PRR Catenary

[nkalanaga]

Peteski:  There are two ways of handling catenary on curves.  The MILW kept the messenger wire directly above the trolley wire, and used pulloffs as needed, so the hangers remained vertical, and the wires were in a series of straight segments.  They didn't bother to zig-zag the wire, because neither their track nor the poles were straight, and the wire usually wasn't over the center of the track anyway.  This would be easy to model with prefab catenary, and is the style used by Sommerfeldt for theirs.

The PRR used "inclined catenary". where the messenger wire was outside the centerline on curves, and the weight of the contact wire, combined with the tension on it, pulled the hangers out of vertical.  The trolley wire was still in straight segments, but it was on hanger spacing segments, so looked like a continuous curve.  No pulloffs were needed, but the hanger lengths were critical, and varied for every curve, because that was all that kept the trolley wire both centered and at the right height.  Very complicated to model, because neither weight nor tension scales properly.

The GN, typically, used a combination of the two.  Some of their catenary looked like the MILW's, except for larger insulators, other sections used the PRR inclined style, but with wooden poles.  I suspect that inclined catenary is preferred for longer spans, because the number of pulloffs needed increases with the span length, for a given curve.  The MILW, and GN, used 150 ft pole spacing on straight track, where the PRR used 300 ft.  A 300 ft span, and MILW's curves, would have put the poles out in a farmer's field to get the backbone wire clear of the track in the middle of the span.  Many of the MILW and GN curves had pole spacing considerably less than 150 feet, to minimize the number of pulloffs.

[peteski]

The PRR used "inclined catenary". where the messenger wire was outside the centerline on curves, and the weight of the contact wire, combined with the tension on it, pulled the hangers out of vertical.  The trolley wire was still in straight segments, but it was on hanger spacing segments, so looked like a continuous curve.  No pulloffs were needed, but the hanger lengths were critical, and varied for every curve, because that was all that kept the trolley wire both centered and at the right height.  Very complicated to model, because neither weight nor tension scales properly.

Thanks for the thorough explanation Nick. 
Still, as you mentioned, the trolley wire segments between the hangers would have been straight, but because of the larger amount of smaller segments, the wire might have appeared to be curved.

I would say that in N scale one could easily get away with slightly simplifying the PRR catenary on the curves. Sometimes close enough is good enough. IMO, using the PRR-specific poles and PRR-style etched catenary wires would give the layout so much PRR flavor that nobody would complain about the lack of inclined hangers on the curves. The alternative is no catenary at all, since it is too difficult to model it accurately and in-scale.  I think that sometimes we get a bit unreasonable in our modeling quest for prototypical accuracy.

[sd45elect2000]

I should have qualified my statement concerning my desire for nickel silver wire. I intend to have live catenary and N/S doesn't oxidize as badly as the others making for better operation.

The North Shore interurban also used inclined catenary on the Skokie Valley route but as was stated earlier it would be next to impossible to build. Each hanger length is calculated to force the contact wire into a curve so each etching would need to me customized to each curve.

I also have some Milwaukee road catenary but I have forgone the Milwaukee's practice of using two parallel contact wires. They did this to compensate for the fact they didn't use feeder wires.

Randy

[chicken45]

I should have qualified my statement concerning my desire for nickel silver wire. I intend to have live catenary and N/S doesn't oxidize as badly as the others making for better operation.

The North Shore interurban also used inclined catenary on the Skokie Valley route but as was stated earlier it would be next to impossible to build. Each hanger length is calculated to force the contact wire into a curve so each etching would need to me customized to each curve.

I also have some Milwaukee road catenary but I have forgone the Milwaukee's practice of using two parallel contact wires. They did this to compensate for the fact they didn't use feeder wires.

Randy

Oh...you're talking about OPERATIONAL catenary.

[Ed Kapuscinski]

Hell, I'm interested in a few poles (get it out of your system now Josh).

If for demonstration purposes only.

Also, I really need to throw this into any discussion of N scale catenary.





This all worked, including across modules.

It was incredible.

Where's @Hiroe? It was all his...

[Lemosteam]

@peteski In the picture below you see how the curve of the trolley wire is managed by the messenger wire and hangers.  To attempt this with an etched piece in the flat would surely create kinks and non-smooth transitions. 

Also, the fixed length of the etching would then in turn determine where the poles would be rather than specific spacing per the prototype.



