Science & Nature Facts : What Is a 3-Phase Power Supply?

[alwlad]

three generators connected together are the same as one machine pushing and stopping? I really did not understand it

[wzbzbz]

Perfect introduction. Thanks!!

[Cmonty007]

what makes each phase 120 degrees out of sync and not just a strong single phase?

[theUltinator]

@Cmonty007 On his board in green represents the three phases. In the centre is 0 V. Outside is 230 V. Because there are three phases needing to be balanced and all three need to connect at 0 V, they must be equally separated therefore 360(degrees) / 3 (phases) = 120(degrees). Also industry uses 400V because (230v x 230v) [square of each phase] x 3 [three phases] = 158,700 V. Then the square root of 158,700 = 398 or 400V. SIMPLES 

[MrDrekon1]

Nice ;)



[hamalqa]

Very gooood explain

[electronic2012]

P(AC)= I*R*COSA

[t0f0b0]

Thank you. :)

[Mykem1977]

Very well said.

[iaw1000]

You are the number one instructor to made it easily to understand about 3 phase system. The electrical power on the airplane is the 3 phase system. Thanks for this video

[Froede1]

No idea how i got to this video, but very good explanation, i do understand

[mjbcisy]

thanks for the informative video, the only thing that i cant understand how we get energy while the current in pushing and pulling, power + and power - , isn't that mean 0 , and why there is a neutral line and live one I think momentarily the live line should be live when it is pushing and then it should be neutral when its pulling

[thaitanium2005]

@mjbcisy POWER = Voltage x Current

see also "rectifier"

[ActiveStorage]

thank you that cleared things out a bit but i wish i could learn more about WHY or HOW exactly 1 or 2 phase generator would blow up. What's the mechanics of developing such "imbalance"?

[Dusty754]

Sounds fishy. Why would an alternator stop if it were producing one phase. It is producing a posetive moving wave, then produces a negative moving wave. Thus it is still pushing electrons. I just don't see the machine shaking as if it were pumping a liquid back and forth.

[salimkhan007]

can any one explain why neutral is necessary for the single phases and not in three phase.if you have vedio or other explanation plz send to me 

[Dusty754]

@salimkhan007 Perhaps for the same reason that a neutral is not necessary when using 220.

[darthkahn45]

Thankyou for explaining that in such a simple way.

[hystat]

single phase generators last 5 minutes and then ex,...plode?.... haha

this explanation assumes balanced loads on all phases. What should be discussed is that balance has nothing to do with the alternator and everything to do with how loads are connected to it.

[popimp88]

information well spoken...on a menu of smarter vs the hardheads..thanks

[bicnarok]

But if you have 3 generators producing 1 phase each and the phases being mixed up, then they, the single generators,  will each stop when they stop producing in that gap bit you mentioned at the start.. AC electricity seems a bit daft when you think about it

[Dusty754]

@bicnarok Daft? Seems to work rather well here. Nikola Tesla seems to have worked out any problems. Of course we do not have alternators that generate single phase current. Instead the alternator has three different windings set 120 degrees apart thus you don't need three seperate generators but one alternator.

[xrebxtoc]

Well explained my friend! I'm a powerline technician apprentice and theory is what my whole job pertains to! This will help me have a better understanding of whats going on! Thank you very much!

[nikhiljain103]

too good...

[DanNixon2007]

So what about those small domestic generators used for camping etc. do they use a seperate phase for each outlet? as most have more than 1

[weesenz]

who is he? i like the way he explain :D very clear and brief..i can possibly throw away my books after watchin tis :D

[thewii552]

@weesenz he's steve johnson. :)

[ApolloWasReal]

@shotgunsniper1 He's talking about very large (utility scale) AC generators, which are in fact always 3-phase. Small single-phase AC generators are common and I'm sure he knows that. But single phase AC is inherently unable to transfer constant power throughout a cycle, so single phase generators need things like flywheels to dampen the constantly changing torque. 3-phase AC generators can transfer constant power throughout a cycle, so a flywheel isn't needed.

[tonydeadlock]

yea dat makes sense but if ur machine runs of a battery that is recharged by the gen can u just double that to produce more from 3 to 6 or would that not work

[domyaska]

excellent teacher...!!!thanks a lot from italy!!!

