7.4.2. Operating principles
The rotational direction of a direct current motor changes either when the rotor current I2 changes its direction (-M = C • Φ • (-I)) or the exciter current alters in the exciter winding (-M = C • (-Φ1) • I2).
Where both values change, which corresponds to exchanging the conductor mains of a direct current series motor, then the motor retains its rotational direction:
M = C • (-Φ1) • (-I2)
Therefore a single-phase commutator motor also operates in case of alternating voltage.
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