                            Electrical Machines - Basic Vocational Knowledge (IBE - Deutschland; 144 pages)  Introduction  1. General information about electrical machines  2. Basic principles   2.1. The magnetic field   2.2. Measurable variables of the magnetic field   2.3. Force action of the magnetic field   2.4. Voltage generation through induction    2.4.1. General law of induction    2.4.2. Stationary induction (transformer principle)    2.4.3. Motional induction (generator principle)  3. Execution of rotating electrical machines  4. Synchronous machines  5. Asynchronous motors  6. Direct current machines  7. Single-phase alternating current motors  8. 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

 U0 general voltage of a motional conductor in a magnetic field B magnetic flow density of a magnetic field l conductor length in the magnetic field v motional speed of the conductor N 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

 c machine constant (constructive values) n 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?   