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  #1  
Old 12/16/06, 07:11 AM
 
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Single phase and 3 phase

I have been doing electrical work sense I was an 8 year old kid helping by BIL on side jobs. I have worked as an electrician many times as a journeyman but the is something I still don't understand and I have asked general foremans and superintendtants and they can't give me an answer.
120 volts is single phase and that is simple enough to understand and 3 phase is simple enough to understand, but why is 240 volts 2 phase??????????
The way I look at it is. Can anyone make me understand this problem. It ranks right up there with where is the end of the universe at. There has to be an end, but at the same time there can't be, because somewhere has to exist on the other side of the end.

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  #2  
Old 12/16/06, 08:52 AM
north of the lift bridge
 
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the answer is on the other side
120/240 is single phase
240/480 3 phase is 3 phase
two classes of power so you dont mix motors up[check nane plate on motors]
you can use parts of 3 phase to run single phase motors[1-2 of the 3 leades + common for 120 volt]
also watch out for those nasty high legs in 3 phase[they make the smoke come out of circut boards real fast]
hope this helps

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  #3  
Old 12/16/06, 10:21 AM
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"watch out for those nasty high legs "

Only had a few really bright lights....

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  #4  
Old 12/16/06, 10:36 AM
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I am not a skilled electrician but would think 220/240 is called 2 phase because it is a pair of single phase supplies. Not a known fact from this end, just a possibility.

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  #5  
Old 12/16/06, 10:52 AM
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There is a two phase power, but its not very common. Each leg is at 90 degees.

120/240 is called single phase, even with the two legs at 180 degrees to each other.

Three phase power has three legs, each at 120 degees to each other. The neat thing about three phase is it makes a rotating field (3600 rpm) that can be used to power a simple electric motor. Single phase motors require a starting circuit.

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  #6  
Old 12/16/06, 05:59 PM
 
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There are two kinds of 3 phase out their. Delta is 3 wires at 120. The other is Y 2 wires 120 and 1 at 240. You need to know what kind you have. They will not mix. The way to tell is to look at the transformer that they come from. Delta has two transvormers the Y has one.

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  #7  
Old 12/16/06, 06:28 PM
north of the lift bridge
 
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delta/y

old vet,got a question
I have a 10kw dayton generator
got it wired in delta and the power to common is 120/130/208 on the leggs
have I got somthing messed up with the wiring in the generator
the other dayton unit I had [40kw] was wired in delta and got 120/120/120
any thoughts

ovendoctor

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  #8  
Old 12/16/06, 11:21 PM
 
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Delta 3-phase will have a "stinger" or high leg, and will only have one transformer. Wye 3-phase will have the same voltage on each leg, and will have to have 3 transformers. Any 3-phase motor will run on either version of 3-phase of the correct voltage. While the stinger will read the high voltage to a neutral, when read with either other leg you will only get the rated voltage. For instance, let's suppose you have 240 volt delta. Your legs will read 120/120/240 to a neutral, but if you read any two hot legs you still only get 240.

The only thing you have to really be concerned about on Delta voltage is your 120- (or 277-) volt circuits. You can't put the single pole breaker on the high leg. Any 2- or 3-pole circuit won't matter. And on both types of voltage you have to watch your rotation, because exchanging any two wires will reverse the rotation of the motor.

Your generator that is reading 120/120/120 is Wye, not Delta.

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  #9  
Old 12/17/06, 07:59 AM
north of the lift bridge
 
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sooooooooo I need to re wire the generator to Y instead of delta right.

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  #10  
Old 12/17/06, 08:58 AM
 
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You shouldn't need to do anything. If you're reading 120 on each leg it is wired in wye. I'm not sure what you're doing with the generator. If you're running 3-phase motors you only need to make sure your rotation is correct. If you're feeding a 3-phase panel from the generator you would need to run 4 wires, 3 hots and a neutral. You could then run any circuits off any busbar since you don't have a stinger to avoid on single pole circuits. If you're feeding a single phase panel you can pull off any two hot legs and run two hots and a neutral. Make sure the generator is grounded. There is usually a terminal on the generator to run to a ground rod.

