GE locomotives, throttle controls
GE locomotives and diesel locomotives prime mover's power output is primarily determined by its rotational speed RPM and fuel rate, which are regulated by a governor or similar mechanism.
The governor is designed to react to both the throttle setting, as determined by the engine driver and the speed at which the prime mover is running.
GE locomotives power output, and thus speed, is typically controlled by the engine driver using a stepped or "notched" throttle that produces binary-like electrical signals corresponding to throttle position.
This basic design lends itself well to multiple unit operation by producing discrete conditions that assure that all units respond in the same way to throttle position.
North American locomotives, such as those built by EMD or General Electric or (GE locomotives), have nine throttle positions, one idle and eight power as well as an emergency stop position that shuts down the prime mover.
When the throttle is in the idle position, the prime mover will be receiving minimal fuel, causing it to idle at low RPM. In addition, the tractive motors will not be connected to the main generator and the generator's field windings will not be excited or energized, the generator will not produce electricity with no excitation.
Therefore, the GE locomotive will be in "neutral". This is the same as placing an automobile's transmission into neutral while the engine is running.
To set the locomotive in motion, the reverser control handle is placed into the correct position forward or reverse, the brake is released and the throttle is moved to the run 1 position the first power notch.
An experienced engine driver can accomplish these steps in a coordinated fashion that will result in a nearly motionless start.
The positioning of the reverser and movement of the throttle together is basically like shifting an automobile's automatic transmission into gear while the engine is idling
Placing the throttle into the first power position will cause the tractive motors to be connected to the main generator and the latter's field coils to be excited.
With excitation applied, the main generator will deliver electricity to the tractive motors, resulting in motion. If the diesel locomotive is running light, or no train car coupled to it and is not on an ascending grade, it will easily accelerate.
On the other hand, if a long train is being started, the locomotive may stall as soon as some of the slack has been taken up, as the drag imposed by the train will exceed the tractive force being developed.
An experienced engine driver will be able to recognize an impending stall and will gradually advance the throttle as required to maintain the pace of acceleration.
As the throttle is moved to higher power notches, the fuel rate to the prime mover will increase, resulting in a corresponding increase in RPM and horsepower output.
At the same time, main generator field excitation will be proportionally increased to absorb the higher power. This will translate into increased electrical output to the tractive motors, with a corresponding increase in tractive force. Eventually, depending on the requirements of the train's schedule.
The engine driver will have moved the throttle to the position of maximum power and will maintain it there until the train has accelerated to the desired speed.
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