The Power Network

Electricity is transmitted from generating facilities to consumers in successive stages: firstly, via the main transmission network, which is designed to carry large quantities of energy over long distances, and then via the sub-transmission network, which is designed to carry smaller quantities of energy over shorter distances. Electricity is transmitted locally at medium voltage (20,000 volts) and low voltage (380 volts and 220 volts) by the distribution networks.

The main transmission network

Electricity is transmitted nationally, and even right across Europe, mainly at 400,000 volts. The main transmission network is an electric superhighway consisting of more than 13,000 kilometres of power lines, capable of carrying electricity over extremely long distances. The high voltage level used helps to reduce line losses (heat dissipated in the conductors themselves).

The network's main job is to:

• maintain the balance between electricity generation and consumption across France and to correct any imbalances that occur within or between regions, or between different countries,
• allow countries to provide each other with a backup electricity supply if one registers a generation deficit or a sudden rise in consumption, to limit the risks of a widespread black out,
• allow exchanges of energy across France and with neighbouring countries on the European electricity market.

The sub-transmission network

Electricity is transmitted regionally or locally at 225,000, 90,000 and 63,000 volts. The system is quite similar to the road network, with main roads (225,000 volts) and by-roads (90,000 and 63,000 volts) which transport electrical energy to distributors' delivery point substations. Major industrial customers are usually connected directly to the sub-transmission network.