Can a 3 phase motor be somehow used as a generator?

On 19/11/2013 4:29 PM, Lloyd E. Sponenburgh wrote:


In proper circumstances they work well- such situations would be similar to the Scottish application where advantage can be taken of small streams, using a turbine and induction motor. The motor can be run up as a motor-then the turbine gates are opened(or in reverse order). No synchronizing or voltage control needed. In such a remote application, it is simpler and cheaper than a synchronous machine. True- they must have a source of excitation and need to draw reactive from the grid or grid + capacitors and in the latter case varying loads are a problem. They cannot supply reactive to any load, nor can they (without some other source of reactive) operate if the grid connection goes down.
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wrote:

IIRC when I was in high school or even a bit before, our class visited a Consolidated Edison power plant in Manhattan. The were using turbine driven alternators. At that time, a much smaller machine on the shaft to provide dc excitation for the alternator's armature. Years later, with what I think was the 1965 East Coast blackout, external auxiliary power seemed to have taken over.
I remember an IEEE trip to San san Onofre. They were rethinking reliance of offsite auxiliary power. They were thinking of diesel driven generation rather than attaching dc machine onto alternator shafts.
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Sam

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On 19/11/2013 7:42 PM, Salmon Egg wrote:

In early days, and external DC machine was commonly used but later on it was mounted on the alternator shaft - in some cases there were two DC machines- one supplying the alternator field and the second smaller machine supplying the field of the larger machine. Common in hydro plants such as those at Shipshaw, Kemano, Grand Coulee, etc. In later years, such things as magamps replaced the pilot exciters (faster response) and modern units use fully electronic control- there is feedback from the alternator through scr's supplying a stationary winding which induced AC in a 3 phase winding on the rotor- which feeds the alternator field through a bridge, essentially making it self excited and no commutators/brushes involved. Smaller, cheaper, less maintenance and more responsive than the old exciter/pilot exciter The idea of a separate on site power source for auxiliaries is common -Grand Coulee has some auxiliary units. Tthese were not used for excitation. Hydro plants do have the advantage that even a good battery bank will supply control needs and allow start up- the rest follows. Thermal plants have higher needs (feedwater pumps, etc) so a hefty source is needed to get a unit up and running. The problem in the 65 blackout was that many thermal plants were isolated and some form of external power (or internal diesel units) was needed to get a unit on line to supply other thermal plants. Hydro plants could quickly be brought on line- although for a while, they were restricted due to the need to get thermal plants up rather than immediately supply other loads.
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<...> >An extreme case that I know of was where a farmer with a single phase

Why didn't he just use a rotating phase converter? A three-phase motor is often the cheap solution. These are often used by hobbyists to make use of surplus three-phase power tools.
http://www.kayind.com/basics/what.htm
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On 20/11/2013 2:10 PM, snipped-for-privacy@attt.bizz wrote:

Essentially a 3 phase induction motor at no load and excited on only one phase is a single to 3 phase converter. This is what I was referring to in the farmers case- I got off topic.
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I guess I misread what you posted. It sounded like you had a large motor driving a smaller single-phase motor. Haven't seen that before. I have seen the unloaded three-phase motor used as a phase converter many times.
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It sounded to me like the small single phase motor just spun up the three-phase rotary converter. jsw
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On Thu, 21 Nov 2013 18:17:25 -0500, "Jim Wilkins"

Yes, I guess that makes more sense. Don?
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On 21/11/2013 4:34 PM, snipped-for-privacy@attt.bizz wrote:

Yes-I didn't state it clearly, the single phase motor was used only to rotate the larger motor.
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On Sat, 16 Nov 2013 20:03:47 -0600, "Lloyd E. Sponenburgh"

Not true. Induction motors CAN be used as generators Usually using a bank of capacitors. Look up induction generators.
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snipped-for-privacy@snyder.on.ca fired this volley in

