ELECTRIC POWER SYSTEMS (Module 1)

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BEE 3243ELECTRIC POWER SYSTEMS

(Module 1)

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BEE 3243 Electric Power Systems – Module 1

Objectives

(1) To understand the electric power systems

(2) To have knowledge on the main components of an electric power systems

(3) To learn the basic knowledge of power flow

(4) To conduct fault analysis in power systems

(5) To get approach on power systems protection schemes

Lecture Plan

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Learning Outcomes

At the end of this course, student should have the ability to:

(1) describe the structure and the main energy sources for an electric power systems

(2) explain the basic components which are consist in an electric power systems

(3) determine various types of generating system such as thermal, hydro, nuclear, and renewable energy station

Cont…

Lecture Plan

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Learning Outcomes

(4) analyse the short, medium, and long transmission lines

(5) perform and study of simple power flow program

(6) describe the important elements in a distributionsystem and its protection schemes

(7) analyse the possible fault in an electric power systems

(8) design various protection schemes for electric power systems

Lecture Plan

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Syllabus

• Module 1 – Introduction to Power System (1-2)• Module 2 – Components of an Electric Power System (3-4)• Module 3 – Generation System (5)• Module 4 – Transmission System (6-7)• Module 5 – Distribution System (7-8)• Module 6 – Introduction to Power Flow Studies (9-10)• Module 7 – Fault in Electric Power System (11-12)• Module 8 – Power System Protection (13-14)

Lecture Plan

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Teaching & Assessment Approaches

Teaching Approaches• Lecture (14 weeks)• Tutorial (Each module)• Project & Assignment

– Prototype of Electrical Power System (Due: Week 5)– Matlab Simulation on Power Flow/ Fault Analysis

Assessment Approaches1. Quiz : 05%2. Assignment : 05%3 Test : 30%4. Project : 15%5. Others : 05%6. Final Examination : 40%

Total : 100%

Lecture Plan

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References1. Electrical Machines, Drives and Power Systems; Theodore Wildi, Prentice

Hall, 2006.2. Electric Machinery and Power System Fundamentals; Chapman Stephen J.,

McGraw-Hill, 2002.3. Power System Analysis (2nd Edition); Hadi Saadat, Prentice Hall, 2004.4. Electric Power Systems (4th Edition); Weedy B. M. and Cory B. J., John

Wiley & Sons, 1998.

Other References :1. Electrical Power and Controls (2nd Edition); Timothy L. S, William E. D.,

Prentice Hall, 2004.2. Power System Analysis and Design (3rd Edition); J. Duncan Glover and

Mulukutla S. Sarma,a. Brooks/ Cole Thomson Learning, 2002.3. Introduction to Power System Technology; Theodore R. Bosela, Prentice

Hall, 1997.

Lecture Plan

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Introduction to Power System

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Introduction to Power System

1.1 Introduction1.2 History of Electric Power System1.3 The Sources of Electric Energy1.4 Modern Electric Power System1.5 National Grid, Malaysia1.6 Representation of Electric Power System1.7 Basic Computer Analysis of Electric Power System

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Introduction

What is Electric Power System?Electric power system is a composite system of generation, transmission, and distribution systems.

Generation Stations

Transmission Lines

Distribution Systems

Step-up Transformers

Step-down Transformers Consumers

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Introduction

The electricity produced by a generator travels along cables to a transformer, which changes electricity from low voltage to high voltage. Electricity can be moved long distances more efficiently using high voltage.

Transmission lines are used to carry the electricity to a substation.

Substations have transformers that change the high voltage electricity into lower voltage electricity.

From the substation, distribution lines carry the electricity to homes, offices and factories, which require low voltage electricity.

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Introduction

How is Electricity Measured?

Electricity is measured in units of power called WATTS. 1 W = 1 J/s

1 hp = 745.7 W – use in machine rating.

A kilowatt represents 1,000 watts.

A kilowatt-hour (kWh) is equal to the energy of 1,000 watts working for one hour.For example, if you use a 100 W light bulb 8 hours a day, you have used 800 W of power, or 0.8 kWh of electrical energy.

