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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
close this folder2. Basic principles
Open this folder and view contents2.1. The magnetic field
Open this folder and view contents2.2. Measurable variables of the magnetic field
Open this folder and view contents2.3. Force action of the magnetic field
close this folder2.4. Voltage generation through induction
View the document2.4.1. General law of induction
View the document2.4.2. Stationary induction (transformer principle)
View the document2.4.3. Motional induction (generator principle)
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
Open this folder and view contents6. Direct current machines
Open this folder and view contents7. Single-phase alternating current motors
Open this folder and view contents8. Transformer

2.4.3. Motional induction (generator principle)

Operating principle

Given motional induction a change in the magnetic flow is attained through the movement of magnets, equally through the motion of an electric conductor within a magnetic field.

Figure 20 - Induction through magnetic flow change (movement of a magnet)

1 Induced current, 2 Direction of movement

Figure 21 - Induction through magnetic flow change (movement of a conductor)

1 Induced current, 2 Direction of movement

The following applies to several series switched conductors (coils):

U0 = N • B • l • v


general voltage of a motional conductor in a magnetic field


magnetic flow density of a magnetic field


conductor length in the magnetic field


motional speed of the conductor


number of series switched conductors

Right hand rule (generator rule)

If the right hand is so positioned in a magnetic field that the field lines enter the open palm of the hand and the projected thumb points in the motional direction of the conductor, then the extended four fingers point in the direction of the current in the conductor loop forthcoming through the generated voltage.

Figure 22 - Right-hand rule (generator rule)

1 Direction of the magnetic field
2 Direction of the induction current
3 Direction of movement

An example is indicated in Figure 23.

Figure 23 - Rotating movement of a conductor loop in the magnetic field

Generator equation

The following equation results from applying the induction law:

with v = π • d • n

U0 = c • Φ • n


machine constant (constructive values)


speed of the conductor loop

Questions for repetition and control

1. What causes a magnetic field?

2. How is a magnetic field presented?

3. How are field line direction and current direction related to one another?

4. What are the differences between a magnetic constant field and an alternating field?

5. How is a rotating field generated?

6. What does the speed of the rotating field depend on?

7. What is meant by magnetomotive force?

8. How are magnetic flow and magnetic flow density interrelated?

9. How are the forces directed which similar and opposite magnetic poles exert to one another?

10. Describe the left hand rule.

11. Which values exert an influence on the torque of a motor?

12. Describe the right hand rule.

13. Which values are of decisive importance for the induced voltage in a generator?


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