Electrical Power System Essentials

2.2 THERMAL POWER PLANTS

Thermal power plants, of which a photo is shown in Figure 2.1, convert the primary energy from coal, oil, gas and nuclear into electrical energy. The first step in this conversion process is to transform the chemical energy of fossil fuels into thermal energy, either by combustion (in case of coal, oil and gas) or by fission (nuclear). Thermal energy is used to produce steam at high temperatures and pressures. The steam expands adiabatically (i.e. without heat extraction or injection) in a steam turbine and the thermal energy of the steam is converted into mechanical energy when the steam passes the turbine blades and causes the turbine to rotate. The shaft of the turbine is connected with the shaft of a synchronous generator and by electrical induction the mechanical energy is converted into electrical energy.

Figure 2.1 A thermal power plant. Reproduced by permission of TenneT TSO B.V.

2.2.1 The Principles of Thermodynamics

The first law of thermodynamics is the law of conservation of energy: energy can not be created and can not be destroyed. We can only convert one form of energy into another form of energy. For a gas, the first law of thermodynamics can be written in mathematical form as:

Q the heat added to the system [J]

U the internal energy [J]