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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

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Advanced Materials and Sustainable Energy Lab CBEE Transmission Level Transformer 230 kV surge arrestors 115 kV surge arrestors Oil Cooler Radiators W/FansOil pump

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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