smallspy
Senior Member
The pole shoes are failing due to *over current* not voltage.
Actually, the pole shoes were failing because the last supplier changed the formulation of the carbon shoes. They were slightly longer wearing in dry conditions, but wore out in a fraction of the time in the wet. They've since gone back to the original formulation.
Surface area alone on the pants is multiples more than on pole types, plus the pickup area is swept laterally on pantos as the vehicle moves.
Not so. A CLRV shoe is a U-shaped carbon piece 2 1/2 inches long. The ALRV and Flexity shoes are 4 inches long, due to the higher draw from the bigger vehicles. In both cases, because it is U-shaped it will generally contact the wire on two of the three faces.
A pantograph will have two wipers 2 inches wide, which contact the wire (or contact rail) on one face only.
You can see this on train-lines more than trams where the catenary is actually zig-zagged laterally more than even the random amount from alternate side suspension guying. This also allows much greater heat dissipation from the contact resistance, which can be hot enough to effectively melt the carbon shoe in extreme cases of overcurrent. (in fact, the structure changes, it mostly vaporizes, but that's physics) .
The geometry of the wire in a pantograph-only application has nothing to do with heat disappation, at least not in terms of power draw. The wire will be set up to sweep back and forth across the vehicle in order to prevent grooves wearing into the pantograph carbons, and requiring them to be replaced early. This has already become a problem in Toronto, where they have not adjusted the geometry of the contact wire enough for pantograph use.
There's a multitude of advantages with pantos, not least the need to not 'switch' the pole shoe at junctions.
Absolutely there are. The ability to reverse without requiring additional supervision/help is another. They virtually eliminate dewiring incidents at specialwork, and their effects on shedules. And there is the ability to run lower clearances in situations such as tunnels when coupled with rigid contact rail for the OCS. Generally, maintenance of the OCS is cheaper as the whole of it can be simplified.
But there are also disadvantages as well, mainly upfront and replacement cost. A trolley pole costs $200 to replace, a shoe holder is about the same or less. A dumb pantograph starts at $10k, smart ones like the ones in Toronto can double that. The OCS must be more robust as a pantograph will exert more force on the overhead - again, this is an upfront cost, as maintenance in general should be less.
Dan
Toronto, Ont.