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History of Electric Power Systems

Thomas A. Edison opens Pearl St. Station, NYCWaterwheel-driven dc generator

installed in Appleton, Wisconsin

Frank J. Sprague produces dc motor for Edison systems

Nikola Tesla presents paper on two-phase ac induction and synchronous motors

First three-phase ac transmission line in Germany (12 kV, 179 km)

First transmission lines installed in Germany (2400 V dc, 59 km)

William Stanley develops commercially practical transformer

First single-phase ac transmission line in US, in Oregon (4 kV, 21 km)

First three-phase ac transmission line in US, in California (2.3 kV, 12 km)

1882

1884

1885/6

1888

1889

1891

1893

1882

1882

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• Electricity – flow of electrical power or charge from one

point to another– The secondary energy sources that generated

from the conversion of other sources of energy, such as hydro, boimass,etc

Sources of Electric Energy

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Conventional/ Primary SourcesFossil Fuels

Coal

Oil (Diesel/ Petroleum)

Natural Gas

Nuclear power

Hydropower

Renewable/ Secondary SourcesGeothermal power

Solar power

Wind powerTidal power

Biomass

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Coal – fossil fuel extracted from the ground


-Has been used since the Industrial Revolution

-Easy to use because they require simple direct combustion

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Natural Gas – gaseous fossil fuel consisting primarily of methane


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Nuclear power – is a method in which steam is produced by heating water through a process called nuclear fission


- Other methods for nuclear reaction: nuclear fusion and radioactive decay

- All utility-scale reactors heat water to produce steam, which is then converted into mechanical work for the purpose of generating electricity or propulsion.

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Hydropower – is a process in which flowing water is used to spin a turbine connected to a generator


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Geothermal power – is electricity generated by utilizing naturally occurring geological heat sources


-Geothermal resources:

-shallow ground

-hot water and rock

-magma

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Solar power – describes a number of methods of harnessing energy from the light of the Sun


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Wind power – is derived from the conversion of the energy contained in wind into electricity


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Biomass – (wood, agricultural waste, such as rice husk and bagasse, are some other energy sources for producing electricity.


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Energy Generation According to Fuel Mix in Malaysia - 2003

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• Future Trends of Energy Sources


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Modern Electric Power Systems

A modern complex interconnected power system can be subdivided into 4 major parts:Generation

Transmission & Subtransmission

Distribution

Loads

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Generation• Generators 3-phase ac synchronous generator or alternator. Have 2 rotating fields – rotor (synchronous speed and

excited by dc current) & stator windings (3-phase armature current).

Size of generators – 50 MW to 1500 MW. Mechanical power – prime mover (hydraulic turbines,

steam turbines, gas turbines). Steam/ Gas turbines – high speeds, 1800/ 3600 rpm. Hydraulic turbines – low speed, 150 – 300 rpm.


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• Transformers Step-up transformers are used to increase the voltage

level for long distances power transmission. The power transferred to the secondary is almost the

same as the primary. In modern utility system, the power may undergo 4 or 5

transformations between generator and ultimate user.


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Transformer at Kenyir

Dam Hydroelectric

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Transmission and Subtransmission Transfer electric energy from generating units at various

locations to the distribution system. Transfer of power between regions during emergencies. In Malaysia, transmission voltage are standardized at 66

kV, 132 kV, 275 kV, and 500 kV line-to-line. Subtransmission connects the HV substation through

step-down transformers to the distribution substation. Typical subtransmission voltage level ranges from 66 kV

to 132 kV. Capacitor banks/ reactor banks are used to maintain the

transmission line voltage.


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Step Down Transformer at Subtransmission Network

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Distribution The primary distribution lines are ranging from 6.6 kV to 33

kV. The secondary distribution lines are normally at 415 V and

240 V. Distribution systems are both overhead and underground.


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Loads Divided into industrial, commercial, and residential. Very large industrial loads may be served from the

transmission system. Industrial loads – mostly induction motors. Commercial & residential loads – lighting, heating, and

cooling. Greatest value of load during a 24-hr period is called peak or

maximum demand. Daily Load factor = average load X 24 hr/ peak load X 24 hr.


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National Grid, Malaysia

• National Grid is the primary electricity transmission network linking the electricity generation, transmission, distribution and consumption in Malaysia.

• It is operated and owned by Tenaga Nasional Berhad (TNB).

• More than 420 substations in Peninsular Malaysia are linked together by the extensive network of transmission lines operating at 132, 275 and 500 kilovolts (kV).

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• The power generation capacity connected to the National Grid is 18,391 MW.

• The generation capacity is about :82% : thermal power stations 18% : hydroelectric power stations.

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• Listed below are the power connected to the Malaysian National Grid on Malaya:

• Tenaga Nasional – with 11,296 MW installed capacity

• Malakoff – with 4,393 MW installed capacity • Powertek – with 1,490 ME installed capacity

• YTL Power – with 1,212 MW installed capacity.

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Tenaga Nasional Berhad • Tenaga Nasional Berhad is the largest

electricity utility company in Malaysia and also the largest power company in Southeast.

• TNB's core activities are in the generation, transmission and distribution of electricity.

