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### Converting 3 Phase to 1 Phase in Reverse?

08/11/2012 7:21 AM

I want to set up a hydro generator connected to the grid on my property. I should have about a 25kW system. I will be using an induction motor as a generator. Motors of this size (30 or 40 hp) are invariably 3 phase but I only have single phase on the grid. I need an efficient way to change the 3 phase output of my generator to the single phase on the grid. How can this be done?

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#1

### Re: Converting 3 phase to 1 phase in reverse?

08/11/2012 10:17 AM

Googling, I found this, It could be helpful.

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#3

### Re: Converting 3 phase to 1 phase in reverse?

08/11/2012 1:17 PM

Looks like a very good article. Will take me a while to absorb but looks to be very doable with reasonably high efficiency. Thanks a lot.

Just curious, what did you use a search terms. You had way better results than I have gotten.

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#4

### Re: Converting 3 phase to 1 phase in reverse?

08/11/2012 1:27 PM

Can't remember exactly, but it took me quite a few iterations. Something along the lines "Using 3 phase induction motor as single phase induction generator"

I already knew it could be done by some capacitor arrangement.

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#7

### Re: Converting 3 phase to 1 phase in reverse?

08/12/2012 9:58 AM

To I am learning: I think this indeed should be useful. It is a little over my head but I will get to where I understand it all. Would this create a rather "lumpy" signal instead of a clean sine wave?

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#2

### Re: Converting 3 phase to 1 phase in reverse?

08/11/2012 11:16 AM

Just don't use one of the phases...

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#8

### Re: Converting 3 phase to 1 phase in reverse?

08/12/2012 10:00 AM

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#5

### Re: Converting 3 Phase to 1 Phase in Reverse?

08/12/2012 5:53 AM

Provided you can get a connection to the middle point of the 3 fields, you can have basically 3 x single phase. But they are not "in phase" with each other, but at 120° apart, so don't connect them to each other......

As far as I am aware, all houses, apartments, buildings in Germany (all the ones I have seen or heard about anyway!) are fed with 3 phases and a neutral for example, so you can use what you wish......you just need a three phase distribution box and take off, via fuses what you need and of course the neutral (not fused for safety reasons) for single phase loads.....

The safety ground is developed by both a deep earth spear and connecting the neutral to it as well.....also all metal water pipes in the hose must also be linked to this ground. The ground is also not fused for safety reasons....

Proper grounding and neutral are two areas that are fundamental to safety, which many do not understand.....

Earth Leakage breakers (or a modern equivalent) are still a must to my mind, properly installed and tested...

Maybe something like this will be useful and far easier to arrange for you.....assuming you get your motor working as an alternator, also not an easy business.....and fraught with possible dangers of electrocution.......assuming you are not an electrical professional.....be careful!!! Let us know how it goes please.

You know what is black and hangs from the ceiling?

An amateur electrician.......(occasionally a professional one too!)

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#6

### Re: Converting 3 Phase to 1 Phase in Reverse?

08/12/2012 9:51 AM

Thanks Andy,

I didn't want to clog up the questions with all the details but need to add a couple here. This unit will be the only thing connected to the grid at this point and no houses are anywhere near the generator. My house is about 1/2 mile away. The idea here is to create some income while taking a little of the load off of fossil fuel power plants. I had not put much thought into grounding but it is something that I do need to keep in mind. It would be a requirement for a service connection at any rate. I worked as a journeyman for several years wiring houses but have very little experience with commercial or 3 phase equipment. I also have a degree in mechanical engineering. Some of the electrical stuff is kind of fuzzy for my concrete thinking though. At any rate, perhaps your comments will be useful to those that read this thread in the future.

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#9

### Re: Converting 3 Phase to 1 Phase in Reverse?

08/12/2012 11:40 AM

DG,

One of the main problem I see with this is that single phase supply/load produce a pulsating power at twice the frequency. This is part of the annoying buzz made by induction motors (although some are worst then others).

