Electrical processes, Part I: Overview and generators

3.2.5 Overview

There are two basic approaches to the generation of electrical potential difference from the rotational energy of the shaft. In synchronous systems the magnetic field rotates, whereas in asynchronous generators the conductors rotate.

3.2.6 Synchronous motors

All three-phase generators (or motors) use a rotating magnetic field, as shown in Figure 3.17 (Danish Wind Energy Association, 2008). Three electromagnets are installed around a circle, and each of the three magnets is connected to its own phase in the three-phase electrical grid. The three electromagnets thus alternate between producing a south pole and a north pole towards the centre corresponding to the fluctuation in voltage of each phase. Thus, the magnetic field will make one complete revolution per cycle. The compass needle will follow the magnetic field exactly, and make one revolution per cycle. With a 50 Hz grid, the needle will make 50 rev s-1 or 3000 rpm.

The diagram illustrates a two-pole permanent magnet synchronous motor, as it has only one north and one south pole, is synchronous with the mains supply, and the compass needle is a permanent magnet, not an electromagnet. The three electro­magnets are called the stator because this part remains static. The compass needle is called the rotor, because it rotates.

Updated: September 26, 2015 — 1:05 pm