Diesel electric locomotive
In a Diesel electric locomotive, the Diesel engine drives an electrical generator whose output provides power to the traction motors.
There is no mechanical connection between the engine and the wheels. The important components of the Diesel locomotive propulsion is the Diesel engine, the main generator, traction motors and a control system consisting of the engine governor as well as electrical or electronic components used to control or modify the electrical supply to the traction motors, including switchgear, rectifiers and other components.
In the most elementary case, the generator may be directly connected to the motors with only very simple switchgear.
Originally, the traction motors and generator were DC machines.
Following the development of high-capacity silicon rectifiers in the 1960s, the DC generator was replaced by an alternator using a diode bridge to convert its output to DC. This advance greatly improved locomotive reliability and decreased generator maintenance costs by elimination of the commentator and brushes in the generator.
The elimination of the brushes and commentator, in turn, disposed of the possibility of a particularly destructive type of event referred to as flashover, which could result in immediate generator failure and, in some cases, start an engine room fire.
A electric diesel locomotive's power output is independent of road speed, as long as the unitís generator current and voltage limits are not exceeded.
Therefore, the unit's ability to develop traction effort which is what actually propels the train will tend to inversely vary with speed within these limits.
Maintaining acceptable operating parameters was one of the principal design considerations that had to be solved in early electric diesel locomotives development and, ultimately, led to the complex control systems in place on modern units.
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