Hey everyone,
I’m getting into electric speciality and, to be honest, never understood (made it clear in my head) how does AC or DC work, why there are three/single phases used?
by „Make clear in my head” I mean I generally have some knowledge, but couldn’t be able to explain it to somebody else. Thanks!
In: 5
* DC power is like a chain saw.
* It does work by forcing charge carriers through the wire smashing into things along the way.
* AC power is like a reciprocating saw where the teeth move back and forth very quickly.
* You can still do a lot of work that way.
* You can also convert that back and forth motion into straight ahead motion too.
* Single phase AC is just normal regular AC power.
* The voltage swings from 0V to +120V, down to -120V, and then back to 0V.
* It has a line or “hot” leg paired with a neutral leg and a ground leg.
* Three-phase power is the same as single phase except there are two additional “hot” legs that each share the same neutral and ground legs.
* They can share neutral and ground because their phase (fancy term for *when* they swing from 0, +120,-120,0) is sightly off-set from each other and if they are all loaded equally, the current going back down the neutral leg cancels out to 0A.
* Also you can use two of the hot legs instead of a hot and neutral and you can get 208V, which is not quite 240V but is close enough for some devices that need higher voltage.
DC is current that goes the same way all the time. It is naturally produced by batteries and solar cells. It is useful in electronics because it contains no noise, and because many components only work right when current goes one way through them. You can think of it as a bicycle chain.
AC is current that changes direction all the time. You can think of it as a piston. It is naturally produced by electric coils being magnetized. It is useful in motors and transformers. Transformers are great because they can turn low voltages at high current into high voltages at low current, and vice versa. Low current means thinner transmission lines, and low voltage means safe household power.
Three phase AC current is produced when three coils are magnetized in sequence. They’re arranged so that there’s always a balance between the three currents. This means the current from the phase that’s the strongest can always return to the two others, and they gradually trade places. This is useful because it needs no dedicated return wire, and because sending it to three new coils produces a naturally rotating magnetic field, which motors love. One phase or DC motors need to perform various tricks in order to make such a field. This makes three phase power great for power transmission and industrial use.
When you see a sine wave, you should think in terms of a rotating circle. With single phase power you have one connection to the rim of the circle, with three phase power, you have three connections to the rim of the circle 120 degrees apart.
To help visualize it:
Single phase power is like a simple crank: http://507movements.com/mm_092.html
Three phase power is like a Schmidt coupling: https://www.youtube.com/watch?v=ARs3y3i0enE
DC would be something like a bicycle chain.
AC = current alternates, plus a voltage to minus a voltage, in a wave pattern
DC = current is constantly applied at a voltage, think of the average battery
DC is good for short distances, but AC is easier to generate, has less loss over longer distances, and is easier to step voltage up or down, so AC is used from the power station to your house.
Based on the technical explanations, think of the three phase advantage this way.
[This is single phase power.](https://www.electronicshub.org/wp-content/uploads/2019/12/Single-Phase-Supply-Waveform.jpg) Peak power is delivered only twice per cycle, and we are delivering no power every time the wave crosses the middle line.
[This is three phase power](https://www.electronicshub.org/wp-content/uploads/2019/12/Three-Phase-Supply-Waveform.jpg). It’s much more evened out, some power is always delivered, and peak power comes six times per cycle.
This lets us get nearly twice the wattage out of a power source by adding only one more pin (now four).
Think of bike pedals on a bike. There’s a downward driving stroke with one foot while the other foot is opposite. Eventually that foot will be the driving stroke. But there are periods where neither foot is adding driving force in a significant manner. That’s single phase power.
Now imagine that same bike with 3 seats and pedals with each set of petals offset so that at any one time, one of three right legs is giving a downward driving stroke and then one of three left legs is giving a downward driving stroke. That’s three phase power.
You can have all three pedals drive the same wheel or (the analogy breaks down here a bit) they can all use the same chain but each power it’s own wheel.
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