When I was younger, my parents owned a laundromat equipped with with a scary device called a "Bock Power Extractor." Basically, it was a giant 3 phase motor direct driving a tub full of wet laundy (about 20 lbs). Start it up and let it run for about 3 minutes, and you could suck about a few gallons of water right out of the load. When it got up to speed, that thing was going at 1725RPM.
That thing always scared the %^&*% out of me, especially when the mechanical braking system quit. When the brake didn't work, that thing would spin for a half-hour or more with the power off (and, because the lid unlocked when the timer stopped, some fool was liable to stick a hand in the unit to stop the drum).
Anyway, my father figured out that he could bring the thing to a stop fairly quickly if he put 2 legs of the motor through a big old dump load. Got lots of sparks, too, if the relays were even a bit misadjusted. And, every once in a while, the stainless steel containment shell would get a big-old dent if the load should get too unbalanced or the wobble bearing on the axle let go.
I'd be willing to bet that that thing sucked up a lot of electricity starting up -- not that we cared because back then the power company didn't meter us for 3 phase from the pole (very few people knew what to do with it, was their thinking, so it was an absurdly low flat rate). I'd hate to think what we would have paid if we were metered on the Bock -- and I doubt we would have gotten great efficiency out of it if we had tried to recover some of it off the dump load.
Every time I hear about flywheel storage, I get nightmares about that old Bock blowing up in my face.
