Work on increasing speed limits on the NEC

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jis

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So I understand correctly that when I ride the Acela next month the train could operate at 160 mph?
In RI and MA, yes. Of course depends on how soon your next ride is. The current Acela sets will not run at 160 AFAIK. The Acela IIs will.

The mathematics of CAT can become complicated.
You can find everything of importance in the mathematics of catenary on the following page:


The bottom line catenary equation is:

y = a cosh(x/a)

How does Amtrak replaces poles at say 120 feet or just a new pole between present poles spacing them 90 feet apart. That is a decision of engineering. PRR poles carry the 12.0 kV, the 169 kV single phase Amtrak transmission lines, and at some locations 3 phase electrical utility transmission 250+ kV wires. The PRR poles are steel buried directly into the ground with many rusting away below ground level. From time to time new poles are installed on concrete foundations at those locations in the ground keeping steel poles above ground water. Have no idea what spacings may happen at each location.
In most places they have installed the constant tension catenary on completely new set of poles and left the old poles in place where they carry high tension lines and removing those that don't. In a few places even the high tension lines have been moved to the new poles. I guess that is determined by how deteriorated the old poles in question are.

The new poles all appear to have cross beams. AFAICT none have the cross suspension wires.
 
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PRR 60

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In RI and MA, yes. Of course depends on how soon your next ride is. The current Acela sets will not run at 160 AFAIK. The Acela IIs will.


You can find everything of importance in the mathematics of catenary on the following page:


The bottom line catenary equation is:

y = a cosh(x/a)

With high speed rail, the optimum catenary span length is largely a factor of the design train speed. The action of the pantograph sliding along the contact wire imparts some significant dynamics such as waves and oscillations into the catenary system. The longer the span between supporting structures and the higher the design speed, the greater the magnitude of those wire movements. If large enough, those wire movements can cause loss of pantograph electrical contact and mechanical damage to the system. Thus, for any given design speed there is an ideal span length - spans long enough to minimize supporting structure cost and short enough to prevent operational issues and damage from dynamics.

Technically speaking, electrified railroad "catenary" is not catenary in the geometric sense. The sagged strength component wire (called the catenary wire) supports the contact system (messenger and trolley wires) with vertical hangers spaced every so often. It's more like a suspension bridge with the weight transferred to the supporting cable at points, not uniformly. Today's analytic capability permits exact calculations of catenary system loads and wire forces based on the real geometry of the entire system. In the olden days, shortcuts like assuming a parabolic shape made calculation using pencil, paper and slide rules possible.
 

AmtrakBlue

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That makes sense.

When they do constant tension they install new posts because one of the things that goes with constant tension is also reducing the span length to something shorter than what PRR used originally. That is to reduce sideways deflection of catenary I suppose, and get a more stable catenary.
Here’s looking south from NRK.

59229735-5740-412B-A54B-FBB6BB17B23C.jpeg

Most of the work is north of NRK but I didn’t get a good shot of it.
9A3411B8-B6DB-474B-B216-4F6BE7D8BFF5.jpeg
 

jis

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Technically speaking, electrified railroad "catenary" is not catenary in the geometric sense. The sagged strength component wire (called the catenary wire) supports the contact system (messenger and trolley wires) with vertical hangers spaced every so often. It's more like a suspension bridge with the weight transferred to the supporting cable at points, not uniformly. Today's analytic capability permits exact calculations of catenary system loads and wire forces based on the real geometry of the entire system. In the olden days, shortcuts like assuming a parabolic shape made calculation using pencil, paper and slide rules possible.

Interestingly, NEC South with its 11-12.5kV electrification appears to use three wires referred to as (from top to bottom) Catenary, Messenger and Trolley or Contact, as they came with the original PRR electrification. The new constant tension uses three wires in this territory too. The new 25kV electrification up north does not have the middle wire. See photo below. Nor does the new MNRR, even though they are 12.5kV.

NERatKingston.jpg



The additional middle wire makes the catenary installation considerably more complex as is apparent in this photo of the new three wire constant tension catenary at Princeton Jct.

pbytyygghq241.jpg



I wonder what determines whether to use the third wire or not.

In other countries, in 25kV electrifications more often than not there is no middle wire and sometimes the top wire is referred to as Messenger Wire. See for example:


As usual all as clear as mud! :D

Incidentally, the following article from 2019 gives the impression that even County to Midway constant tension catenary is back on the table. So far I have heard nothing definitive from any reliable source about it.

 
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No speed increase as of yet. Guess I'll just keep an eye on the tracker to see if Amtrak ever gets around to implementing the change.
 

cirdan

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That makes sense.

When they do constant tension they install new posts because one of the things that goes with constant tension is also reducing the span length to something shorter than what PRR used originally. That is to reduce sideways deflection of catenary I suppose, and get a more stable catenary.

Maybe it is also that the PRR installations must be simply ancient by now and at some point you just need to bite the bullet and replace old by new. That is probably a better strategy long term than. trying to graft new catenary onto old supports whose condition and remaining lifespan may be questionable.
 
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