• The TNB Group has a generation capacity of 11,296 MW.

• TNB generates electricity mainly from two major types of plant; hydroelectric plants and thermal plants.

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Representation of EPS

One-line Diagram

BY

R

3-phase system single-phase system

One-line diagram is a simplified single-phase circuit diagram of a balanced three-phase electric power system.

It is indicated by a single line and standard apparatus symbols.

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Apparatus Symbols of One-line Diagram

Machine or rotating armature

Two-winding power transformer

Three-winding power transformer

Power circuit breaker, oil/ liquid

Air circuit breaker

Load

Or

Or

Or

Or

Cont…

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Apparatus Symbols of One-line Diagram

A

VOr

Current transformer

Busbar

Transmission line

Fuse

Potential transformer

Three-phase, three-wire delta connection

Three-phase wye, neutral ungrounded

Three-phase wye, neutral grounded

Ammeter

Voltmeter

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One-line DiagramThe information on a one-line diagram is vary according to the problem at hand and the practice of the particular company preparing the diagram.

Load/ Power Flow Study

Transient Stability Study

Example :

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Advantages of One-line Diagram Simplicity. One phase represents all three phases of the balanced

system. The equivalent circuits of the components are replaced

by their standard symbols. The completion of the circuit through the neutral is

omitted.


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Impedance and Reactance Diagrams Impedance (Z = R + jX) diagram is converted from one-

line diagram showing the equivalent circuit of each component of the system. It is needed in order to calculate the performance of a system under load conditions (Load flow studies) or upon the occurrence of a short circuit (fault analysis studies).

Reactance (jX) diagram is further simplified from impedance diagram by omitting all static loads, all resistances, the magnetizing current of each transformer, and the capacitance of the transmission line. It is apply to fault calculations only, and not to load flow studies.

Impedance and reactance diagrams sometimes called the Positive-sequence diagram.

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1

2

3

Load B

T2T1

Load A


Impedance and Reactance Diagrams

Example : One-line diagram of an electric power system

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E1 E2 E3

Gen. 3

Load B

Transformer T2

Transmission Line

Transformer T1

Load A

Generators 1 and 2

Impedance diagram corresponding to the one-line diagram of Example 1.2



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Reactance diagram corresponding to the one-line diagram of Example 1.2

E1 E2 E1

Generators 1 and 2

Transmission Line

Transformer T2

Gen. 3

Transformer T1



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Per-unit Representation Common quantities used in power system analysis are

voltage (kV), current (kA), voltamperes (kVA or MVA), and impedance (Ω).

It is very cumbersome to convert currents to a different voltage level in a power system having two or more voltage levels.

Per-unit representation is introduced such that the various physical quantities are expressed as a decimal fraction or multiples of base quantities and is defined as:

quantity of valuebase

quantity actualunit-perin Quantity

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Example :

For instance, if a base voltage of 275 kV is chosen, actual voltages of 247.5 kV, 275 kV, and 288.75 kV become 0.90, 1.00, and 1.05 per-unit.

For simplicity, per-unit is always written as pu. For single-phase systems:

11

11

1

2LN

LN

LN

1

MVA baseMW power, Base

kVA basekW power, Base

MVA base

)kV voltage,(baseimpedance Base

A current, base

V voltage,baseimpedance Base

kV voltage,base

kVA baseA current, Base

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33

33

3

2LL

LL

3

MVA baseMW power, Base

kVA basekW power, Base

MVA base

)kV voltage,(baseimpedance Base

kV voltage,base X 3

kVA baseA current, Base

For three-phase systems:

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Example :

A three-phase, wye-connected system is rated at 100 MVA and 132 kV. Express 80 MVA of three-phase apparent power as a per-unit value referred to

(a) the three-phase system MVA as base and

(b) the single-phase system MVA as base.

(a) For the three-phase base,

Base MVA = 100 MVA = 1 pu

and Base kV = 132 kV (LL) = 1 pu

so Per-unit MVA = 80/100 = 0.8 pu

(b) For the single-phase base,

Base MVA = 1/3 X 100 MVA = 33.333 MVA = 1 pu

and Base kV = 132/√3 = 76.21 kV = 1 pu

so Per-unit MVA = 1/3 X 80/33.333 = 0.8 pu

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Changing the Base of Per-unit Quantities The impedance of individual generators and

transformers are generally in terms of % or pu quantities based on their own ratings (By manufacturer).

For power system analysis, all impedances must be expressed in pu on a common system base. Thus, it is necessary to convert the pu impedances from one base to another (common base, for example: 100 MVA).

