Bob, we do it 24/7. They are 600VDC traction power compound motors on all the truck assemblies. The 600VDC comes from rectified 480 3PH. When your rectifiers can put out over 10,000 amps each, you can't just slap a capacitor on to filter out the bumps. What you can do is take advantage of the relative phase shift of d/d Vs d/y secondaries. The rectifier outputs feed a common DC bus. The positive peaks are shifted, reducing the ripple amplitude. This along with rail inductance, smooths out the 600VDC supply. Add to this the fact that most rail sections are fed from both ends. Many substations have 3 rectifiers. If one has 2, d/d and 1, d/y, the next will typically have 1, d/d and 2, d/y. As you can probably imagine, there is absolutely no regulation. 600 is just what we call a voltage that usually isn't.
Joe
