Energy & Sustainability Lecture 8: Electric Power Generation And Distribution February 5, 2009
Illumination Example Input stage Power Station Distribution system Your meter Useful energy!
Electric Power Generation Energy uses today Electric Power Generation Distribution (transmission) Storage Sustainable attributes and issues
Power Generation Historical Intro Wind, tidal, river flows, etc.
Power Generation Historical Intro Wind, tidal, river flows, etc. Steam engine
Power Generation Historical Intro Wind, tidal, river flows, etc. Steam engine Oil & coal
Power Generation Historical Intro Wind, tidal, river flows, etc. Steam engine Oil & coal Electricity generation & motor
Power Generation Historical Intro Wind, tidal, river flows, etc. Steam engine Oil & coal Electricity generation & motor Electric power
Where Do We Get Electricity? Nuclear & Fossil Gas
Where Do We Get Electricity? Non Thermal
Where Do We Get Electricity? Solar insolation
Where Do We Get Electricity? Thermochemical
Electricity Basics Carriers of electricity: electrons Current: Symbol: I = Q / t number of electrons per second Unit: amp or A, 1 A = 1 C/s, e 1.602 x 10 19 C 1 A is defined as the current required to produce a magnetic force of 2 x 10 7 N/m between two infinitely long thin wires spaced 1 m apart in the vacuum Voltage: - Symbol: V = I/t - difference in electrical potential that a supply maintains between its terminals, a measure of the energy supplied to electric charges as they pass through - Unit: 1 V = 1 A/1 s, energy supplied is 1 J
Electricity Basics (2) Resistance: Symbol R = V / I Ohm s law: resistance of a component is the voltage across it divided by the current flowing through it Resistance is component dependent May not be in practice a constant (e.g. increasing current in a wire may cause increasing component temperature and usually causes increasing resistance V = R x I Unit: 1 Ω (ohm) = 1 V / 1 A
Electricity Basics (3) Electric Power: rate at which energy is transformed Proportional to the product of the voltage and the current: P = V x I = R x I 2 = V 2 / R - Relationship holds equally for the electrical power provided by a supply or the power being dissipated as heat in a component - Unit: 1 W = 1 V x 1 A
Electricity Basics (4) The Power Supply: it is important to appreciate that an electrical supply does not supply electrons, it recycles them: - Consider simple circuit such as a bulb and a battery - Free electrons travel along a wire filament of the bulb constantly losing energy in collisions with the ions of the metal, ions gain energy which is observed as heat and light - Electrons gradually energy as they pass along the wire eventually returning to the battery, which transfers energy to electrons
Generation: E&M basics Mechanical Power can be converted directly into electrical energy 1831: dynamo by Faraday 1834: first commercial hand driven rotary generator
Generation: E&M basics Mechanical Power can be converted directly into electrical energy
Faraday s Law of Induction The induced electromotive force EMF in any close circuit is equal to the time rate of change of the magnetic flux through the circuit: EMF = dφ B /dt Electrical Generator
Faraday s Law of Induction Electrical Generator
AC or DC? DC (direct current) flows continuously in one direction (see simple circuit example). AC goes through a complete cycle of changes periodically in time, reversing direction from positive to negative Number of cycles per second: frequency f(hz)= 1/ T (sec) Mains frequency in Europe 50 Hz, in the US 60 Hz
AC or DC? P(t) = V 2 (t)/r Vrms=Vpeak/ 2 (for sinusoidal wave) 1 cycle time
Transformer Transforms voltages in an electrical system Step up or step down Work on alternating currents (mutual interaction of changing electrical and magnetic fields) V p /V s =N p /N s
Now we are (almost) ready for the grid: http://tcip.mste.uiuc.edu/applet2.html