Dr. Laith Abdullah

74 Pages·2014·5.42 MB·English

First Class Course
Assistant Professor Dr. Laith Abdullah Mohammed
Email: [email protected]
Website: www.uotechnology.edu.iq/dep-production/laith/
►Requirements and Grading:
First term Exam: 15%
Second term Exam: 15%
Final Exam: 50%
Homworks, Quizess and Class attendance: 10%
Laboratory: 10%
►Course Materials:
1 - Edward Hughes, [Electrical and Electronic Technology], 11th edition, Prentice
Hall, 2012
2 -Austin Hughes , [ Electric Motors and Drives: Fundamentals, Types and
Applications], 3rd edition, Newnes, 2005
3- Richard Crowder, [ Electric Drives and Electromechanical systems ], Butterworth
Hainemann, 2006
►Lectures:
Lectures are available on department’s website:
www.uotechnology.edu.iq/dep-production
 Definition of Basic Electrical Quantities
 Kirchoff’sLaw in Voltage and Current
►Course topics:  Analysis of Electric Circuits
 Determination of Equivalent Resistance
 Series/Parallel Circuits
These topics are for 30  Delta-Star Transformation
 Thevenin’s Theorem
weeks.
 Norton’s Theorem
 Super-position Theorem
 Maximum Power Transfer
 Complex Numbers
 Response of inductive Circuit
 Response of Capacitive Circuit
 Response of R-L-C Circuit
 Principle of Electromechanical Energy Conversion
 Principle of operation of DC Motors
 Equivalent Circuit of DC Motors
 Types of DC Motors
 Speed –Torque curve Characteristic of DC Motors
 Speed Control of DC Motor
 DC Drives
 Principle of Operation of AC Motors
 Types of AC Motors
 Equivalent Circuit of AC Motors
 Speed –Torque Curve Characteristics of AC Motors
 Speed Control of AC Motors
 AC Drives
 Stepper Motors
 Theory of servo Motors
 Response of servo Motors
Definition of Basic Electrical Quantities
Ideal Voltage source:
It provides a prescribed voltage across its terminals irrespective of the current flowing through it. The
amount of current supplied by the source is determined by the circuit connected to it.
Various representations of an electrical system
Ideal Current source:
It provides a prescribed current to any circuit connected to it. The voltage
generated by the source is determined by the circuit connected to it.
An electrical network is a collection of elements through which current flows.
The following definitions introduce some important elements of a network.
Elements of an electrical network
Branch:
A branch is any portion of a circuit with two terminals connected to it. A branch may consist of
one or more circuit elements . In practice, any circuit element with two terminals connected to it is
a branch.
Node
A node is the junction of two or more branches . In effect, any connection that can be
accomplished by soldering various terminals together is a node. It is very important to identify
nodes properly in the analysis of electrical networks.
Loop
is any closed connection of branches.
The fundamental electric quantity is charge, and the smallest amount of charge that exists is the
charge carried by an electron, equal to:
qe= −1.602 × 10−19 C
the amount of charge associated with an electron is rather small.
This, of course, has to do with the size of the unit we use to measure charge, the coulomb (C)
Current consists of the flow of very large numbers of charge particles.
The other charge-carrying particle in an atom, the proton, is assigned a plus sign and the same
magnitude. The charge of a proton is
qp= +1.602 ×10−19 C
Electrons and protons are often referred to as elementary charges.
Electric current is defined as the time rate of change of charge passing through a predetermined area
(Typically, this area is the cross-sectional area of a metal wire).
imagine ∆ q units of charge flowing through the cross-sectional area A in ∆t units of time.
The resulting current i is then given by:
i= ∆q/ ∆t C/s
The units of current are called amperes, where 1 ampere (A) = 1 coulomb/second (C/s).
In order for current to flow, there must exist a closed circuit.
The current i flowing from the battery to the lightbulb is equal to
the current flowing from the lightbulb to the battery.
In other words, no current (and therefore no charge) is “lost”
around the closed circuit.
This principle was observed by the German scientist
G. R. Kirchhoff and is now known as
Kirchhoff’s current law (KCL).
Kirchhoff’s current law states that because charge cannot be
created but must be conserved, the sum of the currents at
a node must equal zero.
A simple electric circuit
The resulting expression for node 1
of the circuit is:
−i + i1 + i2 + i3 = 0 (assuming currents entering a node as being
negative)
Note that if we had assumed that currents entering the node
were positive, the result would not have changed.
Example: Determine the unknown currents in the circuit of Figure below.
I = 5A I1 = 2A I2 = −3A I3 = 1.5A
S
Find: I and I .
0 4
Solution:
Two nodes are clearly shown in Figure as node a and node b; the third node in the
circuit is the reference (ground) node. Apply KCL at each of the three nodes.
At node a:
I0 + I1 + I2 = 0
I0 + 2 − 3 = 0
∴I0 = 1A
Note that the three currents are all defined as flowing away from the node, but one
of the currents has a negative value (i.e., it is actually flowing toward the node).
At node b:
I − I3 − I4 = 0
S
5 − 1.5 − I4 = 0
∴I4 = 3.5A
Note that the current from the battery is defined in a direction opposite to that of
the other two currents (i.e., toward the node instead of away from the node). Thus,
in applying KCL, we have used opposite signs for the first and the latter two
currents.
At the reference node: If we use the same convention (positive value for currents
entering the node and negative value for currents exiting the node), we obtain the
following equations:
−I + I3 + I4 = 0
S
−5 + 1.5 + I4 = 0
∴I4 = 3.5A
VOLTAGE AND KIRCHHOFF’S VOLTAGE LAW (KVL) Lecture .2
Charge moving in an electric circuit gives rise to a current.
Naturally, it must take some work, or energy, for the charge to
move between two points in a circuit, say, from point a to point b.
The total work per unit charge associated with the motion of
charge between two points is called voltage.
Thus, the units of voltage are those of energy per unit charge; they
have been called volts.
The voltage, or potential difference, between two points in a circuit indicates the energy required
to move charge from one point to the other converting the potential energy within the voltage
source to electric power. the direction, or polarity, of the voltage is closely tied to whether energy
is being dissipated or generated in the process.
The principle underlying KVL is that no energy is lost or created in an electric circuit, the sum of all
voltages associated with sources must equal the sum of the load voltages, so that the net voltage
around a closed circuit is zero.
where the v are the individual voltages around the closed circuit.
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