NEC catenary question

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I have a question for someone such as catenary lineman or engineer.

My common sense tells me that all of the contact wire of the NEC's catenary probably would have been replaced at least once since it was installed by the PRR in the 1930's, but I suspect that the most of the messengers, hangers, auxiliaries and steadies are original construction. Most of the support structures surely are. It has doubtless been engineered superbly, what with the region's wide range in temperature and the potential for extremes in weather. What impresses me is how art and engineering were melded in the PRR's electrification, especially with the graceful curves of the inclined catenary. It appears to allow for economy in support structures, especially on curved track. The PRR's engineers certainly gave the catenary an unusually aesthetic appeal. Despite the fact that it was designed seventy years ago, AMTRAK's newest high-speed Acela trains run under it without hinderance, so I doubt that the design is outdated.

The PRR's catenary design seems quite durable, but I've not seen it emulated elswhere in the world, although the design was also employed by the Reading, Norfolk & Western, Virginian and on parts of the New Haven. Am I correct here? I would appreciate comments.
 

jackal

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Let me start by saying there are people here who are far more qualified than I to speak on such matters.

However, I wanted to bring the point up that--without having any clue on the matter myself--it is possible that the PRR's design, while perhaps aesthetically pleasing and durable--may not be compatible with the newer standard of constant-tension catenary (identified by obvious hanging weights every certain length of wire). Most overhead electric power installations in the world--and certainly all modern high-speed trains--use constant-tension catenary, since otherwise the variable tension in the wire (especially on hot days, when the wire expands and sags) can lead to extremely destructive oscillating waves.

In fact, that's the reason that Acela is limited to 135mph south of New York. North of New York, Acela can reach its design speed of 150mph primarily because of the newer constant-tension catenary implementation.

There was an informative thread here recently discussing the physics behind catenary oscillating waves. If I discover it, I'll post the link here for you.

And welcome to Amtrak Unlimited!
 

jackal

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I think I found what I remember.

Take a look at this post and the subsequent posts, paying special attention to the post by jis three posts later (post #19).

Also, see a related discussion in this and subsequent posts, which discusses oscillating waves in trains with multiple pantographs.
 
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jis

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One other thing to note is that many electrifications in earlier days used double messenger wires because there was possibly a desire to keep the contact wire as level as possible even when tension was lowered because of heat, and also because in lower voltage electrifications the contact wire tended to be much heavier to carry more current.

In modern high-voltage electrification using constant tension catenary, the second messenger wire is seldom used because it is unnecessary. The contact wire is usually much lighter and CT keeps the contact wire pretty even anyway. As a matter of cat even the number of hangers used per unit length of catenary tends to be less than in the past. Contrast the PRR electrification with the new 25kV electrification either east of New Haven, or between Matawan and Long Branch on NJTransit.

So the bottom line is the state of the art in catenary construction and indeed main line electrification has advanced far enough so as to make the PRR design obsolete. AFAIK in modern high voltage electrification only NJT has chosen to use the old Lackawanna derived design on the Montlair-Boonton Line including double messenger wire and anchired variable tension and all. And of course all additional electrification on the PRR portion of NEC that is taking place as a result of track realignments and constructions of new stations are continuing to use pretty much the original design.
 
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Moderator note: This reply is to a topic that is 2-1/2 years old:

Since it would cost billions of dollars to replace all of the PRR catenary with CT catenary, what about modifying the PRR catenary to CT by inserting CT pull-offs at appropriate intervals? Might that be feasible? If so, Amtrak could save gigabucks and allow the Acelas to indulge themselves south of New Haven.
 
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jis

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Moderator note: This reply is to a topic that is 2-1/2 years old:

Since it would cost billions of dollars to replace all of the PRR catenary with CT catenary, what about modifying the PRR catenary to CT by inserting CT pull-offs at appropriate intervals? Might that be feasible? If so, Amtrak could save gigabucks and allow the Acelas to indulge themselves south of New Haven.
Actually New Haven (Amtrak/MNRR Division line) to New Rochelle (actually CP 216 ex-Shell) is already being converted to Constant Tension by MNRR, and is essentially a total replacement, with considerable reuse of original poles and cross bars.

