The asynchronous motor is based on the currents induced in the rotor from the rotating magnetic field of the stator. That's why it's called an induction machine. As to be able to induce an electric current in the rotor it is necessary that the rotor is subjected to a variation of the magnetic flux generated by the stator at the frequency of power, or synchronism, the rotor is demagnetized when it reaches the synchronism, since does not see magnetic flux variation. For this reason the motor rotates at a different speed than the stator field and therefore rotates asynchronously.
Asynchronous or induction motors, being robust and cheaper, are the most widely used motors in the industry. In these motors, the rotary field has the speed synchrony according to the frequency of the feeder line.
The asynchronous motor is the most common type of electric motor. Specifically, the three-phase asynchronous motor is the most commonly used type of motor in the industry. This success is mainly due to the following reasons:
- Compared with the other electric motors of the same power, their cost is lower.
- These are very simple engines with great ease of maintenance.
- The asynchronous motor has better performance with respect to the single-phase motor. For this reason, the single-phase motor is relegated to small-scale domestic appliances and appliances.
An important feature of asynchronous electric motors is that you can not vary the speed, or therefore the power, gradually. The operating speed of the induction motors depends on the frequency of supply and the number of poles.
Types of asynchronous motors
The classification between different types of asynchronous motors depends on the voltage of the alternating current that is used:
- Three-phase asynchronous motor. This type of motor uses 400 volt current.
- Single phase asynchronous motor. This type of motor uses 230 volt current.
A three-phase motor is a type of robust motor and does not require a switch. Most three-phase asynchronous motors have a balanced load. They are engines that consume the same in the three phases, whether they are connected in star or triangle. The voltages in each phase in this case are equal to the result of dividing the line voltage for the root of three. For example, if the line voltage is 400 volts, then the voltage of each phase is 230 volts.
The squirrel cage motor is a type of asynchronous motor. In electric motor type the rotor is constituted by a series of bars arranged in the grooves of the rotor crown, joined at their ends to two rings. The starting torque is small and the intensity they absorb is high.
The vast majority of asynchronous motors are squirrel cage.
Rotor rotor motor
The wound rotor motor is a type of electric AC motor. In this type of motor the grooves of the rotor crown are inserted the windings joined by a common point. This type of motor has some copper rings, called slip rings that rotate with the shaft making contact between it and some brushes that will allow to connect the rotor windings with the outside.
The advantage of the wound rotor is that they allow progressive starting by means of rotor resistors, currently with the use of electric starters and inverters they are not necessary and their manufacture is very limited.