3 Phase power questions
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jsguitar
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"I heard champagne chilling in the background!" Ok, enough hijacking.
cruelkix
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Never enough hijacking, I love it haha.
grandequeso
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A little touchy are we? I didn't post to offend anyone. I'm a service electrician. I work with different nominal voltages in different environments everyday. I just chimed in to be of help, in a area I have more experience than most.
I gave you my math. Tell me where I'm wrong... I'm wrong all the time. I'm open to learn something new. That being said.
Configure it anyway you want. watts are watts. three 5,500 watt elements on one breaker is 16,500 watts and at @ 240volts 3phase it is way more than a 30 amp breaker can handle. Do a google search check for yourself.
Don't worry about it - you did nothing wrong. PJ has done this exact thing before - gets mad and says he quits when he is questioned.
This might help you out, disregard the inaccuracy of the SSR's, you know what they do. This should help you set up a sys that will work individually as well. Each element has 2 pole circuit protection here, remove it if you don't want it.
The line load on each phase will calculated according to the appropriate formula, each element will draw 23a @ 5500w. You may want to increase the breaker capacity to a 32a instead of a 25a to stay under 80% if you wish. The 40a rated ssr's I recommended will be fine.
The line load on each phase will calculated according to the appropriate formula, each element will draw 23a @ 5500w. You may want to increase the breaker capacity to a 32a instead of a 25a to stay under 80% if you wish. The 40a rated ssr's I recommended will be fine.
cruelkix
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swede, you rock. That makes total sense. Thanks for your help on this!!
cruelkix
Well-Known Member
If I set it up with out individual control I will have a lower amp draw though correct?
grandequeso
Well-Known Member
Swede the individual breakers at each element is a really clever idea. If you were to ever short circuit an element you would not have to stop your brew. just cut out that element and continue your brew.
No, that's not really true, the amperage draw per phase is directly related to the element draw. Each phase has two elements drawing on it, unless you switch one off, then the two associated phases would have their draw reduced proportionally.
Glad to help.
porcupine73
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Interesting project ... a few questions/comments ...
Should the element CB's be upstream of each SSR?
Are you required to interrupt all non-grounded conductors to the load?
I think the not exceeding 80% of the breaker rating applies for 'continuous loads' (energized for three hours or more). Or you can get 100% rated breakers?
Should the element CB's be upstream of each SSR?
Are you required to interrupt all non-grounded conductors to the load?
I think the not exceeding 80% of the breaker rating applies for 'continuous loads' (energized for three hours or more). Or you can get 100% rated breakers?
God forbid you bring up his e-stop circuit too.
lol...if your not blowing smoke up his ass and singing his praises he wants nothing to do with you and will not listen to anything you say.
Glad you are all having fun.
I'm still trying to wrap my head around the current draw on 3 phase delta power. The calculation formula is knocking me down.
I think it is this for 3 - 5500W elements rated for 240V. Each element draws 22.9A - times 1.73 = 39.6A per phase.
Is this correct?
I'll put the diagram back up as soon as I can get it figured out correctly and drawn properly.
P-J
I'm still trying to wrap my head around the current draw on 3 phase delta power. The calculation formula is knocking me down.
I think it is this for 3 - 5500W elements rated for 240V. Each element draws 22.9A - times 1.73 = 39.6A per phase.
Is this correct?
I'll put the diagram back up as soon as I can get it figured out correctly and drawn properly.
P-J
If the elements are rated 5500 W at 240 V, then that is what they will dissipate with 240 volts applied whether the power is single phase or three phase. Each element has 240/R amps where R is the resistance of the element. But each line coming into the delta has a current of 1.73 times the current in each element because the currents are out of phase, so some current adds and some subtracts from the current in each element.
