
following major subsystems:

Generation Subsystem


Distribution Subsystem

Utilization Subsystem


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Figure 1: System overview.
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Generation Subsystem
1. Generators:

An essential component of power systems is the
synchronous generator or alternator.

generators can generate high power at high
voltage, typically 30 kV.

The source of the mechanical power, commonly
known as the prime mover, may be hydraulic
turbines, steam turbines whose energy comes
from the burning of coal, gas and nuclear fuel,
combustion engines burning oil.

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Generation Subsystem

With concerns for the environment and
conservation of fossil fuels, many alternate
sources are considered for employing the
untapped energy sources of the sun and the
earth for generation of power.

Some alternate sources used are solar power,
geothermal power, wind power, tidal power,
and biomass.

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Generation Subsystem
2. Transformers

The transformer transfers power with very high
efficiency from one level of voltage to another.

The power transferred to the secondary is
almost the same as the primary, except for
losses in the transformer.

Using a step-up transformer will reduce losses
in the line, which makes the transmission of
power over long distances possible.

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Generation Subsystem
2. Transformers

Insulation requirements and other practical
design problems limit the generated voltage to
low values, usually 30 kV.

Thus, step-up transformers
transmission of power.

At the receiving end of the transmission lines
step-down transformers are used to reduce the
voltage to suitable values for distribution or

The electricity in an electric power system may
undergo four or five transformations between
generator and consumers.
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Transmission and Subtransmission

An overhead transmission network transfers
electric power from generating units to the
distribution system which ultimately supplies
the load.

neighboring utilities which allow the economic
dispatch of power within regions during normal
conditions, and the transfer of power between
regions during emergencies.

Transmission voltage lines operating at more
than 60 kV are standardized at 69 kV, 115 kV,
138 kV, 161 kV, 230 kV, 345 kV, 500 kV, and
765 kV line-to-line.
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Transmission and Subtransmission

Transmission voltages above 230 kV are usually
referred to as extra-high voltage (EHV).

The portion of the transmission system that
connects the high-voltage substations through
step-down transformers to the distribution
substations is called the subtransmission

Capacitor banks and reactor banks are usually
installed in the substations for maintaining the
transmission line voltage.

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Distribution Subsystem

distribution substations to
service-entrance equipment.

The primary distribution lines range from 4 to
34.5 kV and supply the load in a well-defined
geographical area.

Some small industrial customers are served
directly by the primary feeders.

The secondary distribution network reduces the
voltage for utilization by commercial and
residential consumers.

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the consumers‟

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Distribution Subsystem

The secondary distribution serves most of the
customers at levels of 240/120 V, single-phase,
three-wire; 208Y/120 V, three-phase, four-wire;
or 480Y/277 V, three-phase, four-wire.

The power for a typical home is derived from a
transformer that reduces the primary feeder
voltage to 240/120 V using a thre-ewire line.

Distribution systems utilize both overhead and
underground conductors.

The growth of underground distribution has
been extremely rapid and as much as 70 percent
of new residential construction in North America
is via underground systems.

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Load Subsystems

Power systems loads are divided into industrial,
commercial, and residential.

Industrial loads are composite loads, and
induction motors form a high proportion of
these loads.

These composite loads are functions of voltage
and frequency and form a major part of the
system load.

Commercial and residential loads consist largely
of lighting, heating, and cooking. These loads
are independent of frequency and consume
negligibly small reactive power.

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Load Subsystems

The load varies throughout the day, and power
must be available to consumers on demand.

The daily-load curve of a utility is a composite of
demands made by various classes of users.

The greatest value of load during a 24-hr period
is called the peak or maximum demand.

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Load Subsystems

As we said before the electrical energy
consumption is subject to very strong temporal
fluctuations. The consumed power fluctuates:

Daily: Mainly the peaks at noon and at evening
are salient. The consumption is low at nights.

Weekly: On working days the consumption is
higher than on weekends. Holidays are
especially interesting; depending on the season
they show either high or low consumption.

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Load Subsystems

Seasonal and annual, respectively: In middle
Europe more energy is consumed during the
winter than in summer.

In more southern regions the situation is
reversed. There one uses much more energy for
air conditioning in summer.

In many regions where the peak load used to be
in the winter, the summer peaks has often
increased significantly due to an extensive
installation of air-conditioning.

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Is Electricity Safe?

Any source of energy − a tank of propane stored
behind a rural farmhouse, a large millwheel, a
windmill, or an electric line − is a potential
hazard that can injure and even kill if misused.

Electricity is no different, but it is a particularly
safe form of energy when handled according to
standard safety precautions.

One reason it is safe is that it is so controllable,
but a big challenge in keeping it safe is that it
can act quickly, essentially at the speed of light.

Automatic equipment can detect most leaks,
called short circuits or faults, and “shut down”
the electrical flow before substantial damage is
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Typical Ranges of Values

A typical light bulb uses 60 watts − 1/2 amp at
120 volts.

A toaster uses about 1,000 watts − a bit more
than 8 amps at 120 volts;

A television 240 watts – two amps at 120 volts;

A large central air conditioner or heat pump
6,000 watts – 25 amps at 240 volts.

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Typical Ranges of Values

Large amounts of power are often measured in
kilowatts − units of 1,000 watts − and larger
amounts, still, in megawatts − a million watts.

The cumulative demand of a large city or state
might be measured in billions of watts −

Pennsylvania, uses about 8 gigawatts of power
during the peak period of electric usage.

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Ranges for voltage

The power flowing through most houses and
buildings in the United States is between 110
and 120 volts, in Europe about 230 to 250 volts,
and in Japan 100 to 105 volts.

