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

You can explain how electricity is being transported

You can explain why alternating current is related to how it is produced

You can explain why alternating current/ Voltage is also very useful energy wise

You know how transformers work and use this knowledge in calculations

You are familiar with the concepts of Energy, Power, Current en Voltage

Producing Electricity

Producing electricity

Electricity is produced using coiks and magnets which move in relation to each other. These parts are build into a generator.

A fuel source is needed to, in this case, heat up water to produce steam. The steam, in turn, is used to power a steamturbine which powers a generator. 

The generator prodices an alternating electric current, although you can convert this into direct current using a smart setup. 

In the end you can see that it is all hooked up to a transformator to 

step up the Voltage before the electric energy is transfered to yout home. This is done to save on the needed materials to conduct the electricity and to save out on the energy loss in the form of heat.

We use a lot of energy, which is just too much to store in batteries, therefore we need to produce the electricity at the very moment that it is needed.

The changing magnetic field in the generator causes in an electric current to flow through the first circuit. This current will in turn cause an electromagnetic field in the first coil of the transformer. This electromagnetic field will have an effect on the second coil of the transformer which will react to this which in turn causes an electrical current to flow through the second circuit.

Transformers

Up⋅Ip=Us⋅Is

​Vs​​Vp​​=​Ns​​Np​​

A transformer consists of two coils wrapped around a metal core. This metal core makes sure that the electromagnetic field in the coil of the first circuit will induce an electromagneticfield in the coil of the second circuit as well.

The strength of this induced electromagnetic field depends on a couple of things: the strength of the current in the first circuit, the presence of a metal core and  the ratio of the number of turns in each coil.

The 1st coil then transfers its power onto the 2nd coil.

Pp=Ps

Transporting electricity

Electricity is produced at a powerplant (1).  

To prevent energy loss on route to your home it first goes through a step up transfomer (2). There the Voltage is increased before it is send to your home through powerlines (3).  Because it is now at a very high Voltage, it needs to go through a step down transformer first (4) before it is send to your home.

380 kV

10 kV

230 V

supplied energy

consumed energy

Energy loss 

E = P.t

P=U⋅I=I​2​​R

Why use high voltage power lines?

The first and most obvious reason to transport electricity at high voltage is too limit the amount of current flowing through the transmission lines. P = U . I If U is high, I will be low when transferring the produced power from the powerplant to a housing region.

For a very high current you will need a thick and heavy wire, otherwise it will just melt down. So lower currents will save out on used materials and construction challenges.

But there is another reason as well/ When transporting electric energy to your home, you will have some heatloss because of the resistance of the transmission line itself. This loss would be extremely high if you do not use a high voltage since P = U.I = I^2.R.

Since we need to produce electricity when needed, the main challenge for the future is to develop storage capabilities. If this problem is solved it will be the end of fossile fuels!

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