There’s no such thing as a DC motor. If you find that statement surprising, think about it for a moment or two. All motors depend for operation on a rotating magnetic field so, even if a motor is powered from a DC supply, some form of switching must be provided to produce this, which means that the motor cannot be strictly considered as a DC machine. Nevertheless, well into the 20th century motors fed from DC supplies were the workhorses of industry, and the required switching was achieved with brushes and commutators.
As AC supplies became more widespread, wound-rotor synchronous motors took over as the dominant technology, followed by the induction motors that remain ubiquitous in industry today. The main benefit of these machines compared with their predecessors is simplicity. In effect, the ‘switching’ needed to produce a rotating field is an inherent feature of the AC supply. The commutator and brushes, which are costly to produce and require regular maintenance, are no longer necessary.
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