[glyn001]

Well I thought the video was good - I am certainly no electrician and I can't even begin to discuss the physics of this but Iknow more now about the difference between single phase and three phase than before I watched it. Well done.

[kijifled2]

Yes you are right but in the studio we say two phase to avoid confusion when we use balanced power and unbalanced power. Unbalanced has a 0 volt neutral line and balanced has two equal hot lines and no neutral.

[kijifled2]

The generator will not explode single phase generators actually produce two pahse power but it's still called single phase. It makes two phases not one. Your home actually uses 2 phase. Phase has nothing to do with how your generator runs It simply is the difference in time the lines hit their peak and hit zero. Single phase motors do shake more than three phase but that's totally different than a generator.

[kg6625]

People who don't fully understand AC commonly make the mistake of calling single phase power (such as in your house) "2-phase". This is because there are 2 "hot" wires and a "neutral" wire. The 2 "hot" wires together make one single phase circuit.

[matt3dlp]

@kijifled2 its still single phase, your home just uses 2 halves of a single phase totalling 240v (where i live anyway)

[kijifled2]

Haha this was like a comedy it was so wrong "single phase gen. will las 5 min. then explode" no no no it will last till it runs out of gas the current will alternate yes but will not cause any physical movement with the generator. the voltage starts at positive (forward) then drops to 0 then to negative polarity (backwards) then up to zero and back up to positive and on and on and it does that 60 times a second in US and 50 everywhere else.... 50hz or 60hz

[ApolloWasReal]

I wouldn't have explained it quite the way Jones did, but he's essentially right that a large single phase AC generator would quickly shake itself apart. The neat thing about 3-phase AC is that the instantaneous power is a constant just like DC. Provided the phases are balanced, that is. In single phase it's not.

My company had single phase air blower motors installed in a new building, and they vibrated so badly that they had them all replaced with three phase motors.

[apt95]

erm... your statement is incorrect with the chart. that is the power direction, which reverses 50 or 60 times a second. the AC generator itself uses no power.

it will not explode, even a single phase generator, as they exist, and work fine.

good explanation, but incorrect.

i just researched AC generators.

[Nasty0suicide]

I have never gotten why we even use alternating current, wouldnt stable DC current be better for devices?

[danagol1985]

@ Nasty0suicide: It depends what device you intend to use.

A simple filimant light bulb will be happy on either AC or DC, provided the voltage is correct.

However, some appliances use a transformer to step down voltage. Transformers require a current, whos polarity swaps in order to generate a magnetic field, and then collapse it again, very quicky.

So if our houses were supplied with DC, only filimant lamps and kettles would work - no computers, monitors, fluorescent lamps, etc...

[Nasty0suicide]

Aaa I see. Thanks . Hmm so ac was probably used before, when all electric devices were mainly lamps and heaters?

[danagol1985]

@ Nasty0suicide.

Well im not sure on what was used first. But if batterys were out first source of power, then DC was what we used.

Stable DC, from batterys is exellent for small low voltage circuits, like insides radios, laptops, and cell phones. But its just that AC can easily be converted to low voltage DC if needed.

[apt95]

DC was invented first, and an AC generator will last much longer than he said, they are just really complex to make.

I believe Tesla invented the AC motor, years after the DC generator and moteo were(by i believe edison)

[enggizo]

I Liked your anwer to his quesstion ..

[hrbear]

Devices like lamps, kitchen, laundry, dryer, hair dryer, vacuum, use AC directly. These devices use simple resistances which turns the AC current to heat, or electrical AC motors (like the laundry does). All the other micro devices we use like the radio, PC, clock, answering machine, cell phone charger, need very stable electricity source, with a polarizathion of a stable + and - poles (like from a battery). So, we need to turn the AC to DC using the power suplies. These have capacitors, diodes

[hrbear]

(continued). and a stabilizer in order to feed the micro devices with a stable DC current. We don't use DC directly in the our house sockets because of the following reasons. An electrical genarator in the factory only produces AC. The electrical company doesn't want to turn the AC to DC immediately after the generator because it can not transfer it to long distances without much power loss, in fact it's impossible. It had also to turn the AC after the generator to a very high voltage in order

[ApolloWasReal]

Read up on the Intermountain DC tie that runs from a big power plant in Utah all the way to Los Angeles. The line can carry nearly 2 gigawatts. Another DC line from the Columbia River to LA can carry 3+ GW, so I'd say it's far from "impossible".

