Lecture 13
Electric Power
中正大學 化工系
李岱洲
助理教授
Electric Power
•Transport energy
from place to place
•System components
based on magnetism
1
Faraday’
s Law
•Magnetic field varies with time to induce
voltages in loops of wire (in transformers
and generators)
dB
v NA
dt
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/farlaw.html#c1
2
Ferromagnetic Materials
Magnetic Domain
3
http://hyperphysics.phy-astr.gsu.edu/hbase/solids/ferro.html#c4
Generation of Magnetic Field
4
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/transf.html#c2
5
Example
6
Example
7
AC Distribution System
•Electric power is usually generated in
large amount at a power station and
consumed in smaller amounts at many
distant places
•Electrical distribution system
The network used to bring power from the
generators to the consumers
8
•Power generated in the power station
Low voltages
•Step up to perhaps 100 to 750 kV and
then transmit over high-voltage lines
Reduce resistive losses
•Step down to 35 to 69 kV and then shared
among numerous 4 to 15 kV local
distribution line
Three Phase Power
•A single-phase power line the power
pulsates, with zeros occurring twice in
every cycle
•Three-phase connection removes this
shortcoming
9
Electromechanical Devices
Relay
10