Quote:
Originally Posted by instarx
That makes no sense. A generator is not a transmission. A motor is not a transmission, wiring to connect the two is not a transmission. Frankly, I don't know if there is a transmission between the drive motor(s) on a locomotive and the drive wheels, but even if there were it would be mechanical.
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Instarx is correct in the assumption that locomotives are hybrids...
They are
"Series" or "Serial" hybrids. The ICE turns a generator that produces electricity for electric traction motors that turn the axles through gears. These motors are pre-geared from the factory. Locos used for higher-speed operation between terminals are geared differently than those used to shuffles cars in railyards. The amount of torque involved would make "shifting gears" too strenuous on components, so the ratio is fixed. With the current technology, railroads are required to purchase models with pre-configured gear ratios.
To spare brake linings, overheating, and a potential runaway condition, many of these locomotives have the ability to switch their motors into generators for "Dynamic Braking". When activated, the system forces the motors to become generators themselves, in-turn creating their own electricity and producing a braking effect. The spent electricity is dissipated as heat in large, air-cooled, resistor grids. The Diesel engine is accelerated to increase the resistance through the generator.
The advent of AC traction motors has made it possible to to manage larger loads in one locomotive unit more efficiently and accurately (the vast majority of these motors have been DC over the last 60 years). Depending on your location, you may see 2 engines at the front, and one "pusher" at the rear of a coal train. These are newer, carefully configured AC units designed to transport an abnormally heavy configuration.
Hybrid cars like the Prius are
"Parallel" hybrids, where the energy can be stored in some fashion and make use of a transmission-like device to change gear ratios and/or the power source for propulsion, and are preferred for efficiency in vehicle operation.
There are other hybrids (hydraulic/electric, etc.) that can be compared.
RH77