It should be fairly straightforward to wire a pantograph on a 777 straight to the lower voltage side instead of going via a step-down transformer. Some southern region locos had low voltage pantographs for safer yard work.
== Doublepost prevention - post automatically merged: ==
== Doublepost prevention - post automatically merged: ==
I don't think conversion of tunnel and other highly segregated metro sections would bring much safety benefit. Access for maintenance and repairs on such busy railways is already tightly controlled and requires power off and traffic blockage in the appropriate areas. These can be backed up with trackside lockouts operated by the workers. The major risk remaining is people falling from platforms. Having the juice rail on the opposite side of the track from the platform edge helps to control that risk but there's a risk some who fell might stumble over to the wrong side in their confusion and there's a problem with 'spanish solution' platforms with faces either side of the track. Prominent hazard signage and side shielding can help but the most effective measure would be to remove the conductor rail from the platform area altogether, which could be possible if all trains had line haul traction batteries. They all have some small provision for emergencies and depot movements.Minor point - stuff doesn't last forever. At some point renewals need to happen, and that is your opportunity to decide if you spend your budget on replacing like for like or with something better. I can eventually see isolated 3rd rail conversions being considered at renewal time once there's a bit more AC around them.
If the ideal situation was ever reached where the surface sections were all upgraded to OHLE and the tunnels were the last remaining 3rd rail due to the clearances, could it then be viable to use battery+OHLE units to rip out the last of the third rail entirely to improve safety? The batteries would have plenty of time to charge up on the surface sections...
I don't think length is a great concern. It's the detail of clearances and the condition of the tunnel lining. A ceiling conductor rail or similar low-profile system would require a great many anchor points at cost and risk. A low voltage line would be larger in section and thus heavier than a high voltage conductor. A 3rd rail simply attaches to the sleeper by contrast so is bound to be cheaper at full renewalWhat type of OHLE is proposed for the very long Standedge rail tunnel between Diggle and Marsden which is far longer than any Merseyside tunnel?
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