As regards rotor shape, one differentiates between the turbine and salient pole machines. Both rotor types feature a magnetic constant field. For this reason the rotor iron need not be a lamella pack.
The rotor of the turbine-type machine is called a non-salient pole rotor. It is cylindrically set up, rather long and has a relatively small diameter of up to some 1200 mm. A non-salient pole rotor only has a relatively small number of poles. Mainly it only features one pole pair, that is to say a north and south pole. As this machine mainly runs on alternating voltage of f = 50 Hz, this results in a considerable rotor speed. Thus, for example, a synchronous machine with one pole pair and alternating current at a frequency of f = 50 Hz, requires a speed of 3000 rpm.
The salient pole machine features a field spider with distinct poles which bear the exciter winding. This is relatively short and has a big diameter of some 10 m. The considerable number of pole pairs yield speeds of 60 rpm to 750 rpm given alternating voltage at a frequency of f = 50 Hz.
1 Field spider
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