2 Questions about Pantographs

Hi, I've got two questions about pantographs and I was hoping this forum could help shed some light on them.

First, how much pressure does a pantograph exert on the wire? Is it like a violinist dragging the bow softly on the string, or more like a bass guitarist plucking away? Watching SEPTA EMUs cross the Schuylkill by 30th Street, I noticed that the pantos appear to extend slightly when they go between the catenary masts. Is this because they are exerting a great deal of force, or is the catenary arced?

Second, I recall seeing pantos facing both ways under the wire, but "elbow behind" is the position I see most often. It seems to me that running with the elbow to the rear would be more prone to snags, whereas running with the elbow forward would allow the panto to glide under any imperfections in the wire.

Thanks in advance!

A one arm pantograph has no favorable way of travel, it fiunctions same going forward or backwards the internal rods hold right angle.
The pressure on wire is about 30 or so pounds (guessing) from pulling pantographs down in emergencies.

30 lbs is actually pretty much right. It does vary a bit over the range of travel - GE ones have a bunch of adjustments to even it out. Westinghouse used to quote 2 curves - one for raising and one for lowering. Aerodynamics effect it too, which is why some have 'wings' on them. I have the curves for the Pioneer III, SLII/III/IV, E-60, E-44 and a few others at home. It's not a static number. Actually, you really need 2 3D charts to really define it.

The single arm (Faiviley, though everyone makes them now) types work in either direction, but the GE versions tend to do nasty things when they snag - that's why NJT removed them off the Arrow IIIs for the type they have now (which was on the A1s too, IIRC) - it breaks nicer if it hangs up in the wires.

Historically, locomotives tend to run rear pan up, so that the front can be used as a spare in case of a snag, but either pan can be used if it's in working condition.

Pans in general aren't directional, but trolley poles and bow collectors *are*.

On a related note to this, is there any particular advantage to using a single-arm pan over a double-arm (or vice versa)? Most electrics I see are single-arm, with the exception of NJT's Arrows (even Septa's Silverliners, which are very similar, only have single-arm pans), and it makes me curious about why.

Half the roof space.

pgengler wrote:On a related note to this, is there any particular advantage to using a single-arm pan over a double-arm (or vice versa)? Most electrics I see are single-arm, with the exception of NJT's Arrows (even Septa's Silverliners, which are very similar, only have single-arm pans), and it makes me curious about why.

Less mass so they follow the wire better at high speeds.

Stuart

In the US, unless you've got roof bumps like an M-2/4/6/ or SL IV, it's "looks cooler". Seriously, the Stenmann types NJT uses on their MUs are fine for the range of speeds seen in the US, save for the Acela's token 150mph running. Same design was used overseas for 125mph for years....

NJT dumped their Faiviley (actually a GE design/built pan) pans on the MUs for Stenmanns because the latter don't do such spectacular things when they snag. Older pans were designed to come apart nicely if they snagged, so that the wires didn't get as messed up. The GEs don't....

I usually see only one of two pans up, but sometimes I see both up. Does anyone know why this is done? One doesn't conduct enough electricity due to weather conditions or something? I can't figure it out.

Thanks!

Is the entire pantograph live with electricity or is it only at the receptor at the top?

Two pans is done to scrape ice off the wire. On some equipment, the front pan can be disconnected to keep it from arcing.

The entire pan, from the collector shoe to the insulators on the roof, is live and at 12 - 28kv (depending on who's pan and where). As are a lot of other things up there. Suffice to say - stay the heck off the roof!

There have been some locomotives built that require that both pan be up. The ex GN boxcabs that PRR purchased are one example. Each pan powered one motor generator set.