At 40-50 HP, this may become a mechanical problem for your generator/turbine and reduce their life. How much depends on its built and the percent of full load you run it at.

One solution is filtering. An MG set will do that through its inertia but the single phase generator (output) will take the same hit that your generator will take. Although it might be designed to take it better than a three phase unit.

Using an electronic converter could solve the problem if enough capacitance is added to the DC bus to filter the power. My active front end converters could handle it but you might not like the cost.

The main question here is what is the economics? Your revenues might be at best \$0.1/KWh x 40KW x 24h = 96\$/day (gross). What are your expenses in maintenance, insurance, taxes? Capital expenditure? financing cost? In general, unless you live in a remote area where there isn't any power line available, self production economics are questionable at best. There are lots of issues with safety of the utility crew, islanding, and protection coordinations that have to be addressed.

Some area of the world have incentives that offset part of these costs but we don't know how long they will last. In any case, I cringe when the govt take money from productive enterprises and taxpayers to support questionable "investments".

At least if your/some house was nearby, they could use the power from two of the phases and you would sell the power from the third phase. This would help balancing the load and reduce the pulsating power.

I am not trying to insult you here but try to make it a real productive and sustainable project. Not a parasite on you and the society. You will be happier with the results.

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#14

### Re: Converting 3 Phase to 1 Phase in Reverse?

08/13/2012 1:42 PM

Piggybacking on what marcot wrote, make sure you explore in detail the interconnection requirements specified by your local electric utility. Their requirements may blow your economic feasibility right out of the water.

Interconnection may require a main breaker with under- and over-voltage, under- and overfrequency and reverse power relays to protect the integrity of their system if you have a failure of something in yours. You may need synchronization capability, plus you will need revenue-grade energy metering to determine how much you are putting into the grid.

I worked on a similar small hydro system about 10 years ago where a fellow owned an old dam & water-powered mill and was setting up his own small hydroelectric plant. I think it ended up being a tax haven for him, since I'm pretty sure it wasn't profitable in itself. I know he paid my employer a good sum to engineer, build, install, and test the protection and metering equipment he needed.

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#10

### Re: Converting 3 Phase to 1 Phase in Reverse?

08/12/2012 8:02 PM

Best method is generate DC,then use an inverter to synchronize to the grid phases.

You cannot simply "plug in" to the grid;phases and voltage must match perfectly.

With no houses nearby, the grid is probably 13.2KV 3 Phase.(USA) primary, so you need to keep this in mind also.This voltage level requires special training and equipment to service.Chances are, after considering the complexities and expense of doing it right, as well as potential liabilities, you will forget about it.

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#11

### Re: Converting 3 Phase to 1 Phase in Reverse?

08/12/2012 11:37 PM

Cut it out you guys! Andy Germany is the one and only correct one. Feed a part of your house a part from a phase, next part from another phase, etc. It will simply take a 3 phase main panel, and 3 single phase subpanel. If you want to set up a shop with 3 phase motors, that is available too. Do not tell the city about it. They (in the US) are sticklers about not giving 3 phase to homes. Why? That is lost in the fog of history.

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#12

### Re: Converting 3 Phase to 1 Phase in Reverse?

08/12/2012 11:51 PM

As a standalone system 3 phase load reticulation is the obvious thing to do, BUT OP wants to Gridsync and the grid manifests as single phase at his place.

I say forget grid sync and store your surplus instead of selling it. You then have that to use and you will also be saving the buyin/sellout tariff margin.

Unless OP really has loads of water in his dam in which case monetising the resource is the intent (yes?).

Has OP mentioned how the generator will be excited and synched to the grid yet?

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#13

### Re: Converting 3 Phase to 1 Phase in Reverse?

08/13/2012 12:39 AM

I am firmly a disciple of the K.I.S.S. principle. On that basis, I doubt, any sellback idea is reasonable. Rather, the independence, by staying unconnected. Networks, without good reasons are way overrated.

