There are cases on record where the plain flywheels of steam engines (designed to only store the
inertia of 1 revolution) burst with disastrous results. A flywheel burst ranked right up there with
a boiler explosion.

Bob Swinney
"DoN. Nichols" wrote in message
...
On 2008-07-19, Bruce L Bergman wrote:
On Sat, 19 Jul 2008 04:33:40 -0700 (PDT), wrote:

At a local plant, there once was a computer center. The room was fed
with a motor generator to provide clean power to it. I made an
inquiry and the unit might be available.

It has been years since I saw it, but it was a motor, probably 480
3ph, driving a generator with a large flywheel between them.

[ ... ]

They were a good low-tech idea in their day, even if they weren't
very efficient considering all that mass you had to keep spinning.

Well ... They could still save money, by improving the power
factor seen by the service meter.

The ones that were motor=clutch=generator=clutch=engine would
provide output with only a momentary frequency and voltage sag as they
switched over - as long as the engine was kept hot and ready, and it
started normally when they dropped the clutch...

Hmm ... the one where I used to work -- used to keep the chem
lab exhaust blowers working during a power outage -- was a little
different:

motor/generator=flywheel=flex-coupling=clutch=diesel-engine

and when the power failed, and the flywheel cranked the diesel to an
instant start, the three-phase motor became the generator.

But make DAMNED sure you rebuild the bearings before you put it back
in service, and have thermostat sensors and alarms on all the shaft
bearings. Top and bottom halves of the shells.

This is not enough, as proven by what happened to ours. There
were big self-aligning roller bearing assemblies in pillow blocks with
lubricant piped into the shells by rubber hose from reservoirs on the
side rails. There was a thermal switch in each pillow block. One day
on a long weekend the rubber hose got brittle enough to break and drain
all of the oil onto the floor from one pillow block (luckily the one
towards the motor, whose bearings provides some support).

The guard force were the only ones there to hear the screeching
noise form the bearings, and they didn't know who to call. (They should
have, but they didn't. :-)

By Tuesday (long weekend, remember) when the fellow who they
should have called arrived, heard the noise, and shut the system down
(there was a bypass, at least) that bearing was *hot*.

How hot? Well ... the rollers were the size of 35mm film
cassettes, and one which I collected had a lip which *looked* like a 35mm
film cassette, smeared off the steel of the bearing -- all blue-black.

The thermal sensors which should have shut this down
automatically? They were depending on the oil to conduct the heat from
the failing bearing to the sensor -- remember -- the oil in a puddle on
the floor? :-)

FWIW -- they replaced both bearings (but not those in the motor,
which now that I think of it might have been carrying a lot of the load
which the failed bearing should have handled.)

With that much energy stored in a huge rotating mass, if one bearing
gets hot to the point of seizing up I can guarantee that all nine
circles of hell is going to break loose very quickly....

Let's see -- 4' diameter flywheel, about 6" thick, running at
1800 RPM ... If it had broken free, it would have run through the
external parts of the air conditioners, and then run through the office
section of the computer center across the parking lot. Still -- nobody
was supposed to be there on a long weekend anyway. :-)

It has happened in the past, and it will totally trash the power
room and anything else that gets in the way like a bull in a china
shop - including people running to find out what all the commotion is.
People are soft and squish quite easily in those situations.

It was pure luck that it was the bearing towards the motor which
went, instead of the one towards the flex coupling and clutch.

Enjoy,
DoN.

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