I’ve read a lot about electrified lines on, among others,PRR,NH,GN,NP, Milwaukee Road, Virginian,CN, and other roads. What I’ve never beem quite able to figure out, is how does the electric locomotive actually “plug in” to the power grid? Do the overhead lines carry both “wires”, or is one above, one at the rail? Can anyone elaborate please? Thanks
Wire = pos
Rail= Neg
Some railroads had 2 trolley poles, 1 for positive, 1 for negative and some even used the rail for a 3rd phase leg
On most electrified systems ( overhead and 3rd rail) the electricity goes into the loco through the pantograph or contact shoe and it comes out of the wheels into the rails which are used as the return.
On 4 rail systems the electricity goes into the tain through a contact shoe on one power rail and out another contact shoe into a negative power rail.
What is interesting to me is that the pantograph frame itself (the tubing) is what carries all the current from the trolley wire to the motors. I guess if you’re up there on top of the locomotive, you definitely do not want to touch that pantograph tubing, else the current will go right through your shoes to the locomotive roof which is 0 potential, being electrically connected to the rails.
The power through the pantograph doesn’t go straight to the motors. It is a “high” voltage “low” current power so that the catenary and pantographs don’t carry obsurdly high currents.
Adrianspeeder
Nobody goes on top until the pan has been lowered and the current wire switched and locked off. Even if you’re not near the pan that current wire is still there just above your head.
The current is pretty much as high as any locomotive (cept steam)… Current gets the work done !!
So, the overhead wire is basically a “live” wire, hanging above the track with some sort of insulating material on the sides and top?
no insulation at all on the cat wire. The cat will be supported by insulators in the support arms or wires.
dd
What keeps ice and snow from interfering with the floe of electricity? For example, would a major ice storm short circuit the overhead juice?
Ice storms have long played havoc with electrified operations, both overhead and third rail. Ice coating the wire or third rail actually serves as an insulator of sorts and limits current flow. Sleet cutters and ice breakers (not USCGC Mackinaw) are required to deal with this problem.
At any rate, the arcing that results when pantographs break off the ice coating puts on a pretty impressive light show.
This can happen, as can the weight of the ice bringing the catenery down. Luckily the contact wire is not a superconductor, so the current flowing in the contact wire heats it up a bit which may melt ice. Snow is not usually a problem as it’s light and shakes off due to the vibration of the wire.
In France they melt ice from the contact wire by nearly shorting it out (a low resistance shunt is used) which causes the contact wire to heat up a bit.
I know that old fashioned trolley cars used springs on the roof to hold up the trolley pole. Do electric locomotives use the same kind of system? Also, how are the pantographs raised, or lowered? Once they lose their power, is there some kind of on board battery or something to provide power?
Erik
If you are not from the east coast you have no idea how sloppy the snow and ice are in PRR electrifed territory. Slush is a better description. A standing order was that all trains have both pantographs up during sloppy weather to help keep the catenary free of ice build up. Don;t forget that the PRR ran trains four tracks wide with about ten minutes between trains on all four tracks so build up would be minimal. It was also the job of the fireman to get out at every stop and check the pantograph shoes for arc through. The back pantograph was used in dry weather in case it got fouled and ripped off which did happen in which case the front one could the fini***he trip. Originally the PRR used carbon shoes on the pantographs but in the early 50’s switched to steel shoes because of wear and cost. The catenary is not centered over the track but zig zags to even out the wear on the shoe and prevent grooving. The GN engines the PRR purchased were the only engine that required both pantographs be used in operation. This is because they were motor generators in which the AC from the catenary turned a motor that turned a generator to produce DC for the traction motors. In order that the motor not get out of phase with the power the pantograph had to be in contact with the wire 100% of the time. Sometimes they do bounce off the wire so two were the order of the day alsways.
The Pantographs are raised by spring tension. and lowered and locked by air pressure.
