Electrical machines include generators, electrical motors as well as static energy converters such as transformers. A generator produces electrical current from mechanical rotation energy; its frequency is determined by the number of rotor poles and the rotational speed. A motor rotational frequency is determined by the frequency of the supplied current and the number of poles.
All rotating electrical energy converters are based on the rotating magnetic field, the most common being direct current machines, asynchronous and synchronous machines. The direct current machines are no longer used as middle or large industry drives.
The asynchronous and synchronous rotating electrical machines have the same stator composition. A wound stator core composed of core sheet layers embodies grooves in which copper layers are regularly placed throughout the circumferential extent. These copper layers are connected together in three phase-windings. The parts of the windings emerging from the stator core, also called core ends, are connected through a terminal box to the electrical network.
The whole winding of the stator is isolated according to the corresponding voltage and isolation classes. The core ends are supported by complex mechanics and reinforced among each other. This ensures that mechanical stresses do not provoke any deterioration even in exceptional situations. It is highly challenging to perform CFD-calculations for these geometries.
The asynchronous three phase machines, also called induction machines have either squirrel-cage rotors or slip-ring rotors. Squirrel-cage rotors have grooves which are filled with non-isolated compact copper or aluminium stems which are short-circuited on each end by a ring. Slip-ring rotors have isolated windings which are connected to slip rings on the rotor shaft.
The synchronous machines have either pole salient rotors or full poles rotors. Pole salient rotors have fully-developed poles with a magnetic core and coil windings Full-pole rotors are generally made of core sheet layers, they incorporate groves in which isolated copper windings are placed according to a north and south pole connection. Full pole machines are required for high rotational speeds due to their massive steel rotor. Both rotor types are connected to a DC current supply.
Article about E-Cooling in Mai 2017
periodical Engineering Edge
(article on pages 18-19)