How does three-phase electricity works?

[Pawelk198604]

I work at KFC restaurant in Poland? 

My duties include helping cooks in washing dishes, marinating chickens in the famous marinade of a colonel consisting of 11 herbs and spices: D 
And cleaning the flat surface (that is, after cleaning the floor with a mop) and cleaning the kitchen equipment before closing the restaurant. 

Often, to wash the marinator faster (the device in which we marinate the chicken), such a special drum that resembles a concrete mixer and a dishwasher using a sprinkler, which we use for hand washing. 

Our Polish Health and Safety regulations recommend that mechanical equipment should be washed by hand, but we use a rain shower, 

Recently, the manager said to be careful with this washer, because most of the devices in our kitchen uses three-phase electricity (standard power supply in Poland is 220 V and 50 Hz) that he would not want to be in our skin if this current would love us   (pardon expletive but it how google translate, translated it )

 

https://answers.yahoo.com/question/index?qid=20180422212723AAwHEG2

 

Edited April 22, 2018 by Pawelk198604

[Zeiss Ikon]

Most 220-240 V mains power uses two "hot" legs -- that is, either wire is hot relative to ground, at half the rated voltage, but they're in opposite phase.  That is, one has negative charge when the other has positive, so the voltage between the two legs is twice their potential to ground.

A three-phase line can be wired two ways.  There are "delta" lines (named for the Greek letter that looks like a triangle), where the load is placed between each pair of hot legs (so three loads -- these would usually be either a resistance element to generate simple heat, or one coil set in an induction motor), and there are (as called in America, anyway) "wye" lines (named for the Latin letter Y, again because of similar shape on a diagram), where the three loads are between each hot leg and a neutral.  You can tell them apart at the outlet or plug very easily; a delta line has four prongs or sockets, one for each leg and one for ground (like your 220 V line has three, one for each leg and one for ground), while a wye line has five -- one for each leg, one for the neutral, and one for the ground.

The leg-to-leg voltage in both is likely to be 230 V outside the USA (240 V in the USA).  A wye line also give 120 V from each leg to neutral, though there's also a "wild leg" setup that puts one leg at 208 V to neutral.

Either way, a shock from a 3-phase 208-240 V outlet shouldn't be any worse (or better) than one from a single phase 230-240 V outlet -- either one is likely to give severe deep muscle burns as well as surface burns.  Fortunately, your European 50 Hz is significantly safer than American 60 Hz in one regard: very low current shocks (typically delivered by contact with dry skin and a poor ground) won't kill you by stopping your heart.  With our 60 Hz, as little as 30 mA across your chest can result in ventricular fibrillation which, without immediate CPR (ideally including use of a defribrillator) will kill you in a very few minutes.

[magnemoe]

Issue with the 110 V is the amperage or power, 220 volt has half the amperage for the same power. 
The delta / Y configuration is often used for start up and running, remember at my fathers farm stuff like grain elevators and drying fan require you to pull in one position for startup then gear up once it was running. More modern equipment did this automatically. 

3 phase equipment tend to be high power and often has extra requirement then installing, this might scare the manager. It might also been accidents 

[Guest]

 

[GoSlash27]

I love this explanation of 3 phase AC. We use a lot of it at my work because 400 Hz 3 phase is an aerospace standard.
I can show it to the next necktie person who doesn't understand why we refuse to take chances when working on 3 phase systems.

Best,
-Slashy

[steve_v]

That video is pretty good. Why 3 phase? Efficiency, and things that spin.

The things in the kitchen that run on 3 phase power will almost certainly be doing so because they have motors in them, and you can't make a nice quiet efficient induction motor without at least 2 phases (or inefficient tricks with capacitors to split phases).

 

2 hours ago, GoSlash27 said:

we refuse to take chances when working on 3 phase systems.

Three-phase systems aren't inherently more dangerous, they just tend to be found where more power (and therefore higher fault currents) are available. You don't take chances with any electrical system, and the more energy available, the bigger the boom when the smoke escapes. Even the lowly 12v car battery can vaporise steel.

Edited April 23, 2018 by steve_v

[Shpaget]

7 hours ago, Zeiss Ikon said:

Most 220-240 V mains power uses two "hot" legs -- that is, either wire is hot relative to ground, at half the rated voltage, but they're in opposite phase.  That is, one has negative charge when the other has positive, so the voltage between the two legs is twice their potential to ground.

