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Author Topic: Generator to motor  (Read 21112 times)

dskira

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Generator to motor
« on: August 16, 2007, 04:07:10 PM »
Hi, I have a question:
If I use a let say 15 kw generator can I have a three phase 230/460 AC output and run a AC motor of let say 10 hp? Is the surge when I start the lectric motor will be to much and stall the generator?
Thank you for your expert help
Daniel

Doug

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Re: Generator to motor
« Reply #1 on: August 16, 2007, 06:54:44 PM »
If you are generating 3 phase yes you can run three phase loads.

Your starting surge on a large induction motor will vary from 3 to 6 times the name plate so this can be very hard for a small generating set to start. 10 Hp might be a stretch if its a high inertia load. A reduce valtage starter may be able to get you over the hump.

I don't believe in most residential settings you would be allowed to run a 480 or 600 volt three phases system and your insureance company may take issue with it even if you could
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dskira

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Re: Generator to motor
« Reply #2 on: August 16, 2007, 08:23:15 PM »
Thank you Doug, I appreciated your very insight respons.
I try to lean more about the relation between generator and motor.
The main idea behind the question is to try to put together a diesel/electric type of propulsion for a utilty boat.
I find the Listeroid weight (abolutly perfect) and performance (low rpm a real plus) quite perfect for the task, so the natural thought was inset of trying a direct drive thru transmission, investigate the electric propulsion with a Lister generator. The three phase looked appealing, the motor is solid, simple and reversible. But as I said, in the electical field I am a real newby, but I am really interrested to learn more.
Daniel


Doug

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Re: Generator to motor
« Reply #4 on: August 16, 2007, 08:54:34 PM »
There are special considerations for grounding and bonding on ships and I am not qualified to make sugestions for any marine power system big or small.

That much said the power of a roid and the small size of the generator and motor set leads me to thing you will probably waste as much energy as you will probably get at the shaft.

This works in ships because of the ecconomies of scale in large machines.....
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ronmar

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Re: Generator to motor
« Reply #5 on: August 17, 2007, 12:22:46 AM »
The last ship I served on was diesel electric and used large banks of rectifyers on the generator output and DC motors for propulsion.  The primary reason being low tech controllability.  It is far easier to control the generator output and motor torque using field current than to do it another way.  The Coast Guards newest polar research vessel, the Healey is also Diesel Electric, but she is AC and uses a very sophisticated pulse control network to control her motor torque.   

Ron
PS 6/1 - ST-5.

dskira

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Re: Generator to motor
« Reply #6 on: August 17, 2007, 01:02:16 AM »
Thank you all for sharing your knoweldge. I think something can be done, but Ronmar point out that it is more eazy to control a DC system than an AC system. I will investigate toward this solution also.
Please if somebody as other thought I will be glad to hear it.
I definitively want to put a Listeroid at work on a vessel, just the practical solution is not yet here, so I have to dig!

Doug

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Re: Generator to motor
« Reply #7 on: August 18, 2007, 03:45:55 AM »
I've worked on ASEA thyristor controlers originaly intended for small ships and large GE SILPAC systems.

I'm no expert on them, but I can say they offer the best bang for the buck in the simplicity and ecconomy area. I'm kind of scared of the new big all AC systems, mostly lack of experience....

I'm in love with the old, in particular clever electromechanical stuff like the Schrague system and Cycloconverters.

Doug

I'm not sure if an ST head can make clean enough power for the aplication but KB Penta electronics sells a line of very small and simple thyristor AC to DC drives. This might be something to look into.

Here's a couple of small ones by Minarik.
http://cgi.ebay.com/Minarik-DC-Motor-Drive-XL3050-used-working-115-230V_W0QQitemZ110159133962QQihZ001QQcategoryZ78190QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
I have seen larger....