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  #11  
Old 12/17/06, 01:06 PM
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Sounds like the second genny is a "Y" Is there 208v between the phases?

First genny seems like a Delta with one of the legs having a center tap to ground. This one will run 3 phase loads, but be careful if your are connecting up to a panel that has lighting loads. Watch the wild phase to make sure it doesn't connect to any of the 120v loads.

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  #12  
Old 12/17/06, 09:20 PM
 
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Crafty after reading the replies I would still be in confusion, even tho most of the things have been correct,

First of all AC current changes from positive to negative 60 time a second, thus the 60 cycles electricity, and also why induction motors are in a division of 60 3600, two pole motor or generator, 1800, 4 pole motor or generator, 1200, 6 pole, and so on, (over seas it is 50 cycles) in the process there is a voltage fluctuation from positive to negative, and thus produces a sine wave,

single phase is is one sine wave, a positive to a negative,
and this single phase is between (normally) the voltage in our homes or businesses, of 240 volt,

but you say we have 120, no you have 240, that is split,in half, we place a Neutral wire in the center of the 240 and we pull off HALF of the single phase for our normal use, now when we run a heavy appliance you use the two half's or the full 240,

again there is only a single phase, here,

now three phase, IN a since it is like Three single phase generators hooked together thus three hot wires, between any two of them it is single phase, but if all hooked into a motor there is the three phases, a phase that 120 degrees out of sink with each other, on instead of one plus and one negative, you have three plusses and three negatives spaced out 1/3 1/3 1/3, or a very smooth flow of power, and in motors and when it is being rectified in like a DC welder you have a very continuous flow of power, not just 60 pulses of power in a second you have 180 pluses of power in a second, and in a motor when has a shift of phases, has the ability to start it self, (thus the starting winding of a single phase motor, and the capacitors to electronically shift the phase), and not in three phase.

OK that is enough of that,

the term two phase is Wrong, (except as noted in one of the above posts, it does exist but rare, very rare),

yes if you are wiring in a commercial building and you need single phase 240 (delta) or 208 (Y) voltage, you use two of the three hot wire of the three phase to get the SINGLE PHASE POWER, if you put a oscilloscope on it it would only have one sine wave in it,

IN resident wiring they are pulling off of ONE of the three phases, ((coming in to the transformers)very high voltage has two wires, one that is hot and a ground, and normally only one transformer, and out of that is two hot wires, SINGLE PHASE, and is split in the middle by a neutral wire, which at that time is connected to the ground at that time, but even tho when you read the voltage, you have 120 hot to natural and 120 natural to other hot, or 240, between the two hots, ONe Sine wave,

in three phase (as stated you have "Y" and "Delta")

you can have a number of voltages 208 240 440 etc, but lest stay in the 208 or the 240,

in 208 Y the neutral is connected to the center of the Y or the center of the three phases, and when you pull off the center you get 120 volts, (why you ask, it is because it is 120 to the center but if you look at the Y the legs are 120 degrees apart, and you lose because of the angle of the second part of the leg and you get 208, . as you can get 120 from any of the three hot wires to neutral,

the delta 240 like stated is in a delta configuration, /_\ best symbol I can make,

any way you have the three points and at each point there is 240 volts, using three wires you have three phase, if you only use two wires off of the points you have single phase,
(even tho you using two hot wires of "three phase")

I think it is easer to see in the delta configuration, each side of the delta is like a single phase generator, but when the three are tied to gether, are 120 degrees apart,
so any two of the three wires are only single phase, but together, there three phase,

ok how do you get one 120 out of the delta, you tie in a neutral in the center of one of the deltas , (remember how we got 120 out of the 240 single phase), and that neutral is connected to ground as well, (normally), so to the two hots on either side of the neutral it is 120 volts but between the two hots there is 240 volts, just like in single phase,

