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 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 drop IxV 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 vs AC a visual approach DC can supply power . So can AC For transmission AC is superior DC= “direct current” AC=“alternating current”

AC = alternating current Let’s explore why…… DC= “direct current” 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)

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 Demonstration: AC Electromagnet and Wire Loop with Lamp.

Transformer on fire

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 the secondary 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

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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 !

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