I remember hearing stories (not a personal experience) about curing the
coatings on coils of heavy wire in a wire manufacturing and coating plant.
They ran DC current into many of these in series to heat them up. When they
disconnected the power source, the resultant arc from the collapse of the
magnetic field caused some real problems.

They solved it by dumping the energy into a synchronous inverter that put a 3
megawatt surge into the power line. The power company didn't even notice it
apparently.

The work in developing that synchronous inverter was used to manufacture and
market the Gemini inverter, used in many DC windpower installations to use the
power company as a storage system instead of batteries. Now, most wind systems
use 3 phase motors as the generators. Large DC systems are still being used
though with newer inverters giving much better control of the wind machine.
The biggest advantage is that the blades aren't limited to one or two speed
ranges but can vary according to the wind speed.

Earle Rich
Mont Vernon, NH