Understanding Power Stations and Electricity Generation
Compare Both Power Stations:
Both of these are thermal power stations. The first is a nuclear power station that uses the heat of controlled nuclear reactions (breaking nuclei of uranium) to heat water and transform it into steam. The second is a thermal combustion station that uses the heat of burning petrol, natural gas, and coal to heat water and transform it into steam. Then, both thermal power stations use the steam to move a turbine. The turbine is connected to a magnet that produces alternating current (AC).
Alternating Current (AC):
A current is alternating when it periodically reverses the direction of flow. The current moves forward, then backward, then forward… Electrical power stations produce electricity as alternating current at 50 Hz, so the current makes 50 cycles per second. Normal AC supply to houses and schools has a peak value of 325V and a mean value of 230 V.
We use a transformer to change the voltage and the current of an alternating current. As we will see later, this is useful to transport electricity because we can transport the same power with higher voltage but a smaller current. The power losses in a wire depend on current intensity, not on the voltage values. We also use transformers in battery chargers. The transformers reduce the AC supply voltage from 220V to only a few volts.
AC Generator:
An AC generator, also called an “alternator,” is a generator of alternating current. It takes the kinetic energy of rotary movement (from a wind turbine, a car engine…) and transforms it into AC electrical energy. The magnets move, and with them, their magnetic fields. The movement of the magnetic fields “pushes” the electrons to flow.
Direct Current (DC):
A current is direct when it always flows in the same direction.
Transformers:
A transformer works with AC but not with DC. With a transformer, we raise and lower the voltage and the intensity of an alternating current. Power is current multiplied by voltage. If we increase voltage, the current decreases. If we decrease voltage, the current increases. Transformers are very useful to transport electricity over long distances because if we raise the voltage and lower the intensity, the losses due to friction along the wires are smaller.
Electrical Terms:
- Electric Current (I): Unit: Amp (A). Number of electrons that flow along the circuit.
- Electric Tension Difference (V): Unit: Volt (V). It’s the energy of each electron. Batteries give energy to the electrons. Electrons use their energy on the appliances.
- Electrical Resistance (R): Unit: Ohm (Ω). Force that the material exerts against the electron flow through it.
- Electrical Power (P): Unit: Watt (W). Is the product of current and voltage.
Energy and Its Transformations:
We often transform energy from one form to another. The most common intermediate energy is electricity.
Energy: There are different forms of energy: thermal, kinetic, potential, sound… The total amount of energy always remains the same. 1 Cal = 4.184 J.
Power: Power = Energy / Time. It is how quickly or slowly we use energy.
The Production of Electricity:
We generate electricity from primary energy sources. Some primary energy sources are:
Renewable:
- Hydroelectric potential energy
- Wind’s kinetic energy
- Solar light
Non-Renewable:
- The chemical energy from fossil fuels
- The nuclear energy from uranium
On a thermal station, the steam is what makes the turbine move.
On a hydroelectric station, the water is what makes the turbine move.
On a wind station, the wind is what makes the turbine move.
Types of Power Stations:
Nuclear Power Station: Uses the heat from controlled nuclear reactions as the primary source of energy to heat the steam in a steam turbine.
Thermal Power Station: Converts a primary source of energy into heat, which is used to convert water into hot pressurized steam. The hot steam in front of the turbine has high pressure. As the steam passes through the turbine, it loses pressure and heat. The pressure and heat are transformed into the kinetic energy of the turbine. The turbine has a shaft connected to an electric generator, which transforms the kinetic energy into electric energy.
The Transportation and Distribution of Electricity:
Electricity is transported from power stations to consumers through a grid. Power lines cables are made of aluminum. The power lost due to resistance along the cables depends on the current (I) and the resistance (R). If the current is lower, the power lost is much lower. We transport the same power with less current if we increase the voltage. Electrical power is transported through high-voltage power lines with a relatively low current intensity, almost always AC. We use transformers to raise and lower voltage and intensity.
Solar Cells:
The light of the sun goes to the cells, and in them, the light of the sun pushes the electrons to produce direct current, and through an inverter, the DC is converted into AC.