Download Magnetic - benchmark

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
voltage drop
power consumption

= current x voltage drop IxV
= resistance x current IxR
= 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
Edison
AC
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”
Rotation Amplitude Amplitude/Time
AC=“alternating current”
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
0o
90o
180o
0o
N
P
360o
270o
Amplitude vs. time
90o
180o 270o
Positive
Amplitude
Negative
Amplitude
Time
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 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
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 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 !
End of Presentation