North East Corridor (NEC) speeds, new stations and state of repair

[George Harris]

It would appear that the amount of tension might to be higher for each increment of higher speed, As well hanger spacing from the traveler to contact wire may need to be closer? Another is the expected wire temperature extremes causing wire expansion from low to high + a fudge factor. All this to reduce sag of the contact wire with train PANs.

The whole point of constant tension is to eliminate the effect of temperature on sag. That is, at intervals there are weights attached to the contact wire to develop the desired tension. These weights move up and down with temperature change so as to maintain the desired tension. The issue is to provide sufficient distance for travel of the weight. This could (is?) the limiting factor on spacing of these weights. To keep the weight reasonable, there is a set of pulley wheels to provide a multiplier factor. Simply put, if the tension desired is ten times the weight, then the vertical travel of the weight must be ten times the change in length of wire segment with temperature variation.

 

[west point]

The whole point of constant tension is to eliminate the effect of temperature on sag.

Mr. Harris. Isn't constant tension just going to reduce sag? Granted sag will be much less but the Catenary formula still means that there will be some sag between each hanger from the traveler. The math is complicated but variable tension PRR style allows much more sag between each hanger. Of course, the maximum temperature variations will effect the coefficient of expansion of the specific wire metal formula per degree of temp rise of the wire. That number may not be linear.

https://railroad.net/field-guide-to-amtrak-catenary-t26913.html

Everything about CAT construction mainly constant tension. Remember for each increase of MAX authorized speed increase sag has to be reduced. IMO it appears that number of PANs on a train may also effect snags with CAT that may operate with only one pan. Note: the AX-2 test videos appear to mostly only use one PAN?

 

[George Harris]

The whole point of constant tension is to eliminate the effect of temperature on sag.

Mr. Harris. Isn't constant tension just going to reduce sag? Granted sag will be much less but the Catenary formula still means that there will be some sag between each hanger from the traveler. The math is complicated but variable tension PRR style allows much more sag between each hanger. Of course, the maximum temperature variations will effect the coefficient of expansion of the specific wire metal formula per degree of temp rise of the wire. That number may not be linear.

https://railroad.net/field-guide-to-amtrak-catenary-t26913.html

Everything about CAT construction mainly constant tension. Remember for each increase of MAX authorized speed increase sag has to be reduced. IMO it appears that number of PANs on a train may also effect snags with CAT that may operate with only one pan. Note: the AX-2 test videos appear to mostly only use one PAN?

Constant tension does not necessarily reduce sag, it just makes it constant regardless of temperature. With fixed terminals the wire tension gets lower with increased temperature, increasing sag and the bounce of the wire from the pantograph pressure. With lower temperatures, the tension in the wire increases, reducing sag and the bounce of the wire from the pantograph pressure. Like many things mechanical, it is like Goldilocks and the three bears, not too hot (stiff), not too cold (slack) but just right.

Actually, what I said was only a partial answer. Constant tension is also to make the bouncing of the cantenary with the passing of the pantographs constant regardless of temperature. Tension also affects/determines the rate of propagation of the wave in the wire resulting from the pantograph load on the wire. Think of how the tone of the wire on a stringed instrument varies with the tension in the wire. There are lengthy studies, and likely books written on the subjects of preferred bounce, wave propagation rates and other factors with different speeds and pantograph pressures. My knowledge of what these should be is essentially nil. By the way, I think the coefficient of thermal expansion for the temperature range and metals involved is essentially constant. I could confirm this from a book I have called the Metals Handbook, Desk Edition which is somewhere over 2 inches thick that would tell me way more than needed to answer these questions. Unfortunately, the book is at my house and I am not.

 

[Literalman]

Why so many catenary problems in this area lately? I've been riding the Northeast Corridor since about 1970, when the electric trains were mainly GG1's and MP54's. The catenary was probably the same as it had been for quite a few decades, and there were occasional problems, but I don't remember problems on this scale until the past few years. Even if some NJ Transit pantographs are contributing to the problem, they aren't on new equipment, right? Mostly ALP-46's, the DM's, and the same old Arrows, all of which have been running for some years?

 

[railiner]

Why so many catenary problems in this area lately? I've been riding the Northeast Corridor since about 1970, when the electric trains were mainly GG1's and MP54's. The catenary was probably the same as it had been for quite a few decades, and there were occasional problems, but I don't remember problems on this scale until the past few years. Even if some NJ Transit pantographs are contributing to the problem, they aren't on new equipment, right? Mostly ALP-46's, the DM's, and the same old Arrows, all of which have been running for some years?

