Electric Power & Machines “Dr. Ahmed El-Shenawy”
Electrical Power and Machines
Lecture 1
<Dr Ahmed El-Shenawy>
<Dr Hadi El Helw>
Electric Power & Machines “Dr. Ahmed El-Shenawy”
Course Contents
Review on electric circuits & Magnetic circuits.
The law of motor and generator action.
DC Motors and DC Generator.
Core Loss, transformer model and regulation.
AC rotating field.
3-phase induction motor.
Synchronous machines.
Single phase and small motors.
Electric power system.
Plant distribution system.
Protective devices and distribution of electricity in
buildings.
System protection & PF correction.
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Power System Objectives?
• Provide energy services
• System criteria
– Safe
– Reliable
– Cheap
– Clean
– any more?
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Major Elements of Power Systems
• Power Plant
– Fossil fuel powered
– Renewable energy
• Transformers
• Transmission Lines
• Distribution Lines
• Protection and Control
• Customers
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Power Systems Components
electric generator
is a device that converts mechanical energy to electrical energy In a
generator, moving a conductor through a stationary magnetic field generates
voltage. If a coil is rotated through a magnetic field as shown, an alternating
voltage will be produced.
Electric Power & Machines “Dr. Ahmed El-Shenawy”
A transformer is a device that transfers electrical energy from one circuit to another
through inductively coupled conductors—the transformer's coils. A varying current in
the first or primary winding creates a varying magnetic flux in the transformer's core,
and thus a varying magnetic field through the secondary winding. This varying
magnetic field induces a varying electromotive force (EMF) or "voltage" in the
secondary winding. This effect is called mutual induction.
Electric Power & Machines “Dr. Ahmed El-Shenawy”
An electric motor uses electrical energy to produce mechanical energy, very typically
through the interaction of magnetic fields and current-carrying conductors.
Electric Power & Machines “Dr. Ahmed El-Shenawy”
A power cable is an assembly of two or more electrical conductors, usually held
together with an overall sheath. The assembly is used for transmission of electrical
power. Power cables may be installed as permanent wiring within buildings, buried in
the ground, or run overhead.
Electric Power & Machines “Dr. Ahmed El-Shenawy”
Introduction
The present day machines are based on the electro-magnetic
principles. Though one sees a variety of electrical machines in the
market, the basic fundamental 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
Electric Power & Machines “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 Power & Machines “Dr. Ahmed El-Shenawy”
Example: Using Kirchhoff’s Current Law. A node of a circuit is shown
with 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
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Kirchhoff’s Voltage Law
the sum of the voltages around any loop of a circuit at any instant is zero.
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Power
Time rate of expending or absorbing energy
Energy
is the total amount of work done, energy is just the integral of power:
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Electric Power & Machines “Dr. Ahmed El-Shenawy”
Series connection
R1
R3
R2
Req
Req  R1  R2  R3    RN
i
+
Voltage division:
+
v1
R1
R1
R1  R2
R2
v2  v
R1  R2
v1  v
+
v
R2
v2
-
-
Electric Power & Machines “Dr. Ahmed El-Shenawy”
Parallel connection
R eq 
R1R 2
R1  R 2
Current division:
i
+
v
-
i1
R1
i2
R2
R2
R1  R2
R1
i2  i
R1  R2
i1  i
Electric Power & Machines “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.
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Three-Phase Circuit
Y-connected source
∆-connected source
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Three-Phase Circuit
a) a wye-connected load
b) a delta-connected load
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Three-Phase Circuit
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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
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Phasor Representation of R,L and C Circuits
Inductive Reactance
Capacitive Reactance
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Impedance: RLC Circuits