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