how does ac motors spin in one direction if its powered by alternating current , and what is single phase and 3 phase alternating current ?
In: 1
In an electric motor there is a group of magnets on the rotor and stator,
Let’s say we start with all the magnets on the rotor having the south pole point out and the stator magnets have the north point in.
Now the motor will move so that the rotor magents point exactly towards the stator magnets. But then what ? The motor stops because the attractive magnets are already as close as they can get.
So what we actually do is we wait for the rotor to move towards the stator magents, and because of inertia it will overshoot slightly, and what we do then is flip the magnetic orientation of either the rotor or stator magnets: now we have two south or two north poles close together, so they’ll repel each other and the rotor will be pushed further away again.
And then we just repeat this cycle over and over again, switching the orientation of the magnets to make sure the rotor is always pulled in the same direction.
And if you have an electromagnet, the way you switch it’s polarity is by changing the direction of current through the coil.
As for single phase and 3 phase, well a single phase AC is just one sine wave AC and a neutral wire with no voltage. 3 phase is 3 wires that each have their own slightly offset voltage sine wave. These are often used for electro motors because you can put 3 (or 6, 9, 12, etc..) electro magnet pairs on the motor and attach each of them to one of those 3 phases. Because the sine waves are offset, it will naturally cause the polarities of the magnets to switch in a perfect sequence.
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