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 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.
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