The d.c. machine

Abstract

The basic principles underlying the operation of d.c. machines have been discussed in chapter 1 where it has been noted that the field winding is mounted on salient poles on the stator and the armature winding is wound in slots on a cylindrical rotor. The frequency of the e.m.f. generated in the armature depends directly on the mechanical speed of rotation, and the action of the commutator is that of a frequency changer so that the frequency at the commutator brushes is zero in this particular case. Various arrangements of armature windings have been discussed in chapter 2 where it has been noted that the commutator brush is normally situated on the centre line of a main pole, although it is connected to a coil in the interpolar gap. It is usual to use a schematic representation of a d.c. machine in which the brushes are shown in the position of the coil to which they are connected, and the physical arrangement together with the two schematic diagrams to be used in this text are shown in Fig. 8.1 for the particular case of a generator. The torque