The differences exist because these countries
each established a different standard when the
electric industry started there.

Voltage levels in this range (100-250 volts)
provide enough power for typical small
appliances like TVs, microwave ovens, etc., and
even large equipment like air conditioners and
water heaters.

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Ranges for voltage

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Ranges for current

Most household electric appliances require from
1/2 to 10 amps.

Usually, the current carried on electric utility
lines will be in the range of 100 to 1,000 amps,
but again, this is about 1/10 to 1/100 of the
voltage being used.

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Electricity Isn‟t Easy to Store

One disadvantage of electricity is that it is
relatively expensive to store.

To be inexpensive, it has to be made and sent to
the consumer at the moment of use.

In fact, this is perhaps electricity‟s single
biggest drawback compared to other power

Power systems are built so that they can sense
instantly the changing demands of people and
their appliances and respond literally in the
blink of an eye. Equipment and systems are
assumption that power must be delivered when
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Course Contents

Network Calculation: Node equations, matrix partitioning,
node elimination by matrix algebra, The bus admittance and
Impedance matrices, Modification of an existing bus
impedance matrix, Direct determination of a bus impedance

Load-Flow Solutions: Data for load-flow studies, the GaussSeidel method, the Newton-Raphson method, digital-computer
studies of load flow.

Symmetrical Components: Synthesis of unsymmetrical phasors
symmetrical components of unsymmetrical phasors, power in
terms of symmetrical components, unsymmetrical. series
impedances, sequence impedances and sequence networks,
sequence networks of unloaded generators, sequence
impedances of circuit elements, positive- and negativesequence networks, zero sequence networks.
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Course Contents

Unsymmetrical Faults: Single line-to-ground fault on an
unloaded generator, line-to-line fault on an unloaded
generator, Double line to ground fault on unloaded
generator, unsymmetrical faults on power systems, line to
line fault on a power system, double line to ground fault on
power system, interpretation of interconnected sequence
networks, faults through impedance.

Power system stability: Stability problem, swing equation,
the power-angle equation, equal-area criterion of stability,
solution of the swing equation using a computers, factors
affecting transient stability.

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Course Outcomes
1. Students will be able to perform network calculation:
admittance and impedance matrices, node elimination,
modification of an existing bus impedance.
2. Students will learn how to use the numerical techniques
applied to the load flow problems.
3. Students will learn the concept of transient stability in
electrical power systems.
4. Students will be able to evaluate the critical clearing
time using a digital computer.
5. Students will





6. Students will be able to analyze symmetrical
unsymmetrical faults in power systems.

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Hadi Saadat. Power System Analysis. 2nd Ed.,
New York: McGraw-Hill, 2002.
„„Electrical Power Systems‟‟ by Dr Houssem Rafik
El-Hana BOUCHEKARA. Lectures are given using
PowerPoint presentations that I have prepared
ahead of time. These are intended to be a concise
summary of the important ideas and skills that
students have to learn. These presentations may
help students to distinguish “the trees from the
forest”. Copies of the textbook and lectures
presentations can be obtained from Copy centers
in the university or via the university website:

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John J. Grainger., William D. Stevenson, JR.
Power System Analysis. New York: Mc Graw-Hill
Inc, Edition 1997.

M.E. El-Hawary. Electrical Energy Systems. 1st
Ed., CRC, 2000.

Transmission, and Distribution. 2nd Ed., CRC,

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Course Management

The course will be organized in modules according to
main themes:





Introduction to Electric Power Systems

1 Week


Review of Concepts in Electric Power

1 Week


Network Calculation

2 Weeks


Load Flow Solution

2 Weeks


Exam 1
Symmetrical Component

1 Week


Sequence networks

2 Weeks


Symmetrical faults

2 Weeks


Unsymmetrical Faults

2 Weeks


Power System transient stability

3 Weeks

Final Exam

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Methods of Assessing Outcomes

The expected learning outcomes will be
assessed by review of homework, a group
performance on the midterm and Final Exams.

Class Attendance and participation: each
student is expected to attend and participate in
each class. There may be valid reasons why he
cannot attend a class; however, he is
responsible for all business conducted during
regularly scheduled class periods.

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Methods of Assessing Outcomes

Homework/Assignments: Several assignments will be
given over the semester to allow the student to
demonstrate understanding of course material.
completed in class. No late Homework will be
accepted.. Students are encouraged to work in groups
on their homework, but should submit separate writeups. If you do your work electronically, you should
make sure that you did the final write-up
independently (identical assignments will get a zero
score). A few computer projects will be included with
the homework assignments. Some of these will require
MATLAB programming.

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Methods of Assessing Outcomes

Term Projects: Each group of 2 students may work in
each of the attached subjects list. Each group of
students should be able to present his work. Another
alternative of Term project: any student have his own
idea on a related topic can submit a term project
preliminary proposal, proposals should give a brief
description of the project. Instructor will give
suggestion, changing, refusals, of the topic, or go

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Methods of Assessing Outcomes

Unit exams: One unit exams will be scheduled
in the course of the semester, with dates to be
announced in class.
Final exam: At the end of the semester a final
exam will be done.

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Attendance; 5

Project; 5
Homework; 10

Final Exam

Exam 1 ; 30

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Topics for term projects
Project number

Project Title

Project N°1
Project N°2
Project N°3
Project N°4
Project N°5
Project N°6
Project N°7
Project N°8
Project N°9
Project N°10

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Dr. Houssem Rafik El-Hana Nacer E‟Dine
Office hours:
Office hours: Sunday 10h‐12h, Tuesday 10h‐12h,
and by appointment.

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