Author Topic: 3 phase 35 HP Inductive Motor  (Read 5547 times)

LowGear

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3 phase 35 HP Inductive Motor
« on: March 24, 2008, 09:10:52 PM »
A fellow wants to see me one of these - he has 6 of them - to build a net metering system.  I only want to create about 4KW. 

Can I use one leg on a three phase motor?

Should I resume my search for a 5 HP quality inductive motor?

Cheers,

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ronmar

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Re: 3 phase 35 HP Inductive Motor
« Reply #1 on: March 24, 2008, 10:04:23 PM »
Search "induction generator" on the web, there is a way to use a single phase and configure the other two for excitation.  I don't have a link with me, I think it is called the Y2Y method, but don't exactly recall. I will look for it this evening, but as I recall like most uses of an induction motor for a stand alone generator, it is still not great for starting inductive loads.  Most of the thigs I recall reading about were making low budget lighting plants(hydro or engine) for remote vilages in the third world.

35HP is also a real monster and you will burn up a lot of horsepower just spining it past resonant/syncronus speed to use it for a generator.  Regulation might also be an issue, but if I understand the above method correctly, it is a little more stable than pure capacitance excitation.  If all you are looking for is 4KW, why not get a ST-5?

Ron 
PS 6/1 - ST-5.

Doug

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Re: 3 phase 35 HP Inductive Motor
« Reply #2 on: March 24, 2008, 10:29:57 PM »
Look for a 5 hp induction motor.

Any brand name will do but for single phase
I'm partial to Baldor, and Leeson.

There is realy little to no difference between major brands.
Find a motor shop look for a used one as a starting point
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LowGear

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Re: 3 phase 35 HP Inductive Motor
« Reply #3 on: March 24, 2008, 11:45:12 PM »
Hi Ron,

I want to net meter and am somewhere between totally and absolutely ignorant about syncing one of the easy to find ST-5 heads.  The inductive motor idea just caught my imagination for some reason.

LG
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Doug

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Re: 3 phase 35 HP Inductive Motor
« Reply #4 on: March 25, 2008, 12:24:09 AM »
Net metering with an ST-5 opens you to a world of complexity that I don't want to get into.

look for a 5 hp Baldor induction motor off a big home compressor or something
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ronmar

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Re: 3 phase 35 HP Inductive Motor
« Reply #5 on: March 25, 2008, 01:15:17 AM »
Hi Ron,

I want to net meter and am somewhere between totally and absolutely ignorant about syncing one of the easy to find ST-5 heads.  The inductive motor idea just caught my imagination for some reason.

LG

You didn't mention anything about net metering.  You should really consult your local utility to see if they would even allow it with an induction motor. It would also require at a minimum some additional protection circuitry that would most likley be mandated by the utility.

I also don't know where you are located, but if in north america, the power reaching the average home is a single phase of 240V AC. This 240VAC is delivered from a center tapped transformer out on the power pole, with the center tap providing a neutral reference. Hot-Hot 240V Hot-Neutral 120V. Getting an induction motor to match this and feed acceptable power back up the line might be a problem.  It would be much easier if you had a 3 phase feed, which is I believe either 208, 220 or 440V per leg.  Since a grid tied motor gets it's excitation from the line when used as a generator, it should adjust, but that much difference may be beyond it's capability and effect efficiency, especially trying to get a single 240V phase out of a 3 phase.

As Doug mentioned, Getting a ST generator in sync with the utility is a whole world of complexity beyond using an induction motor.  It requires some elaborate sense circuits and an intelligent governor to adjust the frequency thru engine RPM to stay in sync with the utility.

YOu didn't mention what you would be using for a power source, but as also mentioned a lot on this subject, if it burns fuel,  why would you want to even contemplate this.  Even with free fuel, which isn't free, unless you do get it delivered and processed for free, there is just no real way to be competitive with the utility.  I think you will find it a big investment just to be able to say you did it, if the utility even allows it.  About the only viable use of fuel to make electricity on this scale is to be able to provide something the utility can't.  IE: you are $200,000 up the road from the nearest commercial power, or you have frequent power outtages... 

I think induction motors are real cool, and might be pretty efficient as a battery charger to augment a solar installation(hence my interest), but unless I had a couple dozzen feet of water head to build a micro hydro plant that could run 24/7 backfeeding the grid, I would not contemplate something like this...

