2. Setting frequency and active power

Any difference between the electrical power demanded by a network and the mechanical power supplied by the alternator drive machines causes variations in the speed of the alternators, and therefore in the network frequency.

The problem of matching generation to demand at any given moment is therefore closely linked to that of frequency control (Electrical power transmission and interconnection networks. Operation ). This adaptation can only be carried out in two ways:

• by constantly varying production to satisfy consumption; this is the normal operating mode;

• by adjusting consumption to production; this is what we are forced to do in times of shortage (structural or accidental).