Section 1 of 7Stages in a thermal power station
1Burn the fuel
- Burn the fuel Coal, oil or gas is burned in the boiler, releasing the chemical energy stored in the fuel as thermal energy.
2Boil the water
- Boil the water The hot gases heat water in pipes until it boils and becomes high-pressure steam.
3Turn the turbine
- Turn the turbine The steam rushes past the blades of a turbine and makes it spin, transferring thermal energy to kinetic energy.
4Spin the generator
- Spin the generator The turbine drives a generator, in which coils turn in a magnetic field so a potential difference is induced.
5Send to the grid
- Send to the grid The electricity passes through a step-up transformer and out along power lines.
Section 2 of 7Energy transfers
| Stage | Energy store or form before | After |
|---|---|---|
| Burning the fuel | Chemical energy in the fuel | Thermal energy in the water and steam |
| Steam in the turbine | Thermal energy in the steam | Kinetic energy of the turbine |
| Turbine drives generator | Kinetic energy of the turbine | Kinetic energy of the generator coils |
| Generator output | Kinetic energy of the generator | Electrical energy |
Section 3 of 7Recycling the water
Condensing
- Condensing After passing through the turbine the steam is cooled in a condenser, where it turns back into liquid water.
Pumping back
- Pumping back The water is pumped back to the boiler, so the same water is heated again and again in a closed loop.
Wasted energy
- Wasted energy Some energy is lost as heat at every stage, which is why only about a third of the fuel energy ends up as electricity.
Section 4 of 7Why a step-up transformer
Transmission at high voltage
Higher voltage, lower current
- Higher voltage, lower current For a given power, raising the voltage lets the current fall,
- because power equals current multiplied by potential difference.
Less heat in the cables
- Less heat in the cables A smaller current produces less heating in the cables, so less energy is wasted on the journey.
Efficient grid
- Efficient grid The National Grid therefore transmits at very high voltage and uses step-down transformers near homes to reduce it again.
Section 5 of 7Which fuel is used
Same design, different fuel
- Same design, different fuel All thermal power stations heat water to turn a turbine; the only difference is the heat source,
- such as coal, gas, oil or biomass.
Gas in the UK
- Gas in the UK Most UK stations burn natural gas because it is the cleanest fossil fuel, giving less pollution per unit of energy than coal or oil.
On-demand supply
- On-demand supply Fuel stations can raise their output when demand rises, which wind and solar cannot do.
Section 6 of 7Key terms
| Term | Meaning |
|---|---|
| Turbine | A set of blades turned by moving steam, water or wind. |
| Generator | A device in which coils turn in a magnetic field to produce electricity. |
| Condenser | The part of a power station that cools steam so it turns back into water. |
| Step-up transformer | A transformer that increases the voltage, used before electricity is sent along power lines. |
| National Grid | The network of cables and transformers that carries electricity from power stations to consumers. |
Section 7 of 7Exam technique
1
Saying that the fuel turns the turbine directly; it is the steam that does this.
2
Forgetting that the steam is condensed and reused rather than released.
3
Stating that the transformer creates energy; it changes voltage and current but cannot increase the power.
4
Missing the kinetic energy stage in the turbine and generator when listing energy transfers.