catenary technical question

This image is from a model railway, but it shows the catenary for the cross over terminating on the next stanchion.

I'm interested in learning more about the electrical contact. The shoe or whatever it's called that touches the electrical line must create a lot of heat from the friction. How is the heat dissipated? How long does a shoe last?...and the line?

The mainline contact wire probably has 3000 pounds of tension on it.  When a wire comes in from a side track it also has say 3000 pounds of tension on it.  The siding wire can not be tied to the through wire or that would double the tension on the single wire leaving the connection.  So one of the wires is run to a pole and dead end.  Which wire is dead ended depends on where an available pole is, if the wires are to be electrically isolated, etc.  Since the trains may be traveling in excess of 100 miles an hour the wire has to be kept flat and smooth to avoid getting the pantograph bouncing, which causes arcing.  It is also desirable to avoid sharp moves to the side to avoid having to put side pull offs in.  The wire looks very uniform and repetitive, but I think you will find that are many places where the wire is designed for that specific situation. 

The pantograph contact shoe use to be a sheet steel "C" shape with copper alloy wear strips on the leading edges.  The gap between the copper wear strips was filled with solid graphite.  Modern pantographs use a solid carbon bar on the sheet metal pan as the contact surface.  On the Northeast Corridor the trains are going fast so there is lots of moving air to cool the shoe.  Since the voltage being conducted is 11,000 or higher, the current is fairly low and not much heat is generated.  On the lower voltage DC systems like the Milwaukee, South Shore, or Sacramento Northern, the current can get high.  The older steel and copper pantograph shoe was limited to about 500 amps.  If the current was going to be higher than this, a pantograph can be equipped with two shoes.  The different voltage and current levels to be conducted by a pantograph and higher speeds are accommodated by using the appropriate upward pantograph force.  The trolley wire must be designed for the upward force used.  The upper ward force exerted by pantograph can run between 20 to 60 pounds.

This drawing might help you understand the crossover design

http://www.billspennsyphotos.c...oto?photoid=79300734

thank you all, but no answer to question.

Dave Allen your picture appears like the crossover wire crosses over wire on main track before ending on pole. 

My question is how do the real PRR and successors do it, so there would not be a bump. 

Pennsyk4 thanks but I already have that.  

Unfortunately it does not answer the question of what happens when the 2 wires both of which are under 3000 lbs tension meet 1 under 3000 lbs tension.  The wire going to the pole equalizes the tension, but which wire is going to the pole? Namely the main line or crossover?  If they meet and are electrically united running the main line wire to the pole and keeping the crossover wire going would seem to make sense. 

However as I stated earlier I cannot prove it one way or other, without actually seeing a PRR type catenary, which is not practical considering I now live in Arizona.   

I hope I have now more correctly explained my question.

mikeg 

It could be either wire, depending on where the next available pole is.

It appears that in many junction situations the wires simply cross and the pantographs handle the slight changes in wire height. In other case wires are brought approximately parallel and then one diverges to the side. All contact wires are finite length and have to terminate somewhere, with weights for maintaining tension. For modelling purposes the method shown in Dave Allen's photo would seem appropriate and suitably functional.

Very interesting photo.  I noticed the two different gauges and the dual gauge track. I assume this is in Europe, do you know where?  I do not think the Northeast Corridor has changed to constant tension catanery yet, but it may be in the works.  The present system uses a force gauge in the chain tensioning tool to get the tension correct.  There is a standard for the correct tension for any given ambenent temperature.  This method results in really tight wire on cold days and saging overhead when it is hot.  Wires are spliced together and can be many miles long.  I have purchased trolley wire in 5000 foot spools, but I think these are considered a small order.  I think spools with a single piece of wire 4 or 5 miles long are available.  Splicing grooved wire into even longer lengths is easy with a manufactured mechanical splice.

