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 6.4. Circuit engineering and operational features of customary direct current generators 6.5. Circuit engineering and operational features of customary direct current motors 6.5.1. Direct current motor with permanent excitation 6.5.2. Direct current series motor 6.5.3. Direct current shunt motor 7. Single-phase alternating current motors 8. Transformer

#### 6.5.1. Direct current motor with permanent excitation

Circuitry

The permanently excited direct current motor is a small machine in which the exciter field is established through permanent magnets.

Figure 104 - Circuitry and terminal board of a direct current motor with permanent excitation

Dependence of current take-up on the torque (load)

As the curve I = f (M) indicates in Figure 105, current take-up is directly proportional to the torque because of the constant exciter flow.

Figure 105 - I = f (M); Current take-up dependence on torque

Dependence of speed on the torque (load)

Direct proportionality exists between speed and torque in speed-load behaviour.

Figure 106 - n = f (M); Speed dependence on torque

Speed control

Speed control ensues by changing the applied voltage.

Application

Direct current motors with permanent excitation are used mainly for power ratings up to 500 W. Such motors find application in the toy industry, household appliances, measurement and control technology.