Empties up, loads down probably biases the equation to a faster payoff; if we get half the ‘down’ power back as ‘up’ power, and only require (say) 75% power to get up, that starts looking pretty good, no?
Snow does complicate the picture some, (ice on wire, Flash-over on the insulators, etc.) though traction effects and increased drag, etc would not change markedly for a wire hybrid scenario than it would in a single-power situation.
But, cold weather also gives some more options for energy savings: units stationary on the grade ( for whatever reason) could make money (to offset the cost of idling to stay warm) or conserve fuel (depending on electrical engine heaters) by being connected to the grid.
Dave- why DC on the center rail? adds complexity if the ‘native’ power of the line is different than the tunnel power. Complexity = cost.
Elsewhere I have elucidated some of the problems with DC as a motive power; in particular, the problem of sustained arcing would be a problem in the dusty, grimy, oily, possibly damp environment between the rails in a tunnel. Not that AC would automatically be better. . .no matter what sort of power it is, high voltage and oily dirt are a bad combination. (not to mention dragging equipment!) I think we’d be better off with an outside third rail.
But maybe i’m overlooking something?
a note on personnel safety:
Especially in areas where someone might inadvertantly get across the line, AC is probably safer than DC. (despite what Thomas Edison wanted us to believe. . . DC makes muscles clench ; AC causes spasm, tending to throw the victim clear. Of course at 750+V AC or DC, my (personal) biggest worry is that I WOULD survive- minus major parts of my anatomy. I’ve seen it. Big craters and burns, skin grafts that don’t take. . .it’s not pretty.)
Yes, but if we just had a refrigerator sized cold fusion reactor in each locomotive then we could just waste all the dynamic braking energy with no effect on the overall ecomony…
DC ONLY in tunnels and approache/transition zone and only because it is extremely expensive to say raise clearances in the Moffat Tunnel to put in catenary. Center third rail, Lionel style, can give greater current carrying capacity the side third rail, won’t bother special freight cars that might not clear side third rail, and would be powered only when trains are about to enter, are in, and leaving the tunnel. The transition zones would have heated conrete roadbeds to insure no ice buildup on the center third rail and would be as short as feasible. Low voltage dc has less insulation problems than ac (remember that the peak voltage of ac is 1.4 times the rms equivalent power voltage), and is easily designed into compatible locomotives that are a diesel serving as the road slug for the electric in electric territory and the electric serving as the road slug for the diesel when outside the electrification. Snow and ice affecting caternary is a problem that has faced electric railroads for years, but they manage through frequent service, by having two pans (or trolley poles) or more collecting power, and by special sleet and ice cutters on the pantographs. The North Shore interurban continued to provide good service during some really terrible snow storms that closed highways complete for days, and they did it by continuing to run trains back and forth all night. You are absolutely right about third rail not be appropriate for a mountain electrication, but it is the appropriate technology for avoiding having increase tunnel clearances only. I’d use for the Moffat and for other long tunnels, and raise clearances on short tunnels, looking at the cost benefit figures in each case. The voltage has to be much lower in a third rail installation, even a center third rail, then catenary because of the insulation situtation. I think the highest voltage, dc, ever used on a side third rail was one interurban at 1500 volts, and I’m not sure it stayed that way. 500, 600, and 750 is typical in modern rapid tr
In mountain railroading - with combined diesel/electric operations - why electricfy the tunnels at all. With distributed power on long heavy trains, the lead engines could retract their pans while the midtrain/training power continues to push. I know that wouldn’t work for long tunnels like the Moffet but it would work well on the shorter tunnels that are more common - such as the Thistle tunnels on the Soldier Summet grade.
Based on the MILWAUKEE Road electrification you are making way too much of the problems of ice on the trolley than actual practice has shown. Pans and wires work quite well. It is easier to just divert the water away from the wire.
When the MILW was investigating the upgrade of their electrification from 3300 VDC to 10K VAC the added insulation required for bridges and tunnels was in the 2" to 3" range for air insulation. Something like High Density Polyethelene plastic sheeting would likely solve the problem with a 3/4" thickness applied to tunnel roofs.
While it would be nice to capture the electrical energy lost to heat in dynamic braking it does not seem fuel costs are yet high enough to cause a capital investment necessary to recover it. Electrification, especially for short runs will likely be the last option the railroads will apply. Batteries, compressed air and flywheels seem the most likely.
Electrification in the long run will come when the power companies need the railroad rights of way for transmission lines, and when the USA get serious about energh independence, and when oil prices continue to rise and advanced nuclear power reduces electrical energy costs.
the rule of thumb for air insulation is 1" = 10KV, in clean environments (like offices or labs)
the roof of a tunnel with diesel-powered coal trains rumbling through it at all hours doesn’t strike me as the cleanest environment. . . So let’s cut that back to 3" = 10KV. So, if we take a “standard” transmission line voltage of 25kVac, apply the RMS correction (root 2), and we’re looking at 1 foot clearance from the tunnel roof, and a further clearance of 1 foot from the doublestacks. . . Which probably have the occasional corona point (a deep scratch will do) and all sorts of other crap on top of them. (dirty snow comes to mind) So add another couple of inches for safety,
Hey, presto, Dave is right- third rail is the cheap and easy way thru tunnels. That, or limit 'Wire Hybrid" to a smaller loading guage. (not the best way to gain wide accepance)
So we can look at the poly. Plastics attract dirt. (just ask any model railroader about dirt and plastic wheels) Dirt may insulate at 12Vdc, but I’m here to tell you that it conducts pretty well at 30kV. . . . So you’d need a LOT of poly to increase the leakage path to the point where flashover would be minimal even with the dirt. Then you have to worry about all the hot, carbon-laden gas coming out of the exhaust stacks of the diesels and melting the poly, or worse.
Which brings up a point I hadn’t thought of: Diesel soot (carbon and traces of sulfuric acid) on the caternary insulators and wire. . . I wonder what the solution was in the steam days when you had steam under the wire?
Still sounds cheaper to do the third-rail thing . . . or follow dldances’s theory and bull through on diesel power alone and put the pan back up on the other side. Cheaper still except for the odd crew that doesn’t get the pan down fast enough. Or go to the opposite extreme and prohibit diesels from anything other than idle in the tunnel, and run on the wire. The pull-the-pan option seems cheapest to me. . . No fi
On a BART train, about 90 percent of the braking is dynamic braking. Friction brakes cut in around 4 mph or less.
Usually, the dynamic braking feeds a big resistor grid, underneath the car. However, if there is another train that’s in your power circuit, then the other train can use your electricity. However, that usage is pretty local, a train coming down the hill to Orinda can’t help a train climbing the hill after Pittsburg.