The leg-to-leg voltage in both is likely to be 230 V outside the USA (240 V in the USA).  A wye line also give 120 V from each leg to neutral, though there's also a "wild leg" setup that puts one leg at 208 V to neutral.

Either way, a shock from a 3-phase 208-240 V outlet shouldn't be any worse (or better) than one from a single phase 230-240 V outlet -- either one is likely to give severe deep muscle burns as well as surface burns.  Fortunately, your European 50 Hz is significantly safer than American 60 Hz in one regard: very low current shocks (typically delivered by contact with dry skin and a poor ground) won't kill you by stopping your heart.  With our 60 Hz, as little as 30 mA across your chest can result in ventricular fibrillation which, without immediate CPR (ideally including use of a defribrillator) will kill you in a very few minutes.

Most? Perhaps in US, but certainly not in Europe. Over here in Europe live is 220-240 V relative to the neutral which is directly connected to the earth wire just before your RCD (ground fault interrupter).

Electricity is generated in 3 phase state and carried over high voltage power lines. Once it reaches a substation in your neighborhood and is dropped to 220V the three phases are sent each in its own direction and distributed over the neighborhood, so you and your neighbor could but are not guaranteed to be on the same phase. Neutral is the fourth wire that is split in two just before it reaches your RCD (ground fault interrupter) where it becomes neutral and ground. After the RCD they are never connected again.

As for safety difference between 50 and 60Hz. This is the first time I've heard about it, and frankly doesn't seem to hold water. There is nothing in human body that would distinguish such a small difference. There is a small difference between DC and AC, due to zero crossing, but you would not want to get zapped by either.

Bottom line, single phase is just a three phase split into three directions, and one phase is more than enough to zapp you (but if you have wet hands from washing the machine that gives you the shock, single phase is more than enough to kill you), but voltage difference in three phase is higher (400 V) facilitating higher currents through the body.

[YNM]

Three phase is essentially the same as having three plugs. It's just as deadly, but not much more that you'd be electrocuted just by standing too close (not actually touching) with it.

 

[steve_v]

44 minutes ago, Shpaget said:

Most? Perhaps in US, but certainly not in Europe. Over here in Europe live is 220-240 V relative to the neutral which is directly connected to the earth wire just before your RCD (ground fault interrupter).

Likewise. Over here, we inherited the MEN system from the poms. Frankly, I find the US electrical system to be a bit... dodgy. But that's just me.
 

45 minutes ago, Shpaget said:

As for safety difference between 50 and 60Hz. This is the first time I've heard about it, and frankly doesn't seem to hold water.

I have heard this before, but not from a sufficiently credible source as to put any faith in it. 50Hz mains, 60Hz mains, both will kill you stone dead if you fail to respect them.
 

46 minutes ago, Shpaget said:

There is a small difference between DC and AC, due to zero crossing, but you would not want to get zapped by either.

The zero-crossing is kinda important (and the reason straight DC electric fences are illegal in most countries), as it gives you a window to regain control of your muscles and let go of the live thing. Personally, I find DC to be considerably scarier than AC of the same voltage and current capacity - not only does the zero-crossing make it somewhat less directly lethal, it also aids in extinguishing the arc in the case of a flashover. Less severe burns are generally a good thing.

 

52 minutes ago, Shpaget said:

the voltage difference in three phase is higher (400 V) facilitating higher currents through the body.

True, but unless you work in the industry (or fall prey to a real cowboy in such) you're pretty unlikely to find yourself as a conductor between two phases. The vast majority of shocks are to ground.

[Zeiss Ikon]

The specific fibrillation hazard of 60 Hz vs. 50 Hz AC is well documented -- but by the time it was, the US, Canada, and Mexico were already standardized on 120 V 60 Hz home power, obtained by splitting the legs of 240 V double hot single phase.

Still, the fact remains, three phase isn't significantly different in terms of hazard from single phase of the same line-to-line or line-to-neutral voltage.

