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Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

compound-connected DC machine
a direct current machine with two field windings in which one field winding is connected
in series and one field winding is connected in parallel (shunt) with the armature winding. The shunt winding may be connected ahead of the series winding (long-shunt connection), or behind the series winding (short-shunt connection).
DC machine
an electromechanical (rotating) machine in which the field winding is on the stator and carries DC current, and the armature winding is on the rotor. The current and voltage in the armature winding is actually AC, but it is rectified by the commutator and brushes.
permanent magnet brushless DC machine
a machine that is similar in structure to a permanent magnet synchronous machine, containing armature windings on the stator and permanent magnets on the rotor. The permanent magnet brushless DC machine, however, is characterized by a trapezoidal flux density distribution in the airgap instead of the sinusoidal distribution of the synchronous machine. In operation, a DC voltage is applied sequentially to the stator coils to create a rotating field that pulls the rotor with it. To correctly operate, the brushless DC machine requires sensors to determine the rotor position so that the proper stator phases may be excited.
permanent magnet DC machine
a DC machine in which the field excitation in the stator is provided by permanent magnets instead of electromagnets.
shunt DC machine
a DC machine with the field winding connected in shunt with the armature. In shunt generators, residual magnetism must be present in the machine iron in order to initiate the generation process. These machines are also known as self-excited, since they supply their own excitation.