OK, the high leg is when one goes between ground and to the third point, which if we look back to the Y you get 208 as well when the angle of the winding changes, thus the high leg, and you can only get 120 from only two of the hot wires,

so when some one says 240 two phase is that they mean that they have two hot wires, and that is it, it is a mis-statement, and comes from the fact that in a three phase system any two hot wires is only single phase between them. (for you to have "two phase" you would end up with two sine waves 180 degrees apart, and that is not going to happen in that situation),

now there are also many variations of three phase systems in voltages and how there grounded.
but they have three sine waves, and the ground may be the center, of a Y or the center of one of the bars of a Delta,

If your using one only one side of the configuration it is single phase and two hots, and if your using all three sides and three hots, it is three phase, the placement of the neutral is where you get the point to make 120 volts or half of a single phase, circuit,

I hope I have help explane it not confuse you more.

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  #13  
Old 12/17/06, 10:56 PM
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Nice explanation.

In re-reading the posts I guess we had a little phase shift in the thread.

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  #14  
Old 12/18/06, 06:32 AM
north of the lift bridge
 
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Talking sorry abot that

seen an oppertunity to glean some exelent info
didnt intend to shift phases sorry

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  #15  
Old 12/18/06, 09:23 AM
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Farming handy man

very good explanation

one word of caution for others - if you have Y and have a 3 phase deep fryer or other peice of equiptment that uses a 120 relay check to make sure the leg you have it on is not the 208 (wild leg)(high leg) we had a couple of fryers at church for fish fries and found different outlets were wire with the 208 leg in differnt places it was realy just one one outlet wired wrong but
a few minutes with a volt meter will save you the time and cost of replacing relays

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  #16  
Old 12/18/06, 10:05 AM
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Wow, a whole thread on 3 phase power and not a single reference to the square root of three.

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  #17  
Old 12/18/06, 11:45 AM
 
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Quote:
Originally Posted by GREENCOUNTYPETE
Farming handy man

very good explanation

one word of caution for others - if you have Y and have a 3 phase deep fryer or other peice of equiptment that uses a 120 relay check to make sure the leg you have it on is not the 208 (wild leg)(high leg) we had a couple of fryers at church for fish fries and found different outlets were wire with the 208 leg in differnt places it was realy just one one outlet wired wrong but
a few minutes with a volt meter will save you the time and cost of replacing relays
Okay, I'm only gonna post this one last time, and then I'm gonna stay out of this conversation. 208 wye (Y) three phase does NOT have a high leg. Wye will read the same voltage on any single leg to a neutral. Delta has the high leg. If you have a piece of equipment that is rated for 208/240 volt 3-phase, and it uses a 120 volt relay then it will have a transformer built in to step down the voltage to 120. Even if you have 240v delta voltage, if the equipment is wired correctly, you cannot get the "high" leg to the relay, because the voltage will have to go through the transformer first. With 240v delta your legs will read 120/120/240 to a neutral. If you read across ANY TWO hot legs you will still only get 240 volts. Your transformer can then only be fed with 240 volts which will step down to 120 before going to the relay.

The only thing that could cause you a problem is if you have 120v fryers, you have 240v delta in your building, and the 120v receptacles were wired to the hot leg. You would then have 240 volts on a receptacle that is supposed to be 120, which would then destroy your equipment if it's plugged in.
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  #18  
Old 12/18/06, 01:40 PM
north of the lift bridge
 
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up in smoke

ive seen restaurant equipment go up in smoke by changing outlets and location's
the mfg. takes 1 leg of the 3 phase and common to run the controlls.
circut boards contactor coils dont last long on a high leg
the 10Kw and the 40Kw daytons were used at U of M for the football concessions running 6 conveyor ovens each
I just taped off the high leg on the 10 Kw[too many fingers playing with stuff there]

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  #19  
Old 12/19/06, 09:05 PM
 
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Quote:
Originally Posted by ovendoctor
ive seen restaurant equipment go up in smoke by changing outlets and location's
the mfg. takes 1 leg of the 3 phase and common to run the controlls.
circut boards contactor coils dont last long on a high leg
Then that was a poor job of engineering IMHO. Had the manufacturer installed a $10.00 transformer to step down the voltage the equipment could have been used anywhere as long as the voltage was correct. It would not have mattered whether it was wye or delta, or where the "high" leg was.
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  #20  
Old 12/19/06, 10:23 PM
 
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idahodave, the floor is yours, tell us about the square root of three, if you dare.


