 | Electrical Machines - Basic vocational knowledge (Institut für Berufliche Entwicklung, 144 p.) |
 |  | (introduction...) |
| | Introduction |
|  | 1. General information about electrical machines |
| | 1.1. Definition of terms |
| | 1.2. Types of electrical machines |
| | 1.3. Operations of electrical machines |
| | 1.4. System of rotating electrical machines (generators, motors, converters) |
| | 1.5. System of stationary electrical machines (transformers) |
| | 2. Basic principles |
| | 2.1. The magnetic field |
| | 2.1.1. Definition and presentation of the magnetic field |
| | 2.1.2. Magnets Magnetic field |
| | 2.1.3. Magnetic field of a current-carrying conductor |
| | 2.1.4. Magnetic field of a current-carrying coil |
| | 2.1.5. Magnetic fields in electrical machines |
| | 2.2. Measurable variables of the magnetic field |
| | 2.2.1. Magnetomotive force |
| | 2.2.2. Magnetic flow |
| | 2.2.3. Magnetic flow density |
| | 2.3. Force action of the magnetic field |
| | 2.3.1. Force action on cur rent-carrying conductors |
| | 2.3.2. Force action on current-carrying coils (motor principle) |
| | 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 |
| | 3.1. Size |
| | 3.2. Designs |
| | 3.2.1. Definition |
| | 3.2.2. Designation |
| | 3.3. Degree of protection |
| | 3.3.1. Definition |
| | 3.3.2. Designation |
| | 3.4. Cooling |
| | 3.4.1. Cooling category |
| | 3.4.2. Cooling category designation |
| | 3.5. Mode of operation |
| | 3.5.1. Definition |
| | 3.5.2. Operational mode designation |
| | 3.5.3. Frequent nominal cycle ratings |
| | 3.6. Heat resistance categories |
| | 3.7. Connection designations of electrical machines |
| | 3.7.1. Transformers |
| | 3.7.2. Rotating electrical machines |
| | 3.8. Rotating electrical machines in rotational sense |
| | 3.8.1. Clockwise rotation stipulation |
| | 3.8.2. Direct current machines |
| | 3.8.3. Alternating current and three-phase machines |
| | 3.9. Rating plate |
| | 4. Synchronous machines |
| | 4.1. Operating principles |
| | 4.1.1. Synchronous generator |
| | 4.1.2. Synchronous motor |
| | 4.2. Constructional assembly |
| | 4.2.1. Stator |
| | 4.2.2. Rotor |
| | 4.3. Operational behaviour |
| | 4.3.1. Synchronous generator |
| | 4.3.2. Synchronous motor |
| | 4.4. Use of synchronous machines |
| | 4.4.1. Synchronous generators |
| | 4.4.2. Synchronous motors |
| | 5. Asynchronous motors |
| | 5.1. Constructional assembly |
| | 5.2. Operating principles |
| | 5.2.1. Torque generation |
| | 5.2.2. Asynchronous principle |
| | 5.2.3. Slip |
| | 5.3. Operational behaviour |
| | 5.3.1. Start |
| | 5.3.2. Rating |
| | 5.3.3. Speed control |
| | 5.3.4. Rotational sense alteration |
| | 5.4. Circuit engineering |
| | 5.4.1. Starting connections |
| | 5.4.2. Dahlander pole-changing circuit (speed control) |
| | 5.4.3. Rotational reversing circuit |
| | 5.4.4. Braking circuits |
| | 5.5. Application |
| | 5.6. Characteristic values of squirrel cage motors |
| | 6. Direct current machines |
| | 6.1. Constructional assembly |
| | 6.2. Operating principles |
| | 6.2.1. Power generation (direct current motor) |
| | 6.2.2. Torque generation (direct current motor) |
| | 6.2.3. Armature reaction (rotor reaction) |
| | 6.2.4. Excitation |
| | 6.2.5. Value relations |
| | 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 |
| | 6.4.1. Separate-excited direct current generator |
| | 6.4.2. Direct current shunt generator |
| | 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 |
| | (introduction...) |
| | 7.1. Single-phase asynchronous motors (single-phase induction motors) |
| | (introduction...) |
| | 7.1.1. Assembly and operating principle |
| | 7.1.2. Operational behaviour |
| | 7.1.3. Technical data |
| | 7.2. Three-phase asynchronous motor in single-phase operation (capacitor motor) |
| | 7.2.1. Assembly and operating principle |
| | 7.2.2. Operational behaviour |
| | 7.3. Split pole motors |
| | 7.4. Single-phase commutator motors (universal motors) |
| | 7.4.1. Assembly |
| | 7.4.2. Operating principles |
| | 7.4.3. Operational behaviour |
| | 7.4.4. Technical data |
| | 8. Transformer |
| | 8.1. Transformer principle |
| | 8.1.1. Operating principle of a transformer |
| | 8.1.2. Voltage transformation |
| | 8.1.3. Current transformation |
| | 8.2. Operational behaviour of a transformer |
| | 8.2.1. Idling behaviour Idling features |
| | 8.2.2. Short-circuit behaviour |
| | 8.2.3. Loaded voltage behaviour |
| | 8.2.4. Efficiency |
| | 8.3. Three-phase transformer |
| | 8.3.1. Three-phase transformation with single-phase transformers |
| | 8.3.2. Three-phase transformers |
| | 8.3.3. Vector groups |
| | 8.3.4. Application of three-phase transformers in power supply |
| | 8.3.5. Parallel operation of transformers |
| | 8.3.6. Technical data of customary transformers |
7.4.3. Operational behaviour
The value of the yielded torque is also determined in universal motors by means of the general motor equation. As in the case of the direct current series motor, a considerable torque is developed at low speed. Figure 122 depicts the speed-torque curve.
Figure 122 - Speed-torque curve of
the universal motor
As universal motors may be driven by either direct or alternating voltage, it is necessary to heed that the inductive resistance is absent during direct voltage connection. Given alternating voltage connection there is rather more brush sparking because of commutator current change and alternating voltage current direction change. Pole gaps remain small in the rotor field and brush sparking is within acceptable limits. The disruptive effect of brush sparking on radio reception can be eliminated by switching on capacitors (Figure 120).
The circuitry also indicates that, when direct voltage is connected, the number of turns at like voltage and speed have to be increased as compared to alternating voltage feeding. The greater number of turns compensates for the lacking resistance. Although inrush current is greater than rated current there is no likelihood that small motor power might be impaired through disruptive mains overloading. A rotational direction change can be attained in universal motors by switching over the winding at the terminal board. However, where field and armature windings have been soundly connected in series, rotational direction change is not possible. Universal motors are especially suitable for electrical small tools, household equipment and office machinery. Such motors also figure in hoovers, coffee machines and drills.
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