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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
 

6.2.3. Armature reaction (rotor reaction)

Mode of operation

The magnetic main field of the direct current machine runs symmetrically from the north to the south pole (Figure 92 (1)) in the stator. The current-saturated rotor winding generates a second magnetic field which runs vertically (transverse) to the main field (Figure 92 (2)).


Figure 92 - Armature reaction

(1) Main field of the currentless rotor, (2) Armature transverse field, (3) Resultant overall field
1 Neutral zone
Despite rotor rotation the transverse field remains motionless and its value only changes in proportion to the current intensity in the rotor winding.

The armature transverse field superimposes itself with the main field to a resulting field (Figure 92 (3)) whose neutral zone has been displaced with regard to the main field.

The neutral zone is displaced by the armature transverse field. Its rotation ensues in the generator in rotational direction and, in the motor, contrary to the rotational direction of the rotor.

A displacement of the neutral zone leads to brush sparking. Furthermore, the armature reaction weakens the main field and this, in turn, paves the way for a decrease in rotor-induced voltage.

Interpoles

The negative influence of the armature transverse field can be overcome by superimposing a counter-directed magnetic field. So-called interpoles (Cp. Figure 93) are established between the main poles.


Figure 93 - Magnetic field of the interpoles

1 Generator operation
2 Motor operation

The interpole windings are so switched that their magnetic field is counter-positioned to the armature transverse field. In this motor, therefore, a principal north pole is followed by a north interpole in rotor rotational sense.

The interpole shall generate a magnetic field ouncterpositioned to the armature transverse field. The interpoles are in the neutral zone. Interpole and rotor windings have been series connected,

The armature transverse field can also be compensated by a magnetic field which is generated by the so-called compensation winding.

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