Are you hellbent on sellback? Feed your home from 2 (3) phases, and feed back the 3.rd. See, even your conscious is assuaged. Sensibly or not.

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#15

### Re: Converting 3 Phase to 1 Phase in Reverse?

08/13/2012 5:57 PM

You may be able to use a single phase to 3 phase VFD with line regeneration to do what you need. Yaskawa http://www.yaskawa.com may be able to supply what you want.

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#16

### Re: Converting 3 Phase to 1 Phase in Reverse?

08/14/2012 11:23 PM

Seems to be time to chime in again. Here are more thoughts, beliefs and facts about the planned system.

Someone mentioned working in the high tension range of voltage. Obviously this is not the case. There is a transformer between the grid and the generator. I'm not Con Ed. I will have the choice of voltage to work at. 240V might be a good choice to provide a more local "utility" for any future buildings that might be constructed near the generator. On the other hand, 480V might be more practical and probably slightly more efficient. I am trying to keep thing as generic as possible in the event that equipment (eventually) fails and needs to be replaced most economically.

Most people are freaking out about phase and frequency matching of the line frequency. From what I have been lead to believe, once the system is online it is self regulating. Excitation of generator comes from the grid and acts as a sort of "clamp". As the generator tries to overspeed the grid pushes back (phase and frequency wise) to where as the generator tries to lead the grid, the grid holds it back. The harder it tries to lead the harder the grid holds back with the result being more current being pushed into the grid. The end result being generating as much current as the turbine is mechanically capable of producing. Once online, phase and frequency take care of themselves.

Along the same lines, if the grid goes down, the generator looses it's excitation and stops generating preventing islanding (which is not allowed). Shutting down the turbine in the event of grid outage isn't too hard and can be done with a couple of magnetic latches and flow diverters. Simple.

The problem is the startup. If the generator phase doesn't match the grid it will cause a huge spike the will most likely fry my generator (and possibly some utility equipment as well). Of course the generator wouldn't actually be producing anything until it is connected because it needs grid power for excitation. This is uncertain territory for me but perhaps I need not worry about it at all and it will take care of itself as the connection is made. My real plan at this point though is to get the generator running in motor mode before any water is directed at the turbine. This would be a manual process but happens pretty infrequently and isn't hard to accomplish. Said another way, I would use the grid to bring the generator/motor up to speed and then hit the juice. I do not have all the details of how this happens exactly but it would be essentially the same way a rotary phase converter works.

I have to offer my apologies to Solar Eagle here. Perhaps the easiest most economical way to do this is to just use one phase of the motor as generator. It does seem very unbalanced, inefficient and probably would cause equipment breakdown much more frequently though.

Just a dumb thought here but hydro turbines work better at slower speeds. Would it be possible to use a 3 phase, 2 pole motor and rewire it such that it becomes a single phase, 6 pole motor? Just an idea. That would kill several birds with one stone.

I really do not want to go through any from of rectification and inversion. Way too much complexity and expense. Yes I am on a budget. I know how to shop to find equipment for a good price but I dont have deep pockets. Yes there are some grants and tax breaks available but are hard to come by. I will be trying to get those though. By the way, most of the grants are NOT from the government and the way I look at it any tax break I get it just a refund of all the taxes the government has stolen from me over the years.

A note on economics of running the system: Currently the power company pays just under \$0.03/kWh for electricity supplied to them. Where I live, there is an organization that brokers alternatively produced electricity to companies and individuals at a premium. IF I can work through them, I could be getting as much as \$0.08/kWh, that's \$17,500 per year. Now it is starting to look more viable. Believe it or not, If I don't have to spend a wad on electronics, I should be able to construct the system for around 50K.