AC is in fact more hazardous than DC -- the zero crossing gives around 2-3 milliseconds when the current is low enough not to galvanize, which is about 1/100 of human reaction time, even at the reflex level, but the AC, if it passes through the heart, disrupts the heart's electrical rhythm (50 Hz can still do this -- even DC can, if the current is high enough -- but it takes a lot more of it than with 60 Hz, which closely matches the natural fibrillation frequency of the heart).  Electrical safety documentation in the US notes that 30 mA of 60 Hz current across the chest for less than 1/10 second is sufficient to induce v-fib, which is lethal if not immediately treated.  This is why GFCI devices are designed to interrupt power if the imbalance between legs exceeds 10 mA -- to give a margin of safety -- and do it in less than one full cycle of about 16 ms.

AC is used for power grids almost entirely because it's easy and pretty efficient to change voltage (with a transformer), so you can do long distance transmission at 200,000+ volts and have very low current requirements (hence not melt your transmission wires even when they're carrying, say, a hundred megawatts), but step down to 1600 for neighborhood distribution, and 240 for residence lines.  Three-phase transmission is also easily broken down into single phase when needed, and is more efficient both to generate and for large motors (virtually all electric motors over about 2 HP = 1.5 kW are induction type, which work better on 3-phase than single-phase).

[wumpus]

8 hours ago, Shpaget said:

Bottom line, single phase is just a three phase split into three directions, and one phase is more than enough to zapp you (but if you have wet hands from washing the machine that gives you the shock, single phase is more than enough to kill you), but voltage difference in three phase is higher (400 V) facilitating higher currents through the body.

The three phases are supposed be 120 degrees apart and shouldn't add up to 400V unless you start out close to 300V per rail.  The big dangers are a wet environment (like when washing the machine), the issues that these things tend to be connected to inductive loads (if you disconnect a circuit in such a way that you become part of the circuit, the thing will attempt to maintain current regardless of your resistance.  This will be lethal), and the dangers of the delta (no neutral) configuration (all rails can float relative to ground).

The problem isn't "three phase".  All else considered, it is probably one of the safer means of transmitting power (compared to single phase and DC transmitting similar amounts of Watts).  The catch is that three phase is almost always used for high power devices and is a clear signal that you need to be careful.

[Tex_NL]

@Pawelk198604 Pasting your exact question into google gives you hundreds of answers. Including several youtube video's and wikipedia entries. I even found one in Polish for you: https://pl.wikipedia.org/wiki/Układ_trójfazowy

[VaPaL]

32 minutes ago, Tex_NL said:

@Pawelk198604 Pasting your exact question into google gives you hundreds of answers. Including several youtube video's and wikipedia entries. I even found one in Polish for you: https://pl.wikipedia.org/wiki/Układ_trójfazowy

I never understood this kind of anwser, it serves no purpouse. Sometimes I prefer to  ask even after researching, talking about something is better than only reading/watching. Not only that, but this may serve as source for someone in the future, since this forum is open to anyone read.

If you don't think the question worth anwsering, don't lost your time with this "google it" nonsense.

Sorry for derailing the topic a bit, I just need to adress this.

ElectroBOOM channel (linked above) has some very good educational videos. His method of mixing comedy and pain to teach is very good. 

[Shpaget]

1 hour ago, wumpus said:

The three phases are supposed be 120 degrees apart and shouldn't add up to 400V unless you start out close to 300V per rail.  The big dangers are a wet environment (like when washing the machine), the issues that these things tend to be connected to inductive loads (if you disconnect a circuit in such a way that you become part of the circuit, the thing will attempt to maintain current regardless of your resistance.  This will be lethal), and the dangers of the delta (no neutral) configuration (all rails can float relative to ground).

Peak to peak voltage in Europe is around 325V. Figure 220 V (or 240 V) and 110 V, implies RMS which in AC is always lower than peak to peak.

https://www.worldstandards.eu/electricity/plug-voltage-by-country/

https://www.worldstandards.eu/three-phase-electric-power/

[LordFerret]

19 hours ago, Pawelk198604 said:

Our Polish Health and Safety regulations recommend that mechanical equipment should be washed by hand, but we use a rain shower,

Lesson #1: Keep one hand in your pocket when working with electricity.

[Kerbart]

The health and safety board tells you to wash it by hand.

Your boss tells you to wash it by hand.

 

Really, wash it by hand.

