Poll

Would anyone be interested direct drive generators?

12 pole 600 RPM
4 (100%)
8 pole 900 RPM
0 (0%)

Total Members Voted: 4

Author Topic: custom ST generator heads.  (Read 10985 times)

n2toh

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custom ST generator heads.
« on: December 26, 2005, 07:31:47 PM »
If we can get new rotors wound with the extra poles the generators can be direct driven, I think that this configuration is more reliable than belt driven installations.

EDIT I should have clarified the direct drive generators are intended to be driven by a 2 cylinder engine.
« Last Edit: December 26, 2005, 10:23:45 PM by n2toh »
About 60 years is all it takes to make science fiction a reality.

quinnf

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Re: custom ST generator heads.
« Reply #1 on: December 26, 2005, 08:44:24 PM »
   :o  The inertial loads imparted by a one-lung diesel on a direct driven generator rotor would tear it apart.  Belt drive is really not a bad compromise.

Quinn

EDIT:  Same difference on a two cylinder.  You've got a power stroke, then another 180 degrees later, then the engine coasts (slows down) for another 540 degrees (a turn and a half) then another power stroke, followed 180 degrees later by another.  This is not a friendly engine to directly couple to. 

Actually, go out and find ANY diesel that is direct coupled to a generator.  I bet there aren't any.  Perhaps you could use a flexible rubber coupler, but from what George has on his site regarding the mighty Changfas he has done that with, they tend to mash the rubber couplers in short order. 

The belt we're talking about here is a flat serpentine belt, not a V-belt.  They are very efficient, and that efficiency is the primary reason car companies no longer use v-belts on new designs. 

I don't want to belabor the point, but . . . well it looks like I am doing just that!   :P
« Last Edit: December 27, 2005, 04:10:20 AM by quinnf »

hotater

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Re: custom ST generator heads.
« Reply #2 on: December 26, 2005, 09:07:13 PM »
I agree with Quinn,  the belt takes up some of the firing impulse stresses and keeps stress off the rotor AND the connection between the two..  I've got 3400 hours on my first serp belt and I don't see a problem with that many more.
7200 hrs on 6-1/5Kw, FuKing Listeroid,
Currently running PS-Kit 6-1/5Kw...and some MPs and Chanfas and diesel snowplows and trucks and stuff.

RobD

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Re: custom ST generator heads.
« Reply #3 on: December 27, 2005, 05:27:50 PM »
I think the operative word in n2toh's post is that they "can" be direct driven. That does not mean that they "have" to. These units "can" also be belt driven, with any engine, all you have to do is match engine RPMs to Genhead RPM with the appropriate pulleys. It has been many years (25+) since I did motor theory in skool but what I can remember is that the more poles you have the smoother the power generation will be. I know that this is true with motors and I think that it is also true with generators. So from a smooth power perspective (think PC's and other electronics) this might be a good idea.

RobD.

trigzy

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Re: custom ST generator heads.
« Reply #4 on: December 29, 2005, 03:43:58 AM »
"  The inertial loads imparted by a one-lung diesel on a direct driven generator rotor would tear it apart.  Belt drive is really not a bad compromise."

"Actually, go out and find ANY diesel that is direct coupled to a generator.  I bet there aren't any.  Perhaps you could use a flexible rubber coupler, but from what George has on his site regarding the mighty Changfas he has done that with, they tend to mash the rubber couplers in short order. "

A couple comments regarding these points, just for clarification:

I sell 3600RPM single cylinder diesel gens that direct coupled.  I have yet to have one "tear" apart on me, and some units have over 1500hrs on the meter.  (Surprising, given that they are chinese, I wasn't really expecting that much life out of them)

Large commerically produced generators 15+ KVA are all direct coupled, some (expecially the larger ones) without a rubber coupling.  There is just no easy way to move dozens to hundreds of horsepower without creating extra heat/losses and using up a tonne of space.

Granted, these units are all precision made, and aligned at factories, and it's probably not as practical for a lister, but it is probably much more widely used in reality than our serp belts.

Steve
Power Anand 24/2, Brushless 20kW, some other antique iron.
Vendor of AVR's, Small Clones of Yanmar Diesel and Honda Gasoline Engines

quinnf

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Re: custom ST generator heads.
« Reply #5 on: December 29, 2005, 05:22:47 AM »
Ok, Steve, you got me.  I shouldn't have said "any" diesel. 

My point was/is, made in the context of this forum, where the subject is old-fashioned slow speed single and odd-firing twin cylinder engines with huge displacement/power ratios that apply enormous torque for their size to the load.  Direct coupling such an engine to an ST-something generator with a reconfigured rotor, which is what the original post was proposing, isn't (just my opinion) a worthwhile proposition, given that the losses inherent in driving the generator with a serpentine belt are very small.   ;)

Quinn

« Last Edit: December 29, 2005, 05:25:06 AM by quinnf »

trigzy

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Re: custom ST generator heads.
« Reply #6 on: December 30, 2005, 04:49:19 AM »
Agreed on all points.  How about a chain drive?  Any issues??
Power Anand 24/2, Brushless 20kW, some other antique iron.
Vendor of AVR's, Small Clones of Yanmar Diesel and Honda Gasoline Engines

SHIPCHIEF

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Re: custom ST generator heads.
« Reply #7 on: December 30, 2005, 05:48:39 AM »
Chain drive needs oil, and is probably noisy. Serp belt is great. As soon as you see one work you'll be hooked :)
Scott E
Ashwamegh 25/2 & ST12
Lister SR2 10Kw 'Long Edurance' genset on a 10 gallon sump/skid,
Onan 6.5NH in an old Jeager Compressor trailer and a few CCK's

quinnf

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Re: custom ST generator heads.
« Reply #8 on: December 30, 2005, 06:00:41 AM »
Chain has real advantages for DIYers.  Transmits about 98% of the power to the load and as long as it's not too closely coupled, has good shock absorbing properties.  It's readily found in many sizes, is cheap and easy to work with, available in any length, truly modular. 

