Eli5: What’s the difference between a single phase electric current versus a 3 phased one?
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It’s like a rope, one phase is just one so can lift only so much (supply limited power) , 3 phased is like a 3 ropes tied together – you can lift something big or untangle it and lift 3 smaller things at tge same time (suply more power)
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An interesting fact not mentioned here is the phase shift occurring in three phase power.
The voltage in one phase shifts between -240V and +240V constantly.
When you now attach one phase to a motor, it will induce a magnetic field in the metal wires inside.This will help a motor to turn itself since it is a magnet that gets attracted from the resulting electromagnetic field.
If you now use three phases, the voltage is 120 degree shifted which means, that every phase will reach the 240V at a different point in time.
This makes it easy to construct a motor that spins 50 times a second using three coils and the three phases. You now just need to arrange the coils in a triangle and put a magnet in the middle. The magnet will rotate in the frequency of the power network.
PS: living in Europe so voltage may be different but the concept is the same.
Am not an Electrician ( do we have an acronym for that yet?)
But when I moved into my current (no pun) house five years ago, we had single phase. Lights and regular fans working fine, but we had to choose between Hot shower (one of those wall mounted things) or the Fridge being on. We had to choose between the wife having a hot shower or my work Desktop functioning. (I would have included an anecdote with microwave ovens for Americans, but we haven’t used, needed nor missed them for over a decade – microwaves I mean… I think).
We got a three phase installed a week later and every ran smooth. Still does five years later.
For power coming into the house, we use AC – alternating current. The voltage alternates between positive and negative, following a sine wave (what you imagine a wave looks like).
We talk about waves as having a phase. This just means where in the cycle we start/are. For a sine wave, the start, labelled 0°, is usually when it’s in the middle and about to go up. We label the phase from 0° to 360° because the height of a sine wave is just the height you’re at when you go round a circle anticlockwise from horizontal.
Three phase AC uses three different wires to carry the electricity in, each at a different phase. They are spaced 120° apart. You could think of the extra phases as starting ⅓ and ⅔ along the wave, or as starting 120° and 240° around the circle.
Because maths, a properly controlled 3-phase system has a *total* voltage of 0V at all times. E.g. one wire will be very negative and the other two will be slightly positive, so the voltages all add to 0. This means in theory if you grabbed all 3 phases in one hand, you’d be safe. You might get an injury on your hand, but the electricity wouldn’t flow through the rest of your body and kill you. I wouldn’t recommend testing this…
3 phases of power can be delivered using 5 wires rather than the 6 you’d need to run 3 circuits that were all in the same phase, so as more power is transmitted the savings in the cabling alone can very significant (esp with high voltage transmission lines).
So in the UK for example the main grid and the stepdown stations etc will use 3 phase power, and then at the lowest level of substation the 3 phases will be split and distributed between houses and streetlights etc (1st house phase 1, next house phase 2, next house phase 3, next house phase 1 again etc) so in a single phase outage you might only lose 1 in 3 streetlights
Commercial premises with large electricity use will take 3 phase power which can be split for each circuit (so you don’t lose all your lights if one phase goes etc) and any large motors can be 3 phase motors which simplifies wiring and minimises vibrations etc and so tend to be more reliable
Single Phase AC circuits swing up and down creating a consistent wave which helps push energy into things.
3 phase AC has 3 identically sized Single Phase AC waves pushing energy into things, but each phase’s wave is staggered so the top of each wave hits one after another in perfect timing.
Thus works kind of like pushing a pedal on your bicycle, each Phase is like pushing down on your pedal, you need the first phase to push the pedal all the way down on the right so the next phase can push the pedal all the way down on the left.
This is why 3 phase electricity is more efficient than single phase for powering motors (and bicycles would also be more efficient if we had 3 legs to push 3 pedals…), as each phase helps rotate the motor just enough for the next phase to take it further.
The electric grid uses alternating current power (AC). It is generated with 3 phases because the generators have 3 windings. For industrial, commercial, and large apartment buildings, all 3 phases are brought in to spread the load around. For single family houses, only one phase is typically needed and connected to the house. In the US, that phase is split in half so you have a choice between 120v and 240v.
Another benefit to having 3 phase power has to do with how the phases relate to each other. With AC the biggest push to motors happens when the voltage peaks. Since the 3 phases’ peaks are evenly spread out and the tails overlap you have a more constant push. This consistency is also why the generators are built that way, since generators are motors that are pushed by something (usually steam) to generate power.
I compare it to singing a song like “What shall we do with the drunken sailor” but the group is split ino three, and each section starts singing a couple of bars later than the previous, creating a harmonic effect.
The three phases are all singing the same alternating current tune, but start their sinuswave at a different moment. As a result the difference in potential between two phases is larger than would be the case between a phase and a zero wire.
Ok so single phase current is *alternating current* (AC), that means you have one live wire that is changing from positive to negative 60 (or 50 in some places) times per second.
Then you have 2 phase current, where you have 2 live wires that are the opposite charge to each other. When one positive the other is negative etc.
Then 3 phase, the timing is more complex where each goes positive and negative in sequence.
As well as just having 3x the power, a fun use for 3 phase electricity is linking it directly to a motor and because the positive and negative go in a set sequence the motor will turn at a really precise speed, and the motor can be made simpler as well.
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