2. Physical descriptions of ground networks

2.1 Electrical safety ground line

Electrical power is generally supplied by three-phase transformers with a primary input of 25 kV phase-to-phase at a frequency of 50 Hz. The secondary supplies power at 380 V phase-to-phase, with neutral output. This means that energy capture by a single-phase electrical installation or equipment takes place between phase and neutral with a nominal voltage of $380\text{ V/}\sqrt{3}$ , i.e. a potential difference of 220 V.

In most distribution substations, the neutral conductor is earthed via a resistorR _N connected to a local earth connection; figure...