6.2.2. Torque generation (direct current motor)
Section 2.3.2. indicates that a current saturated conductor loop and a magnetic field are required in order to generate a torque. This is attained by applying a voltage to the rotor winding as in Figure 83.
A rotational movement up to the neutral zone arises where direct current flows into the rotor winding.
The forces are then still effective but do not constitute a torque. The current direction in the conductor loop must be reversed in the neutral zone in order to attain a further rotation. Current direction change in the direct current machine is handled by the commutator which switches over the current direction in the conductor loop after a semi-rotation. Thereby the voltage attached to the carbon brushes is transformed in the conductor loop into alternating voltage. Figure 90 depicts this process.
1 Rotational direction
The following diagram emerges if one observes the torque within the conductor loop depending on the rotational angle.
The torque ranges between zero and a peak value. A virtually constant torque is attained by utilising a large number of conductor loops (coils) which are distributed along the rotor circumference.
Conductor loop rotation in the exciter field similarly induces a voltage in this field. This runs counter to the applied voltage and cuts back operating current.
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