1500VDC third rail is rare and the quick look I had seemed to be China based. I think this would seem to indicate there are significant complexities in 1500VDC 3rd rail. Not sure if these lines are just tunnel or surface running.
I believe most 1,500 volt electrification is on lines with level crossings.
Even new commuter networks like Dubai Metro went for sub 1kV 3rd rail.
I wonder if it has to do with the length of these lines, combined with the cross sectional area.
Looking at the modern 3rd rail systems installation with extensive insulation, it doesn't look neither simple nor cheap.
But surely still simpler a cheaper than overhead wires because it still doesn't need gantries or auto-tensioning - usually with weights and ratchets.
I have no idea what freight has to do with it.
For me today the choice of power supply fora greenfield project would be in preference order such as
1) 25kV OH or other high voltage AC
2) 1.5 to 3kVDC OH
3) 3rd rail sub 1kV for tunnel based to allow smaller bore or where OH is visually unacceptable.
I believe that 25kV is only economical for large networks with long line length. Third-rail seems to be the best default for off-street electrification at voltages that don't demand more clearance tha
Considering the Sydney Metro is not interchangeable with Sydney trains I'm a bit surprised they didn't go 25kV. Perhaps the cost of conetting existing sections just didn't stack up?
It's only a single line, and maybe not long enough for 25kV.@br30453The 1500v DC overhead was chosen as it was the best solution at the time when the Melbourne and Sydney systems were introduced.
Did 1,500 volt third-rail exist at the time?Nothing to do with level crossings.
But I did note that third-rail has gaps at level crossings, while overhead doesn't so how can you claim that?If those systems had been electrified with third rail then the clearances in tunnels and to over-bridges would have been less than what now exists.
The clearances would not have been increased with third rail electrification, unless it would make way for taller trains.
So converting to overhead supply would have needed raising of all overhead structures to provide the necessary clearances.
Adding overhead supply always needs that, whether there was previously a third-rail or not.
To convert from 1500v DC to 25,000v AC would be difficult as the "static clearance" for the former is, or was back when I was involved in these matters, 150mm, whereas for the AC system it is 300mm.
Do you mean converting between two standards supplied by an overhead wire?
As noted, converting a large electrified network between one standard supplied by third-rail to another supplied by an overhead wire is actually simpler than converting between different overhead standards, even though the former needs more civil engineering work.
This is because the network, whole or in part, can have both electrical standards at the same time, as opposed to some part only being electrified with one standard and other parts electrified with only the other.