6. Electric generators

There are two types of generators in PCHs:

• alternators (synchronous machines) for all power plants not connected to the grid;

• asynchronous generators for those feeding into a powerful network.

Picocentrales (10 to 100 kW) are sometimes equipped with a DC machine or an asynchronous machine self-excited by capacitors. In this case, the number of capacitors and the load ensure voltage and frequency regulation.

Generators used in conjunction with hydraulic turbines must be mechanically dimensioned to withstand overspeeds corresponding to the runaway speed of the turbines. This runaway speed is between 1.8 and 3 times the rated speed. At present, this runaway ratio is close to 2. The asynchronous machine is, by design, easier to maintain than the synchronous...