[Milsurplus] Motor Generator Sets

[Mike Morrow]

Ken wrote:

> I can imagine what a room full of those big MG sets sounds
> like, though. That would be way over-kill to my ears. I
> wouldn't like that.

The nuclear submarines of my era had large port and starboard 250vdc to 450vac 60Hz MG sets.  Power flowed either way...a 450vac motor turned a 250vdc generator for ship's main battery charging.  Upon loss of reactor steam-generated 450vac power, they turned instantly into a battery-supplied 250vdc motor turning a 450vac generator.  These were large MGs, but like everytbing on a submarine, they were pretty quiet.  We had other MGs as large as 64kW that generated all the 400Hz power needed for missile and torpedo and navigation and weapons fire control systems.  These MGs were also quiet.  None of our MGs were painful to be near for hours each day, day after day, for more than 70 days.  (But I do have terrible hearing, three decades later.)

At some commercial nuclear power stations designed more than 50 years ago, MGs are or were common, including MMG (motor-motor-generator) sets that used an AC motor on the same drive shaft as a DC motor, all driving an AC generator.  That ensured power continuity by having the DC motor ready to instantly assume the load if AC drive power went away.

Very large MGs with 4160vac motors were used to drive AC generators through variable-speed couplers in order to vary the output frequency of power sent to reactor recirculation pumps.

There are even moderate-sized MG sets with a 480vac motor turning a 480vac generator.  That doesn't seem to make a lot of sense...but it was for fault isolation.  The MG isolated the power distribution upstream of its motor supply from a gross electrical fault on the generator side.

Large room-filling solid-state converters and inverters have replaced nearly all of these old MG and MMG sets.

All of those commercial MGs were very unpleasant to be around without good hearing propection.

Mike / KK5F