Clare, exactly how many weeks does it take you to read and respond to a two-line post?
Did you even consider reading the rest before making an inane comment like that?
Sure, Clare... I make a "generator" out of a cork with two wraps of coathanger wire around it, too.
But in BOTH cases, they're lousy generators.
Why don't you spend a little "more time" reading. Hell... you've only spent three weeks, and you've gotten all the way throught the first three posts in a hundred-post thread!
Lloyd
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Ignoramus26083 wrote:

The home power crowd has used big induction motors as alternators for years. One big problem is you have poor/no control of frequency. You spin the motor at somewhat above synchronous speed, and you get a frequency lower than the actual rotor speed, due to slip. It works exactly like the induction motor except everything is reversed. It is called an induction alternator. There area couple other problems with this system. It will not self-excite under load, and if momentarily overloaded output will collapse and you will have to remove all load to get the alternator re-excited. To maintain excitation, you need to put substantial capacitor banks across the terminals. You adjust output voltage by adjusting the resistive load on it, I think, and adjust frequency by varying RPM. If the motor was a 1750 RPM motor, the slip at rated load was 50 RPM, so you'd spin it at 1850 RPM to get something close to 60 Hz out.
If you Google induction alternator and maybe some things related to off-grid power, you should turn up plenty of info.
Jon
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On Saturday, November 16, 2013 8:50:33 PM UTC-5, Ignoramus26083 wrote:

If you connect a internal combustion engine to a " phase converter " , and arrange the gearing between the phase converter and the engine so the engin e puts power into the system, you will have a three phase generator. Could be useful if you wanted to run a honking big three phase welder and did no t have an electric outlet that would provide enough power for the welder.
Dan
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posted some

With a little help certainly.
See instructions for both 3 PH and 1 PH at link below. It does work although I'd use a DMV in conjunction with his "light bulb test".
http://www.redrok.com/cimtext.pdf
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a generator tends to be fed DC power to setup the magnetic field to get things going. Induction motors don't need this. An induction "motor" with a DC winding is an alternator.

yes, under some conditions, but it's as others said, wonky in behavior and not useful outside of experimenting out of curiosity.
You could use an alternator as a motor, but again, it's not optimal and just something you might do for fun.
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Thanks. This makes sense.
i
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http://www.dailymail.co.uk/news/article-2497637/Three-20-year-old-programmers-build-working-Obamacare-website-just-days-government-do.html
<snip> While the Obamacare website still remains broken, three 20-year-old programmers have shown the government how it should be done.
Ning Liang, George Kalogeropoulos and Michael Wasser developed a site in matter of days - and it does things the expensive and faltering healthcare.gov can't do.
From a San Francisco office the men have built HealthSherpa.com, which presents the Affordable Health Care Act data in a much simpler way to the government website.
Problem solving: The three 20-year-old programmers developed a site in matter of days that does things the expensive and faltering healthcare.gov just can't do.
<snip>
'They got it completely backwards in terms of what people want up front,' Liang told CBS News. The programmer continued: 'They want prices and benefits, so that they could make the decision.'
HealthSherpa.com, which is just two weeks old, allows a user to simply input their zip code and view all the health plans available to them. <snip>
Note this is a UK paper. Why isn't this all over the US media?
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message

The excuse I heard was that such a site would reveal the alarmingly high raw cost and couldn't adjust for subsidies without the user's data. Mustn't frighten the herd, you know.
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http://www.dailymail.co.uk/news/article-2497637/Three-20-year-old-program mers-build-working-Obamacare-website-just-days-government-do.html

The above fairly accurately describes how the system works where I live...
In essence, each state has a different set of insurers and laws, all of which adds a tremendous amount of complexity where it concerns attempting to cover all contingencies using a single software suite that must interface with databases which are independantly maintained by some 36 different states...
In other words, if your state decided not set up it's own exchange, then you mostly have yourselves to blame--especially considering that in many cases, the decision was made of belligerance and spite.

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On 11/19/2013 6:26 AM, F. George McDuffee wrote:

it is all over the US media - at least the stations I listen to. Maybe Fox news doesn't want to air it
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