Producing & transporting electrical energy

• Natuurkunde
• Middelbare school
• havo, vwo
• Leerjaar 2,3

Producing & transporting electric energy

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You can explain how electric energy is produced

Dynamo/ generator

Try this 

Simulation

You can produce your own electricity just by changing the magnetic field near a copper coil.

02:17

Wat does a generator do and what do you need to build one?

380 kV

10 kV

230 V

supplied energy

consumed energy

Energy loss 

E = P.t

P=U⋅I=I​2​​R

When current flows through a wire, the wire can become hot.

Think back to Ohm's law: 
The current will then be:

Increasing the Voltage (U) will result in an equal increase in current (I) under the condition that the resistance (R) of the wire stays constant. Increasing the current, however will also increase the risk of electron particles colliding with each other. These collisions result in friction (increasing R of the wire) which causes heat, a form of energy loss.

The powerplant only produces a certain amount of energy (E) during the day (t). Preferably all of the produced energy is delivered to the factories and households without any losses occuring during transport.

You can calculate the supplied power using: 

To calculate the consumed power at home: 

Without any energy loss (efficiency = 100%), the consumed power will be the same as the supplied power. But normally the efficiency is not a 100% because of heat loss during transport. A big current will directly increase the amount of heat loss because of the friction of the electrical particles in the wire. Therefore you want to keep this current as small as possible. The way to do this is by increasing the Voltage using transformers 

Rewriting the formula                         will make it clear why it is vital to lower the current by increasing the Voltage. First thing to do is to replace U with I.R

Doing this will result in: 

As you can see the power lost is equal to the root of the current. Therefore lowering the current will have a big impact.

P=U⋅I=I⋅R⋅I=I​2​​⋅R

U=I⋅R

I=​R​​U​​

P=​t​​E​​

P=U⋅I

P=U⋅I

QUANTITIES

UNITS

Voltage

Current

Resistance

Power

Energy

Time

U

I

R

P

E

t

Voltage

Ampere

Ohm

Watt (Joule/second

kiloWatthour

hour (second)

V

A

Ω

W (J/s)

kWh

h (s)

FORMULAS

U=I⋅R

P=U⋅I

E=P⋅t

1 W = 1 J/s       1 kWh = 3,6 MJ   

Transformers

Transformator are used to increase or decrease the Voltage in a wire and thereby decreasing or increasing the  current.

The secondary coil is influenced by the magnetic field going through the transformer core. You can change this field at the primary input side. The number of turns of each coil will ultimately decide if the Voltage at the seconday coil will go up or down.

Example

In this example the Voltage is decreased from 24 Volts to just 12 Volts. This is because the number of windings in  the secundary side are halved (from 10 to 5). 

If the secundary coil had 100 windings instead, the Voltage would have increased ten fold to 240 Volts.

The output voltage is equal to the ratio of the numer of turns on the primary & secondary coils times the input voltage.

FORMULA

​U​s​​​​U​p​​​​​​​=​N​s​​​​N​p​​​​

      = Voltage at the primary coil

      =Voltage at the secondary coil

      = Number of turns primary coil

      = Number of turns secondary coil

U​p​​

U​s​​

N​p​​

N​s​​

What Voltage do we use at home?

1. 20 kV
2. 380 kV
3. 10 kV
4. 230 V

Why do we need to increase the voltage in the transmission lines?

1. Safety reasons
2. To prevent energy loss
3. For a stable frequenty of 50 Hz
4. That is what devices need

Rendement

Transformator