Op/Ed: Another use for HEP Generator cars

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#1
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.
 
#2
Add the power formerly used for HEP, then subtract the power needed to haul this added car up the hill. How much is left over for traction?

Bruce
 
#3
Add the power formerly used for HEP, then subtract the power needed to haul this added car up the hill. How much is left over for traction?

Bruce
Actually, you've got the math wrong: (Power needed to operate train up grade with HEP generators on locomotives - power needed to run HEP only = decreased demand on locomotives).

My initial thought that was that eliminating the locomotives' responsibility to supply HEP would result in greater locomotive fuel economy and fuel mileage. However, I do not deny that adding the HEP generator car adds additional weight to the entire consist. However, here it is assumed that the generator car--nothing more than merely a diesel-powered electric generator and underbelly fuel tank on a pair of trucks housed within a sheet-metal enclosure--would be no longer than a typical boxcar (about 40 feet--anything longer than that would be just wasted space unless a second engine/generator set were installed), and therefore the generator car would add some weight, but not to the extent that it would neutralize the effects on the locomotives' fuel mileage of relegating HEP duty to the generator car or even decrease the mileage to the point where it is lower than the fuel mileage required to run the train without a generator car.
 
#4
This is in fact what is done with the Talgo trainsets operating here in the PNW for the regional Cascadian service; there's a dedicated generator car with fairings to match it to the much taller locomotives that pull it. But the Talgos are so lightweight that it hardly makes any difference even though a single locomotive is almost always the only tractive power.

Head end power is typically supplied by a separate generator off the prime mover's shaft, or by an inverter powered from the traction generator and from what I've read, it can be turned off to release power for traction. The inverter also operates at a constant frequency independent of the prime mover's rotation speed. A couple of times I've visited the King Street Station in Seattle when an outbound Empire Builder was waiting and the cars were not connected to commercial power, the prime mover was blasting away noisily at a moderate-high rpm.

The Ringling train pretty much needs a generator car or two because it's a >long< train with a lot of residential cars, and is often pulled by available freight locos that don't have HEP. This also results in the Talgo's occasionally being pulled/pushed by whatever could be scraped up on a moment's notice, even an old GP-9.
 
#5
Head end power is typically supplied by a separate generator off the prime mover's shaft, or by an inverter powered from the traction generator and from what I've read, it can be turned off to release power for traction. The inverter also operates at a constant frequency independent of the prime mover's rotation speed. A couple of times I've visited the King Street Station in Seattle when an outbound Empire Builder was waiting and the cars were not connected to commercial power, the prime mover was blasting away noisily at a moderate-high rpm.
Which would you rather have? Either:
A) Sacrifice passenger comfort just to get the train up a steep grade?, or
B) Let the generator car supply an uninterrupted stream of HEP to the cars while the loco's focus solely on hauling the train up the grade?

I'd prefer an uninterrupted supply of power to the cars' electrical systems than spending as long as an hour without lighting heating or A/C.
 
#6
The practice of killing HEP for extra traction doesn't seem to be a common one. Amtrak might look at the use of a dedicated HEP car for each train as an extra operating expense it can barely afford under the best of circumstances. The compromise seems to be having enough locomotives on a given train/route to do the job.

One way of looking at it is whether a HEP car might be more fuel-efficient than locomotive-sourced HEP. And I suspect only the long-distance heavy name trains are the ones that could really use a dedicated HEP car.

The railroads used to run some very long/very heavy passenger trains; I wonder what the practice was to provide the required electrical power? Was dedicated HEP ever employed to a significant degree?
 
#7
You could save the weight of a car for the generator by putting generators under the passenger cars. You might only need one or two per train. They could be used full time or just when HEP was off.

From:
http://www.nwrail.com/distributed_products/stadco_index.html

"Specifically designed for mouting under railway passenger cars, the Stadco RailgenTM diesel generators are a very good solution for small package auxiliary power under the floor of railway passenger cars. Available in sizes up to 180kw continuous rating, these generator sets may be used to provide HEP power to an entire train depending on the load characteristics of the cars."
...
" Connected to a Northwest Rail Electric Generator Control a Stadco generator mounted under a railway passenger car is able to provide automatic backup power so that if the HEP system fails or is disconnected, the generator starts and provides power to the car automatically."

Bruce
 
#8
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.
Lots of locomotives, including AMTRAK's F59 have their own HEP engine. What is the problem that they share a common fuel tank? It would make sense that in the future all new AMTRAK locomotives have a separate HEP engine. Weight isn't an issue because locomotives have so much ballast in them anyways.

The added weight and length of an additional car will overly reduce performance and increase costs exponentially due to maintenance and wear and tear.

Typically when HEP is cut out for large hills it is because there is a problem with one of the locomotives and the crew is just trying a work around, this isn't standard practice on certain grades.
 



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