Page 640 - Basic Electrical Engineering

In a compound motor two separate field windings are wound around each
pole. One is shunt field winding and the other is series field winding. The
shunt field winding is connected in parallel with the armature while the series

field winding is connected in series with the armature as shown in Fig. 7.22.
The flux produced due to the shunt field current remains constant but the flux

produced by the series field current increases with the load current. The
characteristic curves of a compound motor will be in between those of shunt

and series motors.
The series field winding produces flux which is proportional to the

armature current, i.e., the load on the motor. The flux produced by the series
field either aids the shunt field or opposes the shunt field. (cummulative
effect or differential effect). The characteristics relating T, N, I get modified
a
from the shunt field characteristics as shown in Fig. 7.23.

Figure 7.22 Shows the connections of shunt and series field windings of a compound motor