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9/6/2016 References • Basic physics - http://www.physicsclassroom.com/ • Electric circuits - http://hyperphysics.phyastr.gsu.edu/hbase/electric/ecircon.html • Textbook - Module -01 Industry Overview Community College of Rhode Island 9/6/2016 Community College of Rhode Island 1 History Summary 9/6/2016 2 Edison and Westinghouse • Benjamin Franklin Born in 1706 – 1752 kite experiment • 1879, Thomas Edison invents a more efficient light bulb • 1882, Edison puts in operation the Pearl Street Plant • Between 1750 and 1850 electricity and magnetism is explored by – – – – – Volta Coulomb Gauss Henry Faraday – first direct current (dc) distribution system – New York City, powering over 10,000 electric light bulbs • George Westinghouse developed a device called the “transformer.” • Inventions – – – – – – battery (1800), generator (1831), electric motor (1831) telegraph (1837 telephone (1876) light bulb (1879) Community College of Rhode Island – The transformer allowed electrical energy to be transported over long distances efficiently 9/6/2016 3 Community College of Rhode Island 9/6/2016 4 Simplified Electric Power System Generation-Transmission-Distribution The Grid – Edison-Westinghouse-Tesla • Edison –DC grid • Westinghouse – AC grid • Tesla – Components for the AC grid • Worlds largest network • The most important achievement of the twenty century. • Mostly one-way communications Community College of Rhode Island 9/6/2016 5 Community College of Rhode Island 9/6/2016 6 1 9/6/2016 Voltage Current • Voltage is the potential energy source in an electrical circuit that makes things happen(Electromotive Force or EMF) • EMF unit is the volt • Current is the flow of electrons in a conductor (wire). • Electrons are pushed and pulled by voltage through an electrical circuit or closed-loop path. • The electrons flowing in a conductor always return to their voltage source. • Current is measured in amperes, usually called amps • One amp is equal to 628 × 1016 electrons flowing in the conductor per second • Voltage tries to push or pull current • When there is a complete circuit, voltage will cause current to flow – The volt was named in honor of Allessandro Giuseppe Antonio Anastasio Volta (1745–1827), the Italian physicist who also invented the battery. • Electrical voltage symbol “e” or “E.” – (Some references use symbols “v” or “V.”) • Voltage is either direct or alternating • Electric power systems are based on alternating voltage applications – from low-voltage 120 volt residential systems – to ultra high voltage 765,000 volt transmission systems Community College of Rhode Island 9/6/2016 7 Community College of Rhode Island Power 9/6/2016 • Electrical energy is the product of electrical power and time. • Electrical energy is watt-hours (Wh) • Common units of energy is kilowatt-hours –kWh – ( 1,000 watt-hours) for residential applications – Your electric bill is payment for energy • Large energy applications is megawatt-hours-MWh – (meaning 1,000,000 watt-hours) for industrial and utility companies 9 Community College of Rhode Island dc Voltage ac Voltage and Current 9/6/2016 10 Frequency • Direct current (dc) is the flow of electrons in a circuit that is always in the same direction • Example of dc is a battery • Alternating current (ac) occurs when the voltage source alternates in polarity • Example of ac is home electrical wiring • ac in mathematical terms is describes a sine wave • sine wave period - length of time it takes to complete one cycle in a second • sine wave frequency – number of cycles per second Community College of Rhode Island 8 Energy • The basic unit (measurement) of power is the watt (W), named after James Watt (1736–1819), who also invented the steam engine • Voltage by itself does not do any real work. Current by itself does not do any real work. • However, voltage and current together can produce real work. • The product of voltage times current is power. • Power is used to produce real work • Power is only produced when current flows through a load Community College of Rhode Island 9/6/2016 • Frequency is the term used to describe the number of cycles in a second-hertz (Hz) • Hz named after Heinrich Hertz (1857–1894), a German physicist • frequency is a term used only for ac circuits • United States, the standard frequency is 60 