Chemical, Biological and Environmental Engineering Generating
Electricity
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Advanced Materials and Sustainable Energy Lab CBEE
COMBINED-CYCLE PLANT
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Advanced Materials and Sustainable Energy Lab CBEE Combined
heat and power fuller utilization of heat Appropriate in high
density places Dont add efficiencies. Calculate utilization, :
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Advanced Materials and Sustainable Energy Lab CBEE
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Advanced Materials and Sustainable Energy Lab CBEE COAL-FIRED
POWER PLANTS
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Advanced Materials and Sustainable Energy Lab CBEE COMBUSTION
GAS TURBINES Industrial gas turbines (100kW to 150 MW) Large, high
thermal capacitance, high moment of inertia Large units (above 10
MW) are 35-40% efficient Used as peaking power plants (Run only
intermittently) Microturbines A.k.a. aero-derivative turbines Made
of thin, light, super-alloy material Start fast, quick
acceleration, easy adjust to load changes Can handle many
start-up/shutdown events They are easy to fabricate & ship to a
site Efficiencies in excess of 40%
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Advanced Materials and Sustainable Energy Lab CBEE Energy
conversion Thermal energy converted to motion using turbine Steam
Steam-Turbine-Generator Combustion gases Gas-Turbine-Generator
Turbine subject to device efficiency and Carnot efficiency Motion
of turbine blades Rotates the shaft of electric generator Converts
the rotational energy into electricity
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Advanced Materials and Sustainable Energy Lab CBEE Faradays law
where | | is the electromotive force (emf is also what we call
Voltage) Easy way to get d /dt: Move conductor through magnetic
field (or move mag. field)
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Advanced Materials and Sustainable Energy Lab CBEE Flux
linkages and Faradays Law If magnetic flux links an N turn coil
Where V is the voltage and is the flux linkage If all flux links
all turns then =N
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Advanced Materials and Sustainable Energy Lab CBEE Mnagnetic
cores To ensure all magnetic flux flows through coils we employ
magnetic core High magnetic permeability material Guide magnetic
fields through electrical devices Usually made of ferromagnetic
metal such as iron (steel)
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Advanced Materials and Sustainable Energy Lab CBEE Relative
Permeability MediumRelative Permeability (/ 0 ) Mu-metal20,000
Permalloy8000 Electrical steel4000 Ferrite (MFe 2 O 4 )16-640 High
Carbon Steel100 Nickel100-600 Aluminum1.000022 Air1.000,000,37
Vacuum1
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Advanced Materials and Sustainable Energy Lab CBEE Simple
generator
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Advanced Materials and Sustainable Energy Lab CBEE Multiple
pole generator The following figure shows a 2-pole and a 4-pole
synchronous generator
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Advanced Materials and Sustainable Energy Lab CBEE Magnetic
Excitation Rotor is electromagnet, contains field windings
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Advanced Materials and Sustainable Energy Lab CBEE Rotation
Speed The frequency of generated voltage in U.S. is 60 Hz Europe,
Japan = 50Hz Therefore, the shaft of generator must turn at a
certain speed: N S is called the synchronous speed
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Advanced Materials and Sustainable Energy Lab CBEE Increasing
number of poles Increasing number of poles increases number of
times magnetic flux changes per revolution of the rotor.
Synchronous spped depends on number of poles (p) and output
frequency (f) Allows shaft to turn slower (easier to
build/maintain)
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Advanced Materials and Sustainable Energy Lab CBEE Generating
three phase power Three voltage sources with equal magnitude, but
with an angle shift of 120
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Advanced Materials and Sustainable Energy Lab CBEE Advantages
of 3 Power Can transmit more power for same amount of wire (twice
as much as single phase) Torque produced by 3 machines is constant
Three phase machines use less material for same power rating Three
phase machines start more easily than single phase machines
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Advanced Materials and Sustainable Energy Lab CBEE Balanced 3
Phase (3 ) Systems 3 phase system has equal loads on each phase
equal impedance on the lines connecting the generators to the loads
Bulk power systems almost exclusively 3 Single phase is used in low
voltage, low power settings (e.g., residential, light
commercial)
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Advanced Materials and Sustainable Energy Lab CBEE Three Phase
Transmission Line
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Advanced Materials and Sustainable Energy Lab CBEE Power
transmission Generation: 2.3 to 30 kV
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Advanced Materials and Sustainable Energy Lab CBEE Electric
Grid
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Advanced Materials and Sustainable Energy Lab CBEE US
Electrical System
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Advanced Materials and Sustainable Energy Lab CBEE Actual
System Interconnections
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Advanced Materials and Sustainable Energy Lab CBEE TRANSMISSION
GRID The following figure shows the one-line diagram of an HVDC
link
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Advanced Materials and Sustainable Energy Lab CBEE
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Advanced Materials and Sustainable Energy Lab CBEE TRANSMISSION
LINES The following figure shows the tower configurations
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Advanced Materials and Sustainable Energy Lab CBEE TRANSMISSION
LINES
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Advanced Materials and Sustainable Energy Lab CBEE TRANSMISSION
& DISTRIBUTION
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Advanced Materials and Sustainable Energy Lab CBEE Frequency
Control Steady-state operation only occurs when the total
generation exactly matches the total load plus the total losses too
much generation causes the system frequency to increase too little
generation causes the system frequency to decrease (e.g., loss of a
generator) AGC is used to control system frequency
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Advanced Materials and Sustainable Energy Lab CBEE April 23,
2002 Frequency Response Following Loss of 2600 MW
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Advanced Materials and Sustainable Energy Lab CBEE Power
transmission Generation: 2.3 to 30 kV, Transmission: 138 kV to 765
kV (why?)
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Advanced Materials and Sustainable Energy Lab CBEE Transformers
Overview Power systems have many different voltages 765 kV down to
240/120 volts. Ability of simple change of voltage levels is the
key advantage of AC over DC systems Transformers are used to
transfer power between different voltage levels
Advanced Materials and Sustainable Energy Lab CBEE 115 kV 35 kV
distribution transformer
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Advanced Materials and Sustainable Energy Lab CBEE
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Advanced Materials and Sustainable Energy Lab CBEE Ideal
Transformer Lets examine an ideal transformer no real power losses
magnetic core has infinite permeability no leakage flux
Nomenclature I may use: primary side is power in secondary is power
out
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Advanced Materials and Sustainable Energy Lab CBEE Flux
linkages and Faradays Law If magnetic flux links an N turn coil
Where V is the voltage and is the flux linkage If all flux links
all turns then =N
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Advanced Materials and Sustainable Energy Lab CBEE Ideal
Transformer: Turns Ratio
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Advanced Materials and Sustainable Energy Lab CBEE Ideal
Transformer: Voltage and Current
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Advanced Materials and Sustainable Energy Lab CBEE Residential
Distribution Transformers Single phase transformers used in
residential distribution systems Most distribution systems are 4
wire, with a multi-grounded, common neutral