3 ms·
Third rail systems typically work at 1500V, can't go very much higher than that due to risk from arcing. Most overhead lines use 25kV, allowing much more power
by jabl 5y ago
Third rail systems typically work at 1500V, can't go very much higher than that due to risk from arcing. Most overhead lines use 25kV, allowing much more power to be transferred, over longer distances.
Which is why third rail systems are usually only seen in metro lines and similar. I'd guess in urban environments sprinkling more substations around isn't such a huge issue, as access to the power grid is seldom an issue. Also metro trains need much less power than a high speed passenger train or a heavy freight train.
- bobthepanda 5y agowith metros the additional consideration is tunneling. generally speaking, third rail allows for a smaller tunnel diameter than overhead systems. (third rail is located near the wider section of tunnel in the middle whereas overhead requires extending the height.)
- bluGill 5y agoThere are overhead rails you can use in tunnels. Nothing stops the high voltage arc issue (the whole advantage of overhead is high voltage), but without all the equipment to tension the cables you don't need as much room and the power will be one the middle of the tunnel. Anyone building new tunnel should allow the little extra room for overhead, but retrofitting may not be worth it.