Catenary

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Catenary
Posted by daveklepper on Monday, March 6, 2017 8:34 AM

One topic I do not remember having been discussed in detail, either iun the magazine or in a forum, is the difference between classic and modern constant-tension catenary.   Also, the triangular New Haven catenary shopuld be included.  What was its advantage and why was in not more widely used? 

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Posted by rcdrye on Monday, March 6, 2017 5:44 PM

Experts - feel free to add, edit, dispute.  Here's a basic outline:

NH's triangular catenary was considered too stiff (even by New Haven) and required a lot of finicky maintenance. The biggest initial advantage was that the two messengers allowed a bit of curvature to be created between towers. At that, it lasted over a hundred years in service.  New Haven's later suspension of the main catenary mesenger from a crossbar cable-suspended between towers was also a New Haven-only design. Inclined catenary construction gave all of the advantage of triangular catenary on curves, with less maintenance.

Classic catenary does not generally use weights to maintain tension, relying on the short segments between hangers to minimize contact wire sag.  The practice of using 250 to 300 foot sections of messenger between poles or crossarms negates some of the sag reduction, particularly at high temperature.  There was some use of tensioning weights on classic catenary construction, but they were generally used near switches and crossings to maintain alignment.  Stiffeners were used at switches to maintain constant height on crossing wires.

Modern constant-tension catenary uses relatively short segments with tensioning weights. Better sag control allows for simpler construction, since there is less likelihood of vertical misalignment.  The main cost is that the number of poles per mile is around double that of classic style.

All three types can be constructed as simple (messenger, hangers, contact) or compound (messenger, hangers, secondary messenger, secondary hangers, contact).  A lot of recently-installed catenary is simple rather than compound.

 

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Posted by Paul_D_North_Jr on Monday, March 6, 2017 8:04 PM

Thanks for that start, rcdryeThumbs Up  Now we need some photos and diagrams . . . starting with that classic one of the PRR's, maybe the one with the men sitting on the cross-cable (terminology ?)

- PDN. 

EDIT: Here are some: 

http://www.billspennsyphotos.com/photos/PRR-Locomotives/PRR%20CATENARY%20DIAGRAM%20E9393%204-19-32%20EE13642%20b.jpg 

http://www.nyctransitforums.com/forums/topic/23938-catenary-improvements-continue-on-metro-norths-new-haven-line/ 

https://en.wikipedia.org/wiki/Overhead_line 

- PDN. 

"This Fascinating Railroad Business" (title of 1943 book by Robert Selph Henry of the AAR)
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Posted by rdamon on Tuesday, March 7, 2017 7:06 AM
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Posted by Paul_D_North_Jr on Tuesday, March 7, 2017 9:05 PM

Good info, rdamon!

Here's some more I found (via a Google Image search for "rail electrification catenary" or similar), of varying relevance:

http://www.bathnes.gov.uk/sites/default/files/sitedocuments/Planning-and-Building-Control/Planning/nr_a_guide_to_overhead_electrification.pdf - esp. pages 12 - 22 (blue streak 1, also pgs. 8 - 11)

http://www.railsystem.net/rigid-catenary-or-overhead-contact-system/ 

Book from German authors and apparently mostly about German practice - though it looks to be highly recommended by most reviewers - a mere 595 British pounds ! (I think) 

https://www.amazon.co.uk/Contact-Lines-Electrical-Railways-Implementation/dp/3895783226 

- PDN. 

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Posted by rcdrye on Wednesday, March 8, 2017 8:03 AM

Paul_D_North_Jr
Thanks for that start, rcdrye ! Now we need some photos and diagrams . . . starting with that classic one of the PRR's, maybe the one with the men sitting on the cross-cable (terminology ?)

They're called "span wires"

Amtrak has begun the replacement of older PRR-design cat with new stuff in New Jersey.  The work on tracks 3 and 4 I saw (from a train on track 2) involves an incredible amount of "juggling" to get from fixed-tension to constant-tension.  At one of the material yards along the way the amount of stuff ready for installation was just amazing.

RME
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Posted by RME on Wednesday, March 8, 2017 10:23 AM

That rigid catenary system is interesting -- might be a useful item for use in the rebuilt PRR tunnels.  If you suspend it every 15' or so, which wouldn't make sense in 'open air' but is do-able in tunnels, it can support any practical speed in the bore -- 100mph could be possible with proper handling of the airflow and lining.

Note why the little 'wings' on the aluminum extrusion are profiled as they are.  It would not be difficult to modify the extrusion so it could handle multiple contact wires, which in turn might simplify some of the thermal expansion problems (and mismatch between copper and aluminum expansion).

Something I don't see mentioned is what is done when the extrusion takes a 'set' with age.  Perhaps they intend to shim the trolley wire, or run the extrusion sections through something that arches the top of the profile to restore the 'spring action' at the bottom?

Just the opposite of constant tension, and reminiscent of at least one scheme I remember as being roughly contemporary with the New Haven triangular arrangement (remember the heavy crossbars meant to control and tune vertical bounce?)

Constant tension requires better design and deflection control of the supports than fixed does, which may be some of the problem with implementation on the NEC.  Note the fun involved with the constant-tension analogue to pulloffs on curves when maintaining both line and tension in the trolley wire...

RME
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Posted by RME on Wednesday, March 8, 2017 10:59 AM

Paul_D_North_Jr
Book from German authors and apparently mostly about German practice - though it looks to be highly recommended by most reviewers - a mere 595 British pounds ! (I think)

https://www.amazon.co.uk/Contact-Lines-Electrical-Railways-Implementation/dp/3895783226

Buy it!  Even with express overnight shipping, you could put it up for resale on Damnazon and make a theoretical very large profit, if the prices I see for this otherwise "unavailable" book actually result in sales...

Not so sure that, in this particular case, "Easy_Sell_Books" will have so easy a time making their sale...

 

As an alternative, there are a number of editions of this book (2012, 2008/9, 2001) and here is the WorldCat list of libraries containing one of the editions.

Note that HathiTrust has a scanned copy that some of you may be able to access.

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Posted by ATSFGuy on Wednesday, March 8, 2017 1:09 PM

While we're on the subject, what kind of electrical system did the Pacific Electric and Los Angeles Railway use?

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Posted by Paul_D_North_Jr on Wednesday, March 8, 2017 1:43 PM

I'm short on time at the moment, but I do want to reply to RME's post: 

All those prices take my breath away, but as to that Easy_Sell_Books one: LOL !! Laugh  Don't forget the $3.99 shipping (though at that price, you'd think they'd absorb it, right ? Whistling )  Maybe we should 'crowd-fund' a purchase of it from one of the others ?? Smile, Wink & Grin

Thanks for finding that info.  Bow

- PDN.  

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Posted by CSSHEGEWISCH on Wednesday, March 8, 2017 1:51 PM

ATSFGuy

While we're on the subject, what kind of electrical system did the Pacific Electric and Los Angeles Railway use?

 
Like most interurbans and street railways, they used direct suspension overhead.
The daily commute is part of everyday life but I get two rides a day out of it. Paul
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Posted by rcdrye on Wednesday, March 8, 2017 5:58 PM

CSSHEGEWISCH

 

 
ATSFGuy

While we're on the subject, what kind of electrical system did the Pacific Electric and Los Angeles Railway use?

 

 

 
Like most interurbans and street railways, they used direct suspension overhead.
 

PE did have some catenary on its San Bernardino line.  Outside of the Skokie Valley route, the North Shore was all direct suspension, on which trains regularly hit 80+.

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