Generators - Wind Energy Systems for Electric Power Generation - page 41

a) b)

Fig. 3.13 Load characteristics of a laboratory setup with SEIG and ohmic load ( a )curvesat
n = const, capacitance C as parameter; ( b )curvesatC= const, speed n as parameter

3.3 Synchronous Machines

3.3.1 Principles of Operation

Synchronous machines as considered here feature a stator carrying a three-phase
winding, called the armature winding. The rotor, traditionally called the induc-
tor, supplies the magnetic flux. This is done either by an excitation winding or by
permanent magnets. D.c. excitation current is normally transmitted to the rotor by
slip-rings and brushes. Concepts without slip-rings, where the excitation current is
supplied by a coupled polyphase exciter and rotating semiconductors are known,
but are common only in turbo-generators for power stations.
Figure 3.14 depicts a circuit diagram of a three-phase synchronous machine with
star connected stator winding, the terminals U, V, W supplied from the lines L1, L2,
L3 of a three-phase grid. The rotor carries the field winding, the terminals F1, F2
connected to be fed by d.c. current via slip-rings and brushes from a separate d.c.
source with lines L+ , L

. The inductor flux may also be supplied by permanent
magnets which in the model replace the excitation winding. Note however that this
implies fixed rotor flux, different from the case with excitation winding where the
flux is adjustable by supplying field current from a suitable source.

−

Fig. 3.14 Diagram of
three-phase synchronous
machine with separate
excitation