Distributed traction

In rail transport, distributed power (DP) refers to the physical distribution—at intermediate points throughout the length of a train—of separate motive power groups. Such 'groups' may be single units or multiple consists, and are remotely controlled from the leading locomotive. Distributed Power (invented by General Electric in the United States) allows locomotives to be placed anywhere within a train when standard multiple-unit (MU) operation is impossible.

The system allows up to 10 additional radio-controlled locomotives to be distributed with control signals for power and dynamic brake settings via dedicated radio frequencies. The DP units have their air brake systems set up so that brake pipe reductions affect them just as they do rail cars in the train. The system is highly automated and each DP unit to be added is entered by road number into the control display of the lead locomotive. In the DP units the same thing is done with the lead locomotive's road number and once the systems are properly set, the units are "linked" via radio frequency.

The greatest benefit of Distributed Power—and the reason for development of the original concept—is the reduction of drawgear draft forces, permitting the doubling in the size of trains without exceeding draw-gear strength, through the use of mid- or rear-train locomotives. There are also potential train handling benefits; over an undulating track profile, a skillful engineer can manipulate the relative power outputs (as well as dynamic and air brake applications) to minimize run-in and run-out of coupler slack throughout the train."

Reduced draft forces along a train will reduce the lateral force between wheel and rail on curves, thus reducing fuel consumption and wear on various running-gear components as well as the potential for a 'stringline' derailment.

Another benefit is quicker application of standard air brakes. With all braking control at the front on a conventional train, it can take several seconds for brake-pipe pressure changes initiated by the engineer to propagate to the rear. Under radio-controlled distributed power operation, the brakes are set at remote locomotives simultaneously with the command initiated on the lead locomotive, providing a more uniform air brake response throughout the train.

The main disadvantage is the operational time needed, and track configuration required, to add and remove additional locomotive consists. Secondary disadvantages are the costs associated with equipping locomotives with the extra control apparatus and the potential for the intermittent loss of the telemetry signal. This latter is known as 'Communication Interrupt' and is coped-with by fail-safe software controls.

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Wikipedia