cycles/second or 60 hertz (Hz) • European countries have adopted 50 hertz (Hz) • Countries outside the United States and Europe use 50 and/or 60 hertz • Direct current (dc) has no frequency 9/6/2016 11 Community College of Rhode Island 9/6/2016 12 2 9/6/2016 Comparing ac and dc Voltage and Current Electric Voltage and Current Relationships • dc Power Source • Continuously supplies power • Equivalent heating = dc voltage x current • Voltage step-up and stepdown is complex (inverter is needed) • dc power transmission is cost effective over three hundred miles • Voltage is the source of power • Current is what flows in a load and electric circuit Current Load Voltage Source Community College of Rhode Island 9/6/2016 13 Community College of Rhode Island 9/6/2016 14 Real and Reactive Power Three Types of Electrical Loads • Real and reactive power must be considered with inductive or capacitive loads • Total Power = Real power + Reactive power • Real power (watts) – does useful work • Reactive power (VAR) – extra cost • Motors are an example of the need to consider reactive power (+ VAR) • Reactive power increases the cost of power transmission • Capacitors (- VAR) are used to offset inductive reactive power • Resistive loads- current flow produces heat – resistance (ohms) • Inductive loads – current lags voltage – (henrys) • Capacitive loads – current leads voltage –(farads) Community College of Rhode Island 9/6/2016 15 Bulk Energy Generation Community College of Rhode Island 9/6/2016 16 Energy Distribution • Non-Renewable: Non-Variable • Distribution of Bulk • Distribution of Storage • Capacitor Bank Distribution • Control, Measure, Protection • Record and Optimization – Nuclear – Coal – Gas • Renewable : Non-Variable – – – – • ac Power Source • Increase and decreases power • Equivalent heating = rms voltage x rms current (rms = root mean squared) • Voltage step-up and stepdown is easy with transformer • Most power transmission today is ac Hydro Biomass Geothermal Pump Storage • Renewable: Variable – Wind – Solar Source: IEEE Source: IEEE Community College of Rhode Island 9/6/2016 17 3 9/6/2016 Energy Customers Energy Operations • • • • • Residential Commercial Industrial Smart meters Two-way communications • Customer generation • Energy Domains • Domain Flow Control • Substation two-way communications • Monitoring and reporting control • Customer network data gathering and control Source: IEEE Source: IEEE Electrical Power is Low Tech to High Tech Power Engineering Components • • • • • • • Community College of Rhode Island 9/6/2016 Sensors and Measurement Generators Transmission lines Transformers Switches Capacitors Current Protection Sensors 21 Sine Wave Voltage Effective voltage of the AC power system is 0.707 times the peak voltage. Peak voltage is about 170 volts. Thus the 120 volts is really an effective voltage. Effective voltage is sometimes known as the rms (root mean square) voltage. • • • • • • Electric Current Voltage Power Voltage-Current Phase angle (Power Factor) Temperature Harmonics Community College of Rhode Island 9/6/2016 24 4 9/6/2016 Reasons for Alternating Current Waveforms • Electromechanical generators produce alternating current • Less energy loss in transmission lines if power (P) is transmitted at higher voltages (V) and lower current(I). Lower current yields less power loss (Pl). • P=IxV • Pl = I2 x R (R = resistance in transmission line). • Voltage can be altered by transformers only for AC. For example to lower transmission voltages (e.g.,345Kv) to 120 v for household use. Community College of Rhode Island 9/6/2016 Converting DC to AC Simple inverter (top = mechanical switch, bottom = transistor switch) 25 Community College of Rhode Island 9/6/2016 26 Converting AC to DC Half-wave rectifier: Capacitor and Inductor Filter Full- wave rectifier • Using capacitors and inductors we can level the voltage output of a rectifier • A capacitor opposes changes in voltage • An inductor opposes changes in current Community College of Rhode Island 9/6/2016 30 5 9/6/2016 How Power Grids Work Generator Utilization http://www.loc.gov/rr/business/hottopic/electricpower.html 60 88% 50 74% 40 59% 30 44% 20 29% 10 15% 0 10:15 AM Capacity Utilized Power Used (kW) Average Generator Capacity Utilization over a Day 0% 4:15 PM Community College of Rhode Island 10:15 PM 4:15 AM 10:15 AM 9/6/2016 31 6