Trolley Pole v. Pantograph

ExCon90 wrote:

mtuandrew wrote:

typesix wrote:Both use carbon shoes so that the wire is not worn down, the carbon also serves as a lubricant.

Except those lines that used trolley wheels.

Trolley poles are definitely cheaper and more lightweight, and standard overhead is much cheaper than catenary (especially constant-tension catenary.) Still, pantographs with CT catenary are much less likely to dewire or tear down the wire, especially when reversing, and there's not even a remote electrocution hazard for trainmen since they never have to futz with a pantograph.

Surprised more American heritage lines don't use bow collectors on their streetcars. Not as versatile as the pantograph, but cheaper, probably lighter, and looks more authentic. Also, it obviates the need for wire frogs that trolley shoes and wheels need.

The Skokie Swift had very good results with what amounted to a bow collector, for those very reasons. It didn't exactly look authentic, since it was unique (at least in the U. S.), but it did the job.

Well, the CTA really went cheap to put those collectors up. They simply grabbed a couple of trolley bases and put them on the car with the collector across the ends. The standard spring loading was not enough to hold the contactor on the wire, as the mass of it would cause the collector to bounce down as the wire changed in height/tension. So, someone came up with the idea of airfoils, since the problem was seen only at speed.

And lastly, with a pantograph the operator doesn't have to put up with some wiseguy walking up behind the car and giving the trolley catcher rope a healthy (and dewiring) yank while loading passengers at a stop.

standard overhead is much cheaper than catenary (especially constant-tension catenary.)

Actually catenary is cheaper than single suspension trolley wire, except for very light use lines like heritage trolley lines! The reason is that, except for these very lightly used lines, feeder cables are required to provide enought electricity in either case. With trolley wire systems the feeder is either above ground on the line poles or underground (typical in major cities) where it may be out of sight, but more expensive! In modern catenary design the copper feeder wire is used as the catenary messenger (the top wire), so no additional feeder is needed. The major cost savings is in line pole spacing. On straight track, line poles are required every 100 feet for trolley wire. With typical modern catenary, the pole spacing is about 200 feet, so far fewer poles are required.

mtuandrew wrote:

typesix wrote:Both use carbon shoes so that the wire is not worn down, the carbon also serves as a lubricant.

Except those lines that used trolley wheels.

Trolley wheels were developed partly to prevent wear-and-tear on the electrical contract surface as there is only rolling (static friction) contact with the wire, so in perfect operation, zero abrasion. But of course it just moves the friction contact onto the trolleypole between the wheel and its mounting.

I am under the impression that the maintenance costs are lower with carbon shoes nowadays. I think they weren't when trolleypoles were invented because carbon shoes were more expensive.

Trolley wheels were developed partly to prevent wear-and-tear on the electrical contract surface as there is only rolling (static friction) contact with the wire

If you look back at pictures, you will see that trolley wheels were among the first items used to pick up power. And, at slow speed, they could bounce over rough spots in the wire. Old hangers (I have some books clearly showing this) were wrapped around the wire, and sometimes soldered onto the wire. In many cases, especially at special work, the turnout casting was simply clamped onto the wire, and the collector had to navigate a sudden 1/4" or bigger blunt end. A large wheel would track nicely; it would DESTROY a slider.

Wheels worked fine until the speed increased, and the power consumption increased. Wheels have a very small area of contact and arcing is a real problem when you are trying to pull big amps. HIgher speed causes the wheels to bounce at every imperfection; and getting them to simply roll that fast can be problemmatic. So, for poles the sliders were invented. Mostly the contact in the shoe is carbon; but some lines used steel and greased the hell out of their wire.

(And, BTW, in answer to the original question: the wire DOES wear down even with carbon inserts. The old South Shore wire is FLAT on the bottom, and in many cases has lost over half its original height.)

JohnD1 wrote: If you look back at pictures, you will see that trolley wheels were among the first items used to pick up power. And, at slow speed, they could bounce over rough spots in the wire....

Thank you for the lesson in trolley tech history and engineering. It was very interesting. I don't have many books or references on the early days of trolleys.

What about the "plow", as used in Washington, D.C.? Somehow the idea of 600 VDC just a few inches below the surface of the street in a "slot" doesn't strike me as the safest or most trouble free idea.

From what I've heard conduit, or slot for a plow, wasn't very trouble free, but I don't think it was any less safe than trolley wire.
Whether conduit or overhead wire, you're still talking about half of the electric circuit, the other half usually going through the running rails, even in streetcar track.

There was little danger of pedestrians getting electrocuted.
Yes, with conduit someone could try really hard, dangle a wire down into the slot to engage the electrical conductor, which I assume was something like a 3rd rail as opposed to a trolley wire, and then reach over to one of the running rails to complete the circuit, but it would still require some effort. I think that's not much less effort than it would take to toss a conductive wire up and over an overhead trolley wire, and again make contact with a running rail to complete the circuit.

