Lister Engines > Lister Based Generators

custom ST generator heads.

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RobD:
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:
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

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