Generating Electricity To generate a voltage (electricity) you need: a magnetic field a conductor...
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Transcript of Generating Electricity To generate a voltage (electricity) you need: a magnetic field a conductor...
Generating Electricity
To generate a voltage (electricity) you need:
• a magnetic field
• a conductor
• movement
The size of the voltage induced depends on:
• strength of the magnets (magnetic field)
• the length of coiled wire (conductor)
• speed of movement
V
The Dynamo
coil
rotating magnet
electrical output
As the dynamo is turned, the magnet rotates beside the coil of wire.
An A.C voltage is generated in the coils
Power station generators are much bigger and use electromagnets.
STATOR(stationary coils of wire)
ROTOR(rotating
electromagnets)
Generator turbine shaft
Generator turbine shaft
Turbine Blades
M.A.R.S Floating Wind Powered Generator
Info
Speaking of R2-D2, this M.A.R.S. Floating Wind Generator looks a lot like a flying R2 droid on its side. This helium-filled, horizontal-rotating M.A.R.S. (Magenn Power Air Rotor System) will go into production with its 4.0 kw unit this year with 7 more models planned for release in the next 4 years. The 2010 and 2011 planned models will be able to power a small town on their own.
The generated electrical energy travels town its 1000-foot tether rope, with the energy available for immediate use. With its helium, balloon-like flying system, M.A.R.S. can fly higher than other wind turbines, able to reach altitudes with much higher wind speeds.
http://www.gearfuse.com/mars-floating-wind-power-generator/
Size of Voltage
Experiment
dynamooscilloscope
Results
slow speed high speed
greater amplitude (bigger voltage)
higher frequency (faster rotation)
Transformers
A transformer consists of 2 coils of wire and iron core which passes through both coils.
iron core
primary coil
secondary coil
transformers require an AC voltage
The circuit symbol for a transformer is:
An AC voltage in the primary coil induces (creates) a voltage in the secondary coil.
The size of the secondary voltage depends on:
• size of primary voltage
• number of turns on each coil.NP
VP VS
NS
P
S
P
S
NN
VV
Quantity Unit
secondary voltage (VS)
primary voltage (VP)
secondary turns (NS)
primary turns (NP)
volts (V)
volts (V)
** NO UNIT **
** NO UNIT **
Example 1
Calculate the secondary voltage for the transformer shown.
1000 T
230 V
ACVS
52 T
V 230VP
turns 1000NP
turns 52NS ?VS
P
S
P
S
NN
VV
100052
230VS
52230V 1000 S
100011,960
VS
V 12VS
This is a STEP DOWN transformer
Example 2
Calculate the secondary voltage for the transformer shown.
300 T
50 V
ACVS
12,000 T
V 50VP
turns 300NP
turns 12,000NS ?VS
P
S
P
S
NN
VV
30012,000
50VS
12,00050V 300 S
300600,000
VS
V 2000VS
This is a STEP UP transformer
Current in Transformers
S
P
P
S
NN
II
NP
IP
NS
IS
Example 1
Calculate the current in the secondary coil.
1000 T
0.1 A
50 T
IS
A 0.1I P
turns 1000NP
turns 50NS ?I S
S
P
P
S
NN
II
521000
0.1I S
0.11000I 52 S
52100
I S
A 1.9I S
Example 2
Calculate the voltage and the current in the secondary coil.
10,000 T
0.05 A
500 T
IS
turns 10,000NP
turns 500NS ?VS
P
S
P
S
NN
VV
10,000500
230VS
500230V 10,000 S
10,000115,000
VS
V 11.5VS
VS230 V
Voltage
V 230VP
Current
A 0.05I P
turns 10,000NP turns 500NS
?I S
S
P
P
S
NN
II
50010,000
0.05I S
0.0510,000I 500 S
500500
I S
A 1I S
Transformer Power & Efficiency
If the transformer is 100% efficient:
primary in power secondary in power
PPSS V I V I
To calculate power we use .
So this gives us the formula
V IP
** NOT on data sheet **
Example 1
Calculate the current in the secondary coil, assuming the transformer is 100% efficient.
0.04 A IS
12 V50 V
A 0.04I P V 50VP V 12VS
?I S
PS PP
PPSS V IV I
500.0412 I S 2I 12 S
A0.17 I S
Example 2
Calculate the current in the secondary coil, assuming the transformer is 90% efficient.
0.08 A IS
12 V230 V
A 0.08I P V 230VP
V 12VS ?I S
PPP V IP 2300.08
Power in PrimaryPower in Primary
V 18.4PP
Power in Secondary
V 18.4 of 90%PS
18.4 0.9W 16.56PS
Current in Secondary
V 12VS ?I S
W 16.56PS SSS V IP
S
SS V
PI
1216.56
A 1.38I S
Power Lines
Electricity is provided by power lines called The National Grid.
25,000 V
400,000 V
230 V
step-up transformer
step-down transformer
The output voltage is stepped up to reduce power loss in the wires of the national grid.
Stepping up the voltage reduces the size of the current.
Smaller current, less power loss.
Example 1
A transmission power line of length 60km has a resistance of 2 Ω per kilometre. The total current in the cable is 50 A.
Calculate the power loss in the transmission line.
602R Ω 120
A 50I
?P
R IP 2
120502 W 300,000P