I work with equipment that operates on three phase electrical circuits. I can’t get my head around the concept of “phases.”
In: 17
imagine electricity as a wave and there is a limit to how much of that wave you can force down a wire. But, if you could start another wave, in between when the first one starts and ends, you can get more power down the same line with less loss.
In electricity, a phase refers to the distribution of a load. there is two-phase and three-phase. Think of it as a group of people working together to get a job done. in 2 phase, two people work together to get the job done. in three phase, three paper are working to get the job done. in essence, three phase will be more efficient because load is distributed to three people compared to 2 in 2-phase.
therefore, a three-phase power supply better accommodates higher loads and is mostly used in commercial and industrial facilities while 2 phase is used for domestic purposes.
A wrong answer for the sake of ELI5.
Imagine you’re rowing a boat. You have half of the stroke pushing against the water propelling the boat forward, but the other half of the stroke the boat isn’t actually being propelled forward since you’re picking up the oars and getting ready for a 2nd stroke.
Imagine if you add a 2nd rower to the boat who times his rows to “push” while yours are pulling. Now the boat will be propelled twice as much in the same amount of time as the original stroke.
Add a 3rd rower and you have 3 phase power.
Phases are your “hot” wires.
Are you in the US? Your workplace likely runs a 480V/277V system.
Each phase carries 277V. And your equipment can be made to run on a hot and neutral. But, the higher the voltage the smaller the wire can be so it is desirable to run equipment at the highest safe-ish voltage possible to keep components smaller.
(That is why high voltage lines are not 6′ in diameter even though the feed a city)
Each phase moves in a wave from +277V to 0V to -277V and so on. But the waves peak at different moments in time on each phase so connecting phase to phase instead of phase to neutral gives you 480V.
“But 277+277 is 554, not 480!” you say.
Take a peek at how the waves go. Pick a peak of any wave, look straight down at where another phase is. You’ll see the other phase isn’t peaked in the negative so you get 480V instead of 554V.
https://upload.wikimedia.org/wikipedia/commons/thumb/c/cc/3_phase_AC_waveform.svg/1280px-3_phase_AC_waveform.svg.png
Single phase works the same, except 120V/240V and the math is simpler because the phases peak at the same time.
https://www.hvacrschool.com/wp-content/uploads/2021/02/240v-waveform.png
Electricity is a wild science.
FYI, when you look at a light it is actually off 60 times per second and your slow human brain just doesn’t process it. *POOF!* mind blown.
Let me take a whack at it. This is also not precise but I think none of the answers are actually ELI5.
Let’s say I make a one way toll route to a super cool place that electrons want to go. Like the Disneyland of electrons. Each one drives by and pays me a little bit of energy tokens that I can use. This is kind of what happens in DC circuits, right?
Well, what if I make a two way toll route and advertise my super cool electron attraction so all of them go this way, and then advertise another attraction on the side they were! After that I keep alternating so they’re motivated to keep crossing. Then they would pass the toll, then turn around and go the other way, then turn around and do it again. So I’d still be making energy tokens even if they don’t get anywhere. Now let’s say my toll employees need a steady income and the problem with this system is that everyone is full force going one way and we make a lot, then news gets out and everyone turns around and in between there’s a period of a low season, where they’re just turning around.
To solve this problem, i divide them into two groups, and tell them where the coolest attraction is at different times so when the first group is turning around, the second group is going full force in one direction. This way I have less peaks of busy times and nadirs of low seasons. This is two phase electricity.
But it’s still a little uneven. I can smooth the whole thing out by adding more complexity but apparently for what I want to do three groups of electrons being motivated to move at different times is enough to keep my steady flow. That’s three phrase electricity.
Well, three phase electrical system is a neat trick to transfer more electrical energy via fewer wires.
Electric current needs at least two wires to propagate. Also there is a limit on how much energy you can transfer via wire of given length/gauge/material. Basically, if you try to squeeze too much energy in a cable it will begin to heat up, converting electricity into heat. In most severe cases it can burn out completely.
Three phase system uses clever trick to transfer electric energy via three wires. Neat thing is that you can transfer 3x more energy via 3 wires than via 2 wires. So, by adding one more wire, you are increasing energy throughput threefold. Those 3 wires are called “phases”. Each pair of those “phases” carries energy independently of others. So you have three pairs: A-B, A-C and B-C, thus three times more energy.
Pedantic reader will tell me that for three phase system you need 4 cables: 3 phases + neutral wire. But neutral wire is needed only in cases when there is imbalance between phases – energy is consumed inequally per phase . In ideal case you don’t need neutral wire at all or it can be very thin, as it carries almost no current. In energy distribution systems ground is often used as a neutral wire. But neutral is always present in last mile connection, because almost any end user will create imbalance between phases. Neutral wire will carry current caused by imbalance.
As an end user you need to know that voltage between two phases is much higher than between phase and neutral wire. So you need to be extra careful near 3 phase junctions/connectors/switches/etc.
As for how three phases work… Well, this is completely different question. It is hard to explain without drawing diagrams.
The phase of any wave is describing “where” your peak is (more generally it describes how your wave amplitude changes in time and space but this isn’t an ELI5 explanation anymore). In EE, AC can be described as a wave, so phase is answering the “where is my peak” question. The problem is that this single phase AC now is literally peaking then tumbling to a low then up again. We fix this problem by making more peaks without increasing the peak itself, i.e adding phases.
Extra phases are generated to make the peak occur more often, so 3 phase means you have one repeating peak that is followed by 2 similar repeating peaks. These 3 peaks are evenly spaced out, so from a hectic up and down AC, you get a less steep, hilly one that can much more smoothly and evenly deliver power.
From what I know as a non-EE, these 3 phases are in separate wires to avoid overheating and they need to be connected in the correct order if you’re ever handling these.
