Main data on alternating current
Most alternating-current machines, synchronous and asynchronous were widely adopted.
Any alternating-current electrical machine consists of two main parts: the motionless part called by the stator, and the rotating part called by the rotor. Between the stator and the rotor there is the air interval, or the gap which size exerts very sushcheyostvenny impact on working properties of the machine. So, for example, in machines of the direct current and synchronous the air gap is done rather big as its increase in machines of the direct current reduces voltage ripple, and in synchronous machines increases overload capacity. In asynchronous mayoshina increase in air gap sharply reduces electrical power factor and the torque of the machine. Therefore in asynchronous machines air gap always small, 0,2 — 3 mm.
The core of the stator is assembled from steel sheets in the form of rings on which internal circle stamp hollows or grooves for laying of the winding of the stator. Steel sheets isolate from each other varnish or scale for reduction of losses by whirling currents. The stator core with the winding is placed in the bed, posredstyovy which the machine fastens on the base and by is transported.
The device of the stator and its winding at synchronous and asynchronous machines equally. Grooves can be open, poluzakrytyyom (b) and closed (fig. 1).
Open grooves do in machines of the direct current and in synchronous machines on the rotor at their neyoyavnopolyusny design. At open grooves it is easy выполять the sample winding that reduces its cost. However at such form of the groove magnetic field in air gap raspreyodelyatsya unevenly.
The closed grooves carry out for short-circuited windings of rotors of asynchronous engines, for the starting and damper (soothing) winding of synchronous machines. At such form of the groove the irregularity of distribution of magnetic field is excluded, but performance of the winding is much more difficult, by the broach method, i.e. the wire is stretched through the insulating sleeve in the groove.
With half-closed grooves the stator of alternating-current machines is carried out most often. The winding can be semi-sample here, i.e. previously prepared on the template in the form of soft coils which rounds put or "pour" on one through the groove cut.
The device of the rotor and its winding at synchronous and asynchronous machines different. Working process in machines proceeds under deystyoviy the rotating magnetic field created by the namagnichivayoyushchy force (N of page) of the symmetric three-phase winding of the stator. At the same time in synchronous machines process of transformation of energy happens with the synchronous frequency, i.e. at rotating speed of the royotor, equal frequency of the rotary field of the stator whereas in asynchronous machines the return, i.e. during the work the frequency of the rotor cannot be to the equal frequency of the rotary field (asynchronous speed).
As well as any electrical machine, synchronous and asynchronous machines have property of reversibility, i.e. can work both in the generator mode, and in the engine mode.
Synchronous generators are the main source of the electrical energy developed at power plants. All electrical energy necessary for needs of the national economy is made by three-phase synchronous geneyorator. Synchronous motors find less wide primeneyony. Their advantage - high power factor (cos ф), the opportunity to consume the leading current from network, compensating the reactive power consumed by other receivers of energy which are switched on in this network.
Therefore use of synchronous motors is reasonable at rather big capacities they worked with consumption of the leading current from network and compensated the reactive power of other consumers, raising cos ф all enterprise. Besides, constancy of rotating speed does reasonable use of synchronous motors in cases when the rigid high-speed harakteriyostika is necessary (sound cinema, players, etc.).
The asynchronous engine which inventors were Tesla and Dolivo-Dobrovolsky, - the most widespread type of elekyotrichesky machines. Simplicity of the design, profitability and high safety in operation of asynchronous engines caused their shiroyoky application in different industries. These dvigayotel make on different capacities ranging from neskolyyoky watts up to several thousand kilowatts.
The potrebyonost in the 0,4 - 100 kW three-phase asynchronous engines is especially big. Asynchronous generators almost do not find practical application as possess the number of essential shortcomings: do not develop reactive power, do not provide constancy of the frequency induced э. of page.
In addition to two main operating modes, the generator and the engine, synchronous and asynchronous machines use in special operating modes. Synchronous machines work kompensatoyory, developing only the reactive power, asynchronous machines - in the mode of the electromagnetic brake, the frequency transformer, etc.
Synchronous and asynchronous machines do in osnovyony three-phase, but apply also single-phase. In addition to sinkhronyony and asynchronous machines, alternating-current collector machines are used, working properties of which are similar to working properties of machines of the direct current.Top