how does ac motors spin in one direction if its powered by alternating current , and what is single phase and 3 phase alternating current ?
AC motors spin in one direction because of the way the internal components are wired. The alternating current (AC) flows in a wave pattern, and the motor takes advantage of this wave pattern to create a rotating magnetic field. The components inside the motor are wired in such a way that the rotating magnetic field causes the motor to spin in one direction. Single phase alternating current is a type of AC power supply that uses a single phase. This means that the current alternates in one direction, and then reverses direction. Three phase alternating current is a type of AC power supply that uses three phases. This means that the current alternates in three directions, and then reverses direction. This allows for a more efficient power supply, and is used in many industrial applications.
AC motors spin in one direction because of the way their internal components are designed. Inside the motor, there are two sets of coils called windings. When AC power is applied to the windings, the current alternates between the two sets of windings, creating a rotating magnetic field. This rotating magnetic field causes the motor shaft to rotate in one direction. Single-phase AC power is a type of alternating current that has only one voltage waveform. This waveform alternates between positive and negative values. Three-phase AC power is a type of alternating current that has three voltage waveforms. These waveforms are 120 degrees out of phase with each other, which helps create a more consistent and powerful flow of current.
Single phase alternating current is a current that rises to a maximum value in one direction, then falls to zero at which point it reverses, then rises to its maximum value in the other direction, then falls to zero again. This is called a cycle. In North America, the power grids are all 60 cycle.
Three phase current is three single phases arranged in a very particular manner. Call the individual phases A, B, and C, though most generation stations actually identify them by color. A phase is as described in the single phase description. B phase is the same, except it reaches its maximum current in the first direction 1/180 of a second after A phase does. C phase, again, is the same as A and B phase but it reaches its maximum current in the first direction 1/180 of a second after B phase does, and 2/180s of a second after A phase. And 3/180s of a second after A phase reaches its maximum, A phase does it again in its next cycle. This is what’s known as a phase sequence, A-B-C. As there is no beginning or end to a sequence, there are only two. The second one is commonly called B-A-C.
A three phase motor has a winding (a group of coils) for each phase so that when the current is applied, it creates a rotating magnetic field that drags the rotor around with it. Reversing the motors rotation is as simple as interchanging any two of the three power supply leads.
As for single phase motors, there are a great many different styles. I’m going to assume you’re interested in the squirrel cage types as they do the bulk of the work. Even among just the single phase squirrel cage motors, there are a handful of different types, but they all do the same thing, just in different ways.
A single phase motor with a single winding would not rotate, it would pulsate. That would be enough to keep the motor running, but it can’t start it. To start it they manufacture a second phase inside the motor. In smaller ones it’s done by installing a shading pole. It’s a rather inefficient, but cheap, way to do it, but it’s limited by its very low starting torque. Another is the permanent split capacitor motor. More efficient than the shaded pole, but more expensive, and you don’t get much more starting torque. Finally there are the split phase motors. They include capacitor start and capacitor start-capacitor run motors. They use capacitors to make a more efficient 2nd phase for both starting and running.
Excepting the shaded pole type, they all use the same configuration. There are two leads for the main winding and two for the starting winding. A main lead and a starting lead are connected to one power lead, and the other main and starting leads are connected to the other power lead. To reverse, just interchange the starting leads.
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.