Electrical Machines - Basic Vocational Knowledge (IBE - Deutschland; 144 pages) Introduction 1. General information about electrical machines 2. Basic principles 3. Execution of rotating electrical machines 4. Synchronous machines 5. Asynchronous motors 6. Direct current machines 6.1. Constructional assembly 6.2. Operating principles 6.3. Operational behaviour of direct current machines 6.3.1. Direct current generators 6.3.2. Direct current motors 6.4. Circuit engineering and operational features of customary direct current generators 6.5. Circuit engineering and operational features of customary direct current motors 7. Single-phase alternating current motors 8. Transformer

#### 6.3.1. Direct current generators

The induced voltage is determined by means of the equation U0 = c • Φ • n

Thus we derive the value of U0

1. through the construction (C)
2. through the exciter flow (Φ)
3. through the speed (n).

The construction constant (C) which results from the construction of the generator take in, for example, the number of pole pairs, the number of rotor conductors and the interconnection of the rotor windings. The exciter flow can be controlled by changing the exciter winding voltage. This is possible by series connection of an alterable resistance to the exciter winding. This is called resistance strain field actuator. Exciter voltage, exciter current and excited flow are interlinked like this:

If U0 = f ((Φe)) is considered one can also investigate U0 = f (Ie) as Φe is dependent on Ie. The following diagram is forthcoming for a constant speed n (Figure 95): In the case of a lesser exciter current the curve is almost linear. The curve flattens out following increased pole iron saturation.

Figure 95 - U0 = f (Ie); induction voltage as an exciter current

Figure 96 depicts the relationship between rotor speed and induced voltage U0. Thus, the original voltage can also be attained through the speed.

Figure 96 - U0 = f (n); induction voltage as a speed function

The induced voltage of a direct current generator can be controlled by altering the exciter current or the speed.