Here is hte info link I was thinking about earlier.
 http://www.educypedia.be/electronics/generatorasync.htm

Good Luck

Ron     
« Last Edit: March 25, 2008, 01:17:52 AM by ronmar »
PS 6/1 - ST-5.

LowGear

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Re: 3 phase 35 HP Inductive Motor
« Reply #6 on: March 25, 2008, 02:46:35 AM »
I live at Camp Aloha on the Big Island of Hawaii.  Hawaiian Electric Lighting Company or Helco as it's foundly known here charges about 35 cents a kilowatt and I don't forsee the price dropping. 

We are putting in a net metering solar system of about 3.5 KW which is nothing new to Helco or the county nor NRCS (grant guys).  With the equipment for DC synchronization I was first tempted to install a DC generating system but then heard about inductive motors and became fascinated.  This all started about a year ago when I saw my first Lister or Listeroid.  Then I heard a couple run.  My life has not been the same since.

Is there a support group?  I am willing to stand-up and admit my problem.  I believe I can even do a 12 step program all the way through.

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ronmar

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Re: 3 phase 35 HP Inductive Motor
« Reply #7 on: March 25, 2008, 05:15:05 AM »
Well now, depending on the acceptable range of DC into your inverter system, you may be able to use a 3 phase motor like an auto alternator to feed that existing net metering system.  I don't know your background, but this is what I am looking into.  An auto alternator is a 3 phase AC generator.  Those 3 phases are rectified into DC and combined. 
When you rectify single phase AC


into DC you get this.  There is a huge ripple which requires a large bank of filter caps to clean up.  The ammount of capacitance is related to the ammount of current being drawn so a high current filter bank would be massive.


When you rectify 3 phase AC and combine the outputs, all the tips overlap at a much higher voltage and you only get a fraction of the ripple.

The output DC would actually look more like this,only showing the waveforms above that point at which they meet.


This requires much less filtration to improve the DC quality.  Auto alternators typically have very little or no filtration and batteries deal with this ripple well and finish the cleanup process.  Something that I just learned fairly recently though is that because of their claw rotor design, auto alternators are not terribly efficient at turning mechanical into electrical energy.  Perhaps 50%-60% depending on load and RPM.  For years I thought they were better than that.  They were designed to provide power in a small lightweight package and they do that well. 

If you were to take an induction motor and add running caps to each leg, it would self excite when spun beyond it's syncronus RPM.  The ammount of capacitance controls the ammount of excitation and therfore the output voltage in this standalone generation mode.  If you then rectified and combined the output DC, you should be able to get the same low ripple waveform as above, but at nearer 90% efficiency? Now of course none of these numbers are even carved in mud, but I know some pretty smart people who think this is possible, and I have a 5HP 3 phase motor to experiment with so I plan on exploring the possibilities. 

Add to this a switching DC to DC supply to provide some regulation, or perhaps some switched capacitance to provide some regulation at the source, you might be able to get within the input specs for that grid tied DC inverter.  The good thing about the net metering inverter is that it's load should be pretty constant.  Up to it's capacity, either you are using the power or it is going back onto the grid. 

But again, you are on an island, if it isn't found naturally there for fuel, it has to be delivered and the utility producing in mass will probably win the price war.  With the ammount of coin in a grid tied solar setup, you might be better served with more panels, but then that dosn't get you a roid to play with.  One bad thing about a net metering system is that when you have a grid power outtage, your lights go out as well, even if you have good power comming from the panels(prevents backfeeding power down the line).  Now if you added batteries and just didn't use any power from the grid at all, the roid would serve the usefull purpose of topping up the cells during low sun and to provide for proper battery maintenance and equalization.  Self generation would allow you to maintain your power when the neighborhood goes dark(never happens in Hawaii:))

Ron
PS 6/1 - ST-5.

LowGear

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Re: 3 phase 35 HP Inductive Motor
« Reply #8 on: March 25, 2008, 07:34:00 PM »
Again, What great information.

We've been here for eight years and our longest outage has been four hours.  We get a couple of one or two hour gaps a year.  I'm really not up for batteries and their associated problems.

I'm meeting with the inductive motor / net metering expert of the island this weekend and will report back.

Thanks again,

LowGear
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