The segment between New Brunswick and Morrisville will be converted to CT as part of the $450 million work on the New York - Philadelphia segment of the NEC by 2017. The new structure will be single messenger wire instead of the current messenger and auxiliary wire system. And no, it won't cost many billions of dollars and certainly not tens of billions of dollars, to replace the catenary. It will initially be done in only those areas where speeds in excess of 135mph is possible with the current track alignment or some minor realignment thereof.

Not only will CT be a full replacement of the existing catenary, it will also shorten spans by adding additional posts. Furthermore, if Amtrak decides to increase track centers to 15' to allow higher speeds in the future, they will have to bring down remove many of the existing catenary support to achieve that anyway. So no, in general doing a half way fix will at the end cost more money, not less than full replacement.

In the process they will also fix an enduring undesirable design choice made by the PRR, that of using cross hangers to suspend catenaries on all four track which has the unfortunate property of bringing down catenaries on adjacent tracks when catenary on one track is damaged by a pantograph failure. Those will be eliminated and replaced by cross beams wherever conversion to CT is carried out.
 
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benjibear

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I was driving along the old PRR Port Deposit branch below Columbia, PA and that had me thinking. I always find it interesting that many PRR routes that are no longer electrified still have the catenary poles. It is probably just cheaper to let them stand then take them down. Also, to note on this line is the PRR signals are no longer there. Not sure when that was done but they are all new signals.
 

Acela150

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Moderator note: This reply is to a topic that is 2-1/2 years old:

Since it would cost billions of dollars to replace all of the PRR catenary with CT catenary, what about modifying the PRR catenary to CT by inserting CT pull-offs at appropriate intervals? Might that be feasible? If so, Amtrak could save gigabucks and allow the Acelas to indulge themselves south of New Haven.
Actually New Haven (Amtrak/MNRR Division line) to New Rochelle (actually CP 216 ex-Shell) is already being converted to Constant Tension by MNRR, and is essentially a total replacement, with considerable reuse of original poles and cross bars.

The segment between New Brunswick and Morrisville will be converted to CT as part of the $450 million work on the New York - Philadelphia segment of the NEC by 2017. The new structure will be single messenger wire instead of the current messenger and auxiliary wire system. And no, it won't cost many billions of dollars and certainly not tens of billions of dollars, to replace the catenary. It will initially be done in only those areas where speeds in excess of 135mph is possible with the current track alignment or some minor realignment thereof.

Not only will CT be a full replacement of the existing catenary, it will also shorten spans by adding additional posts. Furthermore, if Amtrak decides to increase track centers to 15' to allow higher speeds in the future, they will have to bring down remove many of the existing catenary support to achieve that anyway. So no, in general doing a half way fix will at the end cost more money, not less than full replacement.

In the process they will also fix an enduring undesirable design choice made by the PRR, that of using cross hangers to suspend catenaries on all four track which has the unfortunate property of bringing down catenaries on adjacent tracks when catenary on one track is damaged by a pantograph failure. Those will be eliminated and replaced by cross beams wherever conversion to CT is carried out.

I would imagine NBK and Morrisville as it's so straight between the two points??

Is the voltage and cycles going to be the same as north of NHV?

How does one plan to transition from old PRR to the new??
 

PRR 60

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I would imagine NBK and Morrisville as it's so straight between the two points??

Is the voltage and cycles going to be the same as north of NHV?

How does one plan to transition from old PRR to the new??
The new catenary will be installed on a 24-mile section of the NEC from south of New Brunswick to north of Trenton. I'm not sure of the exact limits, but I assume they want to avoid as many interlockings as possible.

As far as I know, the voltage and frequency (11kV, 25hz) will not change.

A special structure(s) will be installed at each end that will dead-end the new and old catenary and permit seamless transition from the old to new system.
 

jis

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Will those transitions be Deadsections??
Not for any electrical reason. No need to be dead sections since electrically the new catenary will be part of the same single phase 25Hz grid. For operational reasons they may have breaks to allow sectionalization, but that does not require a dead section.
 

PRR 60

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Will those transitions be Deadsections??
I don't know the design details (and the design may not even be to that point), but I suspect it will be a short isolation element between the live circuits. The would not be different than the existing means of provide catenary isolation points for sectionalizing.