For those that are curious, the hydro part of this system is as such:

3200' of penstock (6" pipe) giving 400' of head supplying 12LPS of water to the turbine. The dam is only about 4' high. I'll be using 3 different thicknesses of PE pipe, above ground across my property. The turbine will be a Pelton type possibly fabricated locally with replaceable spoons.

Someone mentioned maintenance. After initial startup and testing, maintenance should really be minimal. There isn't a whole lot to wear out or break down if this gets done right.

To all the negative Nells out there, stop telling me why I can't do it and help me figure out how TO do it, cheap!

I am going to need an EE to do consulting work and sign off on the system design. I have a lot of old EE colleagues but the guys I know work mostly in automation and high tech. None of them are comfortable with power generation engineering. Anyone that is interested, please contact me mystic_one1953 at yahoo. I don't think you need to be a PE but it couldn't hurt.

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#17

### Re: Converting 3 Phase to 1 Phase in Reverse?

08/15/2012 9:09 AM

You might not need a PE but you need to understand generator synchronisation, power factor, and protections to do what you want to do. This takes a lot of studying and practice to master. The control of an on-line generator is complex. You need electronic governer and excitation controllers that work together. Your present understanding is not good enough to succeed and you are refusing to listen to those who know what they are talking about. You called us the Nelly's to insult those who graciously tried to show you the difficulties that you are facing. This is not a good start.

Have fun trying, avoid playing with what you don't understand you can injure yourself.

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#18

### Re: Converting 3 Phase to 1 Phase in Reverse?

08/15/2012 11:49 AM

HECK, MAN. Which part of Andy Germany and Mine you did not understand, that there is NO PROBLEM at all. Capiche? A large portion of the world practice loading each of the 3 phases, and live to tell about. So, get on, and solve real problems.

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#19

### Re: Converting 3 Phase to 1 Phase in Reverse?

08/15/2012 11:50 AM

The way the excitation works is thusly:

A supply form the grid is used to provide excitation to get the turbine generator bootstrapped.

A manual adjustment is used to synchronize the phases.A cheap way to do this is to have a clear,10 watt bulb across one grid phase, and the corresponding generator phase.Adjust the speed till the light goes totally out.Observe the filament closely.This is the reason for the clear bulb,so you can see the filament. This means the phases are matched.

You may now transfer the generator to the grid.Keeping it regulated is another matter, and I will leave it up to you and your insurance company.This is the cheapest way I know to synchronize phases.Very low tech but was used for many years before solid state came on the scene.

You speak of killing two birds with one stone, but if you are not very careful, you will kill more that birds.

An old saying goes:"There are bold electricians, and there are old electricians,but there are no bold,old electricians."

You have been advised and warned.

"Weak men believe in luck.Strong men believe in cause and effect."

I have seen the effects, and I know the causes.

Good luck to you, and may fate favor your survival:physical,mental, and financial.

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#22

### Re: Converting 3 Phase to 1 Phase in Reverse?

08/16/2012 5:27 AM

In the RN we used 3 lamps, one connected as you wrote, the other two "cross phase connected" across the other two phases, that way when the lamp you mentioned is out, the other two are at full brilliancy.....

We put the three lamps in an isosceles triangle shape on the switchboard, the top one being the "out" one connected across the same phase of each alternator, the other two for the base of the triangle, Each one of those connected to one of the other phases on one and the other phase on the other alternator.....but not the same phase you understand......

This gives a great "extra" effect (when correctly done/switched) that when the oncoming alternator is faster than the grid (the correct situation for switching in parallel and taking load immediately), the "off" lamp revolves clockwise. When the oncoming alternator is slower than the grid, the "off" lamp revolves anti-clockwise.

We also had a phase meter (belt and braces), but most of us just used the lamps.....

I had charge of over 11 Million UK Pounds of equipment on a county class destroyer, a lot of money in the 60's. Today it would be 100's of millions of UK Pounds.....

I hope that I was able to explain it in a manner that anyone will understand....

