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#16468 - 11/12/02 05:47 AM Trains!  
C-H  Offline
Joined: Sep 2002
Posts: 1,497
Stockholm, Sweden
When I sat on the early morning train today I looked at the reflections on the snow from the arcing between the "tap" and the overhead line. This made me wonder about the power to trains: There must be terrible disturbances in the power judging from the intensity of the arcing.

Anyone who knows this field?

(Most trains here run on 15 kV, 16 2/3 Hz)

Work Gear for Electricians and the Trades

#16469 - 11/12/02 07:11 AM Re: Trains!  
Trainwire  Offline
Joined: Mar 2002
Posts: 360
I can't speak from hands on experience, but my grandfather was a powermaster for the Pennsylvania Railroad for many years, and electric locomotives are a favorite of mine. I work around steam locomotives every day.
The electric trains around here don't arc much. I think the answer to your question is, brute force is a wonderful thing. By the time you get the power transformered down to something that the rest of the equipment can use, most of the "junk" is filtered out. This is assuming that the trains "over ther" work the same way as the electric trains do over here.

The latest electrics actually convert incoming "juice" into dc, then run it back through converters, to control both the frequency, and the voltage to the motors. This is the same controls that the new deseasels use too. By the time the electric is run through all of that curcuitry, it is cleaned up quite a bit.

I'll root around a bit, I might be able to find a better answer from the museum across the street.


#16470 - 11/12/02 09:12 AM Re: Trains!  
C-H  Offline
Joined: Sep 2002
Posts: 1,497
Stockholm, Sweden
I should perhaps add that the arcs only occurs when the line is covered in ice. But as this is the case a good many mornings during the winter and the trains doesn't seem to have a problem with it I became curious.

Several other things fail because of the ice and snow: The switches freeze (despite the electrical heating) and moving parts in the undercarriage of the train jam. (Only last night was my train delayed 20 minutes due to a switch problem) Last winter the trains looked like balls of ice when they rolled into the station. If they maintenance crew managed to get them rolling at all, that is.

(New trains were ordered early this year: the spec calls for operating temperatures down to -35°C (about the same in °F))

Trainwire: I've got another question. When the trains here derail, they have on at least two occasions in last three years torn down the wire too. I can't see how the "tap" (what is it called?) can tear the wire down. Can you explain how this happens?

#16471 - 11/12/02 09:48 AM Re: Trains!  
Trainwire  Offline
Joined: Mar 2002
Posts: 360
Not being very familiar with railroading in your country, I can only relate what I know about it in this country.
the "american" term for the funny thingy on top, is a pantograph. Some of them have ice breakers on them for just the situation that you are describing. The arcs you see are the result of the pantograph being pushed off of the wire by the ice, electrically it probably isn't all that much of a big deal. It is of such short duration, the voltage and current being what it is, it just puts on a cool light show.

If a derailment brings the wire down it means that the pantograph is hooking over the wire. The contact shoe on US loco's are fairly wide, so to hook over the top of the wire the loco needs to rock pretty hard as it's coming to its unplanned stop. If my memory serves, European loco's shoes are much narrower, meaning that if the loco rocks to the side and then straigtens up it can hook over the top of the wire then catch on a support wire, and bring the whole thing down on your head.
A derailment is usually pretty catastrophic, especially at speed, it's a wonder that any of the equipment even stays upright. Now imagine trying to put 1.5 million pounds back on the rail. That's how much the biggest steam engines weigh.


#16472 - 11/12/02 01:37 PM Re: Trains!  
SvenNYC  Offline
Joined: Aug 2002
Posts: 1,691
New York City

I always thought the current-gathering part of the pantographs just rode on the bottom side of the overhead wire instead of hooking into it? At least that is what it always seemed like from the ground. [Linked Image]

When I was in San Francisco in 1998, I would occasionally see a trolley-bus ride off it's overhead wire. The driver would have to get out and use a long pole with a hook to get that springloaded arm back into contact with the power line. Granted the trolley arms are long enough and swiveled so it doesn't happen often...

At the end of the arm (don't know the correct term) there is a grooved roller that pushes up against and rides on the underside of the wire (and occasionally throws out a few sparks).