Per-unit impedance of a circuit element

2kV) voltage,(base

MVA) (base X ) impedance, (actual

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old

new

2

new

oldoldnew MVA base

MVA base

kV base

kV baseunit Z-perunit Z-Per

The equation shows that pu impedance is directly proportional to base MVA and inversely proportional to the square of the base voltage.

Therefore, to change from old base pu impedance to new base pu impedance, the following equation applies:

Example 1.5:

The reactance X” of a generator is given as 0.20 pu based on the generator’s nameplate rating of 13.2 kV, 30 MVA. The base for calculations is 13.8 kV, 50 MVA. Find X” on this new base.

pu 306.030

50

13.8

13.20.20x"

2

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Representation of EPSExample :

A 30 MVA 13.8 kV three-phase generator has a subtransient reactance of 15%. The generator supplies two motors over a transmission line having transformers at both ends, as shown in the one-line diagram below. The motors have rated inputs of 20 MVA and 10 MVA, both 12.5 kV with x” = 20%. The three-phase transformer T1 is rated 35 MVA, 13.2Δ – 115Y kV with leakage reactance of 10%. Transformer T2 is composed of three single-phase transformers each rated at 10 MVA, 12.5Δ – 67Y kV with leakage reactance of 10%. Series reactance of the transmission line is 80 Ω. Draw the reactance diagram with all reactances marked in per unit. Select the generator rating as base in the generator circuit.

Cont…

1

2

(13.8 kV)

k n(120 kV)

l mT1 T2

p

r

(12.9 kV)

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Representation of EPSThe three-phase rating of transformer T2 is 3 X 10 MVA = 30 MVA.

and its line-to-line voltage ratio is 12.5 – √3 X 67 = 12.5 – 116 kV.

A base of 30 MVA, 13.8 kV in the generator circuit requires a 30 MVA base in all parts of the system and the following voltage bases:

In transmission line: 13.8(115/13.2) = 120 kV.

In motor circuit: 120(12.5/116) = 12.9 kV.

The reactances of the transformers converted to the proper base are:

Transformer T1: X = 0.1 (13.2/13.8)2(30/35) = 0.0784 pu.

Transformer T2: X = 0.1(12.5/12.9)2 = 0.0940 pu.

The base impedance of the transmission line is

(120 kV)2/30 MVA = 480 Ω

and the reactance of the line is (80/480) = 0.167 pu.

Reactance of motor 1 = 0.2 (12.5/12.9)2(30/20) = 0.282 pu.

Reactance of motor 2 = 0.2 (12.5/12.9)2(30/10) = 0.563 pu.

Cont…

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Eg Em2Em1

jo.15

j0.0784 j0.167 j0.0940

j0.282 j0.563

p r

nmlk

Reactance diagram :

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Basic Computer Analysis of EPS

For a power system to be practical, it must be safe, reliable, and economical. Hence, many analyses must be performed to design and operate a power system.

However, the pre-requisite before the analyses can be performed is the modelling tasks – to model all components of electric power systems.

The modelling and analysis of a power system require the aid of PC.

The basic analyses of an electric power system are:– Load flow/ power flow analysis.– Fault analysis.– Stability analysis (steady state, dynamic , and transient

stabilities).

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Load Flow / Power Flow A load flow study is the steady-state solution of an

electric power system for determination of the voltage, current, power (both active, P and reactive power, Q), and power factor at various points in the network.

Load flow studies are the backbone of power system analysis and design such as planning, operation, economic scheduling, transient stability and contingency studies.

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Fault Analysis Fault studies concern about the determination of bus

voltage and line currents during various types of faults. Faults occur in power system due to: (1) Insulation failure in the equipments.

(2) Flashover of transmission lines initiated by lightning stroke.

(3) Mechanical damage to conductors and tower.

(4) Accidental faulty operation.

Faults are divided into three-phase balanced faults and unbalanced faults (single line-to-ground fault, line-to-line fault, and double line-to-ground fault).

The relative frequency of occurrence of various faults are 3-Φ fault (5%), double line-to-ground fault (10%), line-to-line fault (15%), and 1-Φ to ground fault (70%).


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Stability Analysis Because the power system stability is an electro-

mechanical phenomena, it is thus defined as the ability of designated synchronous machines in the system to remain in synchronism with one another following disturbances such as fault and fault removal at various locations in the system.

Three types of stability are of concern: steady state, dynamic, and transient stability. Steady state stability relates to the response of a synchronous machine to a

gradually increasing load. Dynamic stability involves the response to small disturbances that occur in the

system, producing oscillation. Also known as small signal stability. Transient stability involves the response to large disturbances, which may cause

rather large changes in rotor speeds, power angles, and power transfer.

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