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 · F · (-I)) or the exciter current alters in the exciter
winding (-M = C · (-F1) ·
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 · (-F1) ·
(-I2)
Therefore a single-phase commutator motor also operates in case
of alternating
voltage.