Good question. Could one possible reason be a reduced maintenance of way force, compared to back then?
If so, it could mean more frequent incidents, or a longer time to repair any…

Also, isn’t there more rail traffic compared to back then?

 

[west point]

Riding since 1970? Someone posted that then pollution was very bad. Is it possible since the days are much clearer today that wire temperatures are higher in the direct sunlight? If so, that would mean PRR CAT would sag more today than in the 1970s? Add constant tension now?? Unfortunately, Portal bridge replacement (2-1/2 miles), Sawtooth bridge (1-1/2 / miles ?), Dock bridge, Secaucus, various track relocations. All those projects means replacing with constant tension NYP - Newark Penn Station does not make sense. Only solution may be reduced speeds thast will gum up the schedules.?

 

[jis]

Riding since 1970? Someone posted that then pollution was very bad. Is it possible since the days are much clearer today that wire temperatures are higher in the direct sunlight? If so, that would mean PRR CAT would sag more today than in the 1970s? Add constant tension now?? Unfortunately, Portal bridge replacement (2-1/2 miles), Sawtooth bridge (1-1/2 / miles ?), Dock bridge, Secaucus, various track relocations. All those projects means replacing with constant tension NYP - Newark Penn Station does not make sense. Only solution may be reduced speeds thast will gum up the schedules.?

The other solution is to be more diligent about de-stressing the catenary based on season and temperature forecasts. This is done with both non-constant tension catenary (yes there are miles of it remaining where original DC electrification was changed to AC) and long welded rails, in India. Somehow that is apparently not done here, perhaps in homage to labor cost.

 

[west point]

Maybe there will be some tracks not to be moved that can get constant tension? There is no excuse for Constant tension Newark Penn and south not to be installed. Complete the highest speed sections first. As understood on multi track sections the inside tracks are done first then go to outward tracks.

Now up grading the Amtrak electrical system it is on its own as NJT is all 60 hZ except for partial 25 hZ coast line which is supplied by Amtrak. All partial upgrades for 25 hZ need to be compatible for future upgrades to 60 hZ. It is obvious that Amtrak does not have enough backup electrical circuity to prevent single point failures from cutting power to its CAT.

 

[jis]

Maybe there will be some tracks not to be moved that can get constant tension? There is no excuse for Constant tension Newark Penn and south not to be installed. Complete the highest speed sections first. As understood on multi track sections the inside tracks are done first then go to outward tracks.

Now up grading the Amtrak electrical system it is on its own as NJT is all 60 hZ except for partial 25 hZ coast line which is supplied by Amtrak. All partial upgrades for 25 hZ need to be compatible for future upgrades to 60 hZ. It is obvious that Amtrak does not have enough backup electrical circuity to prevent single point failures from cutting power to its CAT.

According to the NEC Commission Projects database covering now till 2034, there are no plans to either install further constant tension catenary east of County (Jersey Avenue) to New York Penn Station, nor change over any segment from 25Hz to 60 Hz. There are projects to upgrade substations and increase power capacity.

There is also a project to substantially replace all catenary structure between New Brunswick and Newark Penn Station (exclusive) with new fixed termination catenary using SAP (Steady Assembly Pipe) attachment replacing current attachments. You can see SAP attachments in use in the non-constant tension catenary between County (Jersey Avenue) and Trenton (Fair).

Further south in the Mid Atlantic North Region there is a lot of catenary structure replacement and almost across the board SAP installation, but no plans for constant tension catenary as far as funding goes.

 

[BlackDiamond]

Now up grading the Amtrak electrical system it is on its own as NJT is all 60 hZ except for partial 25 hZ coast line which is supplied by Amtrak. All partial upgrades for 25 hZ need to be compatible for future upgrades to 60 hZ. It is obvious that Amtrak does not have enough backup electrical circuity to prevent single point failures from cutting power to its CAT.

I assume by "NJT is all 60 Hz" you mean lines that are exclusively NJT such as the former Lackawanna out of Hoboken.

There is really no reason to convert from 25 Hz to 60 Hz and such a change would require a massive replacement of fairly modern solid state frequency converter substations plus the Susquehanna River dam generators that provide 25 Hz directly. Consider that in Europe Germany and Switzerland (and Austria?) still use 16.7 Hz and have no plans to convert from the lower frequency.