 | 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 |
8.2.1. Idling behaviour Idling features
A transformer idles where mains voltage U1 remains applied to the primary side whilst no consumer is connected to the secondary side (Za) (Figures 125/126).
|
Primary circuit |
U1 applies |
| |
I0 flows (idling current) |
|
Secondary circuit |
Za = ¥ |
| |
I2 = 0 |
| |
U2 = U20 |
Idling current
The applied voltage U drives the idling current I0. This is needed to establish the magnetic field Iµ. This lags behind the voltage U1.
Figure 127 - Indicator image for
idling operation
1 Iron loss current IFe
The phase position of the idling current I0 to voltage U1 can be determined according to the circuitry of Figure 128.
Figure 128 - Circuitry to determine
idling losses
1 Rated voltage
The value of idling current I0 is between 2 and 5 per cent of idling current in big transformers and up to 15 per cent in smaller transformers.
No-load curve
The idling curve I = f (U1) in Figure 129 indicates that no-load current I0 increases proportionally to the input voltage U1. No-load current increases markedly over and beyond the input rated speed U1n. It can, moreover, even attain values greater than the rated current.
Figure 129 - Idling curve of a
transformer I0 = f (U1)
Transformers shall not be driven by voltages greater than the rated voltage.
Idling losses (iron losses)
The active power derived from the circuit in Figure 128 can only be transformed into heat in the input winding and iron core as no current flows into the secondary winding during idling. The active power P0, which is converted into heat in the iron core, is made up of eddy current and hyteresis loss.
The following example shows that the iron losses almost always arise during idling.
Example:
The following idling values were measured in a transformer:
U1n = 220 V; I0 = 0.5 A; P0 = 40 W; R1 = 3.
What percentage of winding losses are contained in idling power?
Solution:
P0 = PVFe + PVW
PVW = 0.75 W
PVFe = P0 - PVW = 40 W - 0.75 W = 39.25 W
Thus, the power loss determined during idling is an iron loss.
Iron losses are determined during no-load operation and are independent of load.
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