Note that there is already a short section of constant-tension catenary in that area. A portion of Track 3 between a point south of Princeton Junction and north of Hamilton had constant tension catenary installed some years ago to permit high-speed testing. That CT section was retro-fitted into the existing catenary support system with structural changes only required at the dead-ending points.

One issue today is that the existing catenary support structures are coming up on 80 years old. Most of them are in reasonably good shape, but they are still of questionable adequacy when modern design standards are applied. If you presume the new catenary will have a useful life of 40 years, does it make much sense to support that expensive facility on structures that will be 120 years old at end-of-life?

However, changing the structures is a really big deal. The railroad has to be kept active during the transition, so there would have to be some way of installing the new structures around and through the existing catenary, signal power, and transmission lines. Then, at least the catenary would have to be relocated from the old structures to the new structures (maybe keeping the transmission on the existing structures), all while keeping the trains in service on at least three of the four tracks. Just replacing one or two catenary structures on the NEC is a big (and expensive) deal. Changing 600+ will be epic.

Speaking of structures, I'm not sure why constant tension would necessarily require shorter spans except possibly through curves. The existing system has spans of about 225 feet. The new construction east of New Haven went with considerably shorter spans than the old PRR design, but other than to make the chords work through curves, I have no idea why.
 

jis

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Speaking of structures, I'm not sure why constant tension would necessarily require shorter spans except possibly through curves. The existing system has spans of about 225 feet. The new construction east of New Haven went with considerably shorter spans than the old PRR design, but other than to make the chords work through curves, I have no idea why.
Generally on HSR catenary is built with shorter spans to reduce freedom of lateral movement of catenary when a train passes by. It per se has little to do with whether it is CT or not. Remember that the excellent PRR catenary design for its time, was for 80 mph operation. For such speeds longer spans are fine even today.
 

acelafan

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This is an old thread but I’ll still post my question here. Trains magazine has an article that discusses the on-going catenary upgrades between Trenton and New Brunswick (April 2018 - Wiring New Jersey for speed). What surprises me is that Amtrak is using 2 methods to do these upgrades – constant tension (CT) south of Midway but variable tension north of Midway.

I thought CT was the industry-standard of new catenary nowadays? Is there a reason why Amtrak is installing variable tension to evaluate its performance? Wouldn’t CT perform better for high-speed trainsets such as the Acela replacements?
 

daybeers

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Because they blew the budget and ran out of money to do the complete job and were able to come up with an argument as to why it is OK to not do a complete job [emoji53]
So is the whole section from Trenton to New Brunswick going to be good for 160 mph operation, or just the part with constant tension catenary?

Below is a helpful fair use quote from a July 2017 article on the budget situation for this project. There is also a video on the page: Wick Moorman starts talking at 2:10, but I would recommend watching the whole thing.

A 2015 report from the Amtrak Office of the Inspector General found “the program’s cost and schedule problems are directly attributable to weaknesses in program management and oversight."

The same report found "gross mismanagement of funds and resources" by a previous manager on the high speed rail project.

"Clearly it did not get off to the great start that we would have preferred," said Scot Naparstek, Amtrak's chief operating officer. "The launch of the project would have been very different today."

Since the OIG report, Amtrak has made sweeping changes to the way it oversees capital construction projects, including hiring Sarina Arcari, an accomplished program manager who now monitors all major construction efforts and looks for ways to make them more efficient.
This thread has more information on this topic. This September 2017 article says the project is scheduled to be completed in 2019.
 

jis

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The argument justifying the lack of need for constant tension in the eastern portion is that it does not need to have a maximum speed of 160mph due to other track alignment factors. I don’t recall what lower max speed they settled on for the enhanced variable tension catenary section. Probably something like 145mph, but that is subject to verification. I’ll look it up when I get on my laptop next.

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acelafan

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The situation is indeed unfortunate, as I assume the variable tension catenary would eventually have to be replaced with constant tension at some future date. Of course, I may not be around to see that date or fast trains requiring the constant tension may not run on that alignment in my lifetime.
 

jis

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If what they say is true there would never be the need to convert that segment to constant tension. Indeed there was no need to even when they applied for the fund saying that there was a need to, but they hadn’t formulated the argument yet. [emoji6]

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daybeers

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I traveled north through the Trenton–New Brunswick section today, and though I wasn't watching the whole time, it seems a fair amount of the new catenary (both wires and supports) is in place.
 
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