Electric Engineering II “Dr. Ahmed El-Shenawy”
Electric Engineering II
EE 326
Lecture 1
<Dr Ahmed El-Shenawy>
Electric Engineering II “Dr. Ahmed El-Shenawy”
Course Contents
DC machines ( Generator / motor)
Transformers
Induction motors
Synchronous machines ( generator / motor)
Special type motors
Introduction to Control Systems
Open loop and closed loop system characteristics
Control system components
Transient performance of control systems
Proportional integral and derivative control and tuning
Moving coil instruments, Moving iron instruments
Dynamometer type instruments
Wattmeters and methods of measuring power , power
factor
Electric Engineering II “Dr. Ahmed El-Shenawy”
Introduction
Electric machines can be broadly classified into electrostatic machines
and electro- magnetic machines. The electrostatic principles do not
yield practical machines for commercial electric power generation. The
present day machines are based on the electro-magnetic principles.
Though one sees a variety of electrical machines in the market, the
basic underlying principles of all these are the same. To understand,
design and use these machines the following laws must be studied.
1. Electric circuit laws - Kirchoff′s Laws
2. Magnetic circuit law - Ampere′s Law
3. Law of electromagnetic induction - Faraday′s Law
4. Law of electromagnetic interaction -BiotSavart′s Law
Electric Engineering II “Dr. Ahmed El-Shenawy”
Review on electric circuits &
Magnetic circuits
Kirchhoff’s Current Law
at every instant of time the sum of the currents flowing into any
node of a circuit must equal the sum of the currents leaving the node,
Electric Engineering II “Dr. Ahmed El-Shenawy”
Example 1.1 Using Kirchhoff’s Current Law. A node of a circuit is
shownwith current direction arrows chosen arbitrarily.
Having picked those directions, i1 = −5 A, i2 = 3 A, and i3 = −1 A. Write
an expression for Kirchhoff’s current law and solve for i4.
so that
Electric Engineering II “Dr. Ahmed El-Shenawy”
Kirchhoff’s Voltage Law
the sum of the voltages around any loop of a circuit at any instant is
zero.
Electric Engineering II “Dr. Ahmed El-Shenawy”
Power
Time rate of expending or absorbing energy
Energy
is the total amount of work done, energy is just the integral of
power:
Electric Engineering II “Dr. Ahmed El-Shenawy”
Electric Engineering II “Dr. Ahmed El-Shenawy”
Series connection
R1
R3
R2
Req
Req  R1  R2  R3    RN
i
+
R1
+
v
R2
-
+
v1
v2
-
Voltage division:
R1
v1  v
R1  R2
R2
v2  v
R1  R2
Electric Engineering II “Dr. Ahmed El-Shenawy”
Parallel connection
R eq 
R1R 2
R1  R 2
Current division:
i
+
v
-
i1
R1
i2
R2
R2
i1  i
R1  R2
R1
i2  i
R1  R2
Electric Engineering II “Dr. Ahmed El-Shenawy”
Sinusoidal Steady State
Electric Engineering II “Dr. Ahmed El-Shenawy”
Three-Phase Circuit
Three sinusoidal voltages form a set of balanced voltages when they have the same
amplitudes and frequency.
These voltages are shifted in phase by 120o with each other
The standard practice is to name those phases by a, b and c and use phase a as
reference.
These voltages represent phase a voltage, phase b voltage and phase voltage.
Electric Engineering II “Dr. Ahmed El-Shenawy”
Three-Phase Circuit
Electric Engineering II “Dr. Ahmed El-Shenawy”
Three-Phase Circuit
Electric Engineering II “Dr. Ahmed El-Shenawy”
Phasor Representation of R,L and C Circuits
Resistance
Both the current and voltage vary sinusoidally, and are in
phase with each other.
The root-meansquare
Electric Engineering II “Dr. Ahmed El-Shenawy”
Phasor Representation of R,L and C Circuits
Inductive Reactance
Capacitive Reactance
Electric Engineering II “Dr. Ahmed El-Shenawy”
Impedance: RLC Circuits
Electric Engineering II “Dr. Ahmed El-Shenawy”
Magnetic circuits
A magnetic filed (represented by concentric magnetic flux line, as shown in
fig.) is present around every wire that carries an electric current. The
direction of magnetic flux line can be found simply by placing the thumb of
the right hand in the direction of the conventional current flow and noting the
direction of the fingers. (this method is commonly called the right-hand rule).
Electric Engineering II “Dr. Ahmed El-Shenawy”
Magnetic circuits
There are many application of the electro magnetic effect such as generator,
transformer, Relay……..
Electric Engineering II “Dr. Ahmed El-Shenawy”
Magnetic circuits
Magnetic flux Φ.
The flux density B

B
A
B=tesla (T)
Φ=webers(Wb)
A=square meters (m2)
The reluctance of a material to the
setting up of magnetic flux lines in
the material is determined by the
following equation.
l

A
(At/Wb)
The
magnetomotive
force
mmf is
proportional to the product of the number of
turns around the core ( in which the flux is to
be established) and the current through the
turns of wire.
mmf  NI
(ampere-turns, At)
Electric Engineering II “Dr. Ahmed El-Shenawy”
Magnetic circuits
V
I
R1  R 2
l
c  c
Ac

g 
mmf
 c  g
lg
Ag
Electric Engineering II “Dr. Ahmed El-Shenawy”
The B-H Relation
The final magnetic quantity that we need to introduce is the magnetic
field intensity, H.
the magnetic field intensity is defined as the magnetomotive force (mmf)
per unit of length around the magnetic loop. With N turns of wire carrying
current i, the mmf created in the circuit is Ni ampere-turns. With l
representing the mean path length for the magnetic flux, the magnetic
field intensity is therefore
the relationship between magnetic flux density B and magnetic field intensity H:
Electric Engineering II “Dr. Ahmed El-Shenawy”
The B-H Relation