Electric machine
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An electric machine is in electrical energy technology used machine , and provides a form of energy converters . It distinguishes between rotating electric machines, including various types of electric motors and electric generators , and stationary electric machines, including transformers belong. What all electrical machines have in common is that they have a magnetic circuit in their structure , which is essential for their function.
overview
Electrical machines use the properties of electromagnetic interaction and are based on electromagnetic induction and magnetic force effects, which are described by the Lorentz force and, for some machine types , by the reluctance force .
For historical reasons , the group of stationary or static electrical machines includes transformers , and especially transformers that are used in the field of electrical power engineering , such as power transformers . With stationary electrical machines, the magnetic force effects only play a subordinate or undesirable role, since no movements are carried out and the function of a transformer is to transform alternating voltages between different high voltage levels.
In the much larger and exclusively shown area of rotating electrical machines, which are characterized by a large number of different designs and areas of application, the magnetic force effects play the central role. They are used to convert electrical power into mechanical power on a shaft . If electrical power is converted into mechanical power, it is called an electric motor , if mechanical power is converted into electrical power in the opposite direction, it is called an electrical generator . Some electrical machine types can be operated both as a motor and as a generator; the specific function is determined by the operating range of the machine. Because of this, there is also some overlap in the conceptual use of motor or generator.
Every energy conversion is associated with a loss of energy in the form of heat. One advantage of electrical machines is that their losses are comparatively small, so they achieve a high level of efficiency . Large electrical machines can achieve efficiencies of up to 99%.
The industrial sector concerned with electrical machines is electrical engineering. Electrical machines are used today in all areas of technology , industry, everyday life, transport, medicine and other areas. The power range of electrical machines extends from orders of magnitude below one microwatt (e.g. clockworks or microsystem technology ) to over one gigawatt (1 GW = 1,000,000,000 watts), as is the case with the turbo generators used in power plants .
Components
Electrical machines have differently arranged wire coils through which the electric current flows. The magnetic flux that occurs is guided in a targeted manner in an iron core, which is also referred to as a magnetic circuit . This core consists of materials that can conduct the magnetic flux well, for example layered electrical steel . The layering, together with the one-sided insulation of the sheet metal parts, serves to suppress undesired eddy currents . In rotating machines, the stator and rotor , also known as armature in some machines , are essential components. The forces generated in each of the two magnetic fields cause a targeted (one-time or permanent) movement of the machine parts against each other.
Electrical machines have insulation areas for electrical insulation of the parts through which current flows from one another and from the external environment. Mechanical support structures and possibly bearings for guiding moving parts are used to mechanically stabilize the machine .
Designs
The rotating electrical machines can be classified according to various criteria; the classifications in the literature are not uniform and are characterized by overlaps. The classification can be based on the type of current used, such as direct current , alternating current and three-phase alternating current (a multi-phase alternating current that generates a rotating magnetic field through the appropriate spatial winding arrangement). Another classification can concern the mode of operation of the machine and lead to a subdivision into commutator machines , asynchronous machines and synchronous machines . Each of these groups is divided into different types of machines, which are divided into further classes.
The following table provides an exemplary and incomplete classification according to the type of current in the vertical direction and according to the operating principle in the horizontal direction, including a reference to possible areas of application, as a simple overview.
| Type of current | Commutator machine | Asynchronous machine | Synchronous machine | Exemplary areas of application |
|---|---|---|---|---|
| Direct current |
DC machine , series machine , shunt machine |
Precision engineering | ||
| Alternating current | Single-phase series motor |
Shaded pole motor , capacitor motor , repulsion motor |
Reluctance motor | Electric tools and household appliances, smaller pumps, precision engineering |
| Three-phase alternating current |
Asynchronous machine , slip ring motor , linear motor |
Synchronous machine , salient , Vollpolmaschine , cascade machine |
Industrial drives, large pumps, conveyor technology, turbo generators in power plants, highly dynamic drives for machine tools | |
| Impulse current |
Brushless DC motor , stepper motor , Lavet stepper motor |
Highly dynamic drives, positioning drives, clock technology |
Asynchronous and synchronous machines require multi-phase alternating current for their motor operation or generate multi-phase alternating current as a generator. Usually this is three-phase alternating current , which generates a rotating field in the area of the rotor. There are also induction machines that are operated, for example, with two-phase alternating current; this is the case with some stepper motors. The asynchronous machine with squirrel cage rotor is widely used as a drive because it is inexpensive to manufacture and requires little maintenance. A characteristic of the asynchronous machine is the slip , which means that the rotor does not move at the same number of revolutions as the rotating magnetic field.
The group of synchronous machines is characterized by a rigid relationship between the rotation of the rotor and the rotating field. Examples of synchronous machines are salient pole machines , which are divided into internal and external pole machines, and full pole machines, which are used in the form of turbo generators in power plants. Synchronous machines also include stepper motors and special designs, such as the Lavet stepper motor, and brushless DC motors, such as the torque motor . With these synchronous motors, the rotating field is generated by means of a frequency converter with a four-quadrant controller, which is required in addition to the motor . For smaller powers, methods such as block commutation are used; for higher powers, processes such as vector control and space vector modulation are used .
In addition, there are also special rotary field machines, such as the cascade machine , which is used, for example, as a generator in wind power plants. A motor used in nanotechnology is the electrostatic motor .
With the help of the commutator, the commutator motors can be operated directly on direct current or single-phase alternating current. Examples of commutator machines are the direct current machine and the universal motor that can be operated with direct or alternating voltage. The DC machines are divided into shunt machines and series machines.
In addition, there are electrical machines with only limited areas of application, such as the unipolar machine , which in generator mode supplies a direct voltage without rectification . The Barlow wheel is a historical design of a unipolar machine . In addition, historical electrical machines exist from the beginning of electrical engineering, which, due to various disadvantages, have found little or no distribution. This includes the Egger electric motor .
literature
- Rolf Fischer: Electrical machines . 14th, updated and expanded edition. Hanser, Munich 2009, ISBN 978-3-446-41754-0 .
- Hans-Ulrich Giersch: Electrical machines. Testing, standardization, power electronics . 5th, corrected edition. BG Teubner, Stuttgart et al. 2003, ISBN 3-519-46821-2 .
- Rudolf Janus, Hermann Nagel: Transformers . Edited by Rolf Rüdiger Cichowski (= systems engineering for electrical distribution networks . Volume 5 ). 2nd Edition. VDE-Verlag et al., Berlin et al. 2005, ISBN 3-8007-2921-0 .
Individual evidence
- ^ A b Rolf Fischer: Electrical machines . 14th, updated and expanded edition. Hanser, Munich 2009, ISBN 978-3-446-41754-0 , Chapter 1: General principles of electrical machines.