In both of these cases I think whatever conductive medium you used would have to be rather thick in order to carry enough electricity to maintain an effective short circuit before it would melt itself and break the circuit. The thicker the medium the harder it would be to stick it into the slot.

So I think the reasons why conduit only got used in Washington DC, and I believe New York 5th Ave, probably had more to do with expense rather than any safety issues.

papabarn wrote:What about the "plow", as used in Washington, D.C.? Somehow the idea of 600 VDC just a few inches below the surface of the street in a "slot" doesn't strike me as the safest or most trouble free idea.

Most traction experts considered the underground conduit system as used in DC and on Mahattan to have been relatively successful. The system did have some unique problems, among them the traffic delays caused by pulled plows which would stop a car and obstruct the track until it could be removed, and the car towed by another car to a plow pit where another plow could be installed. ( There were hatches at intervals in the track system which allowed for removal of the plows in this situation), Additionally, there were dead spots in the conductor rails at locations where two lines crossed, and cars had to coast across these sections. If a car had to stop at one of these locations, it would have to be pushed through the intersction by a following car until the plow could make contact with the contact rail on the other side of the intersection. Heavy snowfalls like the one currently being experienced in DC also wreaked havoc with the conduit system. Finally, at least in DC, the plow pit ( where a line went from the conduit system to the standard overhead wire system) involved stationing an employee in the "pit" whose function was to install, manually, plows onto inbound cars and to remove them from outbound cars. Obviously, this was a much more complicated system, both in its construction and operation, than the standard overhead wire system. There wasn't much danger of electricution of pedestrians, since it would have taken considerable effort for anyone to have made contact with the "live" underground power rail, and the slots through which the plows extended were very narrow. The major reason why the system was used only in DC and NYC was cost as the system was very expensive to construct, maintain, and operate.

Yes, with conduit someone could try really hard, dangle a wire down into the slot to engage the electrical conductor, which I assume was something like a 3rd rail as opposed to a trolley wire, and then reach over to one of the running rails to complete the circuit, but it would still require some effort.

From what I've read so far, in Washington (and some other cities) when operating via the plow, the current was returned via a conductor in the trough rather than the running rails. This was required in New York due to concerns about stray currents from the running rails possibly eroding gas lines. Plus, wasn't the trough lined at least at the surface with steel or iron. I would think possibly an errant piece of sheet metal preflattened by a tire dropping in there might result in some momentary entertainment value if it hit just right. From what I've found so far, the conductors were about a foot apart and about a foot and a half down from the surface. Difficult to reach, and of course back then we had far fewer creative idiots per capita then we do now. I would think though that weather related things like packed snow/ice, corrosion etc. would be an issue.

http://www.dctrolley.org/faqs.htm
http://en.wikipedia.org/wiki/Conduit_current_collection

Type7trolley wrote:One advantage of the pantograph is that it can't ever slip off the wire, meaning the driver never has get out, walk back, and reset it when it comes undone like they sometimes had to with trolley poles. But I'm not sure if that happened often or was just a rare thing.

Sure happened often enough on trackless! Poles get tangled up in the catenary, too--shorts the whole line.

(Not sure those could use a pantograph without some major changes to the overhead--first of all, you'd cause a short at all the frogs, secondly, the trolleybus has pickup and return poles. Steel wheel grounds through the rails.)

polybalt wrote:Pantographs work better at turnouts ( switches). Trolley frogs, required with poles, can be touchy and often in need of adjustment. It is not possible to go through trolley frogs with any speed. I would think 30mph is about it.

What's used instead of a frog?

FFolz wrote:

polybalt wrote:Pantographs work better at turnouts ( switches). Trolley frogs, required with poles, can be touchy and often in need of adjustment. It is not possible to go through trolley frogs with any speed. I would think 30mph is about it.

What's used instead of a frog?

No frog necessary with a pantograph. The (usually) carbon conductor just slides from one wire onto the diverging one, and as long as they're at the same elevation the pan won't get hooked. With a trolley pole running a shoe or wheel, the frog switches the sliding contact's track from one wire to the other.

Here's an example on the National Model Railroad Association's site of a trolley frog, as it would be situated on a full-size railroad.

I've worked with 1:1 trolley wire at the Pennsylvania Trolley Museum for quite a few years. Most of our cars use wheels, there are just a few with sliders. At our speeds, the sliders work just fine with the traditional Ohio Brass fittings.

I've also erected overhead in 1:24 scale. For those of you interested in what the real fittings look like, there's a page on my website www.orery.com that shows old OB products. Or, make friends with someone at your local trolley museum -- or better yet, volunteer to join the line crew.

Ah, yes, that makes sense now (thanks for the link). I had a brainfart (or was thinking about trackless) and was imagining a short when the pantograph made contact with two pickups, but of course that doesn't make any sense whatsoever. X-P

How are the loads balanced throughout an electric rail network? I imagine it's something of a massive parallel circuit with trolleys as the resistors, but you'd have to have drops in voltage the farther you go from the generator, plus the branch lines have to complicate things.

Apologies if this is a stupid question ... background in microcircuitry, not electric rwy!