We have simply connected the six magnets to the three phases in a clockwise order. When we double the number of poles in the stator of a synchronous generator we will have to double the number of magnets in the rotor , as you see on the picture. Otherwise the poles will not match. Obviously, we could repeat what we just did, and introduce another pair of poles, by adding 3 more electromagnets to the stator. With 9 magnets we get a 6 pole machine, which will run at 1000 rpm on a 50 Hz grid.
Most wind turbines use generators with four or six poles.
The reasons for using these relatively high-speed generators are savings on size and cost. Copyright 1998 Soren Krohn. All rights reserved.