45_6575_ee328_2014_1__1_1_ee 328 _lect_01
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Electric Power & Machines “Dr. Ahmed El-Shenawy”
Electrical Power and MachinesLecture 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.
Electric Power & Machines “Dr. Ahmed El-Shenawy”
Power System Objectives?
• Provide energy services
• System criteria– Safe
– Reliable
– Cheap
– Clean
– any more?
Electric Power & Machines “Dr. Ahmed El-Shenawy”
Major Elements of Power Systems• Power Plant– Fossil fuel powered
– Renewable energy
• Transformers
• Transmission Lines
• Distribution Lines
• Protection and Control
• Customers
Electric Power & Machines “Dr. Ahmed El-Shenawy”
Power Systems Componentselectric generatoris 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 Lawat 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
Electric Power & Machines “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 Power & Machines “Dr. Ahmed El-Shenawy”
Power
Energy
is the total amount of work done, energy is just the integral of power:
Time rate of expending or absorbing energy
Electric Power & Machines “Dr. Ahmed El-Shenawy”
Electric Power & Machines “Dr. Ahmed El-Shenawy”
Series connection
Neq RRRRR 321
R1
R3R2 Req
R1
R2
-+
+
-
+
-
v
i
v1
v2
21
11 RR
Rvv
21
22 RR
Rvv
Voltage division:
Electric Power & Machines “Dr. Ahmed El-Shenawy”
Parallel connection
21
21
RRRRR eq
21
21 RR
Rii
21
12 RR
Rii
Current division:
R1 R2
+
-
v
i
i1 i2
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.
Electric Power & Machines “Dr. Ahmed El-Shenawy”
Three-Phase Circuit
Y-connected source ∆-connected source
Electric Power & Machines “Dr. Ahmed El-Shenawy”
Three-Phase Circuit
a) a wye-connected load b) a delta-connected load
Electric Power & Machines “Dr. Ahmed El-Shenawy”
Three-Phase Circuit
Electric Power & Machines “Dr. Ahmed El-Shenawy”
Phasor Representation of R,L and C CircuitsResistance
Both the current and voltage vary sinusoidally, and are in phase with each other.
The root-mean-square
Electric Power & Machines “Dr. Ahmed El-Shenawy”
Phasor Representation of R,L and C Circuits
Inductive Reactance
Capacitive Reactance
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