Dave

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  #21  
Old 12/20/06, 12:28 AM
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The square root of three is kind of the magic number when doing 3 phase calculations. The square root of three is about 1.732

Transformers connected Delta to Y have a step up ratio of 1.732 in addition to the turns ratio of the windings.

If you have a delta service and needed a Y for a load, at the same voltage, you would use 3 transformers (normally all in one box) that have a 1.732 turns ratio.

If you have a 208v Y, the leg voltages will be 208v divided by 1.732 or 120v.

If you have a 100 kva rated generator with a 208v Y secondary, each full load leg current would be 100,000 divided by 208 (P/E=I) all divided by 1.732 or 277 amps. [100,000/(208*1.732)]

A 1.732 ratio comes from the 30-60 degree right triangle used to add the phases when making calculations.

About the only time you might need this stuff is when trying to figure out how many amps you can get out of a generator rated in kva.

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  #22  
Old 12/20/06, 11:00 PM
 
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Farminghandyman, I have been answering questions on DIY jobs on the Yahoo Answers and I am going to be like them. You get the best answer award along with several others. It all added up to make sense to me finally.
I have put the rubber gloves and aprons on and made hot taps on 17,000 volt lines at the Goodyear tire plant In Danvile, Va., when I was just a helper, and my boss couldn't explain it too me because he didn't understand it any better than I did, but what everyone has said, added together, fills the puzzle out for me, but I still think they should call 240 2 phase, if for no other reason, just for the h@#$ of it, LOL.

Now one more thing. I had to do some welding today, and had to wire a recptical to hook up a little 220 buss box welder and the only place I had to hook it up was a 3 phase disconnect that had a 50 H.P. air compressor hooked to it before they closed the tire store down. I had 125 / 125 / and a 260 volt high leg. Where in the dickens did that come from.

And now, even one more question, sense I seem to have found some friends that know what I am asking. I have read a great dael about building hydro electric power plants. I may be wrong. The Good Lord knows it wouldn't be the first time by a long shot, but I am satisfied in my own mine, that if I built a water whell that made , lets just say 50 h.p. on average, with the lest amount being, say 40 h.p. that I could use a 10 h.p. electric motor to keep it moving at the right R.P.M.'s to turn a generator that reguires a 40 H.P. engine.
I don't think I said that quite right, but what I am getting at is useing part of the juice the generator makes to power a moter to keep it at the right RPM's.
The motor would just idle when there was plenty of water to power the wheel, but still stay at the right rpm. It would kick in the power needed when needed.
I think after, touching the calculator, the generator should be making about 37 KWs per hr.
So, you use up 20% of the produced electricity to keep it running at the right speed to stay at at 60 Hrz., and 240 volts.
You have a lazy water wheel, a generator and a motor that makes a positive 29 KW's an hour. X 24 hours a day. X 30.4 days a month. X ??? $.08 per HWhr. Lets see now. That is nearly $1,700 a month or over $20,000 a year.
I sure would like to hear someone out there say I might be own to something here.
Thanks again for your answers.

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  #23  
Old 12/21/06, 09:35 AM
 
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Here was the explanation I posted in another thread.


With 220 V both legs are IN phase, but are opposite polarity.
At Time = 0 both voltages are 0
At time = 1/240 second the voltage on L1 =110 and the voltage on L2 = -110
At time = 2/240 second the voltage on L1 = 0 and the voltage on L2 = 0
At time = 3/240 second the voltage on L1 = -110 and the voltage on L2 = 110
At time = 4/240 second the voltage on L1 = 0 and the voltage on L2 = 0

4/240 of a second is 1/60 second and the process repeats. The voltages on L1 and L2 are IN PHASE but are opposite polarity.

