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Electrical Networks 1
Lecture 1
1
A Question
• Can you point out different types of
electrical or electronic equipments,
devices in this classroom?
• What about if we are not able to use them,
because of no electrical power?
Lecture 1
2
ELECTRIC CIRCUIT IS AN INTERCONNECTION OF ELECTRICAL COMPONENTS
L
R1
R2
vS

vO

+
-
C
TYPICAL LINEAR IRCUIT
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3
Objectives
• To analysis, design and measurement of
linear analog electrical network systems
across engineering disciplines and within
subdisciplines of Electrical Engineering.
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EE Subdisciplines
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5
EE Subdisciplines
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Power
Electromagnetics
Communication/Signal Processing
Digital
Controls
Solid State
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Power
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Generation of electrical energy
Storage of electrical energy
Distribution of electrical energy
Rotating machinery-generators, motors
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Electromagnetics
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Propagation of electromagnetic energy
Antennas
Very high frequency signals ~ 108 Hz
Fiber optics ~ 1G b/s
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Communications/Signal Proc.
• Transmission of information electrically
and optically
• Modification of signals
– enhancement
– compression
– noise reduction
– filtering
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Digital
• Digital (ones and zeros) signals and
hardware
• Computer architectures
• Embedded computer systems
– Microprocessors
– Microcontrollers
– DSP chips
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Controls
• Changing system inputs to obtain desired
outputs
• Feedback
• Stability
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Solid State
• Devices
– Transistors
– Diodes (LED’s, Laser diodes)
– Photodetectors
• Miniaturization of electrical devices
• Integration of many devices on a single
chip (VLSI)
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12
Electric Power
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13
The Electrical Power System
• Power is one of the main subdisciplines of
EE.
• The power generation, transmission and
distribution system is something we all use
all the time.
• It is an excellent example of a case where
electrical networks are used to model the
flow of energy.
Lecture 1
14
Consider what we do here.
• We usually generate a huge amount of
power in a centralized location.
• We ship it to you when you flip the
switch
• You then decide that you will light a
desk lamp located 18 inches above your
desk, about 2 feet in on the right.
• You can easily change your mind and
put the lamp on the left!
• This is magic.
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Electric Load
• The load changes continuously
– Daily
– Seasonal
• The daily maximum occurs
around 4-6 PM , the minimum
at night.
• The load or demand is defined
as the average load (MW) for
15 minutes
• Seasonal changes: Summer
load is higher than the winter
load in AZ.
•
•
•
Base load (large thermal and
nuclear plants)
Intermediate loads (medium
steam and hydro)
Peak load (gas turbine and
combined cycle plants)
Typical Daily Load Curve
P_max
Peak
load
Intermediate load
Base load
0
Lecture 1
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12
18
24
16
What to notice about what
follows
• We do NOT create energy out of
nowhere.
• Instead, we convert some form of
energy. In a fossil power plant, chemical
energy is converted to a mechanical
motion of a rotating turbine and
generator. The result is electric energy.
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Lecture 1
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Electrical Power Transmission
1) The generating station converts the energy of gas, oil, coal or
nuclear fuel to electric energy. The generator voltage is around 1525 kV
2) The main transformer increases the voltage to 230-765 kV. This
reduces the current and losses.
3) The high voltage transmission line transports the energy from the
generating station to the large loads, like towns. Example: Energy
generated at Palo Verde is transported by 500 kV lines to Phoenix,
San Diego, Los Angeles, Albuquerque and El Paso.
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Electrical Power Transmission
4) The high voltage substation reduces the voltage to 120-69 kV. The
substation serves as a node point for several lines.
5) The sub-transmission lines (69 kV-120 kV) connect the high voltage
substation with the local distribution station.
6) Distribution lines (12 -15 kV) distribute the energy along streets or
underground. Each line supplies several step down transformers
distributed along the line.
7) The distribution transformer reduces the voltage to 230/115V, which
supplies the houses, shopping centers etc..
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Generating Station
Type of Generation stations
• Thermal Power Plant. The large (more than 500 MVA) plants
carry constant load (base load plant), Smaller plants loads are
regulated but they operate continuously. Minimum down time is
20-35 hours.
•
Nuclear Power Plant. These plants carry constant load and are
used as base loads plants.
•
Hydroelectric Plants. It is economically desirable to load these
plants to the maximum capacity, because of the low energy
cost. (Water is free). Other factors: flood control, irrigation and
salmon migration.
•
Combined steam and Gas-Turbine Power Plants. High
efficiency plants for variable load.
•
Gas-turbine. Peak load plants, high operating and low
investment cost
• Solar, Wind. Loaded to the maximum capacity, when sun or
Lecture 1
wind power available.
21
Hydro Power Plant
• The water is stored in the lake, which is at higher
ground (Lake Pleasant).
• A canal and pipe system transfers the water to
the power house.
• The potential energy of the water is transformed
to mechanical energy in the turbine.
• The turbine drives the generator and converts
the water mechanical energy to electrical
energy.
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Motion to Electricity
When magnets are moved near a wire,
an electric current is generated in that wire.
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Steam Turbine
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Steam Turbine
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The moving blades are attached to the shaft.
The stationary blades are attached to the casing.
The control valves regulate the steam flow.
The turbine often has three stages: high,
medium and low pressure (right to left)
• The high pressure steam drives the turbine
(3600rpm).
• The generator is connected directly to the
turbine shaft
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Generating Station
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Transmission Lines
Type of transmission lines:
• Extra high voltage lines
– 345 kV, 500 kV, 785 kV
– Interconnection between
systems. (National Grid)
• High Voltage lines
– 120 kV, 220 kV
– Inter connection between
substations.
• Sub-transmission lines
– 45 kV, 69 kV, 120 kV
– Substation and large
customer
• Distribution Line
– 2.4 kV- 45 kV , 15 kV
– Supplies houses
• High Voltage DC lines
– 120 kV- 600 kV
– Interconnection between
regions. (Oregon-California)
Lecture 1
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AC versus DC
• AC is alternating
current
• AC quantities always
vary sinusoidally in
time
• Usually, we will know
the frequency and
solve for the
amplitude and phase.
• DC is direct current
• DC quantities are
always constant in
time.
• DC can not be directly
transformed to lower
or higher voltages.
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Why do we use AC for power
transmission?
• Power levels correspond to V2. Therefore,
to get a huge power out of Palo Verde, we
need huge V’s. We need to step the
voltage down before it reaches our
classroom. The power company wants to
do this in a lossless fashion. AC allows
them to do this by using transformers.
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Why Are There Three
Conductors in Power
Transmissions Lines?
• Most AC power transmission systems
have three conductors.
• The voltage on each phase (referenced
with respect to earth ground) is a sinusoid
with a phase difference of 120 from the
voltages in the other two phases.
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Three Phase
• A three conductor transmission system is
called a three-phase system.
• The power delivered by a three phase
system (assuming a balanced load) is
constant, even though the voltages in
each phase vary sinusoidally.
• Three phase systems are more efficient
than single systems due to reduced power
losses.
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