Chemical, Biological and Environmental Engineering Generating Electricity

Advanced Materials and Sustainable Energy Lab CBEE COMBINED-CYCLE PLANT

Advanced Materials and Sustainable Energy Lab CBEE Combined heat and power – fuller utilization of heat Appropriate in high density places Don’t “add” efficiencies. Calculate utilization, ε :

Advanced Materials and Sustainable Energy Lab CBEE

Advanced Materials and Sustainable Energy Lab CBEE COAL-FIRED POWER PLANTS

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%

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

Advanced Materials and Sustainable Energy Lab CBEE Faraday’s 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)

Advanced Materials and Sustainable Energy Lab CBEE Flux linkages and Faraday’s 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 

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)

Advanced Materials and Sustainable Energy Lab CBEE Relative Permeability MediumRelative Permeability (μ/μ 0 ) Mu-metal20,000 Permalloy8000 Electrical steel4000 Ferrite (MFe 2 O 4 ) High Carbon Steel100 Nickel Aluminum Air1.000,000,37 Vacuum1

Advanced Materials and Sustainable Energy Lab CBEE Simple generator

Advanced Materials and Sustainable Energy Lab CBEE Multiple pole generator The following figure shows a 2-pole and a 4-pole synchronous generator

Advanced Materials and Sustainable Energy Lab CBEE Magnetic Excitation Rotor is electromagnet, contains “field windings”

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

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)

Advanced Materials and Sustainable Energy Lab CBEE Generating three phase power Three voltage sources with equal magnitude, but with an angle shift of 120 

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

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)

Advanced Materials and Sustainable Energy Lab CBEE Three Phase Transmission Line

Advanced Materials and Sustainable Energy Lab CBEE Power transmission Generation: 2.3 to 30 kV

Advanced Materials and Sustainable Energy Lab CBEE Electric Grid

Advanced Materials and Sustainable Energy Lab CBEE US Electrical System

Advanced Materials and Sustainable Energy Lab CBEE Actual System Interconnections

Advanced Materials and Sustainable Energy Lab CBEE TRANSMISSION GRID The following figure shows the one-line diagram of an HVDC link

Advanced Materials and Sustainable Energy Lab CBEE

Advanced Materials and Sustainable Energy Lab CBEE TRANSMISSION LINES The following figure shows the tower configurations

Advanced Materials and Sustainable Energy Lab CBEE TRANSMISSION LINES

Advanced Materials and Sustainable Energy Lab CBEE TRANSMISSION & DISTRIBUTION

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

Advanced Materials and Sustainable Energy Lab CBEE April 23, 2002 Frequency Response Following Loss of 2600 MW

Advanced Materials and Sustainable Energy Lab CBEE Power transmission Generation: 2.3 to 30 kV, Transmission: 138 kV to 765 kV (why?)

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 Transmission Level Transformer 230 kV surge arrestors 115 kV surge arrestors Oil Cooler Radiators W/FansOil pump

Advanced Materials and Sustainable Energy Lab CBEE 115 kV – 35 kV distribution transformer

Advanced Materials and Sustainable Energy Lab CBEE

Advanced Materials and Sustainable Energy Lab CBEE Ideal Transformer Let’s 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”

Advanced Materials and Sustainable Energy Lab CBEE Flux linkages and Faraday’s 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 

Advanced Materials and Sustainable Energy Lab CBEE Ideal Transformer: Turns Ratio

Advanced Materials and Sustainable Energy Lab CBEE Ideal Transformer: Voltage and Current

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