Electric Power Distribution, Generators and Motors

Benchmark Companies Inc

PO Box 473768

Aurora CO 80047

Electric Power Distribution,

New ideas for todayNew 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 IxVvoltage drop = resistance x current IxRpower consumption = resistance x current2 I2xR

Impact of the calculation:Wires waste power as heatDoubling 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 TeslaWestinghouse

DC vs AC a visual approachDC vs AC a visual approach

DC can supply power . So can ACFor transmission AC is superior

DC= “direct current” AC=“alternating current”

AC = alternating currentAC = alternating current

Let’s explore why……

AC=“alternating current”

Rotation Amplitude Amplitude/Time

DC= “direct current”

AC = alternating currentAC = alternating current

As a conductor is rotated within a magnetic field alternating current is produced in that conductor

Rotation within a magnetic field

AmplitudeCurrent

Amplitude vs. time

Positive Amplitude

Negative Amplitude

Time

N P

0o 90o 180o 270o 360o

0o

90o

180o

270o

360o

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 InductionChanging magnetic field produces an electric field

Electromagnetic InductionCurrent in a conductor produces a magnetic field

Electromagnetic InductionAn Induced magnetic field opposes the original magnetic field change (Lenz’s law)

Lenz’s LawLenz’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

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

Click me

Electric GeneratorRotating 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 A motor is a generator run generator run backwards !backwards !

End of Presentation