Does San Francisco still have trolley-buses? I know they're expanding their railed street-car network, but dunno about the trolley bus system. Most of those were pretty dilapidated (just like their gasoline powered brethren). [Linked Image]

#16473 - 11/12/02 02:04 PM Re: Trains!  
Trainwire  Offline
Joined: Mar 2002
Posts: 360
Schven, your right, the shoe of the pantograph only pushes up on the bottom of the catenary. What C-H was asking is why a derailment brings the "cat" down. The cat comes down when the shoe, that is supposed to be under the wire, hooks over the top of the wire due to the locomotive wandering around places it's not supposed to be, eg, the tie's (or sleepers if your in England) instead of the rail.


#16474 - 11/12/02 04:32 PM Re: Trains!  
Hutch  Offline
Joined: May 2002
Posts: 381
South Oxfordshire, UK
Ice on the conductor can bring the service to a complete halt. On the 3rd rail system in southern England (750 V DC) they run so-called 'ghost trains' all night when ice build up is a risk. This is empty stock whose only purpose is to scrape the ice off the conductor rail before it builds up too much. Fantastic night-time fireworks seeing them go by.

#16475 - 11/12/02 06:19 PM Re: Trains!  
harold endean  Offline
Joined: Feb 2002
Posts: 2,233
Boonton, NJ

My grandfather use to work on the Lackawanna railroad in the '20s, then it became the Eire-Lackawanna while my dad worked there. My grandfather was a electrician back then and the E-L would run 13,000 volts DC for their electric lines. Just in the '70-'80s did the E-L upgrade to AC power to mach the Penn-Central. At least that is what I was told. The Penn-Central ran 33,000 volt AC. Any more info on that?

#16476 - 11/12/02 06:25 PM Re: Trains!  
SvenNYC  Offline
Joined: Aug 2002
Posts: 1,691
New York City
The New York City Subway (or metro, underground railway, choose your favorite name [Linked Image] ) third rails are covered on top by a wooden plank that is held several inches above the rail by iron brackets.

The whole assembly (rail and plank) is held about 4 inches above the ties by ceramic insulators.

The primary purpose is to give some semblance of protection to track workers (so they don't step on the live rail while one foot is on the ground). However certain track work calls for covering the entire section of third rail with a thick rubber mat.

On elevated sections, the wooden cover helps prevent snow buildup somewhat.

There are 600 volts across the third rail and ground. I believe it is DC for traction and until recently was generated by rotary AC/DC converters in substations running both at 25 hertz and 60 hertz AC.

The 25 hertz ones have since been taken off line and substituted with solid-state equipment. The train cars each have their own traction motors (modern cars are permanently lashed together in consists of 6), batteries and other things to power the 110-volt lights and fans and heaters inside the cars.

This is what one of those old rotary converters looked like:

[Linked Image]

and you can read more about them at ] [/URL]

Impressive beasts!!! [Linked Image] [Linked Image]

[This message has been edited by SvenNYC (edited 11-12-2002).]

#16477 - 11/12/02 07:22 PM Re: Trains!  
pauluk  Offline
Joined: Aug 2001
Posts: 7,520
Norfolk, England
The shoe on top of most pantographs also curves downward slightly at its ends, so the train has to move a considerable distance off the straight-and-narrow before the panto will spring up enough to hook over the line. The overhead line isn't usually rigged to run exactly parallel to the tracks however. If it did so, there would be excessive wear at the central portion of the collector. Instead, the line weaves left and right along its length to even out the wear on the collector shoe. If the train happened to lurch off the rails in the wrong direction when the line was over to one side, it might be easier to hook over it then.

The London Undergound also gives quite an impressive fireworks display at night from the third and fourth conductor rails (630V DC). In this case, there are multiple pick-up points along the train, so if a shoe does lose contact with the rail at some point the spark is just the result of a break in one or several parallel paths.

I don't know if they still do it, but years ago on the above-ground sections of the Underground ice was cleared before the first trains of the morning by shorting the rails together at the end of a section and passing low-voltage high-current through the tracks to warm them sufficiently to melt the ice.

In recent years, our regular train service has become a national joke as to what lame excuse they'll come up with next. One winter we were treated to "It was the wrong sort of snow."

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