However, if you look at how power is transmitted in industrial settings you will find that cogged and flat belts (not lossy v-belts) are the standard for delivering power, and have been for many years.  Chain is used mostly for low speed applications.  As a further indication of the direction power transmission is moving, note that more new street motorcycles are appearing with belt or shaft drive.  Less maintenance (no oiling, smoother operation), and don't wear out expensive sprockets.

Quinn

Stan

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Re: custom ST generator heads.
« Reply #9 on: December 30, 2005, 06:06:53 AM »
They recently tore down an immense (largest in N. America, maybe the world) Silver/Lead/zink concentrator in my hometown (the Sullivan mine).  I was priveleged to get a tour by a lifetime worker (now retired).  When I commented on the drive mechanism that coupled the immense electric motors (larger than a VW Van) which drove the crushers he just laughed.  They used 1" manilla rope, tied in loops as drive belts, sometimes fifteen or more of them on a single crusher pulley.  He explained that the pulses caused by large chunks of ore being crushed destroyed even the most complex and high tech couplers/clutches but when the crusher jammed or destroyed the ropes, they just smoked (thereby signalling another $5 replacement part).  He also maintained that many of the rope "belts" lasted many months in the worst environment you could imagine.  Sometimes KISS is better!
Stan

RobD

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Re: custom ST generator heads.
« Reply #10 on: December 30, 2005, 04:55:48 PM »
Yep, Back in Northern Ireland, where I come from, most of the linen and flax spinning mills were powered by steam engines. These steam engines drove a main shaft that ran the length of the mill by means of a rope and pulley system. Our local mill (in Bessbrook) had a 160HP engine that drove an 8 rope pulley. The various machines were then driven off the main shaft via flat leather belts.

RobD

justsomeguy

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Re: custom ST generator heads.
« Reply #11 on: January 16, 2006, 07:33:51 AM »
I don't want to beat a dead horse here, but couplers on larger diesel gensets don't exist.  The generator head only has one bearing, and that's in the back.  The front of the rotor is bolted directly to the flywheel of the engine.  The rear main bearing of the engine doubles as the front bearing of the generator head.  Of course, it's aligned very carefully.  They are also matched and harmonically balanced to the engine.  This is also why paralleling them is a task best left to machines, and not humans..... because there’s no coupler to give if it’s done wrong.  Something larger will break.

Most quality generators over a few dozen KVA also have damper windings in them.  This includes even large steam and hydro power plant generators hundreds of MW in size. Basically it's a squirrel cage induction motor (asynchronous machine!) embedded in the face of the rotor.  A hybrid, if you will.  There are several reasons for this. 

1)the pulsations of the engine make the rotor bounce forward and backward in phase, and every time this happens, the squirrel cage cuts across magnetic lines of force, (slip!) and resists the change.  It's somewhat of an electromagnetic shock absorber.  Why muck around with a flexible physical coupler when you can put the elasticity in the magnetic coupling inside the machine?  The magnetic coupler won’t wear out like the physical one will.

2)When connected to the "solid" grid, the shock absorber for every pulsation of the engine becomes even more important, and removes some of the stresses from the rotor windings, and keeps the flux more constant in the rotor core.

2a)Huge masses such as those in a multi hundred megawatt turbine generator set have more inertia than the local grid.  In this case, THEY are solid, and the grid needs to be able to flex forward and backward in phase without destroying them.

3)It makes the synchronous machine double as an asynchronous machine if it pulls out of phase, and jumps ahead or behind by 360 degrees....  it's much less likely to continue to jump as the damper windings will drag the rotor one way or another and cause it to "lock in" again.  Without damper windings, once slip starts, it usually won't stop without external intervention of some type.  Assuming that a purely synchronous machine can even survive prolonged slip.

4)In some applications where it's used as a synchronous motor, the unit can be synchronized without the synchronous magnets energized.  It just motors up like an induction motor! (because it is!).   Or, the getset gets close to the desired RPM, and it's connected to the grid and slips like an induction motor/induction generator.  Once it gets very close to synchronous speed, the magnets are slowly brought up, and the machine eventually locks in and behaves like a regular old boring synchronous motor, or generator.  All the efficiency of a synchronous machine, with some of the ease of use, and forgiveness of an asynchronous machine.


If the crankshaft and flywheel on the lister can take the stress, a direct coupled generator head can take the stress.  Damper windings would probably be absolutely necessary for grid interconnection.  And they’d be nice even for stand alone operation.  A 12 pole machine would be way cool!  Could the rotor winding for a 12 pole, 600 RPM machine be based on the general design of the Lister flywheel?   The idea isn’t mine, but rather from something I’ve seen before.

Old Fiarbanks-Morse diesel gensets at a local municipal  utility (900 and 1200 RPM, 600-1800 horsepower) are coupled up to generators that look like skinny flywheels at the end of a shaft surrounded by windings.

here’s a link, you’ll know what I’m talking about when you scroll down the page.

http://www.argylewi.org/serv_electric.htm

By the way, that’s NOT my local utility.  Just a quick example of a picture of that type of generator set up.

-Jerry