On Thu, 17 Jan 2008 19:55:22 +0000 someone who may be Tom Anderson
wrote this:-

Or do modern DC trains work by inverting the DC
into a low-voltage AC at the same frequency as an OHLE supply and using
that to work a motor?

In general a system takes low voltage DC from the supply (the
conductor rail) and inverts it to low voltage AC at variable
frequency, to operate the motors. The system will have a range of
input voltages.

To produce an AC version a transformer and rectifier convert the
supply to a DC voltage in the input voltage range.

This double conversion sounds odd to people of an earlier
generation, but the many advantages outweigh the small
disadvantages.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54