@Ed Kapuscinski , I suspect that those modules were painstakingly hand strung.

[Dave V]

I think what I'd do is string them with a little EZ-Line (green for copper) and be done with it.  No, I wouldn't have the graceful sag of the suspender wire but there'd be enough something to suggest catenary without any of the hassle of trying to rerail N scale stuff under rigid catenary.

I need a few for Enola.

BTW, it's looking very likely that this will be a much more permanent home, so I'm revisiting plans to expand the JD after I'm done with the Colorado Midland.  I'm specifically looking at building an "eastern half" of the Pennsy that has wires.  Should I go that route I'll be in the market for mucho cat poles.

[Ed Kapuscinski]

@Ed Kapuscinski , I suspect that those modules were painstakingly hand strung.

Oh yeah. Hand strung and soldered. Drew's work was amazing. Oh, and it was all operable too.

[nstars]

Seeing all the discussions about catenary systems I'm glad that our layout won't feature electrified tracks. .

But I may have some additional information which could be helpful. For those who don't know it, I work for an engineering company which also designs catenary systems. The drawing of Lemosteam does show very well the basic catenary systems. The top version is the simple one, which is easy to construct and easy to maintain, but the contact between pantograph and contact wire is average, especially at higher speeds. It is important to know that more modern systems do have both the messenger and contact wire under tension to create a more even stiffness. This is very good noticeable on modern HS line. Older systems have only the contact wire under tension. Normally this is only used on tracks with slower speeds.

The middle version is a more sophisticated version of the top version to reduce the 'stiff' point around the poles. Advantage is better contact between pantograph and contact wire (especially at speed), disadvantage is construction as it is more difficult to adjust.

The lower version tends to be used more often in DC systems as the main reason for this complicated system is to reduce the 'stiffness' of the system. The cross section of a DC system of both contact and messenger wire is much larger than with an AC system. As a consequence, DC systems are much stiffer, which in the end will reduce the contact between pantograph and contact wire. If contact is lost, a spark will be created between pantograph and contact wire. This aspect is one of the reasons that most HS systems have an AC power supply.

If I look at most systems, an inclined curve is these days in most cases only used in areas with relatively tight curves. Adjusting an inclined curve is also in real life a nightmare and they can be sensitive to temperatures. Lets not forget that both the weather (temperature) and the use of the catenery (=heat) will have an effect on the proper position of the contact wire. However, I guess the PRR probably followed the motto: why make it easy when you can make it difficult. .

Marc

[peteski]

In the picture below you see how the curve of the trolley wire is managed by the messenger wire and hangers.  To attempt this with an etched piece in the flat would surely create kinks and non-smooth transitions. 

Also, the fixed length of the etching would then in turn determine where the poles would be rather than specific spacing per the prototype.

Thanks John!  I see what you mean about the trolley wire appearing to be curved.  The it is also very distinctive.   I suppose that if you want to spend a very long time to painstakingly solder this type of catenary from scratch, there is nothing stopping you from doing that. Personally, I think think it would take too much time relative to other tasks involved in building a layout.

I should have qualified my statement concerning my desire for nickel silver wire. I intend to have live catenary and N/S doesn't oxidize as badly as the others making for better operation.

Randy

Randy, I applaud your plans, but other than than having the bragging rights of constructing a live catenary where the locos actually pick up electricity from the overhead wire, I don't really see any advantage of live catenary. I do like to see pantographs on models actually touch and follow the wire, but that is as far as I think I would go.

The way I see this is that live catenary creates the most unreliable electrical pickup point for your models.  When powered through track a model usually picks up power from all its wheels (usually that is 4 wheels per rail).  The multiple pickup locations improve reliability.  Now if one side of the electric pickup is done through catenary, you end up with a single point of contact - the pantograph shoe and the trolley wire. Even if both pantos are raised, that is still only 2 contact points instead of 4 if wheels were used.  Then since the pantograph made up of multiple moving parts, every articulated joint on the pantograph presents a possible intermittent contact.  That (especially the single point of contact with the trolley wire) doesn't seem very desirable for reliable operation.  Maybe I just don't see the whole picture...

[nkalanaga]

Randy:  I wouldn't use two trolley wires for the MILW for another reason.  N scale catenary almost has to be oversized, so our one wire would look at least as large as their two.  Just do the double hangers and it looks fine. 