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#25

### Re: Converting 3 Phase to 1 Phase in Reverse?

08/16/2012 5:41 AM

Nice one Andy.

..full brilliancy...and then some if you use 240V lamps across 415P-P.

Don't try this with CFLs folks.

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#26

### Re: Converting 3 Phase to 1 Phase in Reverse?

08/16/2012 7:42 AM

Dear Wal,

I did not think that I needed to add that dropper resistors are required, we had phase to phase 440 volts in the RN and on any on NATO warships, since the '50s.....my take was that most would understand that you cannot place 220 volt lamps on that......

OH!!! There is one who didn't......

But some will pick, even if there is really nothing to pick on.....

PS Dear Wal, for you personally I will try to remember to dot the "i's" and cross the "t's" in the future......

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#27

### Re: Converting 3 Phase to 1 Phase in Reverse?

08/16/2012 8:56 AM

Settle down sport!!

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#28

### Re: Converting 3 Phase to 1 Phase in Reverse?

08/16/2012 9:57 AM

I was never "up"! It was just a simple reply to a not well thought out comment, but at least you did it in person.....

I just expected that anyone reading this blog would either imagine that special (high voltage, neons or similar would would probably worked, but not as well as filament lamps. Two x 220 Volts in series would also work...) lamps were in use, or they would be in some manner "made fit for the purpose".

No one, least of all me, was saying "do use wrong voltage lamps in such a device"......

I am very strong on safety, but your comments were out of order and little to do with safety, or you would have mentioned how in fact they are made safe, or you were trying to be more humorous than you really are!

I bet I got more laughs.....

Have a great day anyway....

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#20

### Re: Converting 3 Phase to 1 Phase in Reverse?

08/15/2012 9:17 PM

If your turbine/generator(3 phase induction motor) is not turning when you apply 3 phase electrical power, you will only see normal motor inrush. Even if the turbine/generator is at less than synchronous speed, since the turbine/generator has not had any excitation, you will not see much more than normal motor inrush. If you drop power and immediately re-apply power you can see more than 20 times normal motor inrush. The electrical grid does not care if you motor or generate it will only let the turbine go a few RPM over synchronous speed unless your turbine is producing to much water horsepower(head x GPM/3960), then you may burn up your generator. If you lose grid power, your fail safe should shut down the turbine and the starter so that your generator does not overspeed or do a out of phase re-connect. It would make everything simpler if you can get 3 phase grid power to your generator.

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#21

### Re: Converting 3 Phase to 1 Phase in Reverse?

08/15/2012 10:36 PM

While many things can be done, not all things ought to be done.

While by and large I agree with Grand Poobah, let's touch upon a few mundane issues. It takes a nontrivial permit for a system that can sell back power to the utility. In case of an off-the-self solar, the company obtained the necessary permit. You, as a "manufacturer" got to go that process, unless an off-the-self certified interface is available. You can bet your last dime, that the utility is a stickler on that. So is your fire department, and hence your insurance. I am not interested raining on your parade, but these are the facts. Now, this applies for an interconnected case. Additionally, a mile or so power line will run into the many \$10thousands. And an out-of-phase interconnect will blow your genset sky high.

On the other hand, a strictly standalone system (with maybe a 5kVA gas or diesel single phase backup) is a much more relaxed affair. No worries with phase and frequency, only voltage and rpm regulated. Standard electrical installation is adequate. A 3 phase main breaker panel, immediately followed by 3 single phase subpanels for the actual loads (like upstairs, downstairs, shed and garage). Standard for european homes, and all industrial installation anywhere. Fire departments and insurances know it, no problem.

I do not mind discussing intricacies of interconnects, but not at the expense of a lucky homeowner. Separate, emphatically!