Generation occurs when a wire has relative motion with a magnetic field in such a way the the coils of wire cut the lines of magnetic flux. In other words, wave a coil past a magnet, or a magnet past a coil, and it will induce a voltage in that wire.
Hold that thought. For matters of ELI5, if you wave the magnet down past the coil, it will generate a voltage with a specific polarity. Wave it in the opposite direction, and the polarity will reverse.
Take a magnet and put it on a rotating wheel. Place a coil on opposite sides of the wheel…for imagery, imagine the magnet as the hand of a clock with a coil at 9:00 o’clock and its other half at 3:00 o’clock.
As the hand (magnet) rotates in a clockwise manner, its flux lines will cut the coil at 3:00. Let’s say that generates a positive pulse. As it continues to rotate, it will cut the lines on the opposite side of the coil at 6:00, but since it’s going in the opposite direction (relative to the flux lines), it will generate a negative pulse.
So the magnet is rotating inside the coil. As it approaches 3:00 o’clock, the voltage rises to a peak as it passes 3:00, then decays back to zero as it approaches 6:00 (since it is no longer cutting lines of flux).
As it approaches 9:00 o’clock, the voltage rises in the opposite direction (negative) and decays to zero after it passes and approaches 12:00.
You’ve just built a sinusoidal wave. The voltage builds from zero to a maximum positive peak, then decays back to zero and immediately starts building to a negative peak, before declining again. A single phase generator.
Nice, but inefficient. Let’s add magnets. Put one at 11:00 and 5:00, and one at 1:00 and 7:00.
Time out. Since the clock numbers don’t work, but for imagery, imagine the magnets are equally 120 degrees apart from each other. This is close enough for ELI5.
So now you’ve got coils at three positions. As the magnet passes each one, the voltage in each coil will rise and decay, but each will be 120 degrees behind the next one. Now you’re generating 3 phases, 120 degrees apart, that peak at the same magnitudes, but at different times.
Bear in mind that this can be picked apart technically, but for ELI5, it will give you the basic idea.
Do you remember learning about the sine function in math in your youth? It’s that wavy function that keeps repeating itself. Ultimately it is related to circular motion, so much like you can split a circle into 360 parts and call each a degree (360 degrees in a circle) you can also split that sine function up into 360 steps. The phase is just what step number, or degree, you are at if you are tracing the function.
The sine function starts at 0 at step zero, reaches a maximum at step 90, goes back to zero at step 180, goes to a minimum negative value at 270 and back to zero by step 360, which is also step zero for the next cycle. We
Alternating current electricity is described by this function, where at maximum (step 90, or 90 degrees) the current is going one way and at 270 it is going the opposite direction.
When it comes to producing electrical power, the direction of current doesn’t really matter, just that there is current. So in terms of our steps, or phase, at 0 we have no power, at 90 we have max power, at 180 we have zero power, and at 270 we again have max power.
It isn’t ideal to have our power be cycling up and down like that. We can add in more electrical current on another wire but have it at a different step, or phase of its cycle, so when one is at step 180 and producing no power is the other is at step 90 and producing max power. We would say these electrical currents are 90 degrees out of phase.
Having two is better than one, but having three has some additional benefits as the vector sum of the three balanced currents is zero.
So we have three phase power, which is three currents out of step, or phase, by 60 degrees, so when one is at zero the others are at 120 and 240. By the time the first gets to 120, the others are at 240 and 360, which is the same as zero, and the cycle repeats.
Go to [wolframalpha.com](https://wolframalpha.com) and paste the following into the input field:
plot(Sin(x*PI/180),Sin^2(x*PI/180),(x,0,720))
The line labeled Sin(x*PI/180) in the resulting graph is indicative of the current. It’s just a sine fumction. The one labeled Sin^(2)(x*PI/180) is indicative of the power. The Pi/180 is a conversion factor as wolframalpha uses 2Pi radians rather than 360 degrees for splitting a circle up. Notice the graph goes for two cycles or 720 steps since 720 = 2 cycles*360 steps per cycle.
Let’s look at three phase:
Paste the following into the input field:
plot(1/3*Sin(x*PI/180),1/3*Sin((x+120)*PI/180),1/3*Sin((x+240)*PI/180),(x,0,720))
This is the individual currents or phases of the electrical signal. Notice that each of them is 120 steps behind one and 120 steps in front of the other.
Paste the following into the input field
plot(1/3*Sin^2(x*PI/180),1/3*Sin^2((x+120)*PI/180),1/3*Sin^2((x+240)*PI/180),(x,0,720))
This is the individual power for each phase and you can see that as one peaks and starts to fall another is rising to its peak. This gives you constant power output throughout the cycle.
so 3-phase power refers to the fact that you are using 3 sinusoidal currents, each of them 120 degrees out of step or phase with the other two, leading one and trailing the other. Each of these currents is called a phase, which is kind of lazy and confusing as now “phase” is bother referring to the current in one of the wires and where that current is in its cycle from 0 to 360.
If you start way back at the generator there are 3 stators and a rotor. Essentially the 3 conductors or “phases” are just extensions of this. From generation to transmission to distribution. Phase A at your house is connected to the phase A stator on the generator. In fact every phase “A” on the interconnection is connected like this and synchronized. The rotor in each generator is a magnet with flux lines that pass through the stator to induce ac current forwards and backwards (depending on if the north or south pole of the magnet crossing the stator) producing a sine wave. Gens can have different numbers of poles in their rotors but the rate change relative to the stator is the same producing synchronized waves. Each phase or stator is 120 degrees apart and changes 60 times a second in North America.
We use three phase power because it’s the best bang for the buck. There were other numbers of phases tested back in the day but this became the standardized format.
Sorry for the grammar I’m high AF.
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