[Xonk61]

house wiring would have to be massive to carry the amount of amperage on DC compared to the wiring we use for AC amperage... the cost of the copper alone to wire a house would be monumental. and then there's the transportation of that supply to your home or a business, or industry.  Power transmission lines would also have to be huge, and still the power losses would require some boosting regularly along the way. Research the feud between Edison's DC, and Tesla's AC!

[ApolloWasReal]

You do NOT need massive wiring just to carry DC. Wiring only has to be massive to carry *high currents* and high currents are necessary to send high powers at low voltages.

So it's low voltage that's the culprit. If you can send high voltage DC it can be even more efficient than AC in its use of conductors and insulation. Several of the loss mechanisms present in AC transmission are absent with DC, such as induced eddy currents. DC also makes more efficient use of a line's voltage rating.

[ajgio]

@ApolloWasReal high current = bigger cables high voltage = bigger insulation

[ApolloWasReal]

@ajgio That's right, and bigger insulation is easier than bigger conductors. In fact, most high voltage lines have bare conductors because air is an excellent insulator and it weighs nothing. Just space the wires far enough apart and support the wires with sufficiently long ceramic insulators.

[ajgio]

@ApolloWasReal would the loss's due to eddy current on a 3phase distubution highvoltage line/circuit be low because 1. the lines are connected in delta to the transformers so are balanced meaning if the cables are run correctly in a trefoil aranagement the eddy current will cancel out ? its just when the current is unbalanced such as running from a star connected transformer to unbalanced loads etc that there will be some flux that does not cancel out and induces eddy currents ?? plz explain

[ApolloWasReal]

@ajgio I think you're confusing eddy currents with harmonic cancellation. Eddy currents occur in things like transformer cores in any AC system, and they can cause significant losses. Eddy currents are induced by changing magnetic fields so they're not present in DC systems except when the load changes. This is one of the reasons that DC transmission lines are often more efficient than AC once the conversion at the endpoints has been done.

[ajgio]

@ApolloWasReal Yes but isnt it the MMF/flux which is created from the current going through the cable that induces eddy currents into other things so one could say if you had a 3phase trefoil arrangement on for EG a Cable tray and the 3 lines are balanced then all the flux would cancel out so no residual fluz would be present to be able to get induced into the E.G Metal tray etc. or am i missing something ?

[ApolloWasReal]

@ajgio Any bundle of conductors, single or 3 phase, with balanced currents will have a zero net magnetic field and thus avoid eddy current induction in the conduit. But eddy currents are still generated where the 3 phases are handled individually, such as in each phase of a 3-phase transformer.

The only way to get rid of eddy current losses is to not use AC. Even then you'll have losses inside your DC-DC converters, but they can operate at frequencies chosen to minimize those losses.

[ajgio]

@ApolloWasReal ahh got you. Because the windings in a transformer etc are so spaced apart and in the case of start connected ones are unbalanced eddy currents are still present which induce current into the metal etc. thanks

[mannys9130]

Nasty,

We use AC because of a few reasons. The first is the ease of getting the electricity to you. With AC, it is very easy to send power very far without having to amplify the power. DC cant be amplified, so you would need a powerplant every 5 miles or so. Not good. We use 3 phase AC because it is even easier to transport then single phase. Also, for AC motors, a large current draw can put the sine wave voltage out of phase with current and you will get nothing done. Hope that helps.

[ApolloWasReal]

No, this is not the reason. See my previous comment about high voltage DC transmission.

[apt95]

DC can't be transmitted down long power lines, it needs a lot of power and stations every 10 miles to let the power continue down the lines, otherwise the power will not make any distance.

AC is superior

[ApolloWasReal]

Then why do some of the very longest and biggest power lines use DC?

