The diesel engine in a locomotive is not what turns the wheels;
rather, it turns a generator that powers electric traction motors
that drive the wheels. At slow to moderate speeds, a four-axle
locomotive with a 3,000-horsepower diesel engine produces more
electrical power in its main generator than it can use by itself.
This allows for use of a “Mother-Slug” set in certain
applications.
In a Mother-Slug set, the Mother is a conventional diesel
locomotive that sends its excess electrical power via large cables
back to the Slug, which is similar in general appearance to a
normal locomotive except that it has only traction motors. A
Slug does not have a diesel engine, generator or other components
necessary for a "stand alone" locomotive. The Slug contains a large
block of ballast to replace the weight of the engine, providing
sufficient weight for the Slug to provide traction and pulling
ability.
Coupling a Slug to the Mother allows the Mother locomotive’s excess
electrical power to drive the Slug’s traction motors essentially
for free, using only the power from the Mother. This provides
significant fuel savings compared to using two diesel locomotives,
as well as producing less exhaust emissions. Mother-Slug sets have
been proven to reduce fuel consumption by more than one-third
compared to a pair of conventional locomotives, while benefiting
the environment by discharging much less air pollution.
The Canada, New York/Ohio/Pennsylvania, Oregon and Southern Regions
of GWI currently have 14 Mother-Slug sets in operation.
Next:
Auxiliary Power Units (APUs)