The AC motor (also known as induction motor ) is an electric motor which is powered by single phase. An ability to operate a three-phase motor of an alternating current network, is in operation with a frequency converter for rectifying the alternating voltage and then converts it into three-phase current. This is also a speed control over a wide range is possible. The induction motor was invented by Nikola Tesla.
Universal motor ( single-phase series motor )
The universal motor is a simple form of the AC motor, the principle of which is derived from the DC motor. This engine is suitable for all equipment and tools of daily use, as it due to the high speeds only a small installation space and produces a high starting torque. His speed and power can be adjusted by phase control. These engines are produced today with capacities up to 3000 W.
Single-phase asynchronous motor
To make asynchronous start automatically on single-phase alternating current, they need a self-generated rotating field ( to the main field phase-shifted field). This is done through a condenser ( capacitor motor) or a short-circuit winding ( shaded pole ). In both cases the auxiliary phases may be switched off after the start-up (by hand, with a time relay, comprising a magnetic switch comprising a bimetal switch and a centrifugal switch which is mounted on the ventilation side of the motor on the shaft and turns off at the rated speed of the start-up capacitor ).
When capacitor motor main winding is connected directly to the power supply and an auxiliary winding connected via a capacitor in series to the network. The result is an elliptical rotating field which, although sufficient for starting the motor, but affects the smoothness. For higher starting torques start capacitors (often bipolar electrolytic capacitors ) are used, which have to be separated, for example, at the rated speed by a centrifugal or magnetic switch back from the circuit.
Also, three-phase asynchronous can be operated on single-phase power when they are switched with capacitors ( see Steinmetz circuit ).
Shaded pole motor
When shaded pole motor, the rotating field is generated by a phase-shifted by eddy currents magnetic field. To this end, each pole of the stator is split and one half is provided with a short ring or a turn-off short-circuit winding, so that there the magnetic field is continuous or delayed during startup.
The simplest design of the AC motor is the starter motor. He is cranked by hand. From a certain speed of the motor then runs high even in throw-off direction down to the rated speed. To change the rotation direction of the motor must be stopped and started up in the other direction. The alternating magnetic field exerts on the rotating squirrel cage once a certain speed from a small torque which, however, only close to the rated speed is so great that it can do work. Also, single phase connected three-phase asynchronous motors can be used in this way. The starter motor is rarely used today.
Another type of the AC motor is a reluctance motor, which continues to run contrary to the normal induction motors after the run as a synchronous motor at synchronous speed. Special rotor laminations with salient poles cause this behavior.
Also, synchronous motors can be operated single-phase; they then require a starting aid or " rock " itself " kick in ".