[magnemoe]

14 hours ago, steve_v said:

Three-phase systems aren't inherently more dangerous, they just tend to be found where more power (and therefore higher fault currents) are available. You don't take chances with any electrical system, and the more energy available, the bigger the boom when the smoke escapes. Even the lowly 12v car battery can vaporise steel.

Had an probe light with an needle tip, nice so you could punch trough isolation, was a bit careless inside an car engine and managed to get body of probe hit one main buss while the tip was on ground, ended up getting an flash and the needle was shorter and ended in an 2 mm copper ball.

15 hours ago, steve_v said:

That video is pretty good. Why 3 phase? Efficiency, and things that spin.

The things in the kitchen that run on 3 phase power will almost certainly be doing so because they have motors in them, and you can't make a nice quiet efficient induction motor without at least 2 phases (or inefficient tricks with capacitors to split phases).

It might also be that you use so much power, 3 phase is standard then you get into 100 ampere loads, modern houses tend to have 3 phase in, this save money if you want to put up an serious charger for an electrical car. 

[steve_v]

9 hours ago, magnemoe said:

ended up getting an flash and the needle was shorter and ended in an 2 mm copper ball.

Try dropping a spanner across the battery posts... Actually, don't try that.
 

9 hours ago, magnemoe said:

modern houses tend to have 3 phase in

Huh, wish it were so over here. The extra line charges murder the efficiency savings at household loads, so only commercial / industrial premises tend to have 3-phase.

[Zeiss Ikon]

On 4/24/2018 at 1:36 AM, steve_v said:

Huh, wish it were so over here. The extra line charges murder the efficiency savings at household loads, so only commercial / industrial premises tend to have 3-phase.

I've never seen 3-phase to an American house (though I haven't been in a lot of them).  I'm confident there aren't a lot of them, though, because neighborhood feeders aren't 3-phase out at the pole, and it's much more than a transformer to turn single phase dual-hot into 3-phase.  IF you want/need 3-phase to your home (for instance, to operate heavy motors in a hobby machine shop), it's often cheaper (over a span of many years) to install a 3-phase converter with Variable Frequency Drive than to get 3-phase power to your house/shed -- because the power company would have to run a special feeder line from the last point where 3-phase was available on their lines, which (for a residential neighborhood) is likely to be the substation.

[wumpus]

On 4/22/2018 at 10:32 PM, Aperture Science said:

[embedded video]

First, be careful.  While it certainly helps to be reminded of the obvious, you won't last long in the field while that big a danger to yourself (says the guy who worked with a Senior Electronic Engineer who was missing the use of the fingers in his left hand thanks to using a band saw the wrong way.  Let's just say the technicians kept the engineers away from the power tools much more zealously for awhile).

Second: three phase motors have another large advantage as the sum of the voltage between each two rails is constant (the sum of all three together is zero, but circuits rely on two inputs).  This allows a three-phase motor to deliver smooth power instead of the 120Hz impulses of single phase (in practice this was pretty irrelevant.  Single phase and gasoline engines can simply add a flywheel to smooth out the power, but it becomes much more relevant in modern application where the inverter is only generating power for the motor [because it essentially is part of the motor]).

Finally, his description of "brushless" vs. "induction" motors is all wrong.

"old fashioned" (i.e. 20th century and the Edison vs. Tesla battles up to domination by switching power supplies).
DC motors had brushes and used electromagnets to pull permanent magnets (or vice versa).  The brushes were needed to switch the electromagnets on an off and/or switch polarity.
AC motors were "induction motors" and used electromagnets on both sides.  They were tied to 3600rpm (or a close integer multiple, I think a 3 phase motor would get thee times that) thanks to the fixed frequency coming from the generator.

I think there was also a pretty hard limit of ~30hp (22kW) power limit on AC motors (although I'd think you could get the thing going with a system of kludging relays into square waves for frequencies ~6Hz or so).  DC motors should be more powerful without starting motors or other kludges, but I'm sure they had similar issues at some power level.

