trolley and streetcar power supply

Why newer lightrail system uses 750 volt and pantographs rather thanthe 600 volt and troley poles used in the older streetcars and trolleys?

I can't answer the 600 VDC vs. 750 VDC argument, though I suspect it gives a bit better current flow to the motors so they can accelerate more quickly. Some trolley lines and interurban equipment from the early days even was designed to run on 750 VDC from the factory. In some cases, even the 150 volt difference between designed voltage and current voltage doesn't prohibit elderly unmodified streetcars from modern LRT track.

The pantograph instead of a trolley pole does have some reasons behind it though. First of all, the pantograph wears a lot more evenly and takes longer to wear down than the trolley shoe or wheel. Second, there's no complicated wire frogs to maintain, and no chance that the wheel/shoe will follow the wrong wire path. Finally, the pantograph holds constant tension against a wire a lot more easily, while the trolley pole tends to be a lot more bouncy and less likely to stay in contact with the wire.

On the other hand, trolley poles are a lot easier to manually put up and take down from the wire, and look a lot more graceful IMHO.

mtuandrew wrote:I can't answer the 600 VDC vs. 750 VDC argument, though I suspect it gives a bit better current flow to the motors so they can accelerate more quickly.

That's right. A higher voltage results in lower current flow for any given amount of power demand. This results in less losses. The higher the voltage, the less the losses in the wire from resistance heating as well as a more constant voltage as demand varies. Voltages used would be even higher but there is a trade off for safety since the electric system is in and along streets.

Hi All,

Trolley poles had a nasty habit of popping off the trolley wire and usually in really bad weather. By comparison, a pantograph does not have such problems and the pantograph does not have to be reversed when the car has to reverse and return to its origination point. That is, the motorman does not have to leave the car, in all sorts of weather, and walk the trolley pole around to the other end and place it on the trolley wire. Far more convenient for the motorman.

pennsy wrote:Hi All,

Trolley poles had a nasty habit of popping off the trolley wire and usually in really bad weather. By comparison, a pantograph does not have such problems .....

This is true, and in addition the pantograph is much more suitable for high speed operation than the trolley pole. This is true, even though there were some high speed interurbans that still employed trolley poles. The Cincinnati & Lake Erie Railroad, which operated its trolley pole equipped "Red Devil" lightweight interurban cars at speeds often exceeding 80 MPH, still had to slow them down on curves, though, to keep the poles from dewiring at those speeds. The use of pantographs eliminates that problem, though the conact wire has to be held in a more rigid position than is necessary with trolley poles.

Yep, pantographs are generally used with catenary wire systems so they don't foul the support wires. It's cheaper to construct the single wire system generally used with trolley poles, though, and very few interurbans went with catenaries and pantographs even at the highest speeds.

walt - Yeah, the North Shore Electric used trolley poles and direct suspension wire too, at least when not on the El.

EDIT: Ok, I guess some parts of their mainline did use catenary after all, but all their cars were trolley pole and shoe up until the end - see http://davesrailpix.com/cnsm/htm/cnsm311.htm.

mtuandrew wrote:Yep, pantographs are generally used with catenary wire systems so they don't foul the support wires. It's cheaper to construct the single wire system generally used with trolley poles, though, and very few interurbans went with catenaries and pantographs even at the highest speeds.

walt - Yeah, the North Shore Electric used trolley poles and direct suspension wire too, at least when not on the El.

EDIT: Ok, I guess some parts of their mainline did use catenary after all, but all their cars were trolley pole and shoe up until the end - see http://davesrailpix.com/cnsm/htm/cnsm311.htm.

That's true- current collection on the portions of the North Shore Line outside of the Chicago Elevated was by trolley pole right up to the end of operations in 1963. The Electroliners were trolley pole equipped ( the poles were removed when they went to the suburban Philadelphia's Red Arrow Lines for use on the third rail equipped P&W) and on the conventional cars, the conductor used to lean out of the rear window at speed to raise the pole to make contact with the power contact wire as the cars moved from the 'El onto the North Shore's own trackage. I always wondered why the North Shore never converted to pantographs, as their overhead was catenary in many places, and in general, it was a VERY substanially constructed property.