 | 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 |
8.1.2. Voltage transformation
A few field lines already close before reaching the output coil (Figure 125) so that flow F1 can be divided into a maximum flow FK which saturates both coils and a leakage flow FS.
The leakage flow may be ignored in regard to the unloaded transformer (idling). Therefore the following applies:
According to the transformer equation
and
.
If we relate both equation then
Shortening gives us
During idling no current flows into the output winding, thus there is no voltage decrease. Consequently the induced voltage U20 equal to the terminal voltage U2 (Cp Figure 125):
Figure 125 - Transformer principle
1 Input winding/upper voltage winding/primary winding, 2 Output winding/under voltage winding/secondary winding
U20 = U2
In the event of minimal idling current I voltage decrease in the input winding is negligibly minimal. We therefore have
U10 = U1which results in
The voltages behave like the numbers of turns.
The interrelationship of the numbers of turns is known as the transformation ratio We have:
The rated voltages U1n and U2n are indicated on the rating plate of the transformer.
Example:
What secondary terminal voltage arises in a transformer where 380 V is applied to the primary winding of 980 turns and the secondary winding has 594 turns?
Given: U1 = 380 V; N1 = 980; N2 = 594
Sought: U2
Solution:
U2 » 230 V
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