AC is widely used because you can use simple transformers to increase voltage and reduce losses over long distances. But it's now possible to step DC voltages up and down too; it just takes more equipment. And DC has significant advantages over AC for very long lines, underground and undersea cables. Read up on HVDC transmission.

[ajgio]

@ApolloWasReal ALSO DC insulation is less for the same given voltage of AC due to the peak to peak values of AC not present on DC

[ApolloWasReal]

@ajgio If by this you mean the RMS and peak voltages for DC are the same, while peak is sqrt(2) times RMS for AC, then you're right.

100 MW AC as 1000 A RMS and 100,000 V RMS means the insulation has to take 141,421 V peak.

But 100 MW DC as 1000 A and 100,000 V requires insulation only for 100,000 V.

Although the peak AC current is sqrt(2)*RMS, only the RMS counts from a heating standpoint with DC or AC. But insulation has to be rated for peak voltage, putting AC at a disadvantage.

[ApolloWasReal]

Yes, for many devices DC would be fine. The major exception would be the AC induction motor, a Tesla invention, though now it is easy to convert DC to AC right inside the motor. That's a "brushless DC motor".

The main reason AC won the war of the currents was the ease of transforming it to high voltages for efficient long distance transmission. Today we can easily build DC-DC voltage converters with power semiconductors that didn't exist a century ago.

[hystat]

brutal explanation... but this proves you can't teach 3 phase in 3 minutes...

3 hours would be more appropriate for a basic overview

[polarbear60]

You are Britain and you said we don't use three phase? Hmmm, interesting.

[ApolloWasReal]

@polarbear60 I don't know of a country with electricity that doesn't use 3-phase AC transmission. Including Britain. Maybe he meant that 3-phase power wasn't generally provided to residences. That's true in the USA, and probably in Britain too.

That's the major drawback to AC. Given 3-phase it's easy for a DC power supply to produce a constant output. But when you only have single phase AC your power supplies need to store energy to cover the zero crossings in the supply.

[postchevelle]

The time reference is typical academic explination to show how each phase leads or lags the next from a reference point of zero. This says nothing about the physical world where you can swap any of the two phases (ACB sequence for example) and operate induction motors in the opposite direction.

[mediarocker543]

Because they are transformers. doy.

[randomvideowatcher]

Is the factory generator going through a phase when it explodes? HA HA HA

[zezimashock]

how you make from 240 single fase a 3 fase?

[DjGisME]

good show I like ya

[trimetaler]

I work in power generation, MS5001 GE Turbines 24 MW. This guy is somewhat vague and puts things in a hazy context. He mentions phase as meaning time. No! A "phase" is a voltage_current representation of the magnetic field movement of your generator through the stator. Three phase generators have a rotating eletro-magnet (rotor) and three surrounding windings called the "stator". The rotating electro-magnetic field bisects each winding 120 degrees apart from each other equaling three sin waves.

[mdb1230]

IN the book im reading it says 415V but i guess it cud be higher depends I guess

[windoes98se]

good explinarion, 1phase electricity is verry ineffecient compared to 3phase how mqny volts does 3 phase usualy work at?

[Schneep]

There is not just one voltage that 3-phase works at. It works at multiple voltages. Often, in manufacturing for example, 480 V is used. Now if you are trying 3-phase at Voltages high enough to break down the surrounding dielectric then you could have arcs shorting out phases.

[Schneep]

Don't focus too much on voltage for 3-phase. Think of phase-shifted sinusoidal signals. One complete cycle is 360 degrees. You have each of the 3 phase cycles 120 degrees apart. That is, phase one at 0 degrees (for reference purposes), phase two at 120 degrees and phase three at 240 degrees. Now the next phase in this cycle would be the first again. This guy is just explaining how the phases overlap to stabilize or 'balance' the system.

[DavesTreeFarm]

A generator of single phase electricity will "last 5 minutes and then explode". I think there is a scene missing in that explanation.

[windoes98se]

good explinarion, 1phase electricity is verry ineffecient compared to 1phase

[haleyfamily1975]

Thanks! That was clear and well siad. I learned something!!

[mattyddaddymc]

good clear cheers