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  #24  
Old 12/21/06, 10:48 AM
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Two voltages, represented as -E at 0 degrees and E at -180 degrees, would be used to compute addition and subtraction of voltages. The two voltages are one in phase but negative, and the second positive, but 180 degrees out of phase. Both expressions will plot to the same point and either one can be used for calculations. In phase but negative is the same as positive but 180 degrees out of phase.

Single phase power is derived from only one phase, it may be negative or 180 degrees out but it's still only coming from one phase of the line.

If we wanted to call 120/240 two phase, then to be consistent with naming, three phase power should be called six phase, because the inversions, negatives, out of phase, etc all exist in the three phase world as well.

125/125/260? Line voltage little high not as much load on the wild leg...

Water wheel idea sounds good. Motor acts as speed regulator. Might want to figure out a way to shutdown if the generator gets two far off 60 hz.

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  #25  
Old 12/21/06, 11:04 AM
 
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"I had 125 / 125 / and a 260 volt high leg" It looks like it is is just a "Hot" (high on the voltage) delta or possibly an open delta winding,

your measuring from the neutral or ground, see what it measures from hot to hot to hot,

~~~~~~~~~~~~~~~~~~~~~~~~~~~~
your idea on the generator problem will not work,

most AC motors are RPM controlled by the frequency of the power coming into them, (and are electrically built to best use that frequency to operate, windings, wire gage, laminations, clearances of the windings and armature, etc.) in the US we use 60 cycles or 60 fluctuations per second,

on a 2 pole motor that is 3600 rpm, and on a 4 pole that is 1800 rpm, and a 6 pole it is 1200 rpm, and so on.


since the source of power would be by the generator and since the speed of the generator is not constant, the frequency would fluctuate and so the frequency would fluctuate, and so would the motor that is trying to stabilize it,
also since your generator is larger than the motor it would control the speed not the motor,

If your desire for power was not as great, one could use DC, and the rpm would not be as critical and charge some batteries and an electronic inverter,

If you would use a grid tie system, you could use an Asynchronous generator or INDUCTION GENERATOR, the grid would keep the speed constant, and would then feed back in to the grid the power produced, (since the grid is bigger, you will not over power the grid), and since it is locked on to the frequency the grid is steady,

(induction motors, have slip in them if you look at the name plate on them you will never see a 3600 or an 1800 rpm rating, that is because there is slip in them, [partly why they work, as the slip is were the magnet field is created and thus is pulling the armature around after the electricity that is spinning in the field or windings]
the same happens in an INDUCTION GENERATOR, you over speed the armature of the generator, and the magnetism will start to pull the electricity around the field or windings, thus making electricity, (a motor is a rotary transformer), so as long as it is moving a little bit faster than the speed rating it will generate and if moving slower it will motor,)

most induction motors will generate electricty,
http://www.windpower.org/en/tour/wtrb/async.htm

http://www.google.com/search?num=100&hl=en&newwindow=1&sa=X&oi=spell&resnum=0&ct=result&cd=1&q=asynchronous+generator&spell=1
http://www.madsci.org/posts/archives...5367.Eg.r.html


there are two ways to generate electricity, one grid tie it, (the way most power is produced in the US), using a Asynchronous generator,
but there would be a lot of additional items that will disconnect if the grid goes down and probably a list of regiments that will shut you down before you can begin to grid tie, (the power company's don't want competition).


if not grid tied you need a constant load and match the water flow to the load, to keep the speed constant, thus the voltage,
THe BOOk "motors as generators for micro hydro power" by Nigel Smith
http://www.amazon.com/Motors-as-Gene.../dp/1853392863

or you need a Synchronous generator which is like in a commercial generator, and it frequency is dependant on the speed in which it is turned, (voltage is usually controlled via a variable circuit, now days, (like i said it was a rotary transformer, the older brush units feed the center of the generator with a small amount of power to adjust the magnet field to the strength it needed to be to make the voltage, and on brush less units it is all internal on the center of the generator.

and governor that will regulate the water flow depending on the speed of the water wheel or turbine, that could be mechanical or electronic,

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  #26  
Old 12/21/06, 12:21 PM