The photo provided by Dave Allen is a spectacular bit of modeling.  What is the prototype?  The frame just ahead of the tunnel portal is interesting.  I can not tell from the photo exactly what it's purpose is.  It could be to terminate the messenger wire and run the trolley wire through the tunnel as single suspension due to low over head clearances.  Thanks for sharing the photo.  Is there some place where more photos of this pike can be seen?

David, this photo was from the Sommerfeldt Catenary site, a German company.

Search out Drew's excellent PRR catenary work of the Cherry Valley 0 scale club layout on the OGR two rail side.  

The Cherry Valley club has an open house during the swap meet upstairs  this Saturday in Cherry Hill, New Jersey about 15 minutes east of Philly town in the Merchantvile Grace church.  The layout opens in the morning to early afternoon.  Lots of catenary, lots of switches.

I have to disagree about there being 3000 lbs of tensile tension along the catenary running wire. If that were the case, the 20-50 lbs of upward force by the pantograph would not budge the wire at all. I live alongside the NEC and can verify that every pantograph deflects the wire almost 2 inches, in cold or hot weather.

Drew has done an accurate and outstanding job of replicating PRR catenary at our club. Anyone is welcome to stop by this Saturday, 10am-1pm to have a look.

Some information on PRR catenary design

http://broadway.pennsyrr.com/R...tation/catenary.html

Sorry for 3000lbs tension, I misread previous posters supposition as fact. 

Pennsyk4 that web site provided information that I was not aware existed. 

Wish I could see Drews catenary, but verrrry long drive.  How do I contact Drew?

mikeg

Mike

I had asked the same question several years ago when I was making the Cat for my layout.

The wires your talking about is an air gap. The pantogragh is transfering from one circuit to another. This is the end of one and the start of the other. In the early days of the PRR cat the tension was a problem and the pans were getting torn off the loco's at this point and or diverging points.

I also got the headaches and went cross eyed trying to fiure it out, not to mention almost run over by the train.

The train would start into the interlock and change circuits first then run through the interlocking.

In the interlocking the diverging tracks you would have two wires together on the pan at the same time. the difference in tension would also rip the pan off. They added the boxes to raise and lower both cables together otherwise one would raise with the pan but at some point it will snag the diverging route cable (which stayed lower) and rip the cable down and pan off the loco. Building the box causes both cables to raise and lower simaltaniously.

Since the circuits must remain independant you run the 120' long crossover cables allowing the pan to gently raise and lower them together. I think there are glass insulators holding the support cables close together and assist. The trolley wire is independant except when the pan is on that 20'-30' section where the two are even.

I have about a thousand of pictures of these interlocks and airgaps and hardward. They have to be the hardest thing to look at but easier to look at in a picture.A guy posted some of the old PRR freight Cat at Enola on a PRR electric web site. That stuff is all gone. I have the NE coridoor and some freight supports, K beams, signal towers etc.

Jamie 

Actually, it doesn't show that.    The overhead for the crossover is terminated on the face of the tunnel portal wall;  the two insulators are partially hidden by "the next stanchion", which appears to be an incomplete signal bridge in brass, still under construction. [ This layout appears to be set in Switzerland because of the style of the catenary mast;  hence, the signals for both tracks are to the left for traffic entering the tunnel.]

Terminating catenary on a retaining wall or other fixed structure, a bridge, say, is 'prototypical = model rr legal', at least in Europe.  You'll note that if you look closely at the area where the wires are attached to the wall there are a spare set of holes;  the builder didn't get the wires to line up the first time -- or they did line up but the wire was outside the pantograph head's span on the crossover, and it had to be rerigged.  [ You can imagine how I know this.]

Best, SZ

Here is a link to a collection of some Cat drawings. Air breakes are on there just not the true mainline ones I've looked at.

http://prr.railfan.net/ElectricTraction.html

<http://prr.railfan.net/ElectricTraction.htmlp> 

Could you post some of those pictures. 

