Modular indoor station: diagram
Modular indoor substations for high and extra-high voltages

In most countries, the major transmission and interconnection functions are performed by very-high-voltage (VHV) networks, in France the 400 kV network and to a lesser extent the 225 kV network.

The distribution function is performed by high-voltage (HV) networks, in France the 90 kV or 63 kV network and, to a certain extent, the 225 kV network.

Distribution is handled by medium-voltage (MV) networks, in France the 20 kV network.