The electric tender idea is similar to an idea that I first
proposed more than a decade ago. (If you search, you may
find discussion of this idea in some newsgroup or or mailing
list from way back when.)

Trains is currently holding a piece with a more
detailed explanation.


Basically, my idea is this: You have a three-unit set of
power that is approximately equal to the three units used
on many mainline trains. This set consists of a C-C
diesel electric, a B-B straight electric, and a C-C diesel
electric.

All axels of the above have traction motors. A modern
electric can draw substantially more power than it can
feed to its own traction motors.

The way this set works is that under wire, the electric
draws power from the wire and feeds power to the traction
motors on the diesels, which are acting as slugs. Their
prime movers provide adquate ballast weights.

In non-electrified territory, the electric becomes the
slug. Its transformer is its ballast weight. The traction
motors on each end are fed from the adjoining diesel.


This uses existing slug technology. The reasons railroads
use slugs now is that under certain conditions, particularly
at start-up, the prime mover of one disel-electric produces
more power than the traction motors can use -- so, you may
as well distribute some of that energy to other traction
motors.

Yes, you would need to make modifications to the diesel-
electrics used in these sets, but that would be far less
expansive than buying whole new electric motive power and
changing locomotives at the ends of the electrified segments.

For straight electrics being built for this type of service,
you would need a higher-rated transformer than is used when
the electric operates by itself. But, if you've been inside
a modern European straight electric, the transformer is
surprisingly small and there's actually lots of empty space.


I have run this concept by an acquaintance who is a senior
professor of electrical engineering at a major university --
as well as a railfan, familiar with railroad operations -- and
he says it makes sense.

Yes, you need high-voltage connections between the units, but
that is also now easier than it was some years ago.

Implementing controls that let the diesels control the electric
functions, such as operating the pantograph, is really not all
that difficult. Most locomotive management functions these days
for both straight electrics and diesel-electrics is done with
software. You would need to modify the sofware and have a robust
data bus that runs between the units that not only handles control
commands but which can also report back the status of equipment on
each of the units.


Yes, this is not a perfect solution for all operating situations.
But it would work for many long-distance trains. In territory where
you now use manned helpers, you may also want to use a straight
electric helper either at the back of the train or cut into the train.

European railroads so use electric DPUs on electrified lines, where
a remote electric is controlled from the head end.

-- Ernest