"European" catenary on the North-East Corridor (USA)

I'm somewhat curious about the electric circuitry feeding the catenary. The "new" section has, in addition to the catenary and contact wires, two insulated feed lines (one on each side) plus grounded returns. Nice and simple. In contrast, between NYC and New Haven, there are (old) pylons carrying multiple conductors for the catenaries plus some higher voltage circuits. For example, at the New Rochelle station there seem to be 15 12 kV conductors for track power (plus the catenaries for 4 tracks) there. Why so many?

Also, since the trains are large single phase loads, how do they try to balance the railroad as a whole over the three phase supply?

Where is the switchover between the 25 Hz power to the south and 60 Hz power? Right at Penn Station?

Portland Oregon has the variable weight system for it's Max Train catenaries. Not surprisingly, these were originally designed by a European contractor, I believe.

At certain pylons, there are tensioning weights that can be added or subtracted, as necessary. The system is very similar to the systems I recall seeing in France.

All of the new LRT systems in the US I've seen have constant-tension catenary in sections where they have exclusive ROW. Many use simple trolley wire (variable tension with just a contact wire, no catenary wire) for street-running sections, though.

What is a variable weight system and what advantage could it have over a simple pulley with a fixed weight?

Some of the pylons I've seen in Portland have multiple weights that are semi-enclosed in a metal box. There is a sort of cotter pin arrangement that selects how many weights are actually providing tension.

My guess would be that the tension on the long spans might vary over time (as the wire is stretched). Also there might be seasonal variations throughout the year due to temperature (and conductor sag?).

I'm no expert though. Perhaps someone with specific knowlege of this setup can provide more insight.

... Also, It could be that once a specific weight is set for a particular span... It pretty much stays that way...

The multiple weights could just be for ease in setting a specific level of tension during construction.

Beachcomber wrote, On 2008-03-27 14:58:

Correct.

Adam H. Kerman schrieb:

In theory, a fixed weight works nicely, but in the real world, track has all kind of curves and obstacles, so that you might not have the same length, or the same resistance to the pull, whatever.

In order to get done with the job (of setting up catenary) until the end of the day, you'll simply measure tension, and put up weights as needed. It's done this way since almost 100 years.

Hans-Joachim

Now I'm particularly confused. Of course I expected that the weights hung would be chosen based on observation of conditions, but once the observations are made, the counterweight is chosen.

When is a variable amount of weight used under daily operating conditions? I still don't know what the OP was talking about.

Yes, but typically it will not be one solid weight. For practical reasons, the total weight is divided among smaller more easily handled weight. Just because you observe a number of weight blocks pulling the tension, does not mean that, once set, the tension is varied.

I don't think the weights are varied once set. I have never heard of a specifically designed "variable tension" system (other than the ordinary system where tension is uncontrolled and varies with temperature). The only reason the tension would change would be if gravity varied, not a likely occurrence.

Merritt

Adam H. Kerman schrieb:

If you have 10 standardized concrete blocks already hanging there, why do you want to produce a special one and replace them? Lots of specially produced weights are certainly more expensive than standard weights.

Never.

Hans-Joachim

Ok; that makes sense.

That's what I thought. So there's no such thing as a "variable weight system" for catenary tensioning. You choose the appropriate amount of counterweight and hang it up.

Adam H. Kerman schrieb:

It's not a technology, but a practical question.

But nonetheless, it might come handy later: If you are the SNCF, and want to run a high-speed record to impress the world, you'll first send some guys with additional weights.

Hans-Joachim

----------- I could see seasonally variable weights being of use because temperature changes do have a considerable effect on a catenary -it's "sag" as well as tension. Cold weather reduces the sag and increases the tension appreciably due to the change in direction of the forces involved as the conductor shortens. In hot weather the span may be too loose.

The wire changes length with temperature. The whole point of the weight & pulley scheme is to absorb that change; so you won't care about the temperature..