One way to calculate it is to draw a phasor diagram - x and y axes with three phasors from the origin at 120 degrees apart. Each phasor represents the current in one of the elements. The current in the lines is the vector difference of two of the phasors. For example, take a phasor of magnitude i at 0 degrees and another of magnitude i at 120 degrees. The first one has x component of i and y component of 0. The second has x component of -i/2 and y component of i*cos 60º which is equal to i*sqrt(3)/2. To find the vector difference, we have an x difference of i - (-i/2) = 3*i/2 and a y difference of i*sqrt(3)/2. The magnitude of this difference vector is given by the square root of the sum of the squares of the components:
I = sqrt(9/4*(i^2) + 3/4*(i^2)) = i*sqrt(12/4) = i*sqrt(3) = 1.73*i
BrotherGrim
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Try this:
208-3-phase-WYE
240V-3-phase-Delta
After reading all 5 pages of this I decided to throw my 2 cents into the mix. These drawings are the 2 most likely power distribution systems you are likely to find in a commercial 3 phase system. Industrial 3 phase is a completely different animal and not an issue here. P-J's second diagram is the odds on favorite to show what you are most likely dealing with. This split phase 240 Delta system is what is installed in most Wal-Mart's, Home Depot's, etc. It provides maximum versatility to the building occupants as far as what loads they wish to use. It is a simple check with a meter to determine what you actually have, but I would bet on this one. My employer thinks I am qualified to answer this question, as he pays me to teach and train my employees how to work on this kind of stuff without getting dead. So far so good.
brycelarson
Well-Known Member
I always like to draw it. AC power is a wave - in the US it's a wave with 60 cycles per second. Each leg of a three phase system is 120 degrees out of phase - so the waves don't line up. If you connect any two waves the total voltage isn't twice a single leg - since the waves aren't lined up.
here's a graph of 120v 60 Hz three phase. If you measured from peak to peak on any one phase it's 120v. However, and here's where the math comes in, since the waves aren't in phase (lined up) the sum of two phases isn't twice - it's 1.73x.
so, when you look at the highest combined voltage of any two phases you see +104 / -104 for a total of 208.
is that helpful?
here's a graph of 120v 60 Hz three phase. If you measured from peak to peak on any one phase it's 120v. However, and here's where the math comes in, since the waves aren't in phase (lined up) the sum of two phases isn't twice - it's 1.73x.
so, when you look at the highest combined voltage of any two phases you see +104 / -104 for a total of 208.
is that helpful?
BeerguyNC61
Well-Known Member
UGGG!!! My head hasnt hurt this much since I was going through Basic Electrical and Electronics back in the Navy......
Lets get back to brewing beer and save all the 3-phase theory talk for a different site!
OKAY rant over, brew on.....
Lets get back to brewing beer and save all the 3-phase theory talk for a different site!
OKAY rant over, brew on.....
cruelkix
Well-Known Member
But you're in the Electric Brewing forum
You gotta have fun with the theory sometimes.
I always like to draw it. AC power is a wave - in the US it's a wave with 60 cycles per second. Each leg of a three phase system is 120 degrees out of phase - so the waves don't line up. If you connect any two waves the total voltage isn't twice a single leg - since the waves aren't lined up.
here's a graph of 120v 60 Hz three phase. If you measured from peak to peak on any one phase it's 120v. However, and here's where the math comes in, since the waves aren't in phase (lined up) the sum of two phases isn't twice - it's 1.73x.
so, when you look at the highest combined voltage of any two phases you see +104 / -104 for a total of 208.
is that helpful?
Nice diagrams and very helpful, but I do have one minor nit to pick. You are showing the peak voltage as 120 volts - actually that is the RMS (root mean square) value, so the peak should be about 170 volts, not 120, or a peak of about 340 for 240 volts RMS.
My keg has waves in it when I move it using the power of my arms. If I have three kegs and move them all, do I have three phase power? How many elements can I heat with my three phase waves? Do I have to multiply or divide the rms of the wave height by root 3? Or am I just getting confused?
brycelarson
Well-Known Member
yeah, not my diagrams, but they illustrate the point.
I teach lots of people coming into the entertainment industry about three phase 120/208 power. I always find myself sketching the phases out on scrap paper - these were the first links I found on the interwebz to illustrate the point.
I have 240VAC 3-phase in my house, and over here (Norway) that's pretty normal. As others have pointed out, the way to calculate max power draw from one breaker is:
P = U x I x sqrt3 where P is Power, U is voltage, I is current and square root of 3 is approx 1.73.
If you have a 50A breaker, the max power you can have on that breaker will be: 240V x 50A x 1.73 = 20784Watts
If you divide that by three elements, each element can have a maximum power of 20784 / 3 = 6928W pr element.