The only two that I can absolutely identify are  jct crossover show clearly the wires merge and continue uninterrupted.  One is the crossover at Zoo between the hi line and ny pittsburg subway and other is middle of double crossover in pit at penn station nyc. How they do this I do not know and neither answers primary question. 

FWIW I have learned quite a bit on real catenary, thanks. 

Can anyone help me contact Drew from Cherry Valley?

His input would be invaluable.

mikeg

Hey, who moved my rock!

Mike,

This photo shows both styles of terminating the wire from converging tracks:

On the left/upper one, the terminating wires weave through the continuing ones.

On the right/lower, the terminating wires pull up close enough to transfer the pantograph to the continuing one via pulloff, then veer away to the pole.

Does this help?

--Drew

It's a darn good thing that the railroads never depended on me to figure this out.

You don't want this to happen ...

Pantograph of Electric Locomotive entangled with OHE

http://www.youtube.com/watch?v=2ocbtg1jlpM

Helps a lot, thank you for input. 

I did not move your rock.

mikeg

Mike

I have 5-6 photo's but can't post. Guess I have to go to Google Chrome to get back to my online photogallery. Have not been very active on the forum lately and can't figure out how to send you an email with the shots.

Reviewing some of the shots they look like they only have the wires become parallel then pull back off on the diverging track. Those boxes I discribed earlier only stablize the pair of wires lift and cross over and run away. There is no cast part to merge them together. they're just parallel together. it is a 3-d thing.

I saw your Jan post on House of Duddy. I got lots of insulators from Ed but started working with Model Memories for everything else. Don built alot of cat segments for me and the K beams. He is actualy a New Haven RR guy but did the PRR also. 

Jamie

here is model memories.

http://www.modelmemories.com/

Don May know what happen to Ed's stuff. Sure Ed's still not around?

Jamie

I just yesterday received more insulators and brass cubes from HOD.  Ed is somewhat around and I have no idea what he has etc; only suggestion is leave a voice mail and patience.

I am aware of model memories and at this time with new supplies, should have all I need for my catenary, including 3 interlockings and one substation.

Mikeg

Sounds like you following the same route I did. sorry I have forgotten the terminology for the catenary parts that connect the trolley wire to the support wire don't wrap around the cat trolley wire but go into a grove to pinch the wire and hold it in place. Early wire was rivited and later they went to mechanical connectors.

In one of my photos I caught the cross over, They ran the box of droppers and added the two extra stiffiners to form the x pattern getting smaller and smaller. Then after three of them, a heavier tube was used that probably was 1/2" diameter bent in a u shape, they have maybe just two of them and then pulls up and away from the switch and runs for the K beam support on the next pole. That whole assembly would get pushed up as the pan runs under it. 

On the Air brakes this spot was a curve so it was very complicated. they ran two compound cat lines side by side one raising and the other falling. through the curve. Nice complicated set up. Three track main with 6 cat sections. I used the Landover tower because it was a cut and I could get on both sides of the cat and above it on a bridge and under it. My camera just wasn't the strongest to get very clear shots.

You may want to google Landover Road, Landover Maryland and follow the cat down. The old Landover Tower is still there (It was the tower that notifed Union Station the 4876 was a run away and to evacuate). You can also look for your pole placement at the interlocks and curves in that area. The road also crossed over the Cat at that point just making it even more complicated. Route 50 parrallels the corridoor at that point. Good method for pole placement. I doubt you will see the wire. It is very difficult to photogragh in real life or modeling.

From a modeling standpoint this will be very difficult to model, you could bring your wires close and then set a three cubes somewhat close together, at the cross and then jump the one up and over the back side and head for the pole. I think this will cause a twist in the wiring on the main but will get it done. I Have the K beams set in a straight line to receive the wires. regretably as noted on the Model memories web site I was the last one to use the 1/4" h beams and had to searce the whole country to get enough to finish my K beams and the lenthy delays doing so I lost the interest in finishing the details on the cat. One day I may pick it back up.

I have good tension on the trolley wire and works well.

Jamie