In general, the definition of an electric power system includes some stages. Firstly, Power Plants as a source of power. Then, high voltage transmission lines are used to transfer power from power plants to power substations.
Power substations with their step down transformers are installed for reducing the voltage to suitable levels to be distributed. As a last stage, Distribution systems are used to give the costumer his need of electricity. All these stages are as shown in figure (1).
