Electric motors asynchronous or regularly known as induction motors depict most of the effective electric motors on the market.
These motors have a short-circuit rotor, ie consisting of aluminum bars that are installed in the groove cores of the magnetic plate and at the ends are connected to each other by means of a ring (short-circuit ring).
Due to this fact, the variable magnetic field generated in the stator induces sinusoidal currents in the bars of the rotor cage, which in turn develops a magnetic field in the rotor that opposes the field of the stator. They may also hold a coiled rotor, which is the least-applied solution.
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As the poles, with the same polarity repel each other, there is a force arising in the direction of rotation of the rotor. This rotates with a slightly reduced speed at the sync speed. Due to this peculiarity, these types of motors are able to depart directly from the network, without the cooperation of any other motor or even power electronics instruments.
An important topic of this model of engines is the inequality between the speed of synchronism and the speed rotor, called sliding or slipping.
A rotating magnetic field is at the base of the operating principle of the induction electric motor. This field is produced as follows: a set of three independent coils, 120 ° out of phase in the space, is placed in the stator slots, and three-phase lagged current coils of 120 ° are circulated over time.
The rotating or stationary character of the field of rotating electric machines depends in reality on the adopted reference system. For an observer located in the induction of a synchronous machine with rotating inductor, the field of this machine is rotating. For an observer located in his rotor, the field is stationary. The simplest usual ways of producing rotating fields can be summarized in the use of rotating monophasic windings, powered by direct current.
The synchronous speed is the product of 120 times the frequency in Hz, divided by the number of poles of the motor. From this formula it becomes clear that the higher the frequency that comes to the engine, the greater the speed of its work, and the reverse also influences at a lower speed in an electric motor. And it is this change that the frequency inverter makes: it performs this intervention before the electric motor enters.