|
|
| Addenda - Re: Pantograph for Trackless Trolley vs. Light Rail or MU (486697) | |||
 |
|||
| Home > SubChat | |||
|
[ Read Responses | Post a New Response | Return to the Index ] |
|
||
|
Addenda - Re: Pantograph for Trackless Trolley vs. Light Rail or MU |
|
|
Posted by Robert King on Thu Sep 6 14:10:06 2007, in response to Re: Pantograph for Trackless Trolley vs. Light Rail or MU, posted by Robert King on Thu Sep 6 13:28:01 2007. I forgot to mention one important thing:Wire junctions where streetcars cross a trolley coach line have to be at a sharp angle so that the pantograph slides under one trolley coach wire and then the other, so that the pan doesn't short out the two trolley coach wires. This problem can also be avoided by putting section insulators on the positive trolley coach wire and the streetcar wire so the whole area where the pantograph meets all the other wires is just dead, at ground. That still requires a fairly sharp angle in the intersection to keep the dead section short, to reduce occurences of slow moving vehicles coasting through from stopping under the dead section and getting stranded. There are some other, minor things about streetcar and trolley coach junctions when the streetcars are using poles instead of pantographs: In areas where both are being used in parallel, the trolley coach's positive wire can be shared between the streetcars and the trolley coaches; the streetcars just use the tracks as usual for their ground and the tracks and trolley coach ground wire are connected together. However, this means that even though trolley coaches can be steered around, they still can't pass streetcars without knocking poles off the positive wire. This is why the TTC usually - with only one exception that I know of - kept the trolley coach overhead entirely separate from the streetcar wire. The pair of trolley coach wires would be located at the outside of the road, between the curb and the streetcar wire with the streetcar wires in the centre of the street above the tracks as usual. Section insulators were also used extensively where trolley coach lines met streetcar lines to prevent the ground wire from shorting out the positive trolley coach wire or the positive streetcar wires. The positive wires could be made common without section insulators since they were both 600 volts, but the insulators were usually there anyways to rationalize the flow of the 600 volt direct current around the streetcar and trolley bus systems. Technically, that kind of isolation isn't needed to prevent shorts but it does prevent strange current flows resulting from slight differences in the 600 volt potential in both systems and it allows for greater flexibility in controlling exactly what sections of wire are energized and where. All of this became a non issue in Toronto in 1993 when the TTC abandoned the trolley coaches and the wires came down. They replaced them with the 'environmentally responsible' natural gas buses that turned out to be a noisy, hugely expensive, low reliability, low performance replacement that lasted until sometime early last year. They kept buying natural gas buses well into the late 90s so the new ones didn't last long at all. The only CNG buses left are the ones that got diesel engines from retired diesel buses. Not exactly a ringing endoresement of the trolley coach replacements... -Robert King |
|
|
|