Modern motors of the 21st century:
Brushless: Just like the old fashioned type, except that transistors control the output into the motor instead of brushes.  In practice also expect the control circuits to include most of the parts for a DC-DC converter to send just the right power to the right places.  Also these motors tend to use rare-earth elements to make wildly more powerful permanent magnets.  Generally the powerful rare earth magnets allow for a more compact motor.
Induction: Just like the old fashioned type, except that instead of getting power from the generator as AC, they produce the AC directly (and if powered by AC you can expect this to be first converted to some DC rails used to power the AC inverter, and anyone designing the inverter will nearly always design this in three phase [unless cutting cost and indifferent about efficiency] to balance out the draw against those DC rails).  This allows the motor to produce maximum torque at zero RPM and let a Tesla move the car with 800hp (or whatever "plaid" produces.  The old ones would just have enough torque to move the motors at 30hp and need a clutch once going).  The other benefit to induction motors is that it is far easier to use them as generators while braking.

- note: I suspect that "old fashioned induction" motors to never quite die out for low power sources that operate at a fixed speed with an AC supply.  Brushed DC motors are already dead as the life expectancy of a brushless motor is much higher and the cost already low (the volume just isn't there for a cheaper brushed motor).
 

PS: no matter what his shirt says, a full wave bridge rectifier is drawn like the following (are Canadian drafting standards that different?):

Note to Canadians: is that bit with the meter and the outlet remotely right?  In the US we run a single pair of wires from the breaker box to multiple outlets.  What is shown in the video implies a breaker for each plug in each outlet.  Pretty expensive, but it does have a small advantage.  Is there an option to plug in two plugs and get three-phase power?

Edited April 25, 2018 by wumpus

[Guest]

1 minute ago, wumpus said:

[the greatest text wall you'll have ever seen]

When he "shocks" himself it's usually scripted, most times he sets up a capacitor or something to blow up for comedic effect.

Anyway, I'm not an electrical engineer so I can't say everything in that video is right, although the author is

[wumpus]

1 minute ago, Aperture Science said:

When he "shocks" himself it's usually scripted, most times he sets up a capacitor or something to blow up for comedic effect.

Anyway, I'm not an electrical engineer so I can't say everything in that video is right, although the author is

I figured that, and it is also clear that he makes a clear difference between blowing up his gear (which is much more expendable than his heart) and being shocked directly.

But the point of the thread is that three phase is typically used for hazardous levels of power.  Being careless with the voltages inside a computer is relatively safe (just don't short a car battery or you will learn just how high current can get), being careless with three phase can leave you dead.

[magnemoe]

8 hours ago, Zeiss Ikon said:

I've never seen 3-phase to an American house (though I haven't been in a lot of them).  I'm confident there aren't a lot of them, though, because neighborhood feeders aren't 3-phase out at the pole, and it's much more than a transformer to turn single phase dual-hot into 3-phase.  IF you want/need 3-phase to your home (for instance, to operate heavy motors in a hobby machine shop), it's often cheaper (over a span of many years) to install a 3-phase converter with Variable Frequency Drive than to get 3-phase power to your house/shed -- because the power company would have to run a special feeder line from the last point where 3-phase was available on their lines, which (for a residential neighborhood) is likely to be the substation.

Might be different from country to country or area to area, grew up on an farm in Norway and farms need 3-phase so in rural areas they tend to supply it to all, also larger houses tend to get it even if suburb, might have to do with Norway use electrical stoves and general lots of electrical heating because of history of cheap electricity. 

[Zeiss Ikon]

Americans use electric power for heat (mostly heat pumps, how, less energy for the same degree days than resistance heating), cooking, hot water, and clothes driers.  We just get it on single phase lines.  For those applications, there's no or very little efficiency gain from three-phase (heat pump motors, maybe, but probably only enough to pay for the more expensive service for commercial size units).  Farms in the US might use three-phase; it's been about fifty years since I spent any time on a farm, and I suspect it'll vary depending on what kind of farm (if you raise chickens, you gain little from three-phase power, because your energy expense is mainly lighting and a little heating/cooling, but if you process dairy from a large herd the refrigeration might well make it worthwhile to have three-phase power).

[wumpus]

Assuming that it is roughly (if not moreso) to transmit three phase (delta) than single phase, I suspect that it isn't that hard to get three phase in [USA] farming areas.  The [one] appropriate google hit insists that it is common in grain drying bins and irrigation and wells.

http://www.electriciantalk.com/f2/3-phase-residential-service-17395/