They are available in single and three phase models. The three phase motors are mainly for larger loads, while smaller loads are often driven by single phase induction motors. When connected directly to the grid the motor will speed up to a certain fixed speed, which is a bit slower than the rotating frequency of the applied electric field (this phenomena is called slip). This property is the reason why inductions motor are also sometimes called asynchronous motors. The achieved speed depends on the amount of pole-pairs and the applied electric frequency. The load on the shaft will only modestly lower the speed of the motor (in the order of a few percent).
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