Electric Power Distribution, Generators and Motors. Benchmark Companies Inc PO Box 473768 Aurora CO 80047. Electric Power Distribution,. New ideas for today Magnetic induction Lenz’s law Transformers and power transmission Motors and Generators. Observations about Power Distribution.
Electric Power Distribution, Generators and Motors Benchmark Companies Inc PO Box 473768 Aurora CO 80047
New ideas for today • Magnetic induction • Lenz’s law • Transformers and power transmission • Motors and Generators
Observations about Power Distribution Household power is AC (alternating current) Power comes in voltages like 120V & 240V
Observations about Power Distribution Power is transmitted at “high voltage” like 500KV
Observations about Power Distribution Power transformers are visible everywhere
Observations about Power Distribution Power substations are visible on occasion
Power Consumption in wires • Reminder: power consumption = current x voltage dropIxV voltage drop = resistance x current IxR power consumption= resistance x current2 I2xR • Impact of the calculation: Wires waste power as heat Doubling current quadruples wasted power
Power Consumption in wires • Example: Resistance of 1 mile of power line is 10 Ohms. • Determine the voltage drop across the power line if 200 Amps is transmitted at 240 Volts to power one typical house. The Power consumed across 1 mile is I2xR = 200A2x10 = 400KW is needed before we can begin to deliver power to a typical house.
DC AC Edison Tesla Westinghouse
DC= “direct current” AC=“alternating current” DC vs AC a visual approach DC can supply power . So can AC For transmission AC is superior
DC= “direct current” AC = alternating current Let’s explore why…… AC=“alternating current” Rotation Amplitude Amplitude/Time
AC = alternating current As a conductor is rotated within a magnetic field alternating current is produced in that conductor Rotation within a magnetic field Amplitude Current Amplitude vs. time 0o 90o 180o 270o 360o 90o 0o 180o Positive Amplitude P N Negative Amplitude 360o 270o Time
Power Transmission • For efficient power transmission: • Use low-resistance wires (thick, short copper) • Use low current and high voltage drop • Can accomplish this with AC (alternating current) power transmission.
Click for Bar Magnet And Pick-up coil example
Electromagnetic Induction Changing magnetic field produces an electric field
Electromagnetic Induction Current in a conductor produces a magnetic field
Electromagnetic Induction An Induced magnetic field opposes the original magnetic field change (Lenz’s law)
Electromagnet Transformer Example
Transformer • Alternating current in one circuit induces an alternating current in a second circuit • Transfers power between the two circuits • Doesn’t transfer charge between the two circuits
Transformers • Power arriving in the primary circuit must equal power leaving the secondary circuit • Power = current x voltage • A transformer can change the voltage and current while keeping the power unchanged!
Step Down Transformer • Fewer turns in secondary circuit so charge is pushed a shorter distance • Smaller voltage rise • A larger current at low voltage flows in thesecondary circuit
Step Up Transformer • More turns in secondary circuit so charge is pushed a longer distance • Larger voltage rise • A smaller current at high voltage flows in the secondary circuit
Observations about Electric Generators and Motors • A generator provides electric power • A generator requires a mechanical power • A motor provides mechanical power • A motor requires electric power Alternator
Electric Generator Rotating magnet • makes changing magnetic field • induces AC current in the loop Converts mechanical power into electrical power
Electric Motor Input AC power • AC current makes changing magnetic field • causes magnet to turn Converts electrical power into mechanical power A motor is a generator run backwards !