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Maybe I didn't visualize the setup right. I thought the motor and generator would be tied together mechanically and connected to the water wheel with an appropriate step up so the normal wheel speed would turn the combination motor/generator at 1800 rpm. The motor would be power line driven.

Here's what I thought would happen. At startup assume no load and no water. Motor should turn wheel and generator, and with no load, come close to 1800 rpm speed. Add the load, motor will slow down as slip angle increases, and motor current will increase. Now slowly open the sluice gate, while watching motor current. Motor current should go down as wheel starts to provide power. As more water is added current should go to zero and start back up. When the current starts back up the motor is acting as a generator and returning current to the line, slowing down the wheel. I suggested the off frequency shutdown so if things got too far out, it would shut everything down. (disconnect load and motor)

The whole thing would be a little Rube Goldberg-ish (well OK a lot) but could probably be made to work. Frequency regulation would depend on the wheel vs motor powers. Would it be stable? Probably not, but if the load and water flow were constant it might work.

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  #27  
Old 12/21/06, 02:43 PM
 
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My be I am miss understanding the idea here as well,

there is a lot of information on hydro power, do a google search on "Asynchronous generator" or "INDUCTION GENERATOR" and put hydro behind it,

Asynchronous generator hydro, or
INDUCTION GENERATOR hydro, or
synchronous generator hydro

there are a lot of ideas and ways to go,

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  #28  
Old 12/21/06, 05:45 PM
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I do think that a DC genny with batteries and inverter would be a better way, but a motor controlling the wheel speed does seem like a neat idea.

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  #29  
Old 12/21/06, 06:19 PM
 
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The person I am working for has put in a lot of hydro in the past, and one of his friends made the power to run the National Labs where they developed the bomb. I can ask them about material to study about hydro. I have a small hydro site that I hope to develop someday. The key to getting your setup to make juice consistantly would be in the water delivery. In my application we have determined that we can run at least an eight inch pipe with about 150' of head. as long as your water source is consistant the pressure and volume will also be constant. I was lucky enough to work on a 150kw hydro plant for a day this past summer. It is very cool. My friend also computerized a hydro plant that was installed by Thomas Edison so that the owner could utilize every kw without having to constantly switching loads all day long.

The type of wheel you use is also very important, there is a lot of energy lost getting the water out of your wheel, which is a determining factor in the efficiency rating. Pelton wheels are good, but require clean debris free water. There is also a wheel that looks a lot like a horizontal squirrel cage fan, the water hits the fan from the top and impart some of its energy and then falls through the bottom, again imparting more energy. Picture the cage having a sliding cover, like a pipe over the outside that is used to regulate the flow of water. This may be a solution to variable water supply.

I volunteer at Hancock Shaker Village in Hancock MA. We have two water turbines that the Shaker used, one in the wood shop, and one in the tannery. The bigger turbine makes about 3hp and has an 8" supply with about 41psi of supply pressure, it uses 8 gallons per second. This should give you a rough idea of how much water it takes to make hydro. I belive the hydro plant that I worked on had a 4 foot penstock tube for 150kw.


Dave

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Last edited by Dave S.; 12/21/06 at 06:30 PM.
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  #30  
Old 12/21/06, 08:52 PM
 
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Are you German? Sounds like over engineering to me.

Instead of trying to control the waterwheel RPMs with the assistance of an ac motor, that would require frequency control, microcontrollers, blah blah blah…real nasty stuff, why don’t you just control the flow of water over the wheel? Given enough thought, there is a very real possibility to make it all mechanical! When the wheel speeds up, a swing door directs more water around the wheel instead of over it.

OR!!! I just though of this one…have the main water source poor like a waterfall into a large barrel, say 55gal (could be any size). Have a pipe run from the bottom of the barrel to over the wheel/generator/whatever. The barrel would always be full and overflowing at the top with water. Pressure would always be the same! Water amount and speed would always be the same! I'm like a genius or something…

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