|Electrical Machines - Basic vocational knowledge (Institut für Berufliche Entwicklung, 144 p.)|
|6. Direct current machines|
A direct current machine is a rotating electrical machine which, according to circuitry, either utilises or releases energy.
The direction of power conversion determines operation either as direct current generator or motor. The direct current machine is an external pole machine.
Figure 79 - Basic assembly of a direct current motor
1 Main pole with exciter winding, 2 Compensation winding, 3 Rotor with rotor winding, 4 Interpole with interpole winding, 5 Rotational direction during generator operation
The main poles with the direct current pole winding have been arranged in the stator. These main poles set up the magnetic field (exciter field) which, in the case of smaller machines, is also yielded through permanent magnets. The rotable, pivoted rotor is made from a lamella sheet pack whose grooves retain the winding.
Figure 80 - Rotor-core lamination
Figure 81 - Rotor with coil winding
The coil ends of the rotor winding have been extended to the commutator lamella on which the brushes loop. In this way an electrical connection is established between the direct current network and the rotor winding (Cp. Figure 83). Interpoles whose windings are saturated with rotor current have been interspersed in the field-free (neutral) zone of bigger machines. In addition, under certain circumstances a capacitator winding has been accommodated in the pole shoes of the main pole.
The overall assembly of a direct current machine is set out in Figure 82.
Figure 82 - Overall assembly of a direct current machine
1 Rated height, 2 Stators, 3 Exciter winding, 4 End shield of the A-side, 5 End shield of the B-side, 6 Dynamo sheets (armature), 7 Balance mass, 8 Ventilator, 9 Roller bearing, 10 Pulley, 11 Shaft end (cylindrical), 12 Feather, 13 Commutator, 14 Brushes, 15 Gear