On Milwaukee Road, which had more than its share of mountain ranges and weather conditions, if there was ice on the contact wire, both pans were run up, the first pan broke the ice, the second got good contact. Substation operators could also lower voltage and the higher amperage would heat the contact wire.
Also, the bottom of the contact wire was highly polished from the graphite grease worked into the wire over the years from the pantograph shoes. Kind of like Teflon. You would never see an icicle, for instance, hanging from the contact wire although you might from the steel messenger cable.
This is one of those “theoretical” problems that was not a problem in actual practice.
Best regards, Michael Sol
A few comments… on current. It’s watts that do the work – voltage times current. On the 11,000 volt electrification on the NEC, the maximum draw is on the order of 500 amps per motor (locomotive/engine whatever). That will give you about 8,000 hp – which is what those things put out at max. 500 amps isn’t absurdly high, no… but it’s right up there. One of the major advantages of using AC electrification is that it is very easy to transform the high voltage down to something a little less zippy inside the cab. The other, however, is that the arc which forms when the pan skips on the catenary tends to extinguish itself, as the current drops nearly to zero twice per cycle.
In older catenary designs the heating from the current draw could, and did, cause the catenary to droop, with unfortunate results.
Ice storms cause absolute havoc – not because they insulate the wire (although that was a problem with streetcars, with relatively low contact pressures) but because they either cause the cat to droop too much (and it can get arount the end of the pan, catch, and be pulled down) or just simply break. I’ve seen both happen.
The catenary and suspension wires are never insulated. The insulators are the hangars to the poles or cross suspenders. You definetly do not want to touch – or come anywhere near – energized catenary.
As far as the dangers of energized catenary and induction currents, the Special Instructions in PC employee timetables for those lines stated that there was a danger zone of 24 inches from any energized catenary. Anybody who has been to the Northeast is also aware of the shields on overhead bridges over electrified tracks, including on I-95, which doesn’t have sidewalks.
For many points, all I have to do is change PRR to NHRR and you did all the work for me! Thanks!
BTW, for the many drawbridges the NH had between NH and NY there were gaps in the wire. The train had to glide through the gap - the wire went really high at either side of the gap so the pantograph eased to max height and then made smooth contact again at the other side.
Bouncing pans caused arcing, and if they bounced too hard would vaporize - no joke.
Note that there were a variety of voltages and power used in electrification. Today, a Washington to Boston train starts out using the original 11,000 volt 25-cycle ac electrification, switches to 60-cycle, 25,000 volts just beyond Harold Tower, Sunnyside, on the Hell Gate Bridge approach, then to 12,500 volts to enter Metro North tracks at New Rochelle, keeping 60 cycles per second (“Hz”), then back to 25,000 volts when east of New Haven station and keeps that on the new electrification up to Boston. A restored GG-1 could run only from Synnyside yard to Washington but not up to Nerw Haven or Boston.
And a Metro North commuter train uses 60Hz power from New Haven to Mount Vernon, then coasts while dropping pantographs and having its third rail shoes pick up 650volts dc on the third rail into Gramd Central Terminal.
And Metra Electric and the South Shore both use 1500 volt DC on overhead catenary.
Most new light rail systems use 750 volts DC on catenary and older systems, including new extensions, 600 volts DC on simple trolley wire.
The Milwaukee used 3000 volts DC in its catenary except when on tracks shared with the Butt Anaconda and Pacific where the voltage dropped to 2200 volts.
And Cincinnati and Havana streetcars used two trolley poles like trolley buses because ground return via rails was prohibited because of possible interference with telephone cables in the street.
And the new standard in Europe is 50 Hz AC because that is the standard power frequency there, but there are plenty of 16-2/3 Hz electrications and plenty of 1500 volt DC, 750 volt DC, 3000 volt DC and 600 and 550 volt DC electrifications around.
Those of us who rode streetcars in the old days remember winter storms when the lights would blink out and a lightning display but light up the street as arcs formed between the trolley wheel or shoe and the wire. The most dramatic ride I ever had in such a situation was on the Evergreen line in Pittsburg