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close this bookElectrical Machines - Basic Vocational Knowledge (IBE - Deutschland; 144 pages)
View the documentIntroduction
Open this folder and view contents1. General information about electrical machines
Open this folder and view contents2. Basic principles
Open this folder and view contents3. Execution of rotating electrical machines
Open this folder and view contents4. Synchronous machines
Open this folder and view contents5. Asynchronous motors
close this folder6. Direct current machines
View the document6.1. Constructional assembly
close this folder6.2. Operating principles
View the document6.2.1. Power generation (direct current motor)
View the document6.2.2. Torque generation (direct current motor)
View the document6.2.3. Armature reaction (rotor reaction)
View the document6.2.4. Excitation
View the document6.2.5. Value relations
Open this folder and view contents6.3. Operational behaviour of direct current machines
Open this folder and view contents6.4. Circuit engineering and operational features of customary direct current generators
Open this folder and view contents6.5. Circuit engineering and operational features of customary direct current motors
Open this folder and view contents7. Single-phase alternating current motors
Open this folder and view contents8. Transformer
 

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.


Figure 90 - Torque generation in a direct current motor

1 Rotational direction

The following diagram emerges if one observes the torque within the conductor loop depending on the rotational angle.


Figure 91 - Torque of a conductor loop in dependence on the rotational angle

1 Torque

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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