mmlabbd wrote:

Also why does the Southern train, stop and turn all it's power off
somewhere around Paddington?

It's actually near Mitre Bridge Junction, just south of the Great
Western Main Line near Wormwood Scrubs (not very near to Paddington).
The reason is to change between 25kV AC overhead and 750V DC third rail.
With the trains that Southern and Silverlink have, it's apparently not
possible to do this on the move, as Eurostar does.
--
Richard J.
(to e-mail me, swap uk and yon in address)