The other way around: three elements 240V 5500W connected in delta, each element will see 240V and total power will be 3 x 5500W = 16500W
Breaker needs to be: I = P / (U x sqrt3) = 16500W / (240V x 1,73) = 39.7A
Each element on it's own, connected to either to legs of the 240V three-phase vill draw 5500W / 240V = 22.9A. (if multiplied by sqrt3 is equal to 39.7A in the last example)
In my service panel the three phases of 240V is divided equally(-ish) between all the subcircuits giving single-phase 240VAC (or as it is more correctly called in the school books nowadays dual phase 240V).
No 120V over here, only between one hot leg and ground, but ground fault circuitry will cut power in main breaker if a current draw above 30mA is seen from hot leg to ground.
P = U x I x sqrt3 where P is Power, U is voltage, I is current and square root of 3 is approx 1.73.
If you have a 50A breaker, the max power you can have on that breaker will be: 240V x 50A x 1.73 = 20784Watts
If you divide that by three elements, each element can have a maximum power of 20784 / 3 = 6928W pr element.
The other way around: three elements 240V 5500W connected in delta, each element will see 240V and total power will be 3 x 5500W = 16500W
Breaker needs to be: I = P / (U x sqrt3) = 16500W / (240V x 1,73) = 39.7A
Each element on it's own, connected to either to legs of the 240V three-phase vill draw 5500W / 240V = 22.9A. (if multiplied by sqrt3 is equal to 39.7A in the last example)
In my service panel the three phases of 240V is divided equally(-ish) between all the subcircuits giving single-phase 240VAC (or as it is more correctly called in the school books nowadays dual phase 240V).
No 120V over here, only between one hot leg and ground, but ground fault circuitry will cut power in main breaker if a current draw above 30mA is seen from hot leg to ground.
Protto said:
Don't forget to divide by .8 to find the actual breaker size, which in this case would be 49.6A, rounded up to 50A. If you don't, expect to replace the not too cheap 40A three phase breaker in a year or two when you could have just got a 50A and been good for life.
Another way to do it would be to get a 100% rated 40A breaker, and you could reduce the wire size, but they are pricey. If you have a lot of wire length to run, it can become cost effective... Would have to crunch your own math and get pricing to figure out.
True. The formula only illustrates the actual current drawn by the elements.
How to get the right size breaker and even cable may vary from house to house, or at least country to country.
At least in my country it is not given what cable size you can use on a certain breaker size, it must be calculated according to cable length, short circuit current in the main panel etc.
If you oversize the breaker, everything down the line have to be sized to handle the power the braeker can deliver.
This should be left to a pro. of course.
That said, a normal 16A breaker in my hose (pretty normal size over here) can give 16A continous in most cases. It can even give more, for a while. There are also different types (i.e. fast, slow) and the slowest can take some overcurrent for an hours boil no problem.
You Europeans and your funny electrical setups, that's actually pretty cool. Funny how things we take for granted are so different between countries. We can't really get (unless you want to pay big bucks or have a large electrical service) breakers with different trip sensitivity. If you want that, you have to use fuses.
To specify, that .8 divider would apply to North America. You'd have to consult local electrical code for the wire size based off that breaker. And/or a local electrician.
that's actually pretty cool. Funny how things we take for granted are so different between countries. We can't really get (unless you want to pay big bucks or have a large electrical service) breakers with different trip sensitivity. If you want that, you have to use fuses. To specify, that .8 divider would apply to North America. You'd have to consult local electrical code for the wire size based off that breaker. And/or a local electrician.
grandequeso
Well-Known Member
Correct me if I'm wrong, don't you have 230/400 50hz 3phase over there in norway. You have 230volts line to neutral and 400volts line to line? If I was doing an electric brewery on that nominal voltage I'd use 480volt (common usa voltage for industry) water heater elemets, its not as common as household 240 volt elements, but you could get way more watts without increasing your wire size. maybe even do double batches without changing your feeder circuitry.
You are not wrong
It's pretty common in new houses, or at least in newly developed areas that the power company gives you 400V 3-phase with neutral. Than you get 230V between any hot leg and neutral.The grid I'm hooked up to is a 230V 3-phase, no neutral conductor. (i get 240V, live close to the transformer). This is also very common, but not in newly developed areas.
All this depends on how the transformer on your grid has it's secondary windings set up. Y or delta.
It's very nice to have 3.7Kw out of a single phase 16A breaker using 2.5mm2 wiring. And I agree 480(or 400 in my case) vould be nice in the brewery to save wiring and equipment size.
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