For the MILW, one could probably get away with parallel messenger and contact wires.  That was done in O finescale by Robert Hegge decades ago, and looked fine.  If so, it would be possible to make the overhead in rolls, mass produced, and hang it much like single wire.  All of the hangers would be the same length.

Marc:  Much of the reason DC systems are stiffer is that they have to use larger wire for the same capacity.  I've never heard of anyone using a higher DC voltage than the MILW's 3300V, while mainline AC systems basically started at 11,000V.  The higher the voltage, the lower the current, for a given load, and the smaller the wire needed.  The MILW not only needed two trolley wires, but the two heavy wires on the poles were parallel feeders, with connections to the trolley wires every few poles.  They basically had four wires to within a few hundred feet of the train, where AC systems can get by with one.   They were definitely pushing the limit of DC electrification, and it's a little surprising that it worked as long as it did.

That's also one of the reasons for the electric-diesel combinations they ran in later years.  The electric could pull the train on level or downhill sections, with the diesels helping on the grades, which limited the current requirements.  Of course, the management also wanted to get rid of the electrics, so wouldn't buy new ones, and by the 60s they didn't have enough for the traffic anyway...

Two Little Joes, starting a maximum tonnage train, could burn the trolley wire in two.

[nkalanaga]

Peteski:  Overhead contact is more reliable than it would seem.  First, most pantograph shoes are flat, giving a wider contact than a round wheel on a rounded rail head.  Second, it's a sliding contact, which tends to keep the wire clean by scraping dirt and oxidation off.  And, the contact is on the bottom of the wire, so dirt can't easily settle there, while there is less oil and grease buildup than on the rails, which means less dirt is attracted.

John:  Another problem with etched catenary is that, on anything except single track, the sections for the two tracks would be different lengths on curves.  You'd need to have specific etchings for every curve radius, as well as every pole spacing.  Unless all of your curves were the same radius, AND all of the poles the same distance apart, it would get very complicated.

One thing you might do is etch the hangers.  Prototype hangers usually weren't fastened to the messenger wire, but rather looped over it.  This could be done as an etched "eye bolt" design, in different lengths, which would then be threaded onto the messenger wire, spaced to suit the sag, and soldered to the trolley wire.  If they were etched at the right lengths, once spaced right, usually 15 ft apart, you'd automatically have the sag.  For shorter spans use fewer hangers, leaving the middle ones out.

The MILW still used 15 ft spacing, but staggered the hangers for the two trolley wires, giving the appearance of 7.5 ft, and requiring twice as many hanger lengths.  On many yard and side tracks they used a single contact wire, and it looked like most other DC roads' catenary.  The PRR, as far as I know, also used 15 ft spacing for the short secondary hangers, and 30 ft for the primary.  Why the railroads settled on 15 ft I have no idea.

[nstars]

Your analysis concerning the voltage versus current is correct and not only the MILW needed to use heavy wires. Here at home we have a 1500 V DC systems which needs 2 contact wires, one Messenger wire and in some cases one power wire, which is hung at the end of the poles. In most cases capacity of DC systems are lower than AC systems. Our 1500 V DC system can deliver 4000 Amps at a nominal voltage of 1350 V. In other words, our system can deliver 5.4 MVA or about 7200 horsepower. To give you a comparison, a TGV under 25 kV uses 8.8 MVA per trainset and they run coupled together, which results in 17.6 MVA or about 23000 horsepower.

Marc

[peteski]

Peteski:  Overhead contact is more reliable than it would seem.  First, most pantograph shoes are flat, giving a wider contact than a round wheel on a rounded rail head.  Second, it's a sliding contact, which tends to keep the wire clean by scraping dirt and oxidation off.  And, the contact is on the bottom of the wire, so dirt can't easily settle there, while there is less oil and grease buildup than on the rails, which means less dirt is attracted.

Ok, that makes sense. But how about all the articulated joints of the pantograph itself?  I recall that even you ended up replacing all the sliding contact strips between the truck and circuit board on your Arnold U25C with soldered flexible wire because you felt all those contact points were unreliable.

[Lemosteam]

Thanks John!  I see what you mean about the trolley wire appearing to be curved.  The it is also very distinctive.   I suppose that if you want to spend a very long time to painstakingly solder this type of catenary from scratch, there is nothing stopping you from doing that. Personally, I think think it would take too much time relative to other tasks involved in building a layout.

Aaaaaand that's why I want to train a spider or just imagine them.  John Lennon would be proud.  "Imagine all the Cat wires..."