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#24

### Re: Converting 3 Phase to 1 Phase in Reverse?

08/16/2012 5:38 AM

GA

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#29

### Re: Converting 3 Phase to 1 Phase in Reverse?

08/16/2012 3:02 PM

You are entirely right about having the system certified, the power companies do not like to buy power from individual sources as it is, and if there wasn't a federal mandate to do so, they wouldn't. Also, above all else the system needs to meet all safety issues. The cost of the controls may make this project unfeasible except as an isolated system.

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#23

### Re: Converting 3 Phase to 1 Phase in Reverse?

08/16/2012 5:36 AM

What everyone here is forgetting, is that no energy supplier will allow connection to the grid without a full set of specialist safety equipment that has been supplied by a certified supplier. It costs a bundle in most countries.

No DIYer is allowed to connect.....and if he does, he may not see a profit as a requirement is an electricity meter that can run "backwards", not all modern ones can I am told.......so he may supply the grid "illegally", but see nothing back in return.......

Part of the specialist equipment is a meter that monitors the "direction of flow" in or out, so allowing proper billing....

At legal best, a DIYer will be able to supply himself, but then he needs an AVR system to handle load changing and voltage/frequency control.....

I don't think that the OP has fully understood all the problems.....yet!

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#30

### Re: Converting 3 Phase to 1 Phase in Reverse?

08/16/2012 6:40 PM

Yes you are correct on the assumption that a typical induction motor can be used as a grid tie co gen system directly. I have experimented with it many many times and with many different sizes of single and three phase motors.

Relating to doing the grid connection that's easy just get the motor spun up to its synchronous speed or slightly higher and flip the switch. Being the rotor is unpowered it will not cause the motor to work as a generator by itself so it can be spun at its full rated speed without putting out any power.

As far as the actual motor winding connections are concerned you would probably be best off reconfiguring your 230/460 connections to a 12 lead if its not already designed that way. All that entails is finding the center connection for the one set of windings and breaking that into three independent leads so you can reconfigure all of the phase windings individually.

To get near your full rated output capacity in single phase the 12 leads would need to be reconfigured into a 'Z' connection or Zig-Zag connection. by doing so you would be able to get a two line center tapped output. Given that a 40 Hp three phase motor draws around 100 amps per phase on a 240 volt connection after being reconfigured into a Z connection it would give you a theoretical output of around 280 volts at at least 150 amps single phase output at about 40 KVA which would work out to around 30 KW's of actual returnable power.

Given that you would have 240 volt circuit to connect to the 280 volt theoretical output will help you push power back without having to run the motor much over synchronous speed not that it matters that much.

If its a 2 pole motor it probably ran around 3450 RPM (3600 synchronous speed)which as a generator would require it to be ran over speed by the same amount so its would need an input of between 3600 for no output up to around 3750 for full output give or take.

So yes in my opinion and from personal experiences your idea of using a large three phase motor as a grid tie generator is very doable with minimal amounts of modifications other than some winding lead reconfiguration.

As far as grid tie power monitoring that too can be done easily and cheaply with a off the shelf Programmable Logic Relay unit like a TECO makes (insert Google search here). With one of those you just convert your voltage and current signals plus shaft speeds to basic 0 -10 volt signals and feed them into the PLR and let it do the system monitoring for you with basic digital ladder logic.

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#31

### Re: Converting 3 Phase to 1 Phase in Reverse?

08/16/2012 8:59 PM

One thing to watch out for in your control logic is, if you have a load that shares the utility line, ie; a pump, compressor or other large inductive load, its startup may try to draw the starting current from the generator, lugging the generator down to the point of motoring. Have the logic allow the generator to motor through the load, do not disconnect and allow the logic to re-connect as soon as the generator is back at synchronous speed, because 9 times out of 10 it will re-connect with excitation left in the windings and out of phase. I saw this very thing happen on a field service trip and it would blow the 3 phase breaker off the wall.

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#32

### Re: Converting 3 Phase to 1 Phase in Reverse?

08/17/2012 5:55 PM

Thanks for the PM you sent me. I will try and work up some better details as I have time.

