1. Depending on their size, power plants generate from 690 volts to several kilovolts (kV). The power cannot be transported at these voltages, because too much energy would be lost in the wires due to the material resistance.
2. Different transformer substations in high- and ultrahigh-voltage networks increase the voltage up to 400kV. This reduces the current hence the resistence in the wires, making low-loss transportation of electricity possible.
3. Medium-voltage networks distribute power regionally from high-voltage networks and supply key customers such as hospitals, factories and railways.