Sean R Das
Railfan
Hello. In the world of modern North American passenger trains, Head-End Power is used to supply electricity for the cars' lighting, heating and air-conditioning systems. Introduced after the introduction of Amtrak, it supplanted the use of steam heat and electrical systems powered by self-contained axle-driven generators and lead-acid batteries.
Ordinarily the locomotive or locomotives supply the HEP through their on-board generator (separate from that used for the diesel-electric power train). However, in cases where locomotives without an on-board generator have to be used (case in point: the Ringling Bros/Barnum & Bailey circus train), the HEP is supplied by a separate, stand-alone generator car (the use of this actually dates back to the days of steam heat during when a locomotive without an on-board steam generator had to be substituted). However, I think HEP generator cars can be useful for a completely different reason. It basically has to do with instances where HEP and steep uphill grades intersect.
Bear in mind that the HEP generator on a locomotive is either mechanically driven directly by the prime mover's crankshaft or has its own diesel engine. In either case, the HEP generator and prime mover share a common fuel tank. On a relatively level line, the prime mover works mostly to start and accelerate a train and thus the units have no problem powering the cars' electrical systems at the same time, but when it reaches a significant uphill grade, the story is quite different. On the grade, the units will struggle to pull the train up the grade AND provide electricity to the entire consist at the same time, especially with a long consists, and there will naturally come a point where the locomotives can no longer perform both tasks simultaneously, as this article points out.
This is my personal solution: Rather than shutting off HEP while the train climbs the grade, as the article explains; the ideal situation would be to relieve the locomotives from this taxing chore entirely by coupling a HEP generator car between the trailing unit (in a typical MU lash-up) and the baggage car. This way, the engineer and the locomotives can give the task of powering the train up the grade their full attention, while the generator car does the work of making sure the consist is not without HEP at any time. Obviously, the use of a generator car is dependent on the consist length. On a typical long-distance consist, for example, a generator car would be an overall necessity, while a short-haul or corridor-service consist would not need one as the shorter consist puts much less of a demand on the locomotive.
This technique, of course, does not necessarily require the investment in specialized rolling stock, and can instead be accomplished by adding an additional unit to the consist, provided the additional unit is set up for supplying HEP only and not MU-ed to the other units.
Ordinarily the locomotive or locomotives supply the HEP through their on-board generator (separate from that used for the diesel-electric power train). However, in cases where locomotives without an on-board generator have to be used (case in point: the Ringling Bros/Barnum & Bailey circus train), the HEP is supplied by a separate, stand-alone generator car (the use of this actually dates back to the days of steam heat during when a locomotive without an on-board steam generator had to be substituted). However, I think HEP generator cars can be useful for a completely different reason. It basically has to do with instances where HEP and steep uphill grades intersect.
Bear in mind that the HEP generator on a locomotive is either mechanically driven directly by the prime mover's crankshaft or has its own diesel engine. In either case, the HEP generator and prime mover share a common fuel tank. On a relatively level line, the prime mover works mostly to start and accelerate a train and thus the units have no problem powering the cars' electrical systems at the same time, but when it reaches a significant uphill grade, the story is quite different. On the grade, the units will struggle to pull the train up the grade AND provide electricity to the entire consist at the same time, especially with a long consists, and there will naturally come a point where the locomotives can no longer perform both tasks simultaneously, as this article points out.
This is my personal solution: Rather than shutting off HEP while the train climbs the grade, as the article explains; the ideal situation would be to relieve the locomotives from this taxing chore entirely by coupling a HEP generator car between the trailing unit (in a typical MU lash-up) and the baggage car. This way, the engineer and the locomotives can give the task of powering the train up the grade their full attention, while the generator car does the work of making sure the consist is not without HEP at any time. Obviously, the use of a generator car is dependent on the consist length. On a typical long-distance consist, for example, a generator car would be an overall necessity, while a short-haul or corridor-service consist would not need one as the shorter consist puts much less of a demand on the locomotive.
This technique, of course, does not necessarily require the investment in specialized rolling stock, and can instead be accomplished by adding an additional unit to the consist, provided the additional unit is set up for supplying HEP only and not MU-ed to the other units.