I like these because they are all analog electronics and all the fine tuning is done with a screw driver ( no computures ) they are also simple 2 quad drives with no regen so they are simple as you can get.
« Last Edit: August 18, 2007, 03:51:36 AM by Doug »
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dskira

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Re: Generator to motor
« Reply #8 on: August 18, 2007, 05:36:04 PM »
Thank you Doug for your input, and appreciate your interest. Not easy to solveĀ  ???
If I understand well, it will be more easier to use a DC system to control the motor. But is the DC motor has to run on batteries only, or he can run directly from a DC genset (I try to avoid abtteries beside the one for the starter)
What is the device needed to control the speed and the reverse rotation of a DC motor?
Is the cable to transfert the current from the genset to the DC motor will be to huge? I was thinking about that when I thought about the AC three phase. My washing machine is on three phase AC and looks very simple to control and the wire is very normal normal in size. This was the start on my thought about using a AC three phase. But a washing machine and a electric motor traction for vessel are rather different I suppose!
It seams that the cycloconverter is the aparatus used to control the AC motor. Is the cloconverter can also reverse the rotation of the motor?
Thank you all for digging in your own knoveldge and to share it with me. I am learningĀ  :)

Doug

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Re: Generator to motor
« Reply #9 on: August 19, 2007, 03:58:13 AM »
This is cave man stuff....

Basicaly what the KB and Minarak drives do is chop up the AC power and convert it to variable voltage DC for the speed control you desire.

No batteries are required ( however I have used a drive something like this as a battery charger for a 250 DC system )..

What you would need for this aplication is one of the larger drives for something like a 3-5 Hp motor and a motor probably no bigger than 3 hp. The ST and Listeroid would run at a constant speed and generate 120 Volts or 240  ( what ever you chose, but I suspect the higher would be better ). For a Motor you would need to buy a a PM motor ( preminant magnet ) and speed control would be a matter of truning a 5 K speed pot to increase or decrease speed.

Doug

Check with your local Magnetek electric motor dealer....
My information is probably dated but the did sell a stripped down drive and motor combination that might be in your price range for this brand new. The Magnetek drive was infact a KB drive that 10 years ago sold for around 100 bucks for the smaller up to 2 hp and Motors were around 150 bucks. Can't recall prices beyond that
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Doug

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Re: Generator to motor
« Reply #10 on: August 20, 2007, 02:48:04 AM »
Been thinking about this....

A thyristor drive like the ones I showed you will not work with an ST using harmonic excitation.

The power factor at low speed will be very low and the voltage output from the ST head will droop badly.

The zero crossing dection part of the drive circut used to gate the SCRs may not be able to function properly. Same issues as the guys using UPS systems fed from ST heads are having.

sorry for possibly leading you down a blind alley dskira.

Someday I'll test a KBIC 120 drive I have with the ST head.

Doug
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dskira

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Re: Generator to motor
« Reply #11 on: August 21, 2007, 01:15:45 AM »
Doug I realy apreciate your comments. But I have to tell you, I am lost, and for me it's like trying to understand Chinese! I am sorry to don't be more receptive to your very knoweldgebale input.
Well perhaps the link I am missing is: how to control the speed and the reverse of a three phase AC motor.  Could you explain me what is the piece of equipment which do that, and don't forget you are explaining to a complete ignorant in that matter! Thank you.

Doug

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Re: Generator to motor
« Reply #12 on: August 21, 2007, 05:20:24 AM »
Well I often don't explain things well.

This little device
http://cgi.ebay.com/Minarik-DC-Motor-Drive-XL3050-used-working-115-230V_W0QQitemZ110159133962QQihZ001QQcategoryZ78190QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
converts AC power to variable voltage DC so you can run a DC motor at any speed you like. This is not 3 phase AC and probably won't work with a ST head.

Basicaly what I am saying is sadly I have no easy solution to your question....
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Holter

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Re: Generator to motor
« Reply #13 on: August 21, 2007, 09:41:18 AM »
Hi,

if you do not want to have any electronics it might be a possibility to get some good relais (I am sorry, but I do not know the correct english terms) and make the motor start with a lower power (is ist called star/delta?) If the asynchronous Motor has different windings you could also realize different reductions (Dahlander?) and of course reverse "gear".
The setup could be even more simplified with the use of a direct drive Permanentmagnet Generator. This way you could make a Transmission for various speeds without any gear, belt, clutch or semiconductor.

Christian

Hibbo

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Re: Generator to motor
« Reply #14 on: August 21, 2007, 05:11:39 PM »
To reverse a 3-phase motor you simply swap two of the phases over.

To control the speed and torque though requires quite complex power-electronics.

Torque depends on field current - so it is a case of adjusting the voltage across the motor.
Speed control is a bit more difficult as it depends on frequency.
Hibbo  -  Enjoying the Scottish 'summer'