10.1 - Squirrel Cage
This is the most commonly used engine in the industry today. It has the advantage of being more economical compared to single-phase motors in both its construction and in its use. Moreover, choosing the ideal method of starting, has a much wider range of applications. So let us examine in detail this engine.
The squirrel-cage rotor consists by a core of ferromagnetic plates, isolated from each other, which are placed on aluminum bars (drivers), arranged parallel to each other and joined at their ends by two rings drivers, also in aluminum, which short-circuit conductors (see Figure ).
The motor stator is also composed of a laminated ferromagnetic core, the armholes of which are placed windings fed by three phase alternating current network.
The advantage of this rotor for the rotor winding is resulting in construction of the induced faster, more practical and cheaper.
This is a robust engine, cheap, fast production, not requiring collector (body sensitive and expensive) and a fast network connection.
be noted that the bus bars of the cage are generally placed with an inclination to avoid the chatter and noise resulting from electromagnetic action between the teeth of the arches of the stator and rotor.
The main drawback concerns the fact that the starting torque is reduced compared to the current drawn by the stator.
This is essentially a constant speed motor.
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The engine differs from the wound rotor motor rotor squirrel-cage rotor retaining only the . The rotor consists of a laminated ferromagnetic core on which are housed the coils forming the phase winding, usually the star. The three free terminals of each phase winding coils are connected to three slip rings. These three rings link externally to a rheostat starter consisting of three variable resistors, also connected in star. Thus the rotor windings are also closed circuit.
The function of the rheostat starter, connected to the rotor windings, is to reduce the high starting currents in the case of high power motors.
As the engine is gaining speed, the resistors are progressively removed from the circuit until they were short-circuited (withdrawals) when the engine starts to operate at its rated speed. Thus, the wound rotor motor also works with the elements of the rotor in short circuit (such as the motor of squirrel cage rotor), reaches its nominal speed.
The induction motor rotor winding replaces the rotor squirrel-cage powers in very high due to the lower starting current permitted by the configuration of the rotor.
Despite being used in cases with constant speeds of service as mentioned in the last paragraph applies preferentially when the service speeds are variable.