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Lecture-1

ESO 210/ESO203A

Introduction to Electrical Engineering

(Units 3-1-2-13)

(2014-15, First Semester)

Introduction to Electrical Engineering

(Units 3-1-2-13)

(2014-15, First Semester)

• Instructor: N K Verma (nishchal@iitk.ac.in)

• Office: 107 ACES

• Tel: 6524

• Lecture: Monday, Wednesday and Friday (from 10am to 11am)

• Lecture Venue: L-8

• Tutorial: Thursday(from 10am to 11am)

• Tutorial Venue: T203/T204/T205/T206

• Lab: Monday and Wednesday (from 2pm to 5pm)

• Lab Venue: WLE 313

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• DC and AC sources, Concept of phasors, Single phase circuits, KCL and KVL, Thevenin

and Norton Theorems, Nodal and mesh equations, Y-Δ conversion, power calculations.

• Three phase circuits, Power calculation in three phase circuits.

• Magnetic Circuits, Mutually coupled circuits

• Transformers, Equivalent circuit and performance

• Direct Current Machines (DC Machines):

Constructional details, Separately excited and shunt excited DC motors/ generator, Series

DC motors, torque speed characteristics, Compound machines, Application of DC motors &

generators.

• Induction Machine (3-ph):

Constructional details, equivalent Circuit, Torque- speed characteristics, speed

control,starting and applications.

• Synchronous Machines:

Constructional details, Equivalent circuit, Generator and Motor operation, Power angle

characteristics.

• Single phase induction motors, Stepper motors and their control

• Principles of industrial power distribution

Syllabus:

Suggested readings/reference books

• Electrical Engineering Fundamentals, V. Del Toro

• Engineering Circuit Analysis: Hayt, Kemmerly, and Durbin

• Basic Electrical Engineering, Nagrath & Kothari.

• Principles of Electrical Machine and Power Electronics, P.C. Sen.

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Distribution of Marks

• Mid –I 20 %

• Quiz 10 %

• Tutorial 10 %

• Lab 15 %

• Class performance 10%

• End Sem 35 %

Total 100 %

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Brief History of Electrical Engineering

• William Gilbert (1540-1603), English physician, founder of magnetic science. • Charles A. Coulomb (1736-1806), French engineer and physicist, published the laws of electrostatics in seven

memories to the French Academy of Science between 1785 and 1791. His name is associated with the unit of charge.

• James Watt (1736- 1819), English inventor, developed the steam engine. His name is used to represent the unit

of power. • Alessandro Volta (1745-1827), Italian physicist, discovered the electrical pile. The unit of electrical potential

and the alternative name of this quantity (voltage) and named after him. • Hans Christian Oersted (1777-1851), Danish physicist, discovered the connection between electricity and

magnetism in 1820. The unit of magnetic field strength, Oersted (Oe) is named after him. • Ander Marie Ampere (1775-1836), French mathematician, chemist, and physicist, experimentally quantified

the relationship between electric current and the magnetic field. The unit of electrical current is named after him. • Georg Simon Ohm (1789- 1854), Germen mathematician, investigated the relationship between voltage and

current and quantified the phenomenon of resistance. His name is used to represent the unit of resistance. • Michael Faraday (1791-1867), English Experimenter, demonstrated electromagnetic induction in 1831. His

electric transformer and electromagnetic generator marked the beginning of the age of electric power. His name is associated with the unit of capacitance.

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Brief History of Electrical Engineering

• Joseph Henry (1797-1878), U.S. physicist, discovered self induction around 1831, and his name been designated to represent the unit of inductance.

• Carl Friedrich Gauss (1777-1855) , Germen mathematician, and Wilhelm Eduard Weber (1831-1891), Germen physicist, published a treatise in 1831 describing the measurement of earth’s magnetic field. The gauss is a unit of magnetic field strength, while the weber is the unit of magnetic flux.

• James Clerk Maxwell (1831-1879), Scottish physicist, discovered the electromagnetic theory of light and the law of electrodynamics. The modern theory of electromagnetics is entirely founded upon Maxwell’s equations.

• Ernst Werner Siemens (1816-1892) and Wilhelm Siemens (1823-1883), Germen inventors and engineers, contributed to the invention and development of electrical machine, as well as to perfecting electrical science. The modern unit of conductance is named after them.

• Gustav Robert Kirchhoff (1824-1887), German Scientist, gave two fundamental laws of circuit analysis.

• Heinrich Rudolph Hertz (1857-1894), German scientist and experimenter, discovered the nature of electromagnetic waves and published his findings in 1888. His name is associated with the unit of frequency.

• Nikola Tesla (1856-1943), Croatian inventor, Immigrated to the United Sates in 1884. He invented poly phase electrical power systems and the induction motor and pioneered modern AC electrical power systems. His name is used to represent the unit of magnetic flux density.

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Some Important Electrical Quantities

Charge: Electric charge is a physical

property of matter which causes it to experience a force when near other electrically charged matter.

Classically, electric charge comes in

two types. These are called positive and negative.

Two positively charged substances, or

objects, experience a mutual repulsive force, as do two negatively charged objects. Positively charged objects and negatively charged objects experience an attractive force. The SI unit of electric charge is the coulomb (C).

Current: Electric current means, depending

on the context, a flow of electric charge (a phenomenon) or the rate of flow of electric charge (a quantity).

This flowing electric charge is typically carried by moving electrons, in a conductor such as wire; in an electrolyte, it is instead carried by ions, and in a plasma by both.

The SI unit for measuring the rate of

flow of electric charge is the ampere, which is charge flowing through some surface at the rate of one coulomb per second. Electric current is measured using an ammeter.

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Some Important Electrical Quantities

Voltage: Electric potential is the energy required to move a

unit electric charge to a particular place in a static electric field.

Voltage can be measured by a voltmeter.

The unit of measurement is the volt. The voltage between two ends of a path is the

total energy required to move a small electric charge along that path, divided by the magnitude of the charge.

Mathematically this is expressed as the line

integral of the electric field and the time rate of change of magnetic field along that path.

Historically this quantity has also been called

"tension” and "pressure". Pressure is now obsolete but tension is still used, for example within the phrase "high tension" (HT) which is commonly used in thermionic valve (vacuum tube) based electronics.

Power: Electric Power consumed is defined as the

multiplication of voltage deference in the medium and current flowing though it.

The unit of power is watt

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Electrical Network: A combination of various electric elements (Resistor, Inductor, Capacitor, Voltage source, Current source) connected in any manner what so ever is called an electrical network. We may classify circuit elements in two categories, passive and active elements. Passive Element: The element which receives energy (or absorbs energy) and then either converts it into heat (R) or store it in an electric (C) or magnetic (L ) field is called passive element. Active Element: The elements that supply energy to the circuit is called active element. Examples of active elements include voltage and current sources, generators, and electronic devices that act as power supplies. A transistor is an active circuit element, meaning that it can amplify power of a signal. On the other hand, transformer is not an active element because it does not amplify the power level and power remains same both in primary and secondary sides. Transformer is an example of passive element.

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Bilateral Element: Conduction of current in both directions in an element (example: Resistance; Inductance; Capacitance) with same magnitude is termed as bilateral element.

Unilateral Element: Conduction of current in one direction is termed as unilateral (example: Diode, Transistor) element.

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Source of Electrical Energy:

There are two possible types of

Energy sources used in network

studies: a voltage source and a

current source (fig 1.1) and they are

represented as shown

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+

-

(t) i(t)

(a) (b)

(b) Current Source

Fig 1.1

(a) Voltage Source

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The sources can again be

classified as independent and

dependent types;

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Independent voltage source:

An ideal independent voltage source is one

which maintains a constant (specified)

voltage across the terminals irrespective of

the current it supplies or receives.

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In reality even the best possible source will have some voltage drop with the increasing current due to its internal resistance; for an ideal source the v-i characteristics will be as shown in Fig 1.2.

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V

i

Ideal

Real

Fig 1.2

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We can see that an ideal voltage

source with a perfect short circuit

at the terminals is an

impossibility and is a

contradiction of terms (Fig. 1.3).

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Shorted

a

b

+

_

Fig 1.3

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An ideal current source is an

element that will maintain a

specific rate of flow of charge

regardless of the voltage that

appears across its terminals.

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The v-i characteristics is as shown in Fig. 1.4.

i

i(t)=I

b

a

Fig.1.4

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A current source can never be an

open circuit – it must have a

path for the current to return.

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Thus a real voltage source

will be represented by a source

voltage V along with an internal

resistance Ri ( 0, for network

computation in many situations)

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and a real current source by a

source current along with a

shunted internal resistance (of

appreciable value)

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Dependent Sources

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If the voltage of a voltage source

and the current through a current

source depend on some other variable

(say a voltage or current) in some part

of the network, then such sources are

dependent sources.

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There are four types of dependent sources (fig 1.5)

as shown.

+

-

+

-

K(t)=ij(t)

Current controlled Voltage Source (CCVS)

K(t)=j(t)

Voltage Controlled Voltage Source (VCVS)

iK(t)=A ij(t)

Current Controlled Current Source (CCCS)

iK(t)=j(t)

Voltage Controlled Current Source(VCCS)

ij=Current through jth element in the network

Vj=Voltage across an element j of the network

Fig. 1.5

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(i) Current controlled voltage source (CCVS)

(ii) Voltage controlled voltage source (VCVS)

(iii) Current controlled current source (CCCS) and

(iv) Voltage controlled current source (VCCS)

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Ex 1.1: If Vc = -10v and I1= 3A Calculate

I2 through R2 and voltage of the VCVS

0.1Vc 50I1

R2 R1

+

Vc

-

I2

I1

VS

+

-

50 I1= 50 3A = 150A= I2

/VCVS = 0.1Vc = -1V

Solution

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Series and parallel connections of sources i) Series connections of voltage

sources

n

i

i tvtv1

+ -

+ -

+ -

+ -

1(t) 2(t) 3(t) n(t)

+

- (t)

Fig1.6

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Parallel connections of ideal

voltage sources, is not defined,

except when they have identical

voltages.

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ii) Parallel connection of current

sources

)()(1

titin

k

k

i2(t) i1(t) i3(t) in(t) i(t)

Fig. 1.7

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iii) Replacing parallel / series connections of a set of ideal voltage/current sources.

1(t) = 2(t) = --- = n(t) = (t)

(t) 1(t) n(t) 2(t) 3(t)

+

-

+

-

+

-

+

-

+

-

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Fig. 1.8

i1(t) = i2(t) = i3(t) = i4(t) = i(t)

i(t) i1(t) i2(t) i3(t)

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iv) Voltage and current sources in series and parallel

Fig. 1.9a

(t) i(t) (t)

(t)

i(t) i(t)

+

-

+

-

+

-

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Ex 1.2 : Calculate x, iy, iz and the power supplied by the two sources in Fig. 1.10.

x= -2 3V = -6V iy= 2/4 A = 0.5A iz = -(2-0.5) A = -1.5A

2A 4

iy

3

iz x

2V +

-

Fig. 1.10

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Power supplied by voltage source = 2 -1.5 W = -3 W Voltage across the current source = (2 + 6) V = 8 V Power supplied by current source = 8 2 W = 16 W

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