The railroads have been using DE since the 1930's, so it's not really anything new. When stopping, slowing, or maintaining speed on a decending grade, we use Dynamic Braking. Basically, the traction motors on each axle are reconnected to work as generators. The throttle handle becomes a notchless rheostat. The further into it's range of travel you move it, the more electricity is developed by the traction motors, & the more braking effort is developed. The heat generated is dissipated through fan blown grids. Some of the energy developed is used to power the grid fans. Maximum DB will develope about 900 amps per traction motor, more than enough to slide the wheels, if wheel/rail adhesion is less than perfect. On BNSF, we are limited to about 28 axles of DB effort on a conventional train, any more that that, can cause damage to, or squeeze out cars near the head end, and can turn over ourside curve rail in some cases. Pulling, wide open at walking speeds, I've seen 1800 amps per motor many times. We have to observe short time ratings then, to avoid smelling plastic & slinging solder from the motors. They will usually take around 1200 amps continous, depending on gearing, & HP per motor. Years ago before diesel electrics, some RR's used straight electrics on mountain grade districts. The trains on decending grades using dynamic brakes fed the electricity generated by the traction motors back into the trolly wire, rather than having it go to the atmosphere as wasted heat energy. It was said the trains moving down grade were actually helping pull trains on the upgrade, with the electricty they were making.
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