Fist thingiI would suggest is looking fore schematics for 9 lead and 12 lead dual voltage three phase motors then read up on what a zig zag or 'Z" connection is regarding getting single phase form three phase. Basically its a delta connection where the bottom phase is shifted to the left or the right making what looks roughly like a Z laying on its side.

Sort of like this ' _/\ ' or this ' /\_ ' Phase A is at the bottom and phases B and C are the two top ones. It turns a delta connection into a single phase connection with fairly equal current sharing properties on all three phases but at 2X the delta voltage and creates a point that can be used as a center tap.

On many multi voltage generators its how a 120/240 volt single phase output is achieved from a three phase winding set that normally produces either 120/208 3 Ph Wye connected or 120 3 Ph delta connected without overloading any of the individual phases.

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#33

### Re: Converting 3 Phase to 1 Phase in Reverse?

08/17/2012 7:51 PM

Hi dg1953, sounds like an interesting project - when you say "induction motor"do you mean squirrel case motor? If this is so you will have difficulties developing a strong controlled rotating field. Alternators mostly rotate the field to reduce weight, heat and infrastructure. The field sshould also be controlled. Think of a car's alternator. The most efficient way to convert 3 phase to single phase is to use an inverter. Cheers

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#34

### Re: Converting 3 Phase to 1 Phase in Reverse?

08/18/2012 12:09 AM

Actually for doing grid tied co gen a common squirrel cage type induction motor is a good choice being it by design wont produce any power on its own without being connected to the grid by at least one phase or more.

All thats needed to make one do co-gen work is to spin it proportionally faster than the slip differential of its synchronous speed. That is if its a 4 pole motor working on a 60 cycle power source it would have a synchronous speed of 1800 RPM however at full load it has a relative slip effect to it which is how induction motors always come out with the odd speeds like 1725 or 1740 RPM opposed to an exact 1800 RPM.

What this means is that if you have a 10 Hp (7.5 KW) 1740 RPM motor all you need to do to make it work as a 7.5 KW co-gen generator is use an external power source to mechanically spin the motor shaft at 1860 RPM. The feedback power is fairly proportional above the synchronous speed so if you spin it at around 1830 RPM it will feedback about 3 KW give or take.

The down side is that to keep from overdriving the motor in Co-Gen mode either a method of reading the output amps is required and a way to use that reading to govern the mechanical drive source is needed or the use of a motor that has a working capacity greater than the input power source is capable of producing is necessary.

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#35

### Re: Converting 3 Phase to 1 Phase in Reverse?

08/19/2012 8:07 AM

I don't personally know of such an inverter for 3 to single phase (but I don't know everything either), but you did remind me that years ago, we used "Rotary Converters" for both phase, voltage and frequency conversion....

I expect they are "old hat" nowadays and might be available cheaply from somewhere, ebay?

Can someone shine a light on such equipment? I only used it, I never remember it ever going wrong......

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#36

### Re: Converting 3 Phase to 1 Phase in Reverse?

10/06/2012 6:23 PM

The piece of equipment you need to purchase is called a phase inverter sized to meet, your design needs, IEEE standards, local Utility interconnection requirements, as well as National Electric Code (NFPA 70) and National Electrical Safety Code (NESC) standards. The Hydro system will also need to regulate flow through the impeller (prime mover) such that the motor shaft speeds maintain approximately 1800 or 3600 RPMS - dependent on how many poles the procured motor has. 40HP, single phase, AC induction motors are available.

Another solution is to use the AC induction motor with a closed-loop speed control system that monitors speed and drives a 25kW AC to AC power converter. This would dissolve any need for maintaining a constant head pressure on the impeller.

WoodCraft Electric is a small electrical power design and consulting firm, located in Charlotte, Vermont. Please feel free to contact me at pwood@woodcraftelectric.com for further feedback on your design task. It sounds very interesting and is right up our alley.

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