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Post by nickf on Oct 6, 2016 15:58:55 GMT
Apologies for what must be a very naive question, but it has been bothering me. I have understood that all London Underground lines have third and fourth rail electrical supply partly to avoid leakage to earth and the electrolysis of nearby infrastructure that would occur if the current used the running rails as part of its path. But Crossrail as I understand it will be using the running rails as part of its traction current circuit. So what is different? Is it that the supply will be AC rather than DC, or is the tunnel lining a better insulator, or something I haven't thought of?
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Post by domh245 on Oct 6, 2016 16:15:34 GMT
Crossrail will be using 25kV AC OHLE (to match the existing railways on either end). The traction current circuit goes: OHLE > Pantograph > Transformer > Wheels > Running Rails, and is a lower current than an equivalently powered DC train (P=IV and all that) which helps in part. The biggest factor is the use of primarily (or is it almost entirely? - ie everything bar the bolts and fittings holding the lining rings together) concrete tunnels rather than the steel tunnels used on most LU lines means that it is better insulated
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Post by nickf on Oct 6, 2016